Hemmingway 5cc diesel engine build?

[911hillclimber]

Thanks for all the helpful details, but...

 

Not a good day at the lathe today.
Wasn't quite in the mood, but pressed on.

Made a piston 'blank' that seemed a good fit in the cylinder, tight'ish at the TDc and slightly loose'ish at BDC.

Drilled and reamed the wrist pin hole 3/16", no probs.
Re-aligned the piston in the cross slide and started milling the inside of the blank to take the con rod.
I happened to machine it 90 deg out, so no slot for con rod to articulate.

Ok, turned the piston to allow correct slot position.
Machined the 3/16" slot which sounded not quite right....
Removed the piston to find the cutter had gone throu the piston and was 1/16" off-set.

Got my arithmetic wrong.

God, I'm good at this stuff.

Made another piston, all thou or so tighter (practice makes perfect), drilled holes, milled slots all in the right position. (practice makes perfect).
Assembled the lot together and the movement is tight, cannot see any touching points of the con rod to the case to the cylinder etc so reversed the piston on the rod. Same condition, so something not square.

I cannot see how to find and get rid of this high friction point, so seriously thinking of tarting the outside of this lump of metals, and put it on a stand.

I finally think I'm a mechanic not a machinist.

73T 911 Co

[Jonathan W]

Frustrating! Milling is a lot easier in a vertical milling machine than in a lathe. For one thing, you have better visibility of what you are doing without a large lathe chuck being in the way. I think even a practised machinist would find it a challenge with the equipment you are having to use.

 

That has to be the model engine world's longest piston. The amount of friction will be considerable. Something of a detail I know, but I'd be tempted to relieve the skirt below the gudgeon pin by a thou. At least that ensures that the crown is the biggest diameter.

[KEITH BEAUMONT 1]

I did find when making mine,that the passages in the crankcase for the con rod to swing in required quite a bit of fettling before it was clear.

Also, I am a bit concerned that you have made the piston in the wrong sequence, Having to grip the outside diameter,on what should be a lapped finished surface, risks bruising or distorting it. If you have to start again I suggest you turn the C/I to a diameter 0.025" larger than finish size and a length long enough to allow gripping in your chuck, plus space to part off. At this point do all the intenal milling ETC. the slot for the con rod is, in my opinion, too narrow and can easily be widened by another 1/16". This will allow more space for the con rod and lighten the heavy piston, (Sparey  had the ,now disputed, theory, that a long piston would give better compression by the fact that it would take longer for gas to go passed it. These days the friction problem is taken care of by the tapered Bore.)   Sparey was a pioneer,so can be forgiven.

When the milling is to you satisfaction, make a stub mandrel,as I have suggested for the Contra, super glue the piston onto this,making sure it is square and concentric, Then finish the outside surface by turning with fine cuts, to about 0.002"larger than bottom bore of cylinder, followed by lapping to a fit just above the exhaust. When happy with the fit ,heat to push off the piston and you are ready to go again. Do not rush things.

Good luck

Keith.

PS, Looking again at your con rod, I think you can remove more metal from the corners and make more room for the swinging.

[KEITH BEAUMONT 1]

Just to encourage you, I attach a photo of my recently finished 5cc version of the Nalon Viper Diesel, on test ,doing 10,000 RPM PLUS.

It is a powerful, very noisy engine.

Keith

Edited April 5 by KEITH BEAUMONT 1

[911hillclimber]

Thanks as ever.

You have more patience than me.

I have nothing to loose, so will widen the rod swing slot in the piston.

This may allow some float and allow the piston some freedom, or less binding.

If I slacken the cylinder nuts off the cylinder the crank can be revolved much easier

 

The prop arrived today too, it would fit a Tiger Moth….

Edited April 5 by 911hillclimber

[KEITH BEAUMONT 1]

That sounds like the flange surface of the crankcase is not 90 Degrees to its bore and tightening down is distorting the cylinder. Can you remove the studs, push the cylinder in by hand and look to see if the mating flange is in perfect contact all round. I suspect you will see a slight gap on one side.You will need to file/scrape the Ali surface to achieve a constantfit.

Keith

[Engine Doctor]

If your crank case is not square suggest re facing the surface and then cut a shim for base to correct the height of cylinder. If case is ok check cylinder base for square. 

[Jonathan W]

12 hours ago, KEITH BEAUMONT 1 said:

Just to encourage you, I attach a photo of my recently finished 5cc version of the Nalon Viper Diesel, on test ,doing 10,000 RPM PLUS.

It is a powerful, very noisy engine.

Keith

 

Your Viper looks fantastic, Keith. Where can one find plans for this? Internet search came up with lots of promising leads which ultimately all came to nothing.

[Engine Doctor]

20 minutes ago, Engine Doctor said:

If your crank case is not square suggest re facing the surface and then cut a shim for base to correct the height of cylinder. If case is ok check cylinder base for square. 

Another possibility is that the bores in the conrod are not parallel. This can easily be checked by fitting a drill shank or some metal rod of appropriate size in both the  big and little end journals and check for parallel. Easier to check this first .

[Jonathan W]

3 minutes ago, Engine Doctor said:

Another possibility is that the bores in the conrod are not parallel. This can easily be checked by fitting a drill shank or some metal rod of appropriate size in both the  big and little end journals and check for parallel. Easier to check this first .

Also, if the piston pin bore in the piston is not exactly perpendicular. All these things can cause the piston to bind in the cylinder.

[KEITH BEAUMONT 1]

John W, There are no drawings for the 5cc Viper. I scaled up from the drawings of the original 2.5cc version, which were avilable on Ron Chernics Model engine news site, but I agree ,they seem to have vanished from it. I do however have a PDF of the set, so if you can send me a message with your e mail address, I will forward it to you. The drawings do not contain any of the neccessary clearences for the ball races to avoid  a clash with other parts. Also I made a standard crankshaft length, with a split collet for the prop driver.

Keith.

[Jonathan W]

Thank you Keith, I have sent you a personal message 😄

[911hillclimber]

Fresh day.

Loaded with all this good advice, thought I would sort ot this binding problem using these advice notes:

 

Having slept on this problem and taking advice from Those Who Know on a model aero plane forum, set to to find why the engine is in bind.

After 10 mins it was found, the problem that is, and the solution was easy enough.
The cylinder mounting flange to the crank case was out by 10 thou, the cylinder was thus at an incline to the crankshaft.

Solution was to place a razor blade under the rear half of the flange and nip the nut up and the engine rotated freely.

The blade is 10 thou thick so I needed to machine the cylinder (very high risk option) or to reface (by hand) the crank case face by good old files.

This was quite easy and I crept up on the change until all was good.

So, the lot assembled and tight the crank/piston etc all are smooth. I've marked the front of the piston on the crown just in case this lot has to come apart after running in.
Similarly the con rod as it can go onto the crank pin 2 ways.
I'm pleased to say the exhaust ports are fully open when the piston is at BDC, I hope this is correct.

After a good clean of the lathe of cast iron granuals and a good oiling of the bed, I took a look at mounting the crazy large diameter wood propeller.

Decided to make a sleeve nut, tapped M6 to suit the crank shaft and 8mm dia to suit the hole in the prop.

Not a sensible idea as this would leave very little wall thickness to the sleeve of the prop nut, so that nice piece of alum bar which was perfect is now scrap.

A visit to ebay again for some bar, but also for some diesel fuel and start-up (or an attempt) is not far away.

Need some gaskets first...

73T 911 Coup

[Jonathan W]

Looking good now!

I'm wondering though if you lapped the piston, or only turned it to size? Anyway, will see what happens when you fire her up.

[KEITH BEAUMONT 1]

Why not just make an Ali bush for the prop?  Much more simple solution. Brown paper  is good fpr gaskets. Use the method in the notes that came with the kit. Also, remember to cut out the little aperature that connects to the fuel bypass on the cylinder.. When I made mine I could not make it run for more than the few seconds that an exhaust prime gave. Then I realised that I had not cut that small piece out from the gasket!

Keith.

[911hillclimber]

The prop was bought to start it, not sure I can get my fingers out of the way fast enough!

Ouch, or A&E ….

[KEITH BEAUMONT 1]

When you get to the point of starting it, DO NOT, REPEAT , DO NOT, use you finger to flick it over, An engine of this size is powerful and a backfire will cause real damage to your finger. Make a  starting stick from a piece of broom handle, or a piece of suitable size dowel that can push into a piece of garden hose. This will protect the prop in the event of a backfire. Put the engine on the compression point, set prop at 2 o'clock,  then flick it hard through TDC.  My Sparey runs happily on a 16" x4" APC nylon prop at 4,500 RPM.

Keith.

[KEITH BEAUMONT 1]

Also ,it is a good idea to paint the blade tips of the prop yellow, so that you can see where to keep you fingers, when adjusting engine.

Keith.

[911hillclimber]

A starting stick is a very good idea!

Thanks as ever.

Can't I simply cut the tips off the wood prop and re-balance?

[GrumpyGnome]

Personally, I'd never tinker with a wood propeller. I have slightly amended props of other materials, where the tip is chipped - cut down and rebalanced as you say.

 

Just a reflection on my woodworking skills potentially! 

[KEITH BEAUMONT 1]

What size prop have you obtained?

 

Keith.

[911hillclimber]

It is a wooden 16 x 6 with a 8mm/5/16 crank shaft hole.

 

Penn models' site say they have 12 and 14" x 6 but their stock is not always as per the web site. Oddly, they are 1/2 the price of ebay vendors.

 

A lot concluded today.

The Last Chapter is opening on this project.

The Myford compound slide is back in it's box. Best £17 I spent on this lot. This means No More Milling.

The cast iron scrap pile I hope/think is finished, this lot represents a lot of wasted time and a few bob on cast iron.

The tube prop nut is made and holds the huge prop. Will try to get a smaller one from Penn Models when open on Tuesday, they have a 12 x 6 in plastic. £10 and 1/2 the price of the wood one.
Will get 1/2 litre of fuel too.

Did the final dry fit up on all the parts and thus just the fiddly gaskets to make, later this afternoon/tomorrow's task.

Thoughts turned to running the thing.

Found a nice piece of 10 mm alum plate, so cut that to suit the engine mounts and then 2 M6 bolts to attach to the work mate. I guess this will need tethering to the lawn (if it starts...)

Made the wood starting 'aid' from a piece of dowl to keep my small fingers being chopped-off even smaller.

Found an old engine stand I bought a very very long time ago , but it is so nice shame to butcher it for this thug of an engine. Little Enya engine is seized.

So, what can possibly go wrong over the next days?

I have little confidence it will run. I do not feel a lot of compression, and if it does run not sure if all the parts will tolerate the shock, let alone me.

I want to get a picture of it running, clean it down of fuel and put it on a stand.

Only then will I have proof that you can get by on a 1924 Drummond round bed lathe.

73T 911 Coup

[KEITH BEAUMONT 1]

That Prop will be fine. If you cannot feel much compression dont be disapointed if it will not fire. For the initial attempt at starting, do not put fuel in the tank. Prime by putting a few drops of fuel directly in exhaust.  Flick about six times for each prime, increasing compression screw a quarter turn after each flick until you reach a point, Hopefully, that it starts to bang. If you overdo the prime and it locks up, blow through the open exhaust to clear excess fuel. When you have found  the bang position, you can the put fuel in the tank. open needle valve about three turns, put finger over end of carb,turn prop slowly to suck in about three turns. At this point  you finger should have some fuel  on the part that blocked the tube.Exhaust prime again and start flicking hard over TDC.  Good luck! You might get other suggestions on how to start a diesel, but this method always works for me.

Keith.

[KEITH BEAUMONT 1]

Make sure you have both clamps tight and even on that Workmate, I had an engine rig peel out and fly across my worshop,due to clamping not being even. I now fit a tee piece across bottom of part clamped and slide rig in from end.

Keith

[Martin Harris - Moderator]

It certainly looks the part.  The one thing that’s bugging me is the “optional weight reduction” in the piston - how on earth did they advise machining it?