# ML Midge Build



## jack620

Ladies and Gents.  I thought it would be a good idea to have one thread for my ML Midge build rather than start a new thread for every part.  I am building two Midges from a set of metric plans supplied by Ron Chernich.

So far I have completed the outside machining of the crankcases, the heads are finished and the cylinder liners have been machined.  The last pic shows what I've done so far.

The boring of the crankcases is waiting until I receive a 10mm ER40 collet to grip the "nose" of the crankcase.

In the meantime I would like to drill and mill the transfer ports in the cylinder liners.  I intend doing this with my lathe's milling attachment.  I'm thinking of securing the liner vertically in the mill chuck with an aluminium "bung" in each end to improve the grip of the liner in the chuck.  Since the chuck is hardened and ground I will probably slip a piece of emery paper between the chuck jaws and the bungs for added grip.  Pics below.

All ports are located vertically with reference to the flange in the middle of the liner. Since I don't have a DRO, I plan to use my dial indicator to set the vertical slide for drilling the 4 holes.  I will also need some method of keeping the liner centred as I rotate it to the 4 positions for the holes. Otherwise I'll have to re-find centre every time.  Maybe a small V-block?

Please let me know your thoughts.

Chris


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## Ramon

Hi Chris - Its all looking very good so far Thm: very nice work indeed.

Re setting up to mill/drill your porting.

Radially these are not too critical as long as they align reasonably well with their respective passages but relative to each other vertically and to the flange certainly is, for any deviation here will affect the timing as designed.

Going about it it as you envisage will require breaking the set up for each hole but there is a method by which you can set up just once and it will also allow the radial movement with a degree of accuracy

First off is to make a plate clamp from a piece of bar wide enough to fit in your vise but allow the cylinder to be outside the jaws. Something like this ....





This type of clamp, if made to a reasonable fit on your cylinder, will exert a high degree of clamping pressure with very little torque on the clamping screw





If you scribe a line across the diameter of the bore on the plate and two more at the angle of the transfer ports then a single line on the cylinder aligned with each will give you the radial movement required by releasing the clamp screw and rotating the cylinder without losing its vertical or horizontal alignment. That way the 3 x .5 passages can be milled last of all without moving the slide other than for the vertical displacement of the holes

Given what you are doing I would think that something about 10mm-3/8 thick ali or steel would be more than enough. 

If required the plate can be recycled over and over for other parts and has many uses - R/T, Faceplate, Angle plate etc

There may be other ways to approach it but with the kit you have available this does mean you only set up the once.

One last point - if you feel something may move in a vise or clamped to a table then inserting a plain piece of copy paper will give you all the grip you need to prevent movement. There is a certain amount of 'give' in emery - particularly cloth - and parts can sometimes 'skid' on the grit or the backing

Regards - Ramon


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## jack620

Ramon,
That's perfect.  I never thought of that setup, so I'm glad I asked the question.  The scored lines will make setting the angles dead easy. I have a piece of ali perfect for the job.

Thanks for the copy-paper tip too.

Chris


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## Ramon

Glad that's of use Chris

Something else that may help too is before you do this op is to turn  up a slug of ali to a nice fit in the liner and drill the port holes through into it. This will keep the burrs in the liner to a minimum but twist and remove the ali to break the burr after each hole otherwise it will prove much more difficult to remove. Just make sure you drill into a fresh area on each hole.

Regards - Ramon


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## jack620

Ok, thanks I'll do that too.

Cheers


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## jack620

Today I made the carby bodies.  Then I made up the plate clamp Ramon recommended.  This clamp works beautifully in the lathe vertical milling attachment.  I used a dial indicator to set the height of the intake and exhaust ports.

My tailstock chuck only closes down to 3mm so I had to use the chuck from my pedestal drill in the headstock to drill the 2mm intake port.  This chuck has horrendous runout, but I was still able to get a nice clean hole by drilling 1.5mm first.  Using the aluminium plug (again recommended by Ramon) kept the bore nice and clean.  This port is meant to be centred 4mm from the flange. As best I can measure, it ended up around 3.8mm.  Hopefully that is OK.

For the exhaust port I used a 3mm 2-flute slot drill with a 6mm shank.  This allowed me to fit the tailstock chuck to the headstock spindle.  Despite the much reduced runout in this chuck, I got a lot of chatter drilling this hole.  I suspect the hole was not located exactly right and the slot drill was clipping the flange on the liner. As you can see, the hole is a bit messy and it cuts slightly into the flange.  It is meant to just touch the flange. Hopefully the slight misalignment of the exhaust port won't adversely effect performance too much.  I will need to de-burr this hole.  Not sure what the best way to do this is.  Any suggestions?

I'll hope to do the transfer ports tomorrow.  I will use the slot drill for these too.

Chris


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## Ramon

Hi Chris, Just caught up with this.

Glad the plate worked okay for you - I'm a firm believer in them for all sorts of ops.

Re the cutter giving you problems looking at the pic I'm assuming you plunged this through like a slot drill (which it is of course) however given you are holding this in a drill chuck it would be much better to centre drill, then drill say 2.5 then open up using the 3mm FC3 cutter. The problem arises in the cutter is trying to cut on the centre line and the chuck isn't rigid enough to hold the shank - hard jaws on hard steel are not a good combination. A little tip is to make a split brass collet to slip over the shank of the cutter - or even a shim cut from an ali beer can- you will get a much better grip that way 

If the holes are displaced from the position as drawn it will alter the timing. They need to be relative to each other as best you can get it but it's not absolutely _critical_ however the more deviation the more the potential for the engine not running as well as it should and you could be chasing all sorts of problems when you come to running it, not thinking that the timing could be wrong. As you have it it just means an earlier exhaust opening - shouldn't cause too much problem. Deburring - about the only thing is a nice smooth needle file, I have a few half round ones the very tips of which are ground like a scraper which I find very useful.

Given your chuck set up if you have a smaller FC3 cutter 2-2.5 then I'd run that down the port slot first leaving about .1 in the bottom then finish with the 3mm. If you dont have anything smaller then do it in several .15 passes. This will give the cutter the best chance of not pulling over to one side or over widening the slot -though that's not critical at all.

Hope you don't mind my input 

Good luck with it - Ramon

Just thought - I think you said you have collets - make a steel holder for the FC3 cutter that you can hold in a collet - ream it 6mm and cross drill for a grub screw - much better


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## jack620

Thanks Ramon.  I certainly don't mind your input.  You've saved me a lot of pain so far.

Yes I did plunge the cutter in one go.  Next time I will drill 2.5mm first as you suggest.  I'll make a small scraper like yours to deburr these holes.

I will buy a 2.5mm FC3 cutter and do the slots in two passes.  I couldn't bear to ruin a liner at the last step.

I do have an ER40 collet chuck, but I don't have a 6mm collet.  I will order one, but postage from Hong Kong is taking forever at the moment.  In the meantime I'll turn up steel holder to allow me to use the FC3 cutter in the 12mm collet.

I ran the timing calculator on Ron Chernich's website using the hole displacements I have achieved and compared them to the design timing figures.  To my inexperienced eye, the 0.2mm error in the inlet and exhaust ports didn't seem to make a lot of difference.  I guess I'll find out when I try to start them.

Chris


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## Ramon

Hi Chris, I don't think I explained the FC3 holder too well

If you take a short 60mm long or so peice of steel say 20 mm dia that will fit a collet you have then drill and ream that 6mm. Cross drill that to take a grub screw and that will hold the cutter much more rigidly than a drill chuck. Oh yes, it wont be so important on this op as the cuts are very fine but always, just as you nip the screw up, pull the cutter outwards onto the screw. If pushed backwards which is the natural temptation the cutter can pull itself outwards on the helix if cutting on the side plunging the cutter deeper into the work.

In commercial use the original FC3 cutter holders were nothing less than above with a screw thread on the end to fit into a Clarkson milling chuck.

You're on the right track using Ron's calculator - a real asset. If you are not seeing too much increase in exhaust opening you should be ok.

Glad to be of help - I'll keep following

Should be making a start on my new engine this week - drawings are near finished.

Regards - Ramon


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## jack620

Ramon,
I started making an fc3 holder today.  It's 16mm OD as that is the biggest collet I have.  It will have to wait until I get my 6mm reamer next week before I can finish it. Progress has stalled until I get my 10mm collet and reamers.  In the meantime  I will make some laps and the offset jig for turning the crank pin.

Good luck with your new build.

Chris


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## jack620

Not much progress on the Midge while I await some tools.  I&#8217;ve made the crankcase backs and the cylinder lap.  Which leads me to a few questions about lapping.  I know what I&#8217;m trying to achieve- a smooth bore with a very slight taper that tightens above the ports.  I&#8217;m still not sure of the technique.

Do you lap with the lathe running in back gear while moving the liner back and forth along the lap to produce a crisscross pattern on the liner?

When lapping the piston to fit the finished liner, you obviously must periodically slip the liner onto the piston to check the fit. How do you prevent the course grit on the piston from scratching the nice shiny bore of the liner?  Do you clean the lapping compound off the piston each time you check the fit?

I'm not having much luck finding carbide powder in the grits I need, so I will probably get myself an ultrasonic cleaner and use diamond paste.  On eBay there's set of 12 x 5g syringes of diamond paste from 40 micron down to 0.5 micron for $25 delivered.  The grits I need are covered in that range, but I have no idea how much I need.  Will 5g of paste do 2 pistons & 2 liners?

Chris


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## rklopp

I lap my liners before I make my piston. Then, I make the piston and contra to fit. Sometimes I might tweak the liner open a little after I make the pistons, using the lap. Sometimes I end up making more than one piston or contra to get the fit right. It's a heck of a lot easier to remake a piston than a liner. I always clean the parts in the ultrasonic prior to any test fitting. I also scrub the liner with a Q-tip to get more crud out. 

Your diamond paste kit will last you four lifetimes. You should need a tiny drop for each liner at most. I usually start with 15 micron or coarser and finish with 3 or 6 micron, depending on the size of the engine. I think I used 6 micron on my Midge.

I lap at around 350-600 RPM, moving the part back and forth to create cross-hatch. I use light spindle oil as the lubricant. I don't fart around much with trying to embed the grit in the lap by rolling or hammering. I get good cylinders just by smearing the tiniest dab of diamond onto the lap and then a couple of drops of oil. I dwell or make short strokes on the places I need to enlarge. I use the kind of lap you show and orient the liner with the bottom toward the screw end. This helps form the desired slight taper in the right direction.


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## Ramon

Hi Chris , I would totally endorse the methods and technique that our friend RK has said. When it comes to the amount of paste it really is very small indeed. However, personally my only reservation is the lap itself. That is not to say it won't work as obviously RK vouches that it does but the method does mean the taper is the wrong way as the liner needs to push on the lap bottom end first to be able to taper the bore below the exhaust. The technique for that is to let the cylinder dwell on the lap in that area as well as to lap in that area slightly more than the bore itself. As said previously the amount of taper is virtually immeasurable with normal means but you will feel it whilst lapping as it loosens off in that area. The object of tapering this area is to reduce friction where a seal is not so important. It also makes for an easier start to ensuring the piston is lapped to the bore without going undersize. Bear in mind when 'going undersize' on these engines you are talking very small tolerances indeed. 

Lapping is a pure hand skill and one which practice makes perfect. I would certainly bore a couple of scrap pieces of steel to practice on before diving in on the liners

I imagine also that the type of lap you have made will also wear on the point of expansion and not remain parallel along itself but on the otherhand it may soon 'lap itself' to the bore however any expansion would surely repeat the situation - How have you found this to work out in practice RK ?

The other thing I would be extremely wary about is the screw - it would be very easy to catch the bore and mark it on the head. Definitely not worth the risk at this stage. I would make this as short as possible and either use a grub screw or remove the head and cut a slot in for a screwdriver

As RK says by the time you get to fitting the piston you should have the bores finished and the piston lapped using an external lap so that it will just fit into the lower part of the cylinder. It's from that point lapping the piston to the cylinder takes over - by comparison this is a slow process as this is where you can make or break the fit you need with ease.
Use a microscopic amount of of the finest grade paste and plenty of lubricant then using a tee bar handle slowly wring the piston in the bore rotating it side to side and gently applying pressure forwards and backwards up the bore. Once the piston is in the bore to its (the pistons) full length, remove, thoroughly clean and lubricate and try in the bore.You may have to do this severral times before eventually the piston wears to the point it will slowly increase its depth in the bore until suddenly it will enter the upper bore. Stop at this point - another thorough clean, lube well and try. If the fit is right you should not be able to push the piston all the way down the bore holding your thumb over the top to seal it.

If the piston siezes at any point during this lapping process dont panic and try to wring it out with the handle - just insert a piece of wood dowel the other end and gently tap it out. Dont put any more paste on but give it plenty of lube and start over. Plenty of lubrication is better than less whilst lapping. - Its a messy process make sure your lathe is well covered to prevent the paste/waste getting on the ways

There are quite a few pics on the Tigre thread of these ops which you may have already seen
http://www.homemodelenginemachinist...g32-1cc-diesel-5cc-version-17674/index16.html

Sounds like you are getting close - I'm about to start machining today

Regards - Ramon


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## rklopp

I forgot to mention that I now use two laps, one for coarse and one for fine lapping. I have done it successfully with a single lap. I don't use a piston lap. I simply make an extra-long rod and polish the OD with 600 or 1200-grit paper and oil backed by a steel rule until I get the fit I want. I make the pistons from this rod. I face off a good chunk of the rod end to avoid barrel shape. I make the pistons tight and then fine tune the fit by lapping the liner some more.


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## jack620

Gents,
thanks for the very detailed answers.

I will order the diamond paste kit from eBay.  Sounds like I'll be passing it down to my kids!

I will replace the SHCS with a grub screw.

I'll have a think about whether to lap the pistons to the liners (Ramon) or vice versa (RK). I guess I want the most foolproof method.  I have already turned my CI piston stock down to 0.5mm oversize and long enough to make 2 pistons and 2 CPs plus some fat (see pic).  My only worry with your method RK is that I might polish the piston stock undersize at the chuck end but I wont know about it until I have parted off the first piston and CP.  I suppose I could just polish the end of the rod for one piston and CP, part them off and then polish the second piston and CP?  I'll have to sleep on it.

Chris


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## Ramon

Good morning guys,

Well I finally made a start on making swarf so its nice to be back on the lathe 

Thanks for the info RK - there is indeed always more than one way to skin the proverbial cat.

I have a couple of reservations in this instance with Chris's lack of material but that is not however to disagree nor denigrate your methods - you've made some very nice engines to prove your way works too.

My main thought is on tolerances - piston to liner. By making a long rod from which to part off the piston means the liner has to be lapped to fit which appears to me to be trial and error until the piston will fit. That presupposes if there are multiples the bores are more or less identical. As I envisage it by doing them individually there is much better control one to one. There is also the wastage of material to consider as opposed to parting off a piston then holding it in a fixture for lapping.

As I'm sure you are only too aware the tolerances are microscopic, part to part, to obtain the right fit - I feel by lapping the piston to the bore that is as close as you can get with the usual basic kit at our disposal and especially if the bore is tapered. However as said the proof is in the pudding and your engines bear testament to your method. As always I guess 'you pays yer money' etc 

The other thought is concerning the piston internal machining. If this is done on the lathe in situ then the piston has to be presented to the liner skirt first. If the inside is machined after then there is the possibility of distortion after lapping. Having suffered that latter on the Racer build I'm reluctant to finish turn and lap until all stress of internal machining are relieved.

As said this is not to disagree just thoughts from a different direction - I'm sure you would agree however that this one part of the build which has to be got right to achieve a runner - after all 'no compression - no ignition'

Chris - at .5mm up on diameter you still have enough material to part off a piston and hold on a fixture for final turning/lapping should you so choose. I usually leave about .075mm max on for lapping. Failing that I would only turn the stock you have reduced enough for one piston to this size plus a little, run a parting tool in to creat a shallow groove then lap either with a flat stone or as RK suggests with 600 grit stuck to something flat. That way you will save material. The groove will allow the 'lapping stick?' to overlap. If you do it this way, one by one ie one piston first followed by the next then the two contra pistons last you will have more control. One other thing the flat piece of material you choose for sticking the 600 grit to wants to be less than or just wide enough to cover the piston width - too wide and the tendency will be to taper the piston.

Now - I'm off to make some more swarf ;D

Regards - Ramon

Oh yes, For those who may wonder I'm posting about this Eta engine build this time over on Model Engine Maker
Having done the Tigres on here I thought that best and will cover the next build whatever that might be on here.


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## jack620

Ramon,
thanks for your wise counsel.  I have re-read your Super Tigre thread and the process is very well explained there.  I will follow your method.

That's not to criticise RK's method, but I feel with my complete lack of experience with lapping, parting-off before lapping will give me individual control over each piston-to-liner fit.

I finally have a set of M2 taps, a 6mm hand reamer and 10mm ER40 collet.  I will bore and tap the crankcases this weekend.  

I went to my usual fastener shop yesterday and bought the M2 screws for the heads and crankcase backs.  He only had stainless steel screws in that size, so I bought them.  Will these be OK in aluminium?

Chris


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## Ramon

Hi Chris, I'm sure RK won't be put out by that -this is a big step you're taking with little material to play with.

M2 screws eh? Well that goes to show how small the engines are you're making  - Yes stainless will be fine

Have a good weekends machining 
Regards Ramon


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## Till

Simply go to your local car repair shop and ask for a very little amount of valve seat grinding compound.


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## jack620

Thanks Till, but from what I have found valve grinding paste is designated as either course or fine.  I found one manufacturer that specifies the actual grit size and their fine paste was 220 grit.  That's too course for what I need.

http://www.chemico.co.uk/products.html

Chris


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## Till

The abradant will break up during the lapping process, forming smaller grit.


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## jack620

Progress has been slow. I have finally bored the cylinder liner hole in each crankcase.

I am now finishing the liners.  I have drilled the 4 ports in each liner and I am about to start milling the transfer slots.  I was planning to start with a 2.5mm 2-flute slot drill and finish with a 3mm 4-flute end mill. However I would like to clarify an issue with the size of the slots.

I have 2 sets of plans- the original inch plans by Mark Lubbock and a metric set by Ron Chernich (which I have been following to date).  The transfer slots on the metric plans are quite a bit bigger than those on the inch plans: 

Metric plan slot = 3mm x 0.5mm = 1.5mm2
Inch plan slot = 2.4mm x 0.38mm = 0.91mm2
Transfer port = #50 drill = 2.48mm2

As you can see, on both plans the transfer slots are substantially smaller in area than the ports they supply. But the transfer ports on the metric plans are 65% bigger in cross-section, making them closer in size to the port. I'm inclined to use the larger slots from the metric plans for better flow, but that only leaves 0.5mm of wall thickness on the liner.  Is that enough?

Why are the transfer slots much smaller than the ports?  Is this common on 2-stroke engines?  

Chris


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## Ramon

Hi Chris - from what you are stating I'm assuming the wall thickness of the liner is 1mm - I've just spent a while trying to find the drawings on MEN both on the web and on the MEN members disc to no prevail -

.5mm wall thickness should be okay and should not cause any problems but if you are concerned go to .4 depth and compromise - it should have little effect, if any, on performance and you can always deepen them later should you really think it neccessary.

I really don't have enough knowledge to answer your last question specificlly but -and I don't wish to be seen as flying in the face of so much that has gone before on these small engines - I've long thought that transfer passages especially in cast cases always seem excessively large in proportion to the fuel required to be transfered - indeed as I see it the larger these passages the bigger the case volume the less the pressure created to transfer the fuel - but then I have no training in such matters and may be totally on the wrong track so don't take that as a guide  The ports themselves obviously only allow fuel through to the limit that the piston opens and closes it - the bigger they are then I would say, within reason, the less restriction in fuel transfering

On the Eta engines I made, the passages in the liners are cut much as the Midge but the case itself is relieved inside to give an increased volume to the passage. There's no way of measuring the volume in the original but proportionally the original 15d has probably twice the volume than my 5cc version. All these 5cc versions run extremely well and give no impression that not enough fuel is available because of the relatively much smaller passages.

This pic might help - but you will need to make a cutter if you go this route. The passages here are just 1mm deep but there are four of them.





Good to hear you've made some progress - my basic cases are nearing completion I'm pleased to say

regards - Ramon

PS Have you got a link to the drawings or did you have to buy them ?


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## jack620

Hi Ramon,
Yes, sorry, the liner walls are 1mm thick.

I bought the plans in PDF format.  There are a couple of screenshots below. The original imperial version with the metric equivalents in red and Ron's metric plans.  I think Ron has just rounded to the nearest 0.5mm on his plans. I'm not sure if he has actually built an ML Midge using his own metric dimensions.  I'm inclined to use the original dimensions for critical parts like the liner.  That's why I drilled the transfer ports #50 and not 2mm.

Are you going to post a thread detailing your new build?

Chris


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## Ramon

Chris, As I'm sure you are aware it's the very top of the transfer port that matters not the centre of where it's drilled. Looking at these two drawings then Ron's version has the hole centre the same relevant to the flange but with a .22 larger hole places the opening point .11mm further up the bore ie an earlier opening. Whether that would make significant difference to the running at this size I'm not sure. In keeping to the original on port size #50 you haven't changed anything - the width of the passages as already said is not so critical. 

Are Rons plans viewable on MEN - I can't find them so far.

The current build is for some new Eta engines and the build for the Mks1 and 2 is destined to be published in ME magazine around April/May time. I have posted a few pics and update on Model Engine Maker but as I don't want to pre-empt the article the pics are being kept to a minimum. I haven't posted about them on here because of the recent Tigre thread besides to post on both sites demands too much time but I will post the next I/C build on here as opposed to MEM


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## canadianhorsepower

Why are the transfer slots much smaller than the ports?  Is this common on 2-stroke engines?  
	

	
	
		
		

		
		
	


	



Transfer ports should never be smaller then the channel
the size difference create a pressure and help your cylinder scavenging


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## Ramon

Hi Luc - Given the very small amount of material that Chris has to play with it's going to be difficult for him to achieve that given the areas quoted are correct - and I assume they are. Perhaps thats why Ron widened the slot on his layout. The only way would be to decrease the area of the port or to widen the slot. Indeed providing they don't break into anywhere they shouldn't the 'slot' could just as well be a flat milled across the liner at two points to give crescent shaped passages. 

I do agree though that the passages should be big enough to carry enough fuel for good scavenging but - ah theres always a but  - at this size and this type of low speed engine is that as quite as important as in something much faster and more powerful? 

Regards - Ramon


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## jack620

Ramon,
Yes I was aware that the top of the transfer hole is critical.  After liaising with Ron I decided to drill the holes #50.  I don't know if Ron has actually built the engine using a 2mm hole. As you say, I can always enlarge the hole later if I need to.

I look forward to the ME magazine article.

Chris


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## jack620

canadianhorsepower said:


> Transfer ports should never be smaller then the channel



Hi Luc,
just to clarify, my transfer ports are larger than the channels.
Chris


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## Ramon

canadianhorsepower said:


> Transfer ports should never be smaller then the channel
> the size difference create a pressure and help your cylinder scavenging


 


jack620 said:


> Hi Luc,
> just to clarify, my transfer ports are larger than the channels.
> Chris


 

oops - just realised I misinterpreted Lucs reply  - call it an age thing 

Ramon


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## canadianhorsepower

jack620 said:


> Hi Luc,
> just to clarify, my transfer ports are larger than the channels.
> Chris


 

:wall::wall: some big typo from my side:wall::wall:

 the port (hole in your case) should be smaller 
then the transfer it self. see this in reality use a garden hose and squeze
the output with your finger. You can direct or scavenge your water
the same thing happen with your motor. I would make the hole smaller
then rquest then finish it up with a dremel with a rectangular shape pointing
 to 50 degree instead of 45

cheers


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## jack620

Thanks Luc,
I thought that's what you meant.  As I have already drilled the ports I will use the larger slots size recommended by Ron.
cheers,
chris


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## canadianhorsepower

jack620 said:


> Thanks Luc,
> I thought that's what you meant. As I have already drilled the ports I will use the larger slots size recommended by Ron.
> cheers,
> chris


  this is what your angle should look like
the smaller the engine better the scavenging must be


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## jack620

Thanks Luc.

I drilled and tapped the M2 holes in the crankcases over the weekend.  All 16 of them.  It was a very tedious job, but I had to stay focussed because a broken tap would have been a disaster. One of the backplates isn't seating properly.  I think I have a burr around the rear hole in the crankcase. Also the cylinder liners aren't fully inserting into the heads.  I will need to mount the heads on some sort of fixture and clean up the top with the boring tool.

Chris


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## canadianhorsepower

They look good Thm:


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## rklopp

I built my Midge per Ron's plans including the transfer slots and ports, and it starts and runs very very well.


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## canadianhorsepower

rklopp said:


> I built my Midge per Ron's plans including the transfer slots and ports, and it starts and runs very very well.


 
I never assume it would not, but there is a difference between 
VERY VERY WELL and
Excelent


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## rklopp

canadianhorsepower said:


> I never assume it would not, but there is a difference between
> VERY VERY WELL and
> Excelent


Yes, one is an adverb and the other is a misspelled adjective.


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## canadianhorsepower

rklopp said:


> Yes, one is an adverb and the other is a misspelled adjective.


 
probablement que vous ne pouver pas ecrire en francais pourquoi chercher
les erreurs qu'an on écrit en englais. 
devenir vieux est une chose, devenir impolit en est une autre.

I hope that one day you can understand my french, and realise your not up to my level YET


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## jack620

rklopp said:


> I built my Midge per Ron's plans including the transfer slots and ports, and it starts and runs very very well.



Thanks, that's good to know.


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## Ramon

Hi Chris - I missed your post and just had a late reminder on email .

Good to see them coming together, they are looking good so far. 

Re the use of small taps - I agree it is always a bit heart in mouth with small taps but something you might like to see - it's a bit late now of course but in case you need it in the future....

Grind a small flat on the side of the tap just above the thread - just long enough to take a grubscrew point. Then turn and knurl a small disc about 25mm dia and 6/7mm thick and drill for the tap. Cross drill for a small grubscrew and you have a very controllable tap wrench for small taps. 25mm dia is just right for 10,8 BA and 2/2.5mm or so. The motion is very 'circular' as opposed to the wringing action of a tee bar. Originally I supported the tap by very lightly closing the chuck jaws - literally just touching but have recently found it much better to drill a small piece of brass to take the tap shank (loose fit) and hold that in the chuck as a guide. 

Here are a couple of pics from the Waller build - its being used on the lathe but the principle's the same. It's 12BA and a smaller diameter wrench- about 19mm.
	

	
	
		
		

		
			











Having been down the route you show - there's even a couple of sprung loaded points to support the tap chuck now lying fairly redundant in the tray I can say this is much the better way, particularly for 'feel' as to whats happening with the tap.

Hope that's of use to you.

Not that much further to go now eh? Whats next to do? 

regards - Ramon


----------



## canadianhorsepower

Ramon thanks for sharing this good idea:idea:


----------



## jack620

Ramon,
Thanks for the tip.  Meullernick posted a picture of a commercially made version of that tool and I did try to find one without any luck.  I don't have knurling tool, but I will get one soon and will make something similar to your setup.

Next?  Well I managed to get hold of some genuine 3/4" StressProof steel, so I will start on the crankshafts.  I will also part off the pistons and drill/ream the wrist pin holes.  I'm waiting for some diamond paste to arrive in the mail and I will buy one of these next week:

http://www.altronics.com.au/index.asp?area=item&id=X0111

Chris


----------



## jack620

I have the crankshafts about 80% completed. The shafts have been polished with 600 W&D on a metal ruler to be a nice sliding fit in the crankcase journals.  I left the first one way oversize and it took forever to polish it to fit. The second one I turned down to about 6.04mm and started with 360 W&D.  That was much quicker.

Today I made an offset jig and started turning the crank pin on one of the crankshafts.  It was a nerve wracking experience.  On two occasions the tool dug in, breaking the tip off the tool and dislodging the crankshaft.  Luckily I had left plenty of 'meat' on the crankpin so I was able to reset the crank in the jig and machine out the gouge in the pin.  I'm not sure why this is happening.  I used a freshly sharpened HSS bit in my diamond tool holder and I was taking very light cuts.  

One possible cause I can think of is that the jig isn't gripping the crank properly and the crank is shifting very slightly causing the dig-in. The reason for my suspicion is that when I made the jig I drilled the hole to 5.9mm and reamed it to 6mm. It seems my new 5.9mm drill bit wasn't very true because the reamer went thru too easily without taking off much metal at all.  It basically pushed straight in for the first half of the depth.  The crank _seems_ to be tight in the jig, but who knows?  I think I'll drill and tap the jig to take a cap screw to clamp the crankshaft.  Currently it only relies on the chuck jaws for clamping.

Maybe a diamond tool holder isn't the best tool for this job either?  It has a LOT of back rake on it and I wonder if this might be causing, or at least exacerbating, the dig-in.  I've used it on dozens of jobs, but never with StressProof steel and never on a job as critical as this.  Can anyone comment on this and/or recommend a more suitable tool grind for this job?

Chris

P.S. The pin is still oversize in the bottom photo.  It will be turned to 3mm and polished to fit the conrod.


----------



## jack620

This is the DTH for those who aren't familiar:

http://www.eccentricengineering.com.au/index.php?option=com_content&view=article&id=2%2


----------



## Ramon

Hi Chris - I haven't used one but I would have thought your tangential tool holder would be okay though it might be a bit large for such a small item. The problem I would say definitely lies in the gripping power of your fixture. You could help matters considerably if you put a very small centre in the end of the crankpin and support it with a tailstock centre. - I usually make the pin overlong and turn the centre away after if required but a small centre left in won't hurt anything.

Regarding tooling have you thought of using FC3 cutter shanks for toolbits?
Held in a steel bar - 3/8 x 1/2 -they make super cutting tools and can be ground to all sorts of shapes......






I find the best way to hold them for grinding is to drill a hole in the end of a short length of round bar as a handle and hold the bit with a grub screw.

I have recently posted this elsewhere - apologies for repeating myself. 

I find that tough steel En24t and the like usually needs a fair degree of top and back rake - nice and sharp for the finishing cuts and a reasonable radius on the tip.

You are getting on with them - not long now. Working on the backplates on mine

Regards - Ramon


----------



## jack620

Thanks Ramon,
I'll put a small pip in the crank pin as you suggest.  I have a couple of mm of extra length in the pin to machine off.

My collection of milling cutters is tiny, but I do have a few 100mm sticks of 6mm round HSS I bought for making small boring bars. I also have a set of the old Armstrong style tool holders that take 1/4" square tool bits.  I have a left, right and straight holder.  To date when I've needed to grind up a tool (like my fin cutting tool) I have used those.  I have a good supply of 2 1/2 x 1/4" sticks of HSS.

I've been following your build on HEM.  They are looking good!


----------



## jack620

Today I finished the crankshafts and I'm very happy with the results.  I tried drilling a small centre in the pin, but the resulting 'pip' wasn't very true and my dead centre would not engage snugly in the pip. Not sure why this happened, but I decided to mill, drill and tap the offset jig for a SHCS. That greatly improved the gripping power of the jig and I was able to turn the second crankshaft without any slippages.

The crankpins were turned to 3.05mm then I used 600 and 800 W&D to remove the rest of the metal until the pin was a snug fit in a 3mm reamed hole in a piece of scrap ali.  Next I will make the conrods and they _should_ also be a snug fit on the pins.

One of the crankpins rubs on the backplate, so I will have to face the backplate slightly, which should be easy enough to do.  I just need to determine from the plans what the gap between the crankpin and backplate is supposed to be.  I suppose I could use a feeler gauge to measure the gap?

Chris


----------



## rklopp

I usually use a crankshaft jig like yours, but without the split. I clamp the work using the screw threads in the end of the crank intended for the propellor stud. I insert a screw through some washers and pull the thrust face of the crank hard against the face of the jig. In cases when the crank threads are male, I use a nut instead of a screw. I don't think I've ever had a slip. I use carbide inserts, nothing too special, but ground to a sharp edge , rather than honed.


----------



## jack620

That's an easier way to make the jig than the method I used.


----------



## Ramon

Hi Chris - glad they worked out okay in the end - doesn't matter how you get there 

I use a different method than the fixture you and RK are using - more 'universal' but I like RKs idea of the bolt right through and I guess, RK, if the shaft has a threaded end you could use a hollow threaded 'nut' as a draw bar if the shaft doesnt protrude through far enough. The only con as far as I can see is that it's dedicated to the one shaft but of course if made large enough it could easilly have three/four holes at differing radii.

The other thing I would like to just say ref 'centering' the pin is that if there is a one in the end and you do happen to have it slip it can quickly be clocked in true again using a wobbler

Regards - Ramon


----------



## jack620

Thanks Ramon.

Both of the crankpins rub on their backplate.  Upon checking my plans it turns out the metric version doesn't include any clearance, so at least I know my machining wasn't the problem. The original inch plans include 0.015" of clearance.  I'm going to have to remount the backplates and machine off the excess.  My options appear to be:

1. mount the backplate on some sort of expanding mandrel (which I will have to make) and face on the lathe, or
2. screw the backplate to a piece of square stock through the screw holes, mount in the mill vice and mill the excess off.

I would appreciate any advice.


----------



## Ramon

Hi Chris, there are a number of options open however the usual expanding mandrel won't be viable as you won't be able to expand it as the screw will be hidden by the backplate.

You could do as you say and screw it to a block and hold in the mill or indeed the chuck on the lathe or..

If you have soft jaws for your three jaw you could machine them to take the flange - that would be my favoured approach but not everyone has a set of soft jaws.

Or (second favoured option) you could turn a ring chuck from ali which is a good method for holding such parts...

Take a short piece of round bar about 12-15mm bigger in diameter than the flange on the BP and turn a step on about 1mm deep and 5mm long then part off about 2-3mm beyond the step.

Reverse in the chuck and drill/bore through to 2-3mm smaller diameter than the flange.

Turn a recess in to take the flange leaving .5mm to come off and then remove from the chuck and hacksaw through in one place.

Return to the chuck with the cut between two jaws and nip sufficiently tight enough to turn the recess to accept the flange.

Pop the flange in, tighten up and face off.

You can make it from anything - Ali, steel etc. and it shouldnt take much longer than describing it 

Hope that helps - Ramon


----------



## Ramon

Hi Chris, just remembered I had this pic which should give you an idea of what I mean....





In this case the ring chuck is actually held in soft jaws but thats not essential - ordinary jaws are just fine. 
By turning the first step as described it helps when locating the short length in the jaws - just push the step up to the jaws for good alignment

Ramon


----------



## jack620

Thanks for the photo Ramon.  Now it's clear what you are suggesting. No soft jaws, so  I'll make up a ring chuck like yours. I've never seen these before and I imagine they are useful for a variety of jobs.  I continue to learn new techniques from this forum.  Building an engine is a steep learning curve, but the techniques learned make it well worth the effort.
Chris


----------



## Ramon

Hi Chris, glad that was of use. 

Yes they are a good little 'get me by' and hold the work extremely well particularly if you want to face something off quite thin. Their limitation is the lack of repeatablity (of concentricity) once taken out of the chuck. Marking where the no1 jaw is can help in that direction but usually the only way to get absolute concentricity is to re use them for something larger and re bore to suit.

As you say the learning curve can be steep but all these things add up to make matters much easier in the coming projects .

Regards - Ramon


----------



## jack620

I made a ring chuck and it worked perfectly. Thanks Ramon. I now have the required clearance between the backplate and the crankpin. Thm:

My diamond paste arrived yesterday.  I have a dozen syringes ranging from 325 grit up to 60,000 grit.  I bought an ultrasonic cleaner which I hope to receive on Mon or Tue. It's lapping time!


----------



## jack620

Today I lapped my cylinder liners.  I can't say I enjoyed the job.  It was slow and messy.

I used diamond paste in grits of 325, 600, 800 and 1200.  I cleaned the liners and the lap in the ultrasonic cleaner between grits. I ran the lap at 300 RPM in the lathe and tried to dwell on the area below the ports in an effort to make that portion slightly wider than the portion above the ports.  Whether I actually achieved this is anyone's guess.

The finish looks pretty good. It's quite shiny.  I hope I didn't polish it too much.  I took about 20 photos, but this was the best I could do.

You can probably see that my transfer slots aren't perfectly centred on the liner resulting in a sloped channel. I thought I had this nailed, but I guess it's the limitation of the lathe milling attachment.  Or maybe it's me.


----------



## canadianhorsepower

Wow Jack that's awsome lappingThm: great work
where did you get your diamond kit from, I can't find a supplier on this side of the globe


----------



## jack620

Thanks Luc.  I bought it from this ebay seller:

http://www.ebay.com.au/itm/150913509389?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_1028wt_1114

I made an offer of $20 and it was accepted.

Chris


----------



## GailInNM

Luc,
Diamond compounds are everywhere in the US. 
Shars and Amazon both have good prices on them and as I recall Shars ships to Canada by USPS on request.  Most other sources are two to three times the price. Lots on ebay also.

http://www.shars.com/product_categories/view/10501/Compounds__Compositions

http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Dtools&field-keywords=TEMO+DIAMOND+PASTE&rh=n%3A228013%2Ck%3ATEMO+DIAMOND+PASTE

http://www.use-enco.com/CGI/INPDFF?PMPAGE=307&PARTPG=INLMK32

http://www.mcmaster.com/#diamond-lapping-compounds/=lr17ao

http://www1.mscdirect.com/cgi/NNPDFF?PMPAGE=1033&PMITEM=05652490&PMCTLG=54

Gail in NM


----------



## canadianhorsepower

thanks Gail Ill try your sugestion
greately apreciateThm:


----------



## Ramon

Hi Chris, looks like you've done a fine job there, they look very good. Now comes the testy bit - getting a good fit on the piston .

It's difficult if nigh on impossible to measure the bore to get the size you need and you don't have much piston material to play with but if you turn up a piece of brass that will just enter as a tight fit in the bore then measure that you will get some idea of where to start on the piston leaving no more that a couple of thou for lapping. The brass will also give you an idea of whether you have lapped that clearance under the exhausts. 

If you are unlucky enough to go undersize with a piston don't bin as it it may be reclaimable but shan't go into that now. 

Yep you're right it is a messy business - hope you covered your lathe ways over 

Regards - Ramon

Edit - When I said 'two thou for lapping' that's referring to lapping the piston on the lathe using a piston lap to size it so it will just fit into the bore. Then lap the piston to the bore by hand to a final fit - use very fine grit  and an absolute minimal amount with plenty of lubricant. (I use 1000 grit silicon carbide - I don't know how that compares to diamond paste grit size)

Good luck Thm:


----------



## jack620

Hi Ramon, the brass plug is a good idea.  I will be starting on the pistons tomorrow. Hopefully I'll have some good news to report tomorrow night.

Chris


----------



## jack620

I have roughed out the contra pistons and I am about to start boring the innards of the pistons.  I want to clarify something before I do. If I bore the piston internals will I then be able to drill through accurately?  Won't a drill bit skate across a concave surface like the inside of a piston? In the Sketchup diagram below, the small white cylinder represents a drill bit (imagine it has a pointed tip). I have no indexing capability so I don't think drilling from both sides is an option for me. Should I drill the wrist pin hole before I bore the inside of the piston, or am I worrying for no reason?
Chris


----------



## Ramon

Hi Chris, I don't think it will matter either way you decide. 
I usually drill mine as they are turned using a cross slide drilling attachment, the inside having been previously bored out. I just go through with a drill but touch on the opposite face very gently to allow the drill to centre before putting any pressure on. 'Touch wood', I've experienced no deviation so far (except when I hadn't aligned the attachment properly ). If you are that concerned you could grind a 1/8 centre drill down to just under 3mm. I did one down to about 2mm on the off hand grinder using a round bar holder with a grub screw holding the CD in the end.

Can't wait to hear how you get on with the fitting 
Regards - Ramon


----------



## jack620

Ok, thanks Ramon.  I'll stick with Plan A, which is to drill & ream the wrist pin holes in the lathe milling attachment after I've bored them.

I turned up a brass plug for each liner as you suggested.  I was very happy to find that they are slightly tighter in the top of their respective liner than the bottom. If I can just finish these pistons without any mishaps it should be plain sailing from there.

Chris


----------



## jack620

Pistons ready for drilling and reaming of the wrist pin holes. They are 10mm diameter x 10mm tall.


----------



## Ramon

Hi Chris, it's all gone a bit quiet  - I hope it's all going okay for you. Have you lapped your pistons in yet?

My cases are finished, just taking a few days out before tackling the rest.

Hope to hear from you soon

Regards - Ramon


----------



## ShedBoy

canadianhorsepower said:


> Wow Jack that's awsome lappingThm: great work
> where did you get your diamond kit from, I can't find a supplier on this side of the globe



I bought this set and many other tools from this company with no problems

http://www.ctctools.biz/servlet/Categories

Brock


----------



## jack620

Hi Ramon,

No action this week. I have successfully drilled & reamed the wrist pin holes.  I have made a piston holding mandrel like yours and I hope to lap the pistons this weekend.  I plan to take it VERY slowly.

One of the liners has a slightly larger bore than the other, so I will lap the piston for that one first.  That way if I go undersize on the piston I can continue lapping it to fit the smaller liner (hopefully).  Then I'll get a second chance at lapping to fit the larger liner.

I'm still following your thread on MEM.  Those crankcases are very complex. Nice work.

Chris


----------



## jack620

Well, the weekend was a write-off thanks to kids' sport, but today I managed to get a small amount done.  I finished the piston mandrel and the piston lap. I hope to lap the pistons on Thursday.


----------



## Ramon

Nice one Chris - best laid plans and all that eh? Looking forward to hearing more in due course.

Ramon


----------



## jack620

Success!

I pretty much followed Ramon's technique from the Tigre thread with a couple of changes (shortcuts actually).

I started by zeroing the piston in the 4-jaw chuck and turned it down to about 0.08mm (3 thou) larger than the brass plug I had previously made to a snug fit in the liner.  Then I lapped the piston with 600 grit diamond paste and oil until the liner felt like it was just about ready to slide onto the piston.  I cleaned piston (still mounted on the mandrel) and lap in the ultrasonic cleaner and continued with 800 grit until the liner would just slide onto the piston by about a third of the piston's length.  Another clean in the ultrasonic cleaner and then I finished the job by hand-lapping the piston to the liner with 1200 grit and lots of oil. I 'wrung' the piston into the liner until it popped through, then called it quits.

A final clean in the U/S cleaner and I checked the fit with a good film of oil.  Feels nice and snug.  Now onto the CPs and the conrods.

Edit- the shortcut was that I didn't make a special T-handle for wringing the piston into the liner. I just left the piston on it's mandrel (last pic).


----------



## Ramon

Nice work Chris, wont be long now. 

Just a thought - don't know if you've made the wrist pins yet but fitting them with brass pads each end will help prevent the potential of scoring the liner if the pin floats. As they are quite small diameter that might not be quite viable so failing that a nice well polished radius on the ends will do and if you can make them so they are a tightish fit in one side of the piston even better

I'm back on mine as of today 

Looking forward to seeing them finished

Regards - Ramon


----------



## jack620

Thanks Ramon. I've been giving the wrist pins a lot of thought. The plans call for a 9mm long pin with radiused ends. Given that the bore of the piston is 6.5mm where the pin goes through, it doesn't leave a lot of cast iron for the pin to engage in (<1.25mm each end). Brass pads would reduce that even more. I think I will go with polished ends and a tight fit as you suggest.  

A couple of questions if I may:
1. Should I make the pins with a very slight taper by setting the topslide over (say 0.5 degrees)? That way I could turn them over-length then slip the piston on to the point where it's a tight fit, mark the pin and part off.
2. I assume I am supposed to heat treat the drill rod after turning and polishing the wrist pins?

I hope you had an enjoyable day in the workshop.

Chris


----------



## Ramon

I don't think I would turn them on the taper Chris, as that would mean the little end is wearing in one spot. If you are going to turn them make them very slightly up on size overall then 'polish' across (240 grit emery cloth, 320 wet and dry or a fine grade stone) until the pin will slip with a push fit into the piston from one side coming tight on the trailing end as it starts to engage on the other side of the piston. You can still make it over length as you suggest and then cut and finish turn to suit. Polish the ends before and after heat treatment. I don't know if you are familiar with H&T - I know silver steel is usually water quenched but I always use oil to lessen the potential for brittleness. Don't heat them too much either, just a nice uniform dull red and get them in the oil quickly before they begin to cool. Also temper them in hot sand for much better control. I have a small tobacco tin full that I preheat and bury the pins in it but constantly turning and checking them - at the size yours are they will soon heat up and you could take them too far - a nice blue going on brown is about right. 

Hope that helps 

Regards - Ramon

PS yes I did


----------



## jack620

Ok, thanks Ramon.


----------



## jack620

I finished the conrods today. There's a lot of work in these and I found it difficult to get the sides of the rods parallel. 

I started by drilling and reaming 2.5mm and 3mm holes at 20mm centres in 3mm thick aluminium plate. I made a pair of filing buttons from silver steel (drill rod). These are 5mm/3mm for the bottom end and 4mm/2.5mm for the top. 2mm screws hold the buttons and rod to a steel plate with M2 holes tapped at 20mm centres.

Note the Aussie 10 cent coin is the same size as a US quarter.

Chris


----------



## Ramon

Nice work Chris - I'm looking forward to the big moment 

Ramon


----------



## jack620

Thanks Ramon.

Today I finished the CPs (I think) and started on the wrist pins. No pics yet sorry.

I am a bit worried about the fit of CPs (maybe too tight). I used the method described on Ron Chernich's website. I super glued the CP to the piston lapping mandrel, set the topslide over a bit less than 0.5 degree and turned the CP with a slight taper. When the CP would just enter the cylinder liner I stopped turning and polished the CP with wet & dry paper and oil. I did this until the CP was a press fit in the top of the liner. I am able to push the CP into the liner with my thumb, but to get it out again I need to tap it out with a piece of drill rod and hammer. I doubt the CP would return itself to the top of the cylinder under compression. However, I figured I would leave the CPs as they are and see how they go. If they stick in the liner in use I will remove them and polish them some more to loosen the fit. 

Half a degree doesn't sound like much taper, but I reckon it's too much. Ron says if the walls of the CP are less than 0.5mm thick, they will compress in the liner and form a nice snug fit. My CPs have walls 0.5mm thick but I don't think they are compressing at all.

Should I try hand-lapping the CP into the top of the liner with some fine diamond paste (say 1200 grit) and oil?

The wrist pins are coming along well. They have been turned over-length, polished to a snug fit in the pistons and parted off. Tomorrow I will put them in a drill chuck and turn them to length. Then I'll heat treat them and lightly polish again (with the Dremel I think).

A question on motor assembly- Are the piston, conrod and wrist pin assembled before slipping the conrod big end onto the crankpin, or after?


----------



## Ramon

Hi Chris, I have tried this taper method myself and have to say did not have much success. Like you I considered the taper too much. That said there are others who have had success with this method but I think the wall thickness has to be pretty thin before it flexes. It's surprising how much force the compression will exert but if it is too tight this places a strain on the conrod and crankpin if the engine is flooded - which it will be at some stage no doubt.

I would say you're not far off if you can push it in with your thumb indeed that might be just a tad to loose so I'd stick with it for now. I certainly wouldn't lap it to the bore - that will be way too loose - but if you need to, just keep stoning it (on the mandrel) until you judge the fit acceptable. Once assembled you should be able to move the CP down the bore with the compscrew without 'forcing' the screw but there should however be some resistance to it. If on the other hand there's little resistance to the screw then the CP is definitely too loose. Unfortunately theres no real 'scientific' way of describing how to get the required fit - it's very much down to feel and experience with the little beggars. 
BTW Having to tap it out is not a problem but don't use anything other than a brass, ali or wood rod in the liner - you could easily score it with something like drill rod.


Usually I assemble the piston to the rod and drop the big end over the crankpin with the crankpin at TDC however some engines just don't have sufficient clearance on the piston skirt to allow this in which case the rod is popped over the c'pin, (screw the backplate in to keep it on the c'pin) then mount the piston on the rod. If you have to (gently) force the rod home mill a half round slot in a piece of wood to support the piston first.

Put the CP in the liner but no further than with the top edges level with the top of the liner then, making sure it's really clean but with a little light oil, pop the liner over the piston and push it home in the crankcase.

It's getting close to trying it - have you thought about fuel yet? Are you able to get fresh fuel? Also what about propellors - do have anything suitable or in mind?

Regards for now Ramon


----------



## jack620

Thanks again Ramon. Dunno how I would build this thing without your advice.

I will leave the CPs and see how they go.

Fuel- I haven't tried sourcing fuel yet, but I was planning to make it from Aerostart which I believe is 24% ether. Here's a recipe from the M.E.N. website for running-in and general purpose use:

PARAFFINIC BASE FUEL	45-60%
LUBRlCANT	20-30%
DOPE	1-2.5%
ETHER 20-25%

Props- I believe a largish wooden prop is best for running in a CI engine. Ron C used a 8x4 wooden prop to run-in a 0.8cc Midge he built. I suppose my 1cc version would want a bigger prop. Any suggestions?

Chris


----------



## jack620

I finished the wrist pins today. I heat treated them then polished the ends with a felt pad in the Dremel and 800 diamond paste.

I've run into a problem. One of the wrist pins doesn't fit into its conrod hole. That's because the wrist pin hole in one of the pistons ended up oversize because I drilled with a 2.4mm drill bit, when I probably should have used a 2.3 or even 2.2mm drill. End result was that the 2.5mm reamer didn't really 'bite' into the piston as it passed through. The wrist pin for that piston measures 2.58mm and the conrod is reamed to 2.5mm. I need to open up the hole in the conrod, but I'm not sure how.

Appreciate any advice.

Chris

This pic shows the piston sitting in an MDF 'cradle' to protect it while the wrist pin is being tapped home with a pin punch. Just clamp two pieces of wood together in a vice and drill a hole with a brad-point drill bit centred on the join.


----------



## jack620

I partially assembled one of the Midges and quickly discovered that I'm going to have to relieve the sides of the crankcase. I think RKLopp said he had to do this to his Midge too. I guess the Dremel will be getting some more work unless anybody knows a more elegant way of doing it?


----------



## Ramon

Hi Chris, this is all part of it at times 

You might be able to scrape enough clearance (you only need ''just enough') using a half round needle file just ground on the end to act as a scraper - just be careful not to get it too hot and take the temper out. I'd be reluctant to use the Dremel in such a small space but if you do be careful not to remove anything in the top of the case bore. You could however set the case up at an angle in your vise, liner bore toward the chuck, and bring in a longish end mill/slot drill - if you haven't one and can make a D-bit driving it from the chuck it will act like a boring tool - much more control that way.

Re the con-rod - if you have a round fine needle file (I wouldn't use a diamond one) try gently inserting it until it stops on the taper then just as gently rotate it 'backwards' to the cut ('forwards' it will just pull itself in) trying to keep it central to the bore and doing it from both sides. Finish off by rolling some 600/800 wet and dry around something smaller - piece of piano wire or similar and tease it with that until the pin will fit.

Re fitting the wrist pins - if you have to tap them in just make sure the piston hasn't swelled in the area of the pin before assembling the piston to the liner.

I thought you might have difficulty with fuel - I haven't had to use any form of starting fluid so can't really advise you - we are still fortunate over here that it's still available but even so from very limited sources.

What I would say however is having mixed your fuel do you have or know anyone who has a commercial, well running engine with which you can try it on. If it works on such then you can concentrate on your engine if it's lax to start but if you don't know the fuel is okay you could be spending a lot of time chasing something that isn't there. Quality of fuel in this case is important.

Prop size 8x4 wood is just fine - a 6" pitch to start with will load it - it's best to let it rev but not to let it get hot.

Glad to be of help Chris - I love messing with these little things - just want to see you have success with yours Thm:

Regards - Ramon


----------



## jack620

Thanks Ramon, I hadn't considered scraping the crankcase for clearance. Since posting I've been thinking of milling the area with either a 1/2" x 1/8" woodruff cutter, or a small boring bar held in my collet chuck. I would enter through the rear of the crankcase and remove a small crescent shaped area on each side. However, there is potential for this to go wrong with disastrous results. Scraping would be a safer way to do it. At least I have 2 crankcases to play with!

I think my wrist pin did swell the piston because it jammed half way into the liner when I tried to fit it. I tapped the piston out and wrung it back in with loads of oil.  I hope I haven't ruined the fit.

I'll have a go at the conrod with a round needle file and some W&D. I was going to make a 2.58mm D-bit, but holding the conrod securely while I ream it might be difficult.

I don't know anyone with a diesel engine who I can test my fuel on. I have found a supplier near me who sells diethyl ether. I just need to find out if they will sell to me without a special permit/licence.

Chris


----------



## jack620

I tried grinding a small scraper out of a piece of round HSS (I didn't want to sacrifice one of my good needle files). Either I'm hopeless at grinding scrapers or hopeless at using them (or both), but I couldn't remove any metal with it. I tried filing with a needle file but that was taking forever. I relented and tried the Dremel with a small toothed cutter. It was very aggressive, so I had to make like passes with a good grip on the Dremel, but it did the job. The finish wasn't pretty, but I was able to smooth it a little with a small wire brush tool in the Dremel. It would have been nice if the clearance had been shown on the plans so it could have been machined while the crankcase was in the lathe milling attachment vice.

The parts are assembled now (minus the CP) and everything moves smoothly. I'll fit the CP next and see how the compression is.

I will have a go at opening up the undersize conrod over the weekend. Then it's on to the prop driver and spinner.


----------



## jack620

I've searched eBay for an 8x4 wooden prop and I found just about every size but. I did find an 8x4 pusher prop, but that's no use to me. Should I go down in diameter and up in pitch or vice versa? I need a prop suitable for running in the Midge and another for use after it is run in. Although it will never actually fly, so the second prop should be chosen for engine longevity, not performance.

 Most of the recommended sizes relate to 2 stroke glow and 4 stroke engines. I gather a CI engine needs a slightly heavier prop to provide a flywheel effect? Any reason why I can't just use a nylon prop?
Chris


----------



## Ramon

Hi Chris, Well at least you've solved the problem. I had the same issue when building the Nova engine and set it up as here to mill out the sides with a long series slot drill...





When I modify a file I only do the very tip - no more than about 8mm long. I use a half round section and just take the teeth off the lower surface holding it on the periphery of the wheel so as to give a small degree of hollow and then just lick the sides to form a cutting edge. The back of the file can still be used as such and the rest of it of course is still okay.

Props - I like to use wood because they are usually much lighter and don't as such load the engine but there is nothing wrong in using nylon. For runnning in though and indeed for general demo running I would stick to 4" pitch - 6" again puts a load on and the engine will soon get (too) hot - it's much better to let these small engines run a bit faster and lightly loaded when running in. If you can't get a 7 x 4 for faster general running then you can always clip the tips of the 8 x 4 but make sure it's still in balance

I have just looked for wooden props here and 8 x 4 is readily available in the UK - 'Zinger' brand. If you really get stuck I can get you a couple and send them if you want.

If you can obtain some of that diethyl ether that will be much better than using starting fluid as you will have a known factor. I don't know what you can use for an ignition improver (dope) Amyl Nitrate is long gone and so is IPN. 'Improver' is availble over here from one supplier but I don't know exactly what it is. You should however be able to get away without using it on these engines but I would keep the oil and ether both at 30% with 40% paraffin. I believe there are additives for (proper) diesel fuel which can be used but have no idea what they are either. There are a lot of Aus control line flyers who use diesels who post on the Barton Control Line Forum -
http://controlline.org.uk/phpBB2/index.php might be worth a post to see what they do.

When you make your prop driver do you have a knurl? or will you have to cut it on the lathe with a side ways mounted tool?

Regards - Ramon


----------



## jack620

Ramon,
Thanks for the offer, but I found a eBay seller in the US with a good selection of Zinger props (but no 8x4s). I will order an 8x4 nylon for running in and a couple of 7x4s and maybe a 6x4 for demo'ing.

Haven't heard back from the ether supplier.  Will call them today. Thanks for the link to the control line website. I'll do a search there and see what comes up.

I have a set of knurls that I was given, but I don't know if they are diamond pattern or straight. I'm away at the moment, so it will have to wait till tomorrow. If the are straight pattern I will make a holder and use that. If they are diamond I think I will use a threading tool mounted on its side to carve grooves with the cross-slide. There's a good "how to" on the M.E.N. website explaining both methods. The pic below is from that "how to". It looks like Ron uses a tapered D-bit to cut the taper in the prop driver.  I was planning to make a very small boring tool and bore the taper with topslide offset 5 degrees. Not sure what to do now.

Chris


----------



## Ramon

Hi Chris - don't know if you've caught up with the Eta build of late but I've just described making the prop drivers which may be of some help.
As you've probably moved the topslide from doing the crankshaft I would turn a taper in some scrap first and blue it to your shaft adjusting the angle if neccessary to make sure the angle is a good match - once you have that making them will be quite straightforward.

Good to hear you've found some props - good luck with the ether.

I'm starting my crankshafts tomorrow 

Regards - Ramon


----------



## jack620

Yes I have moved the topslide since I machined the crankshafts Ramon. I'll do the bluing as you suggest.

I put a post on the control line forum and I have already been offered 250mL of diesel fuel gratis by a member of a local flying club. That has saved me a great deal of trouble. Thanks again for the link.

The Eta build is looking great. Good luck with the crankshafts. Some good info there on the knurling too.

Chris


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## jack620

Today I fixed the undersize hole in the conrod top-end. I thought I had a round needle file, but it turns out I don't. So I decided to try making a D-bit the same size as the wrist pin. I'm glad I did- it worked a treat.

I started by turning a piece of 6mm silver-steel down to 2.58mm and put a slight 45 degree bevel on the end. Then I milled away just under half the thickness to create the "D". I heat treated it and gave it a quick hone on an oil stone. The resulting surface was still a bit rough, with the milling marks still obvious under a 10x loupe. Despite that it did a beautiful job on the aluminium conrod and the wrist pin now fits the rod perfectly. I am completely sold on D-bits!

After assembling the piston/conrod/wrist pin, the piston jammed in the liner just like the other one did. I worked the piston/liner pretty thoroughly with oil and the piston now slides in the bore, albeit tightly. I have assembled the engine but it will need more work to loosen the piston/liner fit.

Chris


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## jack620

Progress has been slow lately. Today I finished the spinners. The prop drivers are finished except for the knurling. I'm awaiting a couple of straight knurls I bought off eBay.

I hope to make the spray-bars this weekend.

Chris


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## Ramon

They're looking really good Chris but my that matchbox shows just how miniscule they are. I'm not sure I'd be able to work so small -that must be very testing. Are you planning on fitting a nut to the venturi thread to stop the venturi rotating?

Glad you got the conrod sorted - D-bits can get you out of all sorts of scrapes 

Don't know what you are planning on using for needles but I find piano wire is ideal - probably 18swg (.048") would be suitable if not 20 swg. I used 18swg on the Nova engine but all the others use 16 swg. The point itself is not too critical - too coarse though and the settings can be sensitive - too fine and the settings too 'open' it does need to be reasonably concentric though. 

BTW the Nova is a great project and easy engine to build 

Regards for now - Ramon


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## jack620

Hi Ramon, the plans call for a 5 mm brass jam nut to lock the Venturi. 

The metric plans call for 1.5mm piano wire while the originals call for 1/16" for the needle. I'll use whatever I can find. Thanks for the tips.

The Nova looks great, but the 0.5mm fins look challenging.
Chris


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## Ramon

Hi Chris, That's a surprise that's quite thick wire for such a small engine. Just something to bear in mind re piano wire - well over here that is -possibly not in Aus.?

'Piano' wire is usually in Standard Wire Guage and as such has 'odd' diameters relative to drill sizes 16SWG -.063", 18SWG -048", 20SWG -.036. The wire itself however can be made into a very functional reamer to give a good fit on the wire. (See the Tigre post)

'Music' wire appears to be slightly different - we have over here 'KS Supplies' in most model shops which is sold in 'diameters' and is often sold as 'Piano' wire but the diameters differ - 1/16 _is_ .062 and the wire is not so hard and definitely less springy and easier to bend than true piano wire. It would still be ideal for making needles of course.

Don't be put off too much by these thin fins - like you I did have concern particularly that they might push over so I made mine slightly thicker -.8mm and very slightly tapered - 3deg. inclusive. 





Because of those thin fins the material chosen was freecutting En1a and no problems were encountered. However my friend John who had encouraged me to build one made his correct to print and had no problems either. One thing that did concern me was whether the transfer port would silver solder successfully due to the lead content but by keeping the heating to a minimum that caused no issues either.

I'm in occasional contact with another of your fellow countrymen - another Chris, Chris Dunn - who has not only successfully made a spark ignition version but recently made an impressive twin (spark) version as well.

Should you need some drawings I have a copy of the original as published in Model Aircraft magazine in 1946. Though there's a couple of ommissions there are no errors and are very good to work to. Let me know if you'd like to know more 

Regards for now - Ramon


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## jack620

Actually the plans do call for music wire Ramon- my mistake. 

The original plans use a 1/16" needle in a very basic spray bar with a 1/16" bore all the way thru.  Ron Chernich's metric plans use a 1.5mm needle in a slightly more elaborate spray bar that has a seat formed by the intersection of a 0.5mm bore and a 1.5mm bore (note the plans show a 1.0mm bore, but I think this must be a mistake- I have emailed Ron for clarification).

I am certainly interested in the Nova plans. I saw a picture of Chris's spark ignition version. If I went down that route I think I would opt for hall effect sensor and electronic ignition rather than points.

Regards,
Chris


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## jack620

Not much progress today. I turned the handle of a $3 screwdriver down to 19mm to be made into fuel tanks. I also turned up a small internal threading tool out of silver steel to cut the threads in the lid of the fuel tank.


----------



## jack620

Progress has been slooow. I finally finished the fuel tanks and lids.


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## jack620

OK, third time I've typed this because I got 'token expired' messages on my first two attempts.

I resumed work on my spraybars today. I drilled 14mm deep with a 1mm drill bit then reamed with a D-bit made from the same 1.5mm music wire that the needle valves will be made from. I slowly peck drilled, withdrawing the D-bit each time to clear the swarf. It seemed to cut very nicely, but as the depth increased the spraybar developed a quite pronounced bend. It was very strange. Maybe the step from 1 to 1.5mm was too big for the D-bit? I would have liked to drill to just under 1.5mm, but I didn't have a drill bit between 1 and 1.5mm. I'd better get some.

The music wire is a nice snug fit in the spraybar, but that may be because of the bend in the spraybar. The first pic is prior to drilling so the spraybar is straight. The second blurry phone pic was taken before the bend had developed very much. The bend is only in the threaded section.

Does anyone have any idea why the spraybar developed the bend as it was being reamed?
Any tips for straightening the spraybar?

Chris


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## jack620

I finally got a 1.3mm drill bit and had a crack at the second spraybar. This time the bending was WORSE. There's something about reaming the spraybar with a music wire D-bit that is causing the spraybar to develop a bend.

I finished the spraybar and decided to try and straighten it using the thimble. Here's the result:


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## Ramon

Hi Chris - just caught up with your difficulties - sorry to hear you're having problems.

Firstly though I have no idea as to why the threaded portion should bend as you describe I can only hazard a guess that the stresses induced when cutting the thread may be releasing as you 'ream' the hole out using your D bit. Bending is usually stress (relief of) related.

I use the wire as a 'reamer' but only to take a couple of thou off. You may have already seen these images but this is how it's ground (just a long slow flat taper) and used delicately.










The hole diameter is the nearest drill size to the piano wire - you may have music wire which is usually 1/16" so a 1.5 drill would be fine. It's important to withdraw the tool and clear the swarf very frequently as swarf build up will quickly jam on the wedge shape however if this reaming is done slowly and carefully then the cutting of a size hole is very good indeed. 

That first pic is reaming a 7BA threaded rod cut about 7/8" long - no room for wander as you can imagine, the second shows about the maximum swarf build up per peck for trouble free operation.

Personally, given the size of the spray bar, I would go for 18swg wire - about .048" - and still going about it the same way. That will leave more wall thickness on the spray bar thread which will help too

Hope this helps a little

Regards - Ramon


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## jack620

Thanks Ramon. On my second attempt I drilled to 1.3mm before reaming. When I make a replacement for the broken spraybar I will drill to 1.4mm then ream with a new music wire reamer with a tapered end like yours. I might even made a threaded sleeve to screw onto the spraybar thread and hopefully prevent the bending.

If that doesn't work I'll track down some 18swg wire and try that.

Regards,
Chris


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## jack620

I tried to straighten the other spraybar today without success. After many attempts at gently bending the spraybar I could only get the thimble to screw on about 6mm. I then tried re-cutting the thread with a button die. That just ruined the thread. That's two ruined spraybars. :wall:

Tomorrow I'll have to make two new spraybars. Hopefully Ramon's tips will stop the bending I experienced on the first two.

Here's the other piece of scrap brass. Excuse the dodgy solder job. I was going to clean that up, but there's no point now.


----------



## jack620

I made two more spraybars today. I used the music wire reamer with a tapered end like Ramon's. I also drilled with 1.5mm drill which was slightly undersize before reaming. The needles aren't quite as tight as they were in the first spraybars, but at least the threads are straight and the thimbles screw on easily.

Thm:

Chris


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## Ramon

Hi Chris good to see you got there in the end.

I'm not wanting to push info before you need it but this is a precaution 

Be careful not to use too much solder if you are soldering the needle into the thimble - it can run through and into the threads .

I use to do it fully assembled ie screw the thimble on, back off 1-2 threads, push the needle home and solder the thimble. Now I do the same but mark the needle position where it enters the thimble and remove both parts setting them back up to the mark before soldering. This only works if the needle is held straight concentrically enough by the thimble.

Good to see your steady progress - not long now eh?

Regards - Ramon


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## jack620

Thanks Ramon. I soldered the needles last night. I used Ron Chernich's method of marking the needle with a china-graph pencil either side of the solder joint. It prevents solder sticking where you don't want it. I was able to solder the needles while they were inserted into the spraybar without solder flowing into the spraybar.  I did apply too much solder to the top of the thimble though which looks awful. I'll make up a 1/8-40 threaded mount and turn the solder blobs off the thimbles.

My knurls never arrived from China, so I got a refund and now I have some on the way from England. Once the prop drivers are knurled I just have to make two compression screws and I'm done!

Regards,
Chris


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## jack620

I finished the carby/tank assemblies today. Just the prop drivers to knurl and compression screws to make and their done.


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## jack620

Here's how I mounted the thimbles to turn off the excess solder. Just a piece of 6mm silver steel turned down to 1/8", threaded 1/8-40 and drilled 1/16" to accept the needle.


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## jack620

Today I finally knurled the prop drivers. I also assembled engine #2. I would have attempted to start it, but I couldn't mount it. I bought some 2.5mm cap screws a while ago, but stupidly didn't buy any nuts! I think I must have been thinking I had a 2.5mm tap. Oh well, I'll get some nuts later in the week.

Note I'm using an M4 cap screw as a temporary compression screw. The plans call for 4mm all-thread to be used to make a simple bent compression screw. That's a joke. The only all-thread I can find is a very sloppy fit in the cylinder head. I've made 3 attempts at cutting my own screws on the lathe, but all have ended in failure (broken screw). Clearly I need a sharper thread cutting tool and lots more practice. I am attemting to make screws like the one by Ramon in the picture below.

I've also included a photo of all the fixtures, laps, jigs, templates, etc that I have made along the way.

Chris


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## jack620

Success of sorts. I was able to get engine #2 started fairly easily, but it runs slowly and very rough, so I need some advice.

A couple of points I observed:
The engine runs with the needle valve screwed fully in, so I obviously didn't solder it into the thimble properly.
The engine runs with the needle valve fully removed! I may try running the engine with the other carby fitted.
There is a very black pool of oil building up on the top of the cylinder head. There are bubbles in this oil from around the comp screw. I guess I have a loose CP? I'm pretty sure I can hear the CP moving up and down when I flick the prop over.
Fuel is 25% ether, 42% kero & 33% castor oil plus IPN.
It vibrates so badly it loosened the screws that secure the back plate.

Whats with the black sludge? Is that a normal colour for diesel fuel exhaust? I hope it isn't cast iron powder from the piston or CP. I cleaned everyting in an ultrasonic cleaner and/or nitro thinner before assembly.

Here's a video of the engine running (spluttering actually).

[ame="http://youtu.be/WR1X5HOWRPU"]http://youtu.be/WR1X5HOWRPU[/ame]

Chris


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## Swifty

Must be very satisfying to at least have it running. Not really having any ideas about fuel ratio, but maybe there is too much castor oil in the mix.

Paul.


----------



## Ramon

Hi Chris - first off well done for producing a running engine despite its 'apparent' problems. It sounds and appears however that it may be oscillating which is a sign of over compression and too rich a fuel setting. It will vibrate considerably if it is doing this. If you can't close the needle then you have no control over the fuel setting.

Your fuel make up sounds ok but how much IPN did you use - Did you actually get IPN  (lucky fellow). Also what is the prop size.

Other than that taking it one thing at a time -

Bubbly oil coming from the comp screw means only one thing and that is as you rightly say a contra piston too loose. You probably _can_ hear it going up and down with the piston. I wouldn't continue to run it like this until you have sorted that out. If you made the contra piston out of cast iron you may be able to grow it by heat treating it - check out the Eta thread again. I had to do this on two CPs on this last lot. It's a good way of recovering a loose CP but you can only do it the once.

Black gunge coming from the exhaust is usually one of two things especially early on like this. As said you may have it overcompressed a bit so it's running 'hard' which will sound rough also getting hot very quickly which will create a carbon rich exhaust. Once it's running right, it's probably just the parts bedding in and the black content will soon diminish. Again you can see this on the Tigres and the Etas

Setting the needle to re-solder - screw the thimble right in then back off two turns. Heat the solder then at the same time push the needle inwards to seat and close the orrifice - you can check this is closed by putting some fuel tube on the inlet and blowing down it. Being able to run with it right out probably means no more than that the orifice is very small - sufficiently small enough to let the engine run rich.

Don't despair - the fact that it's firing speaks volumes. You'll certainly know when you have the settings right - if it will run like this at the moment it should be more than capable of running much better once you sort these small issues

Any further advice on running just ask - I'll be glad to help
Good Luck - Ramon


----------



## jack620

Hi Swifty,
After a bit of research, 33% castor seems to be what is needed for a plain bearing motor to prevent excessive wear.

Ramon,
Thanks, you've put my mind at ease a little. 

I bought this fuel from my local model club. It was originally 20% castor, so I added more. That dragged the ether content from 30% down to 25%. I believe it has 1.5% IPN.

Prop is 8x4. I also have 7x4 wooden props. Should i change to those now?

I'll re-solder the needle first and see if I can get it to run smoother.
Then I'll try to grow the cast iron CP.

Hopefully I'll have some good news later this afternoon.

Chris


----------



## jack620

Today came and went without much workshop time. I swapped the carbies over and the other carby does allow me to shut the fuel off. However the motor doesn't run any better. I have removed the CP and I'll try to 'grow' it during the week using Ramon's technique (heat & quench in oil).

With the head & liner removed I was shocked at how much the piston wobbles on the conrod. I don't mean in the direction you would expect it to wobble, but front to back. It wasn't like that when I installed it. I must have used a very soft grade of aluminium. The rods were cut out of a piece of 3mm thick aluminium angle. I don't know what grade is typically used to make angle. I think I'm going to have to make two more rods from a tougher aluminium. The plans call for 2024. Wikipedia says this about 2024: _"It is used in applications requiring high strength to weight ratio, as well as good fatigue resistance."_ I think I'd better get some.

Chris


----------



## jack620

After a bit of research it seems likely my conrods are made from 6060 aluminium. While not a strong as 2024, it still has good strength, so I'm surprised my top end has worn so quickly.


----------



## Swifty

Why not make them out of phosphor bronze? The little bit of extra weight surely won't make much difference.

Paul.


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## jack620

Sounds good, but where do I get it Paul? I only need a piece 30x15x3.


----------



## Swifty

Can give you some Chris.


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## jack620

I popped over to Paul's house today and he gave me a piece of bronze. Thanks Paul. 

I will make 2 more conrods out of this bronze. I see no point in persisting with the aluminium ones. Paul showed me his almost finished inline twin diesel. It looks very nice. I hope to see it running soon.

Chris


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## jack620

On closer inspection there doesn't seem to be much point in 'growing' the CP. It's cracked.


----------



## canadianhorsepower

jack620 said:


> On closer inspection there doesn't seem to be much point in 'growing' the CP. It's cracked.


 

Damm is Murphy's law following you :hDe:

I guess it's better to see it now then kicking a rod out
does look very good  Thm:


----------



## jack620

Agreed Luc. Better to get it right before the engine self-destructs.


----------



## jack620

I got my other Midge running today. 

[ame="http://youtu.be/v4mPGnQNQA4"]http://youtu.be/v4mPGnQNQA4[/ame]

Needless to say I was thrilled. It ran very smoothly for two tanks of fuel, then it wouldn't start again. I pulled the head and liner off and discovered the wrist pin had broken in half (sorry about the blurry pic). The wrist pin is W1 steel. Any ideas what might cause it to break? 

When starting the second engine today I was surprised at how little compression was needed to get it to run. This has got me thinking that I had the other rough-running engine over-compressed as Ramon suggested. The piston and rod in the picture are from that engine. Check out the bend in the conrod big-end. I'm obviously doing something wrong. Could over-compressing the engine cause the conrod to bend?

Chris


----------



## canadianhorsepower

> Check out the bend in the conrod big-end. I'm obviously doing something wrong. Could over-compressing the engine cause the conrod to bend?


 Hi Jack, to answer your question over compressing would not do this to your rod. I wonder if your cylinder is not slightly out of alignment with your crank. This would cause a ton of stress on the pivot points and that's what you're getting
my 2 cents


----------



## Ramon

Hi Chris congratulations on another runner and this one far better than the first  It certainly sounds how it should and appears to be running well. Thm:

If the wrist pin was hardened it looks like it was not tempered through enough -W1 steel ? is that equivalent to silver steel? If so, I know its small diameter, but try drilling a small hole - say 0.8mm through its centre and temper it in hot sand to a deep blue/brown colour. Sand allows the heat to build up slowly.

Whilst I agree with Luc that overcompressing per se would probably not cause the rod to bend in a usual 'over compressed' state the fact that you appeared to be oscillating back and forth on that first video possibly between a well overcompressed contra piston certainly could. Something led to that cracked the CP and probably that score across it. To bend a rod normally requires the piston to come up hard against something and I would guess that was the culprit.

Anyway - you've got your first runners - great work Thm:Thm:

For myself I'm taking a break from engine building for a while - off on a new 'tack' - I'm going to have a go at building a model yacht 

Good luck with your future builds.

Regards - Ramon


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## jack620

Luc,
Thanks I'll check the alignment, but I'm confident it is OK. I think Ramon is right- I probably drove the CP into the piston. Hence the cracked CP and bent rod. I wish I had asked an expert to show me how to start it. I would probably have avoided all this damage. :wall:

Hi Ramon,
The W1 is water-quenching silver steel. I didn't temper it at all. oh: Being such a small engine I didn't think it would need it. I will make 2 more using the method you suggest.

Thanks for all your help with this build. I couldn't have done it without you. Good luck with the model yacht. I wish I could return the favour and offer you some advice, but I know nothing about them! 

Chris


----------



## wakeup

6060 is pretty much only good for window frames, sad to say.  Recently I was trying to buy some 2024 T3 or better material for con rods.  It was very expensive, as in not practical.   Legend goes that 2024 is the preferred material because of its high temperature strength.  So I did some digging, what I found was that, certainly 2024 does have better high temp properties, but not to the exclusion of any others, especially 7075 T6, which is available at a sensible price.

If you want a small piece of 2024 T3 PM me your details and I'll stick a piece in the post.

Ramon was spot on with what he said.
cheers
Bill


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## Ramon

You're welcome Chris - it was a pleasure to assist and especially so to see them run at the end despite the small set backs. 

I've messed around with these little power plants since the age of thirteen but the buzz I got from that Nova when it burst into song was just like that first engine so I _know_ just how you feel 

Regards running it's always best to start with the contra piston well backed off to begin with, gradually turning the compression in a third of a turn or so (depends on how coarse a thread on the comp screw) flicking all the time until you begin to feel the compression building. Looks like you had that first one well screwed in to begin with. Never mind it's all part of the learning curve 

My wife Sue and I took up R/C sailing last year. Sue's as keen as I am so it's very much a joint interest. The need is there to build a yacht (or two!) and to some extent that will take over most of my attention for a while but I'll be back on another engine in due course Thm:

Well done Chris - keep on going

Regards - Ramon


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## jack620

Hurry back Ramon!


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## jack620

Here's a belated follow-up on my Midges. I finally remade the 2 conrods using the 2024-T351 that Bill (wakeup) kindly sent me.

Both engines have been reassembled and one of them has been run about 6 times. I actually re-used the cracked CP (see post 123) because the crack doesn't go all the way through and it runs very nicely! I'm very glad, because I really didn't feel like making a new CP.

The other engine is fairly stiff and needs to be "run in" with the lathe before attempting a start. I'll get around to that on the weekend.

A big thank-you to Bill for giving me a piece of hard-to-source 2024.

Chris


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## modelmotor

Hallo Chris,
Your ML Midge model engine looks great.You are a  well skilled person and you might be proud with the results now your engine is ready.
I like to make small engines just like you ,in my case the Boll Aero,Boll Major,B.J.Cicada and now i will start with probably the Little Dragon 1 cc glow engine.
I could n't obtain a plan from the EZE model engine serie,neither a plan from the GNEZ-1.They all are designed a bit equal to each other.
I will start building in the Autumn time so that will be in about 3-4 months.

                                                                                                    many greetings from modelmotor-Gerard-The Netherlands-Europe.


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## jack620

Hi Gerard,
Thanks for the compliments. Just today I tried to get the other Midge running. It's been sitting on the bench in my workshop waiting for me to find the motivation to try and get it running again. It needs to have the compression screw wound in a long way for it to fire. It will then start and run very roughly. If I back the screw out it stops running.

I also think there may be something wrong with my carb. The engine will run (roughly) with the needle jet removed and my thumb placed over the hole that the jet screws into. I have no idea what that means.

Here's a video of it running. I hope that somebody will be able to diagnose the problem for me.

http://youtu.be/_ozAWq1RZCA


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## Rodrigo Castellanos

amazing !   thanks for sharing! i´m new here and i want to start my first build.


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## Chris Murphy

jack620 said:


> Hi Gerard,
> Thanks for the compliments. Just today I tried to get the other Midge running. It's been sitting on the bench in my workshop waiting for me to find the motivation to try and get it running again. It needs to have the compression screw wound in a long way for it to fire. It will then start and run very roughly. If I back the screw out it stops running.
> 
> I also think there may be something wrong with my carb. The engine will run (roughly) with the needle jet removed and my thumb placed over the hole that the jet screws into. I have no idea what that means.
> 
> Here's a video of it running. I hope that somebody will be able to diagnose the problem for me.




Your Midge is running under-compressed and  quite rich-you need to wind the compression screw in further still yet. All these model diesels have a sweet spot of about 1/8" turn (it depends a bit on how fine or coarse the comp screw thread is) for any particular prop load-at which the engine will run smooth without misfiring-less than this optimum and it will run 'rough' as you call it-more than the optimum-and it will start to run 'hard' and laboured. Once you have the comp setting right, then you can play with the needle valve to get it running most economically (ie the setting that it will run longest on)-again-go too far and it will start to misfire and labour to a halt.

The Midge was designed to be easy to make-there was no effort whatsoever put into optimising the design in terms of venturi and porting-for someone prepared to experiment with port sizes, timing, transfer passages, intake geometry etc you could get a bit more performance out of it....but that was never the point of the design-it works, and produces sufficient power to fly a model-so meets the designer's intent admirably.

ChrisM
'ffkiwi'


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## jack620

deleted


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## jack620

Chris Murphy said:


> Your Midge is running under-compressed and  quite rich-you need to wind the compression screw in further still yet.



Hi Chris,
I don't know if you are aware, but my post to you was six years ago! Thanks for the response though. Since then I managed to get the Midge running by placing a seperate fuel tank above the carb so gravity would assist the flow of fuel. I was able to get it to run continuously but it was still a little rough. I was happy with that. I built a pair of Midges and the other one runs beautifully. They were never intended to power a model and both now reside on display stands.

Cheers


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## jack620

Rodrigo Castellanos said:


> amazing !   thanks for sharing! i´m new here and i want to start my first build.



Hi Rodrigo,
Let me know if you want the plans for the Midge.


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## Rodrigo Castellanos

hi Jack! thanks! i already have the plans, i´m thinking about what engine build first, a Boll Aero or the midge....  i have a small lathe, today got a 4 jaw chuck, and tomorrow will get an small mill, so, once i have the mill, will see which is easier to fix in my small machines.    anyway, the midge is my favorite as i´m a free flight guy, and seems any Vic Smeed design can be flow with it. 
by the way... your midge with fuel suction problem.....   the carter have a nice fit?  maybe you have some leak and not enough vacuum to such the fuel...   will be nice to see your engines running!


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## Chris Murphy

jack620 said:


> Hi Chris,
> I don't know if you are aware, but my post to you was six years ago! Thanks for the response though. Since then I managed to get the Midge running by placing a seperate fuel tank above the carb so gravity would assist the flow of fuel. I was able to get it to run continuously but it was still a little rough. I was happy with that. I built a pair of Midges and the other one runs beautifully. They were never intended to power a model and both now reside on display stands.
> 
> Cheers



Jack I wasn't aware-but my response above was just responding to the daily digest I get which shows new daily posts-I must confess I didn't check the date of the preceding post-(your post #135) relative to the last post #136 when I replied.....obviously I should have! That being said, designer Mark Lubbock's intent was to design a motor that was both easy to make-AND produce enough to fly a model.....his 0.8cc version did fly a 2 channel R/c model quite successfully. And we have one locally here which I've seen flying a free flight vintage model......which is where mine will end up when i finally get around to finishing it...

old threads being resurrected years later seems to be a perennial problem-I get this on many other fora as well....often to the extent that the original poster has in some cases either died, or alternatively dropped out of modelling-but you often don't realise the time gap when you get notified of a new post in a very old thread.....

In your specific case it would seem your Midge is lacking suction, which is a rare problem in sideports-which generally suffer from too much rather than too little-but this could arise from multiple issues-slightly too large a venturi bore, not enough restriction from the spraybar, poor atomisation, needle geometry etc.

ChrisM
'ffkiwi'


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