Hemmingway 5cc diesel engine build?

[Jon H]

There has been plenty of comment on the compression, the piston nip etc but its very hard to quantify. Are you able to post a video showing the engine being flipped over with a prop on? Might be able to judge better what it happening. Unless the fit is truly awful, which i doubt, a heavy port prime and gradual increase of compression while flicking should at least get a pop out of it even if it wont run right away. I find it strange that it is completely devoid of life. 

 

[Rich Griff]

As Jon says....

 

If you move prop from bdc,  over compression, and stop at say 15 degrees atdc, reverse direction to 15 degrees btdc, and repeat, how many "cycles" does it take for compression to reduce to zero ?

 

Atom minor, nice...will you be starting a new thread for that ?

 

Still need to read this thread from the very begining to read of the "engineering" involved.

 

I only have a basic machine Mart lathe ( new, small one ) with imperial and metric lead screw etc. and 4 jaw chuck, no milling machine, yet....

 

The old atlas lathe is not "accurate enough" for model IC engine but ok for steam engine and general none high precision jobbing lathe, it's well worn and used quite a bit, being ok if you "work with it"....

 

 

[911hillclimber]

To respond to these thoughts (of which I am very grateful):

 

No video of the ;action' but i will try to express them

 

Engine on a stand, 16" prop and a length of broom handle to flick it over to save my old fingers.

Fuel is MT1000, sure smells of ether!

 

Prop tight on the crankshaft @ 2 O'Clock and the piston right up to compression, maybe 15 deg BTDC.

Sharp flick over compression is the technique.

 

Neat fuel on the ex ports with piston at BDC, rotate to 15 deg BTDC and flick. There is the sharp 'pop' you get from these engines and the prop spins round to 15 deg BTDC and stops.

The compression stops the flywheel effect of the prop going over compression again.

 

I repeated this action a 1,000,000 times varying the compression, the prime and the addition of old Easy-Start spray and noting changed except the snap of the pop, no firing nothing at all, 'lifeless' you might say.

 

To piston/cylinder leaking:

 

Prime the engine via the ex ports and rotate the prop to compression slowly. Ease it over tdc and round again. Just on tdc and holding that position small bubbles form just by the ex ports the neat fuel  leaks by the piston skirt.

Flicking the prop as you would there is none of this bubbling. The action is too quick.

 

I am beginning to think I have over primed this engine and flooding it all though all these attempts; as previously said a few drops only, i was giving it far more than that.

 

A friend I spoke with (an experienced model engineer) had a glow engine in his workshop in pieces.

The piston would not pass into the top of the barrel by hand, and the bore has a taper of 4 thou, wider at the base.

 

Possible actions once I get back to the Sparey will be to make another piston with 'interference' fit at the TDC of the bore, probably mild steel as I can finish to size this easier than cast iron. This would be to test this 'tight at the head' theory.

 

As to the Atom Minor:

Started to machine the main case today which went really well, quite surprised myself!

Not sure there will be too much interest in a build as it shows my low skill set in these matters.

I am far more more at home building big tuned 3.2 litre Porsche air cooled engines!!

[Rich Griff]

You mean assembling the porche engines rather than machining ?

 

Do you live on the llyn ?

 

Back to the diesel, when compression screw backed off a bit, do you hear the sometimes quite loud crack of the contra piston returning, and a small amount of smoke ?

 

May I ask about the atom minor, crankcase machined from solid, or a  casting ?

[Jon H]

From your description it sounds like there should be more than enough compression to me. I was once distracted by a phone call and forgot to put piston rings in a laser i assembled. On test It started and ran, even tuned up, but idle and acceleration was very poor and compression very low so i took it apart to find out why. Imagine my surprise to find no rings! While i appreciate that glow and diesel are not the same, the basic point is these engines should operate to some degree even when the fit is less than stellar. 

 

Also, if you can get the thing running the heat cycles should grow the piston slightly and you may find it all comes good. The trick is getting the thing going in the first place. 

 

I echo the feeling of others who are cautious about an electric starter, but used correctly it might be the way to go as the dynamic compression will be higher than when hand flipped. If you use an electric starter do not prime the engine at all and just let it draw its own fuel. 

 

I am sure there will be a way to get it going. 

[911hillclimber]

Rich:

Yes, assembling the engines, set up and getting them to go. Not always straightforward!

The Atom Minor is a Hemmingway kit, so cast case parts and head.

Casting is surprisingly good, better than the Sparey kit's casting.

 

Jon:

No, the CP slides back, no 'crack' to a decompressed position.

 

When I made the head I used an M6 x 1.00mm pitch thread.

The engine uncompressed to engine fully mechanically impacted to the CP is a radial turn of about 100 deg of the screw.

 

Through all this I feel the engine should start to some degree, but there is nothing.

 

I can't touch the engine now for a few days, but will try later again this week and report back, esp if it starts!