NapierDeltic
Well-Known Member
I see now, it is the sealing foil, like in older soluble coffee tins. Thank you for ideea!
Munich.I first ran my two stroke diesel on petrol to confirm that the ‘two stroke’ induction worked. It was designed to allow this so there was not too much work involved.
You may have rather more work to reduce the compression ratio and get a sensible gas flow to a spark plug, probably a new cylinder head.
Whereabouts in Germany will you be?
Nerd !!!!A brief update. Ive got my head gasket issues sorted well enough. Remilling the head didn't allow the copper gasket to work, I think I simply used up all the available compression of the copper (it measures thinner now). A composite gasket with fire ring was made as planned and is working so far with no leaks.
On to the next problem, fuel. I made a new, heavier spring for the injector, which prevents compression blowing back into the fuel lines quite nicely. However, with the stronger spring tension the injector no longer sprays fuel. Cue half a day spent chasing leaks... The initial culprit was the injector needle seal, which seems to have been damaged. Replacing that led to finding leaks in crush washers, the cone connector to the injector, etc. all easily fixed.
Finally, I got to the plunger and barrel themselves. Bad news there, the fit clearly isn't good enough. I noticed fuel was leaking below the pump, and actually ended up submerging it in kerosene and applying compressed air (using a syringe and tube connected to the fuel inlet). Bubbles leaked from the back of the barrel with only modest pressure. Seems I need a new plunger and or barrel
Now normally I'd just say oh well and get on with it. However, my partner has just recently got a job offer in Germany, and so it's likely we will be away from my shop for two years. I'd like to see the engine run under its own power before we go, so I'm weighing up whether I should convert it to a petrol engine and get some running done to validate the other parts of the design, then revive the diesel side of the project when I get back.
You are a smart guy. You will figure something out.Munich.
The 'dumb' method would be to make an extra chamber that bolts in place of the injector and contains the spark plug, and use a very thick head gasket to reduce the compression ratio. The gas flow to the plug would be awful but maybe that's ok for just getting it running?
That sounds like fun! I'll have to reach out once we get settled. We are planning to move in September, though it remains to be seen whether this is possible given various bureaucratic delays that are inevitable with such things.I agree with continuing with the fuel pump, that's working in the direction you want to go.
Munich is around 4 hrs from me by car or train if you are interested in meeting up. There is also a German model engine maker I know who lives just south of Munich.
Engine cylinder or injection pump cylinder?Nerd1000 !
Can you take pictures of the inside surface of the cylinder ?
It's not too difficult
Phone camera is good enough
Or just need the light behind and use a magnifying glass to see
(What the surface looks like in the picture, it looks like I'm looking at it with light and a magnifying glass)
View attachment 158316
The area you point to at the top of the cylinder is a screw thread. Or do you mean further in near the hole?Personally, I would keep lapping until the surface is really good - like the area in the picture
A little more patience, a little more care: you will do it better.
View attachment 158417
Interesting idea. I think the main challenge with it will be the quality of the dowel pins, I know a lot of them are somewhat 'tri-lobed' due to flaws in the centerless grinding.This might be a totally useless suggestion, but I have had some success with, instead of using a hardened steel barrel, using a brass barrel, reamed slightly undersize and then repeatedly forcing a correct sized dowel pin in and out of the brass to expand the hole and burnish the finish. It works best if the plunger is also made from one of the dowel pins from the same box of pins. The brass should have enough durability for a model engine, yes?
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