# Hubbard Marine Engine



## deverett

For a long time I have considered building the Hubbard 2 stroke marine engine from castings available from Heinz Kornmuller http://www.classic-motors.at/modellmotoren/modelengines.htm

  The fact I have not seen any build articles going all the way to completion, and also only one You Tube video all helped me resist temptation.  There must have been quite a number of casting kits sold around the world; surely there must be more than one model completed?

  On this forum, Ive found only 2 references to this engine:
http://www.homemodelenginemachinist.com/showthread.php?t=20591&highlight=hubbard
http://www.homemodelenginemachinist.com/showthread.php?t=20772&highlight=hubbard

  Brian Rupnow rekindled my interest with his very interesting build of a 2 stroke engine based on the Hubbard.  I waited until Brian had got a working model and then decided to take the plunge and spend the kids inheritance - all 191 EU - on a set of castings.

  During Brians build saga, I started looking for information on the full size engine.  Theres not much out there, but I did stumble on a volunteer helper at Mystic Seaport http://www.mysticseaport.org/  and he has helped me a lot with pictures of engines and answered many queries.  Thank you, Nate.

 The castings duly arrived and looked good and clean.





 The drawings came on a CD to be printed by the user and are very well detailed in both Metric and Imperial measurements (using exact conversion), but the engine if produced to the drawings would be very basic so I am attempting to make a few embellishments to get the engine looking closer to the Real Thing.
  Things that I noticed on the full size engines:
  A priming cup was fitted to the cylinder head.
  There is a cooling water drain on the side of the cylinder jacket.
  The crankshaft was greased by external oilers  one on each crankshaft housing and one in front of the flywheel for the crank pin. 
  The flywheel incorporates a starting handle.
  There is a crankcase drain.
   The cylinder oiler has 2 drip feeds, although I cant find out what the second one is for and anyway, my skills are not good enough to make this type in such a small scale.
  The model carburettor bears no relationship to the original Schebler item.  Looking at the construction of these in full size, there is no way to reproduce it in 1/5th scale.
As time goes on, there may be some other additions.

  On measuring up, the castings have almost no machining allowance: definitely no room for error in setting up.  The diameter of the cylinder jacket is undersize and the crankshaft brackets are undersize on length and diameter.  It seems like the drawings are a guide to making the model and should not be trusted implicitly.

Dave
The Emerald Isle


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## deverett

I have made a bit of progress on the engine before writing this because otherwise there would be long gaps between postings.

  Now to tackle the main casting.  First up was to determine the centre of the crankshaft hole.  I got a piece of aluminium and made 2 plugs that were a tight push fit in the cast holes after filing bits of flash off to get them as round as I could by eye.  A drop of super glue as well as the push fit ensured they stayed put.

With a pair of jenny callipers I found the centre of the future hole.  The curved end of the callipers hooked onto the rim and the point scribed an arc.  This done in several places gave a good indication of where the centre should be.




Standing the casting on its head and checking that it was upright, using shims as required, I scribed a line through the centre on each side of the casting.




 There is no easy way to hold this casting, so with future operations in mind I mounted the casting on a pair of 2-4-6 blocks to machine the underside of the mounting lugs.  The height gauge was used to ensure both centre lines were at the same height using shims as required, the mounting lugs were machined flat.  I was now able to easily hold the casting steady and true for further operations.




 The casting was now held the right way up on parallels in the machine vice and the bore was worked on.  I interposed card between the vice jaws and casting faces to help resist movement and absorb slight inaccuracies in the casting.  Firstly the top was flycut and then the bore was tackled with the boring head.




The bore has two diameters - the main bore and a small step for the  liner to sit on.  The liner will have a healthy dollop of Loctite 574  gasket compound to seal it, hopefully to prevent water leaking in and  fuel leaking out.

Dave
The Emerald Isle


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## kadora

I had intended to build this engine from classic-motors castings
but then i changed my mind and bought castings for De Dion engine.
Anyway keep us informed on your progress.


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## Blogwitch

Good progress Dave.

If ever you have to block up a hole to find centre again, I used to use a sheet of lead to do it, just tap it around the periphery with a small hammer until it automatically wedges itself into the hole, then you are ready to go.

I can't remember what bit I used it on but I should have a piccy somewhere showing the method.

NB.

I remember now, it comes from my Scott flamelicker build.

Lead tapped into hole






Finding centre so that it can be marked out






Also note the digital measure turned into an accurate edge following scriber, an idea shown to me by John Stevenson, and it is a great for a scale that has worn out or damaged tips.


John


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## deverett

Blogwitch said:


> Finding centre so that it can be marked out
> 
> 
> 
> 
> 
> 
> Also note the digital measure turned into an accurate edge following scriber, an idea shown to me by John Stevenson, and it is a great for a scale that has worn out or damaged tips.
> 
> 
> John



John

I like that idea of modifying the blades of calipers.

Dave
The Emerald Isle


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## deverett

There is a protuberance on the bottom of the casting that I suppose is there as a chucking piece, but for what purpose, I cannot think.  So, the first enhancement was the fitting of a (dummy) crankcase drain.  Full size, this was a plate screwed onto the bottom and a drain cock fitted.  The chucking piece was sawn off and the casting held in the four jaw chuck and faced off.  Over to the vice and the four screw holes drilled and tapped and also the centre hole for the cock.  The aluminium used for the casting is very gummy and tapping 10BA holes was very taxing - plenty of WD40 was used.  The largest threads on this model are 7BA - 0.0983".  Strangely, I felt more anxiety tapping this material than harder metals with these small threads.

  I had to do this now because the chucking piece was too long and would not have been allowed the casting to be mounted on the lathe otherwise.




 To machine the crankcase, the casting was set up in the lathe using a centre held in a collet and another centre in the tailstock bearing on the previously marked centre dots to ensure it was level front to back.  Shims were used on top of the wedge blocks so that the height setting was maintained when the holding down bolts were tightened.




 When all was ready, drills were used in increasing sizes until I could easily get the boring head in the hole.  It was just a matter of then increasing the bore until the correct size was reached. Doing it this way ensured both sides would be the same size, regardless of any out-of- truth in the lathe.




Dave
The Emerald Isle


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## Brian Rupnow

Dave--I'm happy to see that somebody is building this engine, just so I can see all the steps required. My engine works very well, however that carburetor with the check ball in it seems to want to run at one speed and that's it. You can gain/lose a few rpm by fiddling with the spark timing, but not much. That engine is rather special to me, because it is the first time I fully lapped a piston into the cylinder with diamond compound and ended up with fantastic compression with no rings on the piston at all. That was a first for me. Good luck with your build, I will be following.---Brian


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## idahoan

Hi Dave

It's good to see you working on a new project; I will enjoy following along with your progress.

Dave


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## Jasonb

Comming on well Dave,

I can only think the chucking spigot was there so you could bore the cylinder and face it off as the first operation and then set everything else out from that.

Then from lathe to rotary table set vertically and skimmed the underside of the mounting lugs and bored for the crank all while held by the spigot.



J


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## deverett

After the bore was done, the first crankshaft bracket face was machined  using the boring head as a fly cutter.  Not a lot of room between the  mounting lugs on the back swing with the tool wound out!




  It was over to the mill and resting the previously machined flange  on parallels, the second face was cleaned up.  I used a piece of 5/8"  HSS to act as a spacer between the side of the vice and the machined  bottom of the crankcase.  A quick check with a DTI on the top of the  cylinder showed it was good enough for me. The casting was now true to  the mill table X axis for future work.  The head end had been chocked up so that  the single strap clamp held everything secure.




 With both faces machined, the various bosses on the front of the  cylinder could be faced off.  Found an omission in the drawings - the  small round blob just above the clamp is not shown!  Fortunately it is  not a problem because the part that screws into it can be adjusted to  suit.  Like I said earlier, the drawings should be treated as a guide.

 The bosses were then drilled and tapped.  From the top, there are 2x 10BA, 2x 9BA and 2x 8BA The round boss will be 8BA.




Dave
The Emerald Isle


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## deverett

The model uses glow plug ignition but the glow plug is rather out of scale.  What I did was to machine the hex of the plug down by 15 thou. on each face.  The round part below the hex was also reduced in diameter.  Hopefully the plug will still work.  The design has the glow plug screwing straight into the cylinder casing, but here again I'm trying to get closer to full size and have made a plate that will screw onto the ignitor boss.  The plug will slip in the central hole and with a bit of luck when screwed tight, I will still have a seal.

  The ignitor plate is a piece of steel about 0.036" thick and this was just sawn and filed to shape after the 4 holes were drilled.  Ignore the top two holes; I was trying to be clever and put one hole too close to the edge.  Don't want to waste too much - these small bits always come in useful.




The drawings show the glow plug on the half way line but full size it is below, so this is what I have copied and the glow plug is 50 thou below centre.  The two lock nuts have since been thinned down to be closer to prototype.




  The boss on the cylinder will need to reshaped somewhat later on.


Dave
The Emerald Isle


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## deverett

Moving on down we come to the push rod bracket.  This required a  piece of 5 x 5 mm steel, of which I had none.  A raid of the potentially useful bits yielded something that didn't take too much effort to get down to the correct cross section.  The easiest way to hold it was in the side of the vice.  A spare piece of the steel was used to balance the pressure of the vice jaws while the holes were drilled and the slot machined out.  The part then had to be turned 90 degrees for the ignitor push rod hole.




  The ignitor pushrod shown (round bar) is a convenient find from a dead printer.




   Lastly, the part was trimmed to length to give:




Dave
The Emerald Isle


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## Blogwitch

Dave,

I used to hate setting up small parts in my 6" milling vice until I invested in one of these.

A 1" Vertex toolmakers vice, just set it down onto parallels and use it to hold all the small parts, no more trapped fingers or bodging up some way to support them. I usually use bits of lathe tool steel as parallels for it.






I could even use large cutters around it.

Mine was rather cheap compared to what they cost nowadays, but if anyone needs something like this, Arc Euro sell them and they have a 10% discount offer at this time.

John


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## deverett

Another good tip.  Thank you, John.

Dave
The Emerald Isle


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## deverett

Now after that little light relief, it was back to the next real job: the crankshaft brackets.

  They have a taper along their length so to hold them in the chuck, the thin end was padded out to get a decent grip.  The chuck is a Grip-Tru, so it was quite easy to get reasonable concentricity.  Man, that aluminium is gummy; lots of WD40 didn't seem to make any difference.




With the register machined, the casting was reversed in the chuck and held by it to turn the taper.  If I had followed the drawings, the taper should have been 5 degrees.  I managed 2-1/2 degrees to keep a decent amount of metal at the front.
The housing was drilled out 9.7mm so that when temporarily fitted to the crankcase I could check the alignment before reaming.
It was pleasing to note that after turning the step in the back that I  got a nice light push-in fit with both brackets in the crankcase.   So it does pay off to measure twice and cut  once after all!




  I did notice that using the small carbide boring bar(dry) that the quality improved considerably while machining the recess.




Dave
The Emerald Isle


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## Brian Rupnow

Still watching Dave. It's nice to see a "real" Hubbard going together.---Brian


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## deverett

With the brackets ready to fit, the first one was pushed in place.  Using the DRO's PCD function, it was easy to set out the 6 holes for the retaining studs.  Tapping holes went through both parts and the bracket was eased out and the holes in the crankcase tapped.




 The metal is less than 80 thou thick so my intention was to fit lock  nuts in the cavity.  That was until the inevitable happened: I had  either too much pressure or perhaps not enough pressure on the tap when  withdrawing it and the thread stripped.  Yes, locknuts are now a definite  necessity!  That was the first side done.  The casting was unclamped and the parallels rotated to give clearance for the bosses on the front of the cylinder.  Same procedure as before to line up the casting and repeat drill and tap.  Well, darn me if the same thing didn't happen again and another thread came out 'rather loose'.  Each housing and the crankcase was centre popped by the top hole: one pop for the front and 2 for the rear,  just in case there is any discrepancy.

  I now needed some studs to hold the three main bits together.  Don't care what the purists might think, but I have some 7BA threaded bar that I'm going to use.  Just need a quick way of getting 12 studs to the same 3/8" length easily.

How I did it:
  Use any piece suitable of material- in this case a piece of HSS -  in the front toolpost as a stop bar + the rear parting tool.
Move carriage towards the headstock so that the parting tool is *Just *clear of the chuck jaws. Lock saddle.




  Adjust topslide so that the distance between the cutting face of the parting tool and the piece of steel is 3/8".




Put the threaded rod in the chuck and wind the cross slide in so that the stop bar makes a stop for the embryo stud and nip up the chuck.  
Wind the cross slide back out and the parting tool will come into play.
Cut off stud, withdraw parting tool, wind in cross slide cleaning up cut  end if necessary and pull out the material from the chuck...  And so  on.  Takes longer to write about it than do it.  12 studs in about 5  minutes.  I held the stud material directly in the chuck, but there was  no damage to the threads.




 With everything ready for a trial assembly I discovered that there isn't sufficient room within the crankcase to fit locknuts; the holes are too close to the walls - not my mistake I hasten to add! 
  A peek inside the crankcase will show what I mean with a potential locknut alongside an inserted stud, so a quick decision determined that two-component locknuts (JB Weld) will have to be used instead.




 After having said elsewhere that the castings were undersize, a measurement over the crankcase flats showed that after machining they are 15 thou over!  I'm not going to argue with that: I need all the metal there that I can get.  I'm sure no-one will notice.

  The crank brackets  were temporarily bolted in place and I was very pleased with myself when the 10mm drill was pushed through to check alignment, and all did indeed line up.




[FONT=&quot]The [FONT=&quot]brackets[/FONT] now needed the bushes, so these were turned up from a suitable piece of bronze that was long enough for both parts.  Taking note of what Brian discovered about wear in the bushings, I made sure I used bronze instead of ordinary brass.







[/FONT][FONT=&quot]The two bushes were pressed into the housings using the vice. A couple of pieces of padding protected the end of the bushing and the face of the housing.   I just started the press and then put a drop of Loctite 638 in the housing as a' just in case' but the press fit was quite tight, so whether the Loctite actually did anything is moot.






[FONT=&quot]Dave[/FONT]
[FONT=&quot][FONT=&quot]The [FONT=&quot]E[/FONT]merald Isle[/FONT][/FONT]



[/FONT]


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## Blogwitch

Coming along really nice now Dave, and a good write up as well, I can understand everything you are doing..

John


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## deverett

The drawings show a groove in the bushes for oiling the crankshaft.  Remembering Brian's wear problems with his crank bushes, I decided to follow full size practice and use proper grease cups.  On the full size engine there is one on each housing and they stick up like butterfly antennae.  I will put a spiral groove in the bushes stopping short of the ends and hopefully keep the crankshaft well lubricated.

  The grease cups were made in 4 parts.  I put a hexagon on a suitable piece of brass bar then turned down a bit on each side to form the union, the cup and cap were simple turning jobs and the stems started life as a tent peg!




  The crankshaft brackets were again temporarily fitted and the assembly held in the vice at the appropriate angle.  Holes were drilled and tapped for the grease cups. 




Dave
The Emerald Isle


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## deverett

Jumping around a bit, I wanted to make a couple of small parts that form the ignition lock out.  Made from 3mm steel bar, the end was threaded 10 BA and then  the 12 BA pivot screw hole was drilled and tapped; the bar was turned 90 degrees so the 1mm slot could be made and the piece parted off afterwards.




  The lever was filed up from some 1mm steel.

  Completed bracket, lever and pin.  A bit closer to the real shape.




  One more little bit to make - the other part of the ignition lock out. P2.7a and P2.7b in the drawing above.   This was done in similar fashion to the previous part.




It is now time to start work on the crankshaft.  I was hoping to have some sort of counterbalance but soon realised that if I did, the crank would not go in the hole so I will have to be content with the published design!

  After facing up the six faces, the holes for the round bits were drilled and reamed.  




  The block was then turned 90 degrees and a rounding over mill was used to get rid of the square corners.  While in one piece, I could do top and bottom on the ends but then the original piece had to be cut into two pieces for finishing off.




The round bits had previously been turned and were press fitted into the webs using the bench vice.  As with the crank bushes, I put a drop of Loctite 638 in the holes before fully pressing together.  They were cross pinned afterwards; the holes being lightly countersunk to receive the piening over.   I used the shanks of old Dremel wire brushes as rivets.

  Here's the crank.  I took the picture after I had tried it in the bushes.  It was a bit tight but I'm sure it will work itself in OK.  Probably better to be too tight than too loose!




Dave
The Emerald Isle


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## deverett

Looking at my pictures, I've realised I didn't mention the crankcase door windows.  They were milled flat and the window cut.   There was very little metal  left in some places.





 The cover plates had previously been squared up and holes made for the securing screws (not shown on the drawings).




 Both sides were done in the same way.  Thinking about it afterwards, I wondered why the crankcase had windows machined when the doors were to be epoxied in place.

On now to the exhaust stub platform.  When this was milled, the area was well undersize for the exhaust stub, so an application of JB Weld will be necessary.




  The water inlet was drilled and tapped at the same setting.  Afterwards, the casting was turned over and the water outlet was drilled and tapped.

  The casting for the exhaust stub was rough-looking and remembering how poor the surface finish ended up on the crank brackets, I decided to ignore it and make the stub from a handy piece of cast iron (that would have been used originally, so that's a good enough reason for me to change it!)




 The drawing shows an 8mm hole through the stub and a 10mm hole through the cylinder body.  Looking at the shape of the casting, I think there may have been a mistake in the stub drawing.  Anyway, I made an extension of the stub with an 8mm hole all the way through that fitted in the 10mm hole and if I am careful, I should be able to get it to a reasonably close fit against the cylinder liner.  The extension was made overlong for trimming later.







Dave
The Emerald Isle


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## Brian Rupnow

Dave--You are doing a marvelous job, and I am following with great interest.---Brian


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## deverett

The engine side of the coupling seems to have been secured by a couple of set screws into dimples in the crankshaft.  One picture I have shows what a mess this became after many years (ab)use.




My coupling started out as a piece of 1-1/8" round bar and I initially used a trepanning tool to make the recess but it didn't have enough clearance for the depth required and so a small boring bar finished the job off.




 I will not be driving anything with the engine so the coupling will be in one piece with a groove to simulate the bolted joint.  Four set screws were made from 3mm square bar and the coupling bolts are 10 BA.





Dave
The Emerald Isle


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## deverett

On now to the flywheel.  The brass casting was very tight and try as I might, I could not get it set up to give me the full dimensions shown in the drawing.

 I faced the first side then drilled the hole for the crankshaft 9.8mm, used a small boring bar to straighten the hole and then ream for final sizing.  I got a nasty shock when I went to use the reamer and found it went straight through!  When I used the boring bar, I didn't take into account the cut on the backstroke while withdrawing the tool.  Nothing for it but to enlarge the hole and fit a new piece in place and start again.  The new piece was press fitted in place with the addition of the Loctite.

  Before drilling, I machined the eccentric which is used to drive the water pump and in full size, the ignition system.  This was done to ensure there was still some wall thickness of original metal round the new insert.  When done, the flywheel was reversed in the chuck and drilled out to 9.7mm.  Using the boring bar cutting a few thou at a time, I enlarged the hole checking when the 9.9mm drill would just start to enter.  Now it was time for the reamer and after trying, the crankshaft was now a nice light push fit.






 The flywheel is held in place with a 1/16" taper key.  I have a Dore slotting attachment that mounts on the cross slide.  The smallest insert bar I have has a 1/16" cutter, but when I tried it the tool would not enter the hole.  Reluctantly I had to remove the flywheel and make up a new slotting tool.  The Dore type would be very difficult to make in a smaller diameter bar, but fortunately Michael Cox came to my rescue.  He had designed a unique keyway slotter to put keys in a modified pulley wheel he was working on.  That would do just nicely, thank you Mike.  http://mikesworkshop.weebly.com/small-hole-slotting-tool.html 
  However, I didn't use his method of hammering the cutter through the hole!  The clamp is to hold the heel of the cutter in place and also act as a length guide.

  As an aside, for those who have not seen his site there are some quite good ideas that can be adapted for other machines.




 Full size, the flywheel is fitted with a retractable starting handle.   This is not shown on the drawings, but is easy enough to make.  Using my centre finder, I lightly scribed a line that went through the keyway and this was carried over to the flange.  The hole for the starting handle was drilled on this line at the half-way point on the flange.  The handle itself was a piece of steel bar threaded at each end.  On the inner end, a collar was attached and Loctited.  The outboard side has a threaded brass button for the knob.   A suitable light spring from the 'spring store' is the retracting mechanism.






 The position of the holes should be rotated from that shown on the drawing and they were repositioned  as far as I could without hitting the counterbalance weight.  There are also an extra 2 small holes that should be drilled.




 The pencil arrow was to remind me which way to offset the holes!




Dave
The Emerald Isle


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## Brian Rupnow

Nice work Dave.--And--You're not the first person to suffer from "Reamer Surprise".


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## deverett

Brian Rupnow said:


> Nice work Dave.--And--You're not the first person to suffer from "Reamer Surprise".



That was down to lack of concentration, Brian!

Dave
The Emerald Isle


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## deverett

I followed the drawings for the construction of the cooling water pump, but as usual I 'improved' the shape somewhat.

  The pump cylinder was the first part.  Just a simple turning exercise.  The full size one had a gland on the top, mine is a dummy.  The cross bar was from a piece of thick wall brass tube, with the outside reduced a bit and bored out a tad.  These two parts were silver soldered together and the cylinder bore was drilled all the way through and then reamed.

  The pump piston was turned to a tight fit then lapped to the cylinder.  The drawings wanted a 5mm O ring as a seal on the bottom of the piston, but I don't have any  so what I have done is to put 3 grooves in the piston to act as a labyrinth water trap.  If it doesn't work, I can enlarge one of the grooves and use some Teflon string as a seal.

  The bottom of the cylinder was sealed with a silver soldered plug.




  The pump uses two balls in the horizontal bore as a check valve.  Three inserts within the horizontal part  trapping the balls form the guts of the pump check valves, the side extensions accept the cooling water hoses. 

  On any water pump that uses balls for check valves that I have  seen always have notches filed on the upstream side, or some other way of allowing the water to pass.  On my drawing these are not shown or even mentioned.  Any potential builder not aware of this would find that their cooling pump would not work!




  The sphere part of the check valves were made with a form tool.  The valves being brass I just used a piece of 3/16" x 3/8" steel.  A hole was drilled in one end and the end machined away to a bit less than half diameter.  A clearance cut on each side and the horns were rounded over.  The tool was then case hardened.




The check valves were machined as a pair.  Slow speed and no chatter gave a good finish.  The swarf came off in nice curls as the ball was formed.




  After the spheres were turned, the filing rest was set up and a hex was filed on either side of them.




  A pilot hole had already been drilled through the pair and this was enlarged so that they would fit on the pump.  They were then parted off as two pieces and then the hex ends were brought to length.  A recess was milled in the spheres to take the screwed cap, which would be Loctited in place.  The screw head was filed square and stuck in place.




Pump finished




Dave
The Emerald Isle


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## deverett

The cooling water pump and ignition are driven from an eccentric on the back of the flywheel.

  The plans show a piece of bent wire soldered to a brass ring for the eccentric strap that would have been a casting in full size.  I made the strap in 4 parts silver soldered together. The strap will not be adjustable - the bolts are dummies.  The ring started as a slice of brass bar and after rounding the circumference was sliced in half with a 1/8" slitting saw.  




The bolting flanges are a piece of 1/8" brass bar trimmed to the right size.  In order to keep these three bits lined up during soldering, I drilled 2 holes in each part for dowels.




  Once these bits were silver soldered, the rod anchor was filed up and a notch milled in the top of the disc.




  The disc and rod anchor were silver soldered in a second operation.  The rod will be trimmed later.




  The top fitting on the eccentric rod - the connector to the pump rod - was drilled clearance for the connector bolt.  It was then shaped while still attached to the parent stock




After being parted from the parent, the part was filed to shape and drilled/tapped for the eccentric rod.
  Final assembly looks like this:




Dave
The Emerald Isle


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## Brian Rupnow

Very nice, very finicky work Dave. I didn't build that part on my home-grown clone of that engine, because I already had a gear pump made to handle the water circulation. I do appreciate the amount of work that goes into a simple assembly like that.---Brian


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## deverett

There have been some serious distractions that have taken me away from the workshop for a while - watching Ireland and Munster rugby teams perform.  Still a few more matches for Munster, so more distractions to come and from tomorrow a week away, hopefully in the sun.

I have to confess that if they had degree courses in procrastination, I would graduate with honours.   I've done everything to delay machining the cylinder and piston but I've run out of reasons not to go ahead, so out with the seamless steel tube supplied for the liner and into the 3 jaw chuck with it.  Fortunately it was supplied in a generous length for easy holding.  It had to be made with a step to sit in the casting.    I aimed for a few thou clearance to give room for the gasket goo sealant.  One of my worries is to make sure that when finally fitted there will be a good seal between liner and casting.  If not, cooling water will leak into the crankcase and probable disaster.




 The bore was machined  out to the correct diameter, less an allowance for lapping.  I'd read that most 2 stroke engine builders aimed for a very gradual reduction in bore towards the head end to ensure best piston seal for ignition, this done during the lapping process.  I nearly followed suit, but then realised in time that most 2 stroke aero type engines have the cylinder bolted to the crankcase and the piston enters the cylinder from the bottom.  This engine is assembled by passing the piston down from the top, so the tapering wouldn't be possible.

I have a few AcroLaps, but of course not the correct size for this application.  Looking at the lap, there didn't seem to be anything very difficult to making a new barrel.  A piece of brass bar was turned, drilled and tapped as required.    Afterwards, 5 lengthways slits were put in with a slitting saw and hey, presto a new lap.  That's the new one at the bottom compared to the nearest existing size, using the same stem and adjuster.




When the adjuster is screwed in, it puts a slight hump in the middle of the barrel.  Using a mixture of very fine lapping compound and thin oil wiped over the barrel, it was quite easy to pass the liner back and forth over the lap until the clearance felt the same along the length.  Keeping the liner over length during the process ensured that there would be no bellmouthing at the top end.

Still to do is to machine the ports and ignition hole.

Dave
The Emerald Isle


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## deverett

I'm back on the case again - at least for a little while.

  Before putting holes in the cylinder liner for the ports, I made a start on the cylinder head.  This is basically an inverted  top hat that sits in and on the liner.




  The central hole on top is for the cylinder priming cup in full size.  With the basic turning done, it was put in the vice and the six holes for the head studs were drilled.




  The engine body was put in the vice next and the holes for the studs were drilled and tapped.  I wanted to put the holes as far from the outside edge as I dared so that the cylinder head nuts didn't overlap the edge.  7 BA nuts are too large across the flats, so I'll have to drill out and tap some 8 BA ones.  I was mightily relieved that the holes were tapped without any problems after my experiences with the crankcase holes.




  The casual observer will notice some filler on the casting.  When I slipped the head into the cylinder liner, it was flush in places and proud in a lot of others.  The cross section of the casting resembled the moon 3 days before full.  The only way I could think of making it round and to the correct size was to apply some (plenty) filler.  It was over 20 thou thick in places at the top to get it circular.

  The reason I made a start on the cylinder head now was that  I can temporarily bolt it in place to clamp the liner  for drilling the exhaust port and glow plug hole.  The drill tip will mark the head so that I can be sure the recess will be put in the correct place.

Dave
The Emerald Isle


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## deverett

I know it's been a while but other things have been distracting me from the job in hand.

Now it is time to put in the exhaust and transfer ports.  The liner was slipped into the cylinder and clamped by the cylinder head; the exhaust manifold was secured to the casting to use as a drilling guide.  After putting the casting in the vice, a piece of 8mm bar was used to line up the exhaust hole.




  Once lined up the exhaust port was drilled through.  The liner was then removed to get ready for the inlet port.  The transfer passage is a good 13mm wide, but the inlet port is only 11mm wide - plenty of leeway.  Just to be sure there was no cock-up, I used a handy narrow 6 inch ruler that happened to fit nicely in the transfer passage and the limits of the passage were marked on the top of the cylinder casting.




The liner was then replaced and the piece of 8mm bar was put through the exhaust  again as a lock so that the position of the inlet port could be marked on the liner - hopefully in the correct orientation.  Then it was out with the liner and off to the vice where it was lined up and the inlet port was machined with a 3mm slot drill.




 There were some burrs where the holes had been put in the liner, so I needed to put the lap through the bore again to remove them.  In hindsight I should have waited until this point before starting the lapping process in entirety.

  Slipping the liner back in the casting I was pleased to note that with the exhaust lined up, and testing the inlet port with a bent scriber, the inlet port came midway between the transfer passage walls as closely as could be judged.

  The reason why I didn't just put the transfer port directly opposite the exhaust port is that the cast  in passage and the exhaust were not exactly 180 degrees apart - about 8 degrees out as far as I could tell.  It won't make any difference to the running of the engine, but if I had just gone ahead and machined without checking, the transfer port would have been partly obscured.

Dave
The Emerald Isle


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## deverett

The last hole to go in the cylinder  was for the glow plug.  Back near the beginning I said I had modified the design to get closer to the original.  Before putting the glow plug hole in the casting I used the stub from the bottom of the main casting which I fortuitously saved.  This was a test to check that I could safely tap the cast aluminium and to check the recess depth for the copper washer.  With the modification, the washer sits below the diamond shaped plate and the circular part of the plug has to compress it while out of sight. 




  Fortunately the threads came out satisfactorily and the washer recess was a good depth.  With that test done, a bar was put through the exhaust port to lock the liner and the head was refitted.  The engine casting was then set up on the milling machine table to put in the real hole.  
  Using a sticky pin, the centre of the glow plug boss, previously centre popped, was picked up.  The actual hole is 50 thou below centre to take into account the modification.




Before drilling, I added another hold down for added security.  Don't want  to let anything move unexpectedly!
  The glow plug tapping drill went through the liner and into the head but the thread was only in the casting.  A quick test with the plug screwed in place showed it will seal OK.




  The head was removed and set up at a 45 degree angle to mill out the combustion chamber recess.  The bottom of the head sits well down in the liner and without the recess, the fuel could not be ignited.




The engine, liner and head ready for assembly.




Dave
The Emerald Isle


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## Jhawk

Dave, glad to see you're well along and doing a fantastic job! I've not started on mine and watching your build is very encouraging and makes me want to get back on it. Hopefully soon. Best wishes......

Hawk


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## deverett

The piston was a piece of cast iron bar, not overly generous on length.  To ensure adequate holding in the chuck I first turned the top part where the baffle would later be milled so that I could work on the main part.  The design of the piston has a piece of brass tube silver soldered across the bore to take the gudgeon pin but I didn't like this idea.  I have read that brass can be silver soldered to cast iron, but it's not something I have done so I made my piston in more conventional style, keeping the wall thickness a suitable dimension to support the pin and slotting the piston to allow the con rod to swing.  It will be a heavier construction, but I don't envisage it creating any problems on this low performance engine.

  When the diameter was  to size, the piston was put in the vice to put in the con rod hole which was drilled and reamed.   I will put a bushing on the small end of the con rod and allow it to swing on the gudgeon pin.



The piston was now upended in the vice ready for the central hole to be made into a slot. To ensure the slot was perpendicular to the hole, a piece of gudgeon pin diameter bar was passed through the hole and using a DTI running along the bar the piston was adjusted to give no deflection.



It was now easy to mill the slot for the con rod.



Back to the lathe and the top end needed a slight taper where the baffle would come and put in the oil retention grooves.



Then back to the milling machine to create the baffle.  The same process as before was used to line up the gudgeon pin hole so that the baffle would be correctly orientated.



  It was then just a matter of milling away the top of the piston to leave the baffle and another part done.



Dave
The Emerald Isle


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## deverett

The con rod was supplied as a piece of aluminium section.  This was drilled and reamed for the two holes.  The bottom end had a bronze bush pressed in.  The drawing showed the little end as just a bare hole in the ally.  As there were oil holes in both ends, I guess the con rod swings on the gudgeon pin but the design of having a brass tube to support the gudgeon pin seems strange if it not to be a bearing.  Anyway,  I didn't like that idea, so decided to bush the top end as well and use that as the bearing.



To shape the rod, I got a scrap piece of steel and drilled it for two pegs the correct distance apart so that the con rod could slip onto them.  It was now an easy matter to cut away the waste on each side.



The rod was now mounted on the rounding over jig and swung back and forward (always cutting against rotation) to round over the big end.  I had previously used filing buttons to round the small end.



As mentioned earlier, I don't like the idea of the gudgeon pin bearing on plain aluminium so as I had to make a bush for the big end, I made another for the small end.  There may be many instances of aluminium running on steel shafts, but I think bronze to steel is a better combination.  Last job then was to drill the oil holes in each end.





  The gudgeon pin was simply a piece of steel drilled through and a rounded over brass plug fitted in each end.



 I now had a trial assembly of the working parts.  I was pleasantly surprised that there was no binding of the piston in the bore.  It felt reasonably tight so there is hope yet for acceptable compression.  

  But unfortunately there is a potential problem:  When I rotate to crankshaft, the piston uncovers the inlet port completely but only comes down just over half way on the exhaust port.  I checked all my measurements and I don't see any discrepancy from the drawings, so an email to Heinz to ask if my situation is correct.  He said my con rod must be too long.  Recheck and it is the correct length.  Hmm.

   I can think of two possible work-arounds: 1. to machine the exhaust side of the piston down so that the exhaust port will be completely open at BDC but by doing this the compression ratio will be lowered considerably, probably unacceptable without other modifications to restore the compression ratio 

or 2. to machine a small half-round cutout in the side of the piston to achieve the desired result of getting the exhaust port completely open.  This is my preferred option at the moment.  Whichever way, the piston at present is about 100 thou too high.

Dave
The Emerald Isle


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## Brian Rupnow

Dave--I am following this thread. I will really be interested in what rpm your engine will run at. The clone I built of this engine runs well but the lowest speed I can run it at is about 900 rpm. I know that it is supposed to run at 300 to 400 rpm, but I think that is pretty optimistic.---Brian


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## deverett

Workshop time has been severely limited recently and will be for a few weeks hence.  However, I managed to get an hour or so this afternoon.

 Well, after some deliberation and without any other thoughts or suggestions, I went ahead and put in a cutout on the side of the piston. Before taking the piston out of the cylinder, I used a scriber to mark the piston where it covered the exhaust port.  The piston was set up in the vice using the previously used method of passing a DTI along a bar in the gudgeon pin hole for alignment.  Using a round nose slot drill I made the cutout 100 thou deep and 250 thou across to match the scriber mark as near as I could judge.



  A quick try of the piston in the cylinder afterwards and it looks OK.

Dave
The Emerald Isle


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## Blogwitch

Hi Dave,

I know exactly what you mean about putting extra bearings in, so here is a chart I have shown before where you can easily determine if the two materials act well together.






Just follow the material selection down and across and where they meet, read the result.

John


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## Jasonb

Dave a lot of the model aero engines run without bearing material in the con rod, provided you use 2014 there should not be any problems. The 30cc lightweight 2-stroke I made is about the same size as your Hubbard and faster reving and that has no bearing material.

More of a problem may be stretching of the now thinner conrod ends if 6082 (HE30) was used.


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## deverett

Thanks for that table, John.  It will come in handy for the future.
JB.  I know about high revving engines using plain ali bearings but with my machining skills, or rather lack of them, I would prefer to use more 'conventional', if somewhat dated practice.  Besides if the engine ever gets THAT much running and the bushes wear, it is much easier to slip in a new bush than having to rebore the con rod and bush it anyway.

Dave
The Emerald Isle


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## deverett

Just a small update, but no pictures - there's not much to see.

The liner uses Loctite 574 as a gasket medium to seal the various gaps between it and the cylinder casting.  With the shape of the bottle, it was easier to squeeze some onto a coffee stirrer and wipe it on the required surfaces in the casting.  To make sure I got 'sufficient' to make a seal, I spread some on the liner as well.  Slid the liner into the casting and gave a slight twist to spread the compound and line everything up.

It was then just a matter of wiping away the excess sealant with an acetone soaked rag.  Afterwards, temporarily sealing the various orifices except one, I blew through to make sure the the transfer passage was clear and that the cooling water passage was clear.

Dave
The Emerald Isle


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## deverett

The preserved engine at Mystic Seaport has a simple wooden stand.  This was copied for my model for when it will be finally mounted on a display board.




  Next on the agenda is a fuel tank.  Old boat engines would probably have used a cylindrical tank, so a handy offcut piece of 7/8" diameter copper plumbing pipe was utilised.  2 nipples were made up - one for the filler and one for the feed pipe and silver soldered in place.  2 pieces of copper plate became  the ends.  These were stuck to a superglue chuck and a thin cut taken to provide a locating spigot.



   After silver soldering the ends, the tank was cleaned up, ready for mounting.



  The fuel level has to be above the fuel needle in the carburettor so a base was made up from some plywood - I didn't have any suitable solid wood.  To make the cutouts the plywood was sandwiched between two other pieces of scrap wood and a hole saw put through the lot.  I made sure that the pilot drill was lined up with one of the tee slots in case I went too deep.



  The plywood was then sawn in half for the two pieces giving nice half round recesses to hold the tank.
  Some brass banding was used to hold the tank to the stand.  I wish I had made the tank a bit longer, but I didn't want it to appear too large alongside the engine.



One of the things I didn't do earlier was to put the balancing holes in the flywheel.  This was partly because I didn't want to see a series of holes in the flywheel.  I had a flash of inspiration and so the flywheel had the required balancing holes put in and these were hidden by a fitted piece of ally drink can cut and glued in place and smoothed off.






Dave
The Emerald Isle


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## deverett

And for a change, a few external fittings.

  The cylinder oiler was made to the words and music from Morrison & Marvin's 1/4 scale oiler, but sized slightly differently and shaped for this engine.  The glass tube was a convenient size cut from a piece of test tube.  The elbow started out as one of a street ell casting tree from PM Research.  The smallest size was still too large, so plenty of filing was needed to get it to an acceptable size.

  The machining jig has been described on this forum before.  The design will hold any of the PMR cast fittings of one size.

Inspiration for the priming cup and crankcase drain was drawn from a Stuart cylinder draincock. 
 I used the same form tool used on the pump check valves to form the spherical parts.  A piece of brass hex was chucked and roughed out.  Then the form tool came into play to shape the body.



   A hexagon was filed at the top of the stem.
  [FONT=&quot]
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  The cross hole for the handle was drilled and taper reamed for the handle.  I did as much work with the part still attached to the parent stock for ease of holding.



     The body was then parted from the stock and the threaded stem was held in a mandrel so the cup could be formed.

  I could not bend the cock handle either cold or hot.  At just over 1/16 diameter, the barrel kept breaking off.  In the end, I turned the  barrel and made a larger boss and silver soldered a handle to it and then filed it down to a reasonable representation of the full size.

  Next was drilling the cross hole for the retaining split pin.  The simple jig is just a piece of square steel stood vertically in the vice and a hole drilled for the bore of the barrel.  It was then turned horizontal and the cross hole drilled through.  This ensures the two holes are on the same line.  Slide the barrel into the long hole and there you have your cross hole.  Just the taper where the barrel goes through the body to machine now.



And this is how they ended up, the cylinder oiler crept into the picture, also.



Dave
The Emerald Isle


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## deverett

I have just got home from attending the Bristol model engineering show, where I'd agreed to show this engine.  Mild panic had been setting in recently as I tried to get the engine finished before I set off to England. I realised a while ago that I would not be able to complete it beforehand, so the engine was temporarily assembled as far as I have got with it and a mounting board was hastily made up to put the engine and sundry bits on, and I took it unfinished to fill a space on my stand.



With family commitments and another local show, it could be a while before I get back to the workshop.


Dave
The Emerald Isle


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## Cogsy

deverett said:


> it could be a while before I get back to the workshop.


 
Is 'a while' up yet? Looking forward to seeing more of this one...


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## deverett

Indeed it is more than 'a while' since working on this engine.

I could not get it to run.  There must be a mistake somewhere in my measurements, but I can't find out where.  The fact that the piston does not completely open the exhaust port would suggest either the con-rod is too long or the piston is too tall/gudgeon pin in wrong place, but all look OK to me.

I have got as far as making a new slightly shorter con-rod and will make a new piston, this time in ally, moving the gudgeon pin higher.  The upcoming problem with these changes will be loss of compression ratio.  The only thing I can think of to combat that is to make a new cylinder head with deeper spigot in the bore.

My attention span on a project seems to be very small especially if things don't go right first time, so it has been put on one side while I to try  and finish off some of the other dozen or so part made projects.

Dave
The Emerald Isle


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## deverett

Over the past few weeks, I have returned to the Hubbard trying to get it to run.  All I can get are a few pops - nothing more.
I've got good compression, there don't appear to be any air leaks into the crankcase.  I've tried flooding the cylinder and turning the engine over until the excess fuel is exhausted.  I don't know what to do now, except paint it and call it a Static Exhibit.


















Next project will definitely not have any 10 and 12 BA threads into soft, gummy aluminium.

Dave
The Emerald Isle


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## natalefr

Awesome !
Do you have video about your fabulous engine ?


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## minh-thanh

WOW ...It is so cool !!!!!!!!!


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## deverett

natalefr said:


> Awesome !
> Do you have video about your fabulous engine ?


'Fraid not - Like I said, I can't get it to run so it is a Static Exhibit

Dave
The Emerald Isle


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## rac37

Very nice! I had the same problem with mine, could not get it to run more than a 15 seconds. Anyway I converted it to a 4 stroke design and she really runs nice. 
What was a winter project turned into a couple year ordeal, but was really fun to figure out.

Bob


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