B.J. Cicada build

[Jasonb]

If you do end up making a new cylinder then bore it undersize by say 1mm or 0.50" so there is less bulk to heat up, solder and then once its all settled down bore and lap to fianl size. Thay way you won't distort anything with the heat, pit the bore or have to clean up the bore.

 

[modelmotor]

Hallo Werowance,,
I have seen a great lot of high tec skills you have.You can really build a very beautifull B.J.Cicada engine.
You might be proud on yourself because all the parts you made are
very proffesional and well made.
My Cicada can n't even stand in the shadow from yours as it comes to craftmanship and beauty.I even went through the maincrankcase with my metal sizel because of having left not enough material at the bottem of the crankcase.
I had a nice nylon hammer and pushed back the very thin(like silver paper) aloy what was left after that mistake.I even have n't glue it to close and lucky i was the engine ran for 90 minutes which made my neighbours left their home in angryness.
I saw your cilinder troubles .The problem is that the cilinder must not be getting it to warm/heat on a sudden spot otherwise the roundness will
be ruined.I will write you a personal message how to do this welding or soldering from the intake tube.
Your B.J.Cicada diserves many likes in my opinion so congratulations with the results.At this moment i am busy with a new project a 8,02 cc model glow engine designed by my engine friend from England Mr.Chris Boll yes the man from the B.J.Cicada,the Boll Aero 1,8 and the Boll Major 4,4 cc.

many greetings from modelmotor

 

[Billitmotors]

G'day Werowance
Jasonb is closer to the money. I would have made the crankcase first and then the front bearing (or as you have called it the snout piece) as it is easier to make the OD fit a bore than the other way round.
You said that you have a boring bar is it a carbide tipped bar or a ground piece of high speed steel ground to a boring tool shape?
The better the fit of the of the boss in the crankcase the less chance that the four screws that hold the two parts together will work loose while running. Also I would definitly take a a skim across the front face of the crankcase adjacent to the 7/8 bore.
I would then mount an angle plate on your faceplate with a 7/8" alignment disc screwed to the faceplate. You then mount the crankcase over thie disc using a finger clamp from the angle plate. You can then move the face plate around until your previously marked out .625" bore is set up on center ready to be bored out. I would also again take a skim across the face adjacent to the .625" diameter.This will give you two square faces to mount the front bearing and the cylinder on.
Boring tools are supposed to be mounted slightly above centre which will always leave a small conical tit as you go past centre, but there is nothing wrong with lowering the tool for a final pass to remove the central tit. High speed steel tools are easy to grind to shape and you can make them to suit any job.

 

[GeorgeGreek]

Hi wero,
There is one point left i.e the developer....
Any idea
Thanks in advance

George

 

[werowance]

Hi wero,
There is one point left i.e the developer....
Any idea
Thanks in advance

George

by the developer, do you mean the person who designed the engine?
from what I gather it was Chris Boll and Rob Jenkins

 

[modelmotor]

Hallo Werowance,

The B.J.Cicada has been developed by Chris Boll from the U.K.,but the story goes a little bit further.Rob Jenkins from Australia a man with lots of experience in building high quality home made model engines did some modifications and refinements at the porting system.Now after all the engine is based on the knowledge from both persons.So Chris decide to give the engine a much more realistic name based on B(Boll).J(Jenkins).Cicada 1.4 model diesel engine.The picture aompagnied with this reply shows all the engines Chris designed ,but still without the big brother which i showed a message ago.That
8,02 cc glow engine is more or a less a kind of test case for me to see if it all works as intended.

many greetings from Gerard-modelmotor-Europe.

 

[Billitmotors]

G'day Werowance
Sorry i haven't seen your posts until the other night, as i haven't been on the site for a while.

I have a couple of questions:-
What sort of lap are you using to lap the bore of your cylinder?
Are you using a split brass lap with a screw in the end to expand the end and add a bit of taper to the bottom end?

What sort of torch are you using to carry out your silver soldering?
You only really need a propane torch to carry out this job as you only have to get the parts to a dull red colour. If you get it much hotter you get scaleing and burning of the parts. When you are silver soldering add your flux and start heating, watch the flux, at first it will dry out, but as you keep heating it will go clear and turn liquid, at this point it is time to touch your silver solder to the job, just brush it against the job and and if it is at the right temperature the silver solder will melt and adhere to the joint. (While doing the heating keep your torch moving the whole time) Once your solder starts to melt if you move the flame in the direction you want the solder to run the silver solder will actually run around the joint, just keep adding a little more solder sparingly and you should get a neat joint.
I should add that the better the fit of the joint the better the solder will run.

Also what sort of silversolder are you using? The best one I have found is easyflow 50% silver, it is more expensive but if every thing is clean ( wipe over all the parts with metholated spirits to remove any oil) and the joint is good, when you reach the right temperature the solder will run very well.

Why did you machine off the top of the crank case and the head to vary the compression, that is what the contra piston is for.

When you make your new cylinder you will need to add the corresponding amount to the bottom of the flange to make up the difference, other wise you will have changed the timing from the original design.
When you make the new cylinder, bore it out to within a couple of thou of the required size, don't ream it, as you can sometimes get an out of round bore which then makes it very time consuming to lap straight and round, also you should aim to end up with a very slight taper at the bottom end of about .001" to .002".
You should also machine everything and carry out all your silver soldering before you start your lapping

When you make your piston and are fitting it to the cylinder, just break the top corner of the piston with a small radius(.002" to .005") aim for it to be just starting to tighten in the bore as it goes past the top of the exhaust port.

I also noticed that your wrist pin looks to be a sawn cut and then polished finish. You really need to machine a large radius on both ends to help stop it from picking up in the cylinder. unfortunately the drawings don't really show this very well.

You were right about the 10X32 UNF thread on the compression screw and head.

Your contra piston needs to be a tight push fit in the cylinder which can be moved down by the compression screw and then when you release the compression screw, the compression of the running engine will then move the contra piston back up.( there should be no blow bye at all past the contra piston)
If you have a look at Model Engine News, look at the DCO contra piston method,it works brilliantly. Ron's site has so much invalueable information on it for motor building it should be read by anyone intending on having a go at engine building.
I hope this helps.
Rob Jenkins

 

[Billitmotors]

G'day Werowance
your fuel mix should be 20% castor oil 30% ether and 50% kerosene.
I noticed your remark about the decanted ether boiling.
Ether has a very low flash point and will boil in sunlight or at 34.6 degrees C It is also dangerous because it is a heavy gas and will move across the floor and doesn't take a lot to find an ignition scource. So it is not a good idea to leave the lid loose as you will loose all thee volatile s from the bottle.
I also noticed that in the photo with the tank set up to run the engine, the tank looks to be quite high which makes it hard to regulate the fuel supply it really needs to be level with the venturi.
Rob.

 

[werowance]

Billitmotors, thanks for your reply,

EDIT - Billitmotors, just spoted the part about not reaming the cylinder in your post i might just make a bigger boring bar so i don't have the deflection. and on the wrist pin, it does have a decent radius on it that i did with a file in the lathe before i polished it so it wouldn't gouge the cylinder wall

1. for the lap I was trying the sand paper on wood dowel, I plan on the next cylinder to ream it then us a real lap made from copper pipe.
2. for the silver soldering, I usually don't have an issue using silver solder, it was just the cast iron piece would not take it. sometimes I use my jewlers torch and sometimes I use my homemade propane burner. the 12l14 takes the solder just fine and i really don't know what was up on the cast iron, but shouldn't have been using castiron for the cylinder in the first place
3. I machined the top of the cylinder just as a last ditch effort incase there was just to much blow by on the contra piston or something, this does not change the timing on this engine. machining the bottom will change its timing.
4. on fuel, thanks for the heads up on the ether and mix ratio, I ended up buying a bottle of pre mixed for diesels from tower hobbies.
5. on fuel tank, i have it so that gravity brings fuel to about .250 inches from the bottom of the carb, in other words there is about .250 inches of air bubble in the fuel line right as it attaches to the carb, if i raise the tank up, then fuel will flow in and keep running in the engine.
6. ill take a look at the dco contra piston thanks for that.

and I know where a good deal of my problem is with the engine, I have a tapered cylinder either caused by my boring or by my lapping method or both. so my next one when I get a chance will be reamed instead of just bored, then laped with a copper lap like the ones on model engine news. I have never made a lap before so i shyed away from it on the other cylinder.
also i just learned from some other posts last week or so ago that my contra piston is not tight enough i machined it from the same stock that the piston was made from exactly the same size diameter as the piston so on the next one i plan to make it just a little tighter as the recommendations from the other posts.

i just have to find the time to get back in the shop. and finish up my dro install which i think will help

 

[Billitmotors]

G’day Werowance
If you are intending on your engine being a runner, sandpaper on a dowel will neither get a round or a straight bore.

Laps are the easiest things to make. Just get a piece of brass that is bigger than the final size required and machine it down till it is .001” to .002”smaller than the bore of your cylinder, your cylinder is approximately 1.6” long so make the machined length of the brass 2” long plus your chucking length.
Once you have machined the parallel 2” length centre drill using a No 2 or No3 centre drill then drill with a 5.1 drill or 13/64” drill around 1.5” deep. Then using a ¼” BSW or 1/4” UNC TAPER tap, only let the tap enter for 16mm or 5/8” of an inch. Next get your hacksaw and cut down the axis of the lap for about 1". Run your tap in again to the same depth remove it and screw in a 1/4" allen headed cap screw until it just starts nipping up.
You can either use diamond past or aluminium oxide lapping paste, I prefer the diamond paste which you can buy cheaply on Ebay.
To load the diamond paste onto the lap put a small amount (it goes a long way) on a flat piece of steel preferably high speed steel and while pressing the lap hard against the flat steel roll the lap over the paste.
Cover your lathe bed with plastic and put the lap back in the chuck leaving a small amount of the chucking piece protruding from the chuck jaws so that the cylinder can touch on it without marking the it.
Set your lathe to run slowly and slide the cylinder, head first onto the lap, use kerosene as your lubricant and turn the lathe on. It can be worth making a shroud that the cylinder is attached to so it protects your hands. Grasp the cylinder and slide it back and forth along the lap. Your aim is to get a cross hatched surface finish over the entire length of the bore. You will need to keep incrementally tightening the screw as the lap wears and the bore size increases and becomes round and straight.
When you first start use coarser grit paste and once the bore gets an even matt finish over the entire length go to a finer grit. It is worth having a second lap prepared to use with the finer grit. Once you are happy with the finish of the bore wash and scrub it clean of any grit before you try and fit your piston and contrapiston.
When you make your contrapiston use the DCO method it really works well. Also what sort of cast iron are you making your piston and contrapiston from. I've been using P4 centrifically cast cast iron, it is really fine grained and machines easily.
I hope that this helps.
Rob.

 

[werowance]

i did see that technique for making a lap on model engine news. the taper of the tap is like making a tapered thread which expands the brass, i am considering it,

but while i was looking around on ebay i saw this :http://www.ebay.com/itm/ACRO-USA-7-...410?pt=LH_DefaultDomain_0&hash=item35e6be471a

at 50.00 its a bit pricey but its got me wondering that if i can find a cheaper one, would 7/16 laping tool work for this engine, it calls for .437 as final size, so would a 7/16 .4375 be correct for a commercial made lap?
do commercial laps start a tad under size and 7/16 is its maximum expanding size or is 7/16 its minimum size and expands out further?

 

[werowance]

and while i am on the subject of possibly buying some tools, i was also looking at an external hone. to me the word hone = scratchy finish and not polished, but also reading on model engine news as well as one of my magazines home shop machinist i saw the use of external hones like the one listed here http://www.modelenginenews.org/~modeng74/faq/hone_art.jpg which i can purchase fairly cheaply. the 2 examples i have seen it used in produced a very smoothe finish from the looks of the pictures. what do you all think.

 

[werowance]

Also what sort of cast iron are you making your piston and contrapiston from. I've been using P4 centrifically cast cast iron, it is really fine grained and machines easily.
I hope that this helps.
Rob.

Rob, i have both dura bar and 2kun5 cl40 gray cast iron.
last piston and contra were made from the dura bar.

but i know for a fact now that my contra pistons have all been way to loose, and i like the idea of tapering the contra as described on the other web site. will have to give that a try. i also liked the idea of a Viton oring since i wont run it very long and have no problem replacing an o ring. even though the oring way was not recommended on that other site.

and thank you for all your help.

 

[Billitmotors]

G'day Werowance
I haven't used one of those commercial laps so I couldn't say how small they go,but you can buy a whole lot brass for $50 and the split lap can also be used to add a little taper at the bottom end.You can also make a whole lot of laps out of it ,it shouldn't take more than 10 or 15 minutes to make a couple of laps.

Your outside lap is good but you still have to be careful nut to turn your piston into a barrel.
Are these external laps for sale over there and if so how much are they?

I am not a fan of Orings in the contrapiston, besides the fit of the contrapiston still has to be done properly and then you still have to machine the groove for the O ring. Sounds like a make work program to me.

Using David Owen's method, tapering the outside of the contrapiston also relies on the fact that the wall section of the contrapiston is thinner than normal which gives it a little bit of springiness and makes for a better seal. I haven't had one failure since I started using this method.

I have just finished a Thaller T39 which is a 2.5cc long stroke diesel I used the DCO method and it worked perfectly. I have attached a few photo's.
Rob.

 

[werowance]

that's a nice looking engine, on the outside lap, the only place I have found it for sale is in the uk. and I was thinking of ordering the kit (tool envy)
here is the website http://www.pollymodelengineering.co.uk/ its in their pdf download

 

[werowance]

I also like the compression screw on your engine there. I might have to steal that idea and replace my tommy bar with a knurled screw like that one.

thanks again.

 

[Billitmotors]

G'day Werowance
The compression screw isn't my design it was from the drawing of the T39. I prefer the tommy bar as you have better control over the compression adjustment. If your contrapiston is a bit tight you can't get a good grip on round headed screw.
Rob.

 

[werowance]

well, got back at it for a little while yesterday afternoon. cylinder 3.0. and I found yet another mistake I had made on 1.0 and 2.0 (aside from the bad bore and lap job) the diameter of the cooling fins, I had left them on both of the previous ones at 1.250, but the plans call for the fins to be 1.100 . no wonder it was so hard to get the screw in at the base as well as get the carb bung soldered on.

anyway I got the cylinder bored and took extreme care and time just barely skimming with each pass until I hit .4365 as best I could measure. I guess + / - .002 isn't going to affect running as long as I match both pistons to it.

It was getting late and I stopped at cutting the cooling fin groves. for the life of me I cant recall do I take .607 and divide by 4 to get the cut points for each groove? I mean really I should know this as this is cylinder 3.0 but I just blanked out last night, and now im at work so I cant realy just make some test marks in blue dye just to tell until tonight.

 

[werowance]

got back at it last night, for the fins its divide .607 by 5 to get the 4 fins. which I managed to mess up during cutting, but it'll do. my parting tool I had used to do the others had so much chatter that it walked on me a little. oh well hopefully if it runs no one will notice.

on the plus side of things, my new dro was awesome fro cutting to depth on the fins. no more making a gauge to judge the depth by. just run it up on the smallest diameter part of the cylinder (in the area where intake and exhaust ports go) with a piece of paper between it and the blade, zero out the dro back it off and go to first fin to cut and go till I hit 0 again then repeat. that's nice.

and while I type this, makes me realize what the chatter was probably caused by. I had set my parting tool to center with my tailstock center thinking I needed to be on center so that the dro would be correct. I realize that it wouldn't have mattered as long as I was touching the cylinder when I zeroed it even if I was just a tad below center line like normal when parting. oh well.....that's another lesson learned.



cant wait to get the final dro for my way. right now all I have it on is the cross slide and milling head.

 

[Billitmotors]

G'day Werowance
I have been away with work for a week without a computer.
Sounds like you have been having fun.

Your right about the final size of the bore so long as you match the piston to it.

I purchased a DRO for my lathe but have only fitted the long slide scale as there isn't enough room to fit the cross slide scale. Having said that the easy way to set your depth of cut is as you said touch the tool against the job with a piece of paper between, zero your dial and at the same time using a marking pen draw a line on the cross slide dovetail casting and also draw a "O" adjacent to it. Then after determining how far you have the wind the cross slide dial in, cut the first groove and stop the machine. Then use your marking pen to place a mark on the cross slide casting and add the reading of the dial so that you don't forget your final depth of cut. Then reposition the tool to cut the next groove and so on.

What sort of parting tool are you using? Is it a piece of HSS that you have ground to size and shape or is it one you purchased already made?

Usually the reason that parting tools walk is either it is being run at too high an RPM, the tool is not on centre or or the cutting angle geometry is incorrect, usually the clearance angles are too great.

Another thing to watch is that during the normal use of your lathe the compound slide with the toolpost on top can end up overhanging the dovetailed slide, which when you start using a tool like a parting tool can can cause vibration, if so reposition the compound slide so that it is fully supported. Also check the adjustment of the gibb strip on the compound slide and cross slide and adjust it for minimal play then take a cut.

When you are parting, being on centre is probably the most important thing, also try to make sure your tool is set square to the axis of the job.

If you are using a two or four way turrret style toolpost have all your tools matched with the correct size packing and keep said packing and tool as individual sets so that you can swap tools at any time and know that each tool is on centre every time. If you are going to set each tool up this way do it with a piece of material in the chuck and take a cut across the face if you are below centre you will end up up with a parallel nib in the centre of the job, if you are above centre you will get a conical tit and if you are on centre it will cut the centre off cleanly.
Rob.