More Snow engine problems

[Gordon]

I have built a Snow and I am having a problem getting it to run. I am sure that it is a compression problem but I am having a problem nailing it down. I can kind of get it to fire on #3 cylinder and occasionally the other cylinders will give a weak pop. The #3 cylinder is the only one which seems to show any compression. If I hold my finger over the spark plug hole I can feel suction or pressure but not much but it does hold for several seconds.

Things I have done:
-I have replaced the CI rings with viton O rings. Not a permanent solutions but good for testing at this point.
-I have made a fitting to fit in the spark plug hole and applied 40# of pressure to the cylinders. That has found a couple of small leaks. One valve was not sealing well and I had a leak at one of the head gaskets to the outside and an internal leak past the gasket into the cooling chamber. At this point I cannot find any more leaks using my extremely faulty hearing or using soap bubbles. Any leaks must be really slow.
-I have made the gaskets first using .015 automotive gasket and then using .015 PTFE. The PTFE fixed the leak to the outside but caused the leak into the cooling chamber.
-The ignition is timed for about 8° BTDC
-Valve timing is set per the instructions to begin EX open 25° BBDC.
-I have tried a couple of different carburetors. Presently I have a ENYA .09 carb which others have had good luck with.
-I presently have replaced the garter spring seals with O ring backed seals because I could not seem to get the garter spring seals on without damaging them but soap bubbles do not show any leakage.

I am looking for any ideas on where to look next.

Thanks: Gordon

 

[dnalot]

Hi

I have a recently built Snow Engine with similar problems.. "Rustkolector" posted a fix involving a new design for the intake manifold. Its summer here so I have not spent much time in the shop but come fall I will take a new stab at the problem. If you get yours going please post your solution.

Mark T

 

[Rustkolector]

Gordon,
I will try to give you a few things to work on. First I would make sure you can make gaskets that seal 100%. I make a die out of two pieces of .125" aluminum flat stock bolted together. Make the bore hole through both pieces and drill the bolt and water passage holes through with a close fit drill size. Using drill rod, make a punch that closely fits each different size bolt and water passage holes. I used to use a drill to cut the small holes, but I had a few failures. Punch the small holes. Make a sandwich out of the two die pieces with a piece of gasket material snuggly bolted between. Cut the cylinder OD and ID with an Xacto knife, and punch the bolt and water passages. Your small holes will cut cleanly and won't leak. PTFE gaskets work on my Snow. The laser and vinyl cutters work very well if you know someone with one.

I have never used O-rings for piston sealing so I cannot comment.

Does your engine bind at any point? If so, it is difficult to get a good feel for compression and the degree of compression bounce, if any. When your engine turns freely and has noticeable compression bounce on all four compression strokes it is good enough to run, all things considered. Valve cages should be removed from the engine to check valve sealing. Use a hand vacuum pump like those found at Harbor Freight for bleeding brakes. You should be able to draw a good valve down to 25" of Hg. If the valve seal is good it should leak down slowly, not rapidly. Use grease or 90 weight oil on the valve guides when testing. Make sure the valve cages seal against the combustion chamber housing. Some builders have had leaks in this area. With smooth machining on the mating surfaces there should be no leaking.

Ignition timing is not critical. It will run anywhere near TDC. Open the plug gap to about .020". Ignition is always suspect on a new engine. Especially the distributor, but the distributor used in the Snow design has been pretty dependable. I used the S/S CDI ignition on my Snow but any good ignition should work well.

The Enya 09 carb should work. Don't try to start the engine with a wide open throttle setting. You won't get good fuel vaporization. If you are not using a hand drill for starting your engine, use one. That flywheel is heavy.

I don't think the shaft seals are an issue as long as you get compression bounce.

As you are finding, there is nothing easy with the Snow, just keep at it. It will run.
Jeff

 

[Gordon]

I purchased a Silhouette plotter so I am making good gaskets. Well worth the $100.
I will try the vacuum pump to see how well the valves actually seal.
I am still having a problem with getting the engine to turn freely so there are binding points. I will try to work on that but I have been operating on the theory that if the cylinder actually fires it will overcome some minor friction.
I am using a drill motor with a one way bearing for turning it over.
I am using the S/S ignition and distributor.
I have tried to test compression by putting a pressure gauge in the spark plug hole with an adapter but it does not tell me much. At slow speeds it does not really read anything and at high speed it just bounces.
As usual I end up spending as much time getting an engine to run as I spend building it.
Thanks for the input.
Gordon

 

[Rustkolector]

Gordon,
Get a compression gauge that has a check valve in it meant to hold the highest reading.

Jeff

 

[Gordon]

I have taken the engine apart and I am in the process of reassembling and checking to try to isolate the problems. So far I have found:
-Intake valve on #4 was leaking around the stem. Stem was under size but I made a couple of extra valves originally so that is fixed. That does not affect the compression but does affect fuel mix.
-#1 cylinder has compression about every other stroke. Not sure yet why it has compression only part of the time. Cams are not operating so it is not a valve timing problem.
-#3-4 cylinder is slightly lower than #1-2 which was causing some binding. I have placed a shim under 3-4 but will probably just mill off the base on #1-2

Gordon

 

[Cogsy]

-#1 cylinder has compression about every other stroke. Not sure yet why it has compression only part of the time. Cams are not operating so it is not a valve timing problem.

For a variable compression issue like this I'd guess it'd have to be valve sealing. I'd say the vacuum is opening one of the valves then it's not sealing properly on close. If it seals some of the time though, then it should fire occasionally and seal the valve properly after a while.

 

[Gordon]

OK After a lot of screwing around I finally have it running. I could not get it running with the ENYA .09 carburetor but I could get it running a little bit with my home made carburetor but still not running more than a few spits and sputters. I finally tried it with a TIM-6 ignition instead of the S/S and it started right up. I have the same problem that others have had with it running for 30 seconds and then not running until it cooled off. Rustkolector made a different manifold so I will try that next.

At least it is running now. I had kind of put it on the back burner for a while and just got back to it.

As usual getting an engine to run takes as much time as building it in the first place. Glad that I am not doing this for money. I would not even make minimum wage.

Gordon