Engine timing

By Staff
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As I sit here hunched over my crystal ball, I think I see the mists within shifting. … What’s this? A flywheel? Another one … hmmm. Does this mean a new engine on the horizon? This one is somewhat unusual – an open crank, diesel sideshaft. I think that makes it three engines for the price of one! Of course, this raises the recurring problem of storage, but one big advantage of a diesel is that there are no electrics to worry about, so it won’t need to be kept warm and dry. I’ve lost count of what the collection is up to now, but there are certainly a few about!

List traffic has been varied over the past month, with no one subject creating an in-depth discussion, so I’ve gone for a guality topic, rather than quantity!

– I’m working on a 3 HP Model K Witte that I just can’t get to run to suit me. The engine cranks when cold with two to four turns of the flywheels. Hot, it cranks with one to two. I have checked exhaust timing and have it set to just past top dead center, approximately 5 degrees. I have also checked spark timing and it is set around 45 degrees BTDC (got this value out of book for an earlier Witte). The engine has great compression. It has new rings and valve springs.

With all this it seems to want to continually eight-cycle, even under load.

I talked with a fellow member of this list and we were thinking it may be air leaking around the carburetor. I have inspected the throttle shaft for excess wear and checked the butterfly to see if it is sealing well; both seem okay. The fit where the carburetor slips into the head seems a little bit loose. I tried spraying penetrating oil around it with the engine running to see if it would pull it in, but I didn’t notice any change. I have tried running the engine on both sides of the carburetor with the same results.

I’m suspecting the choke plate. I have tried different springs, as well as installed a new plate.

Any idea what is going on here?

– If you’ve set the exhaust timing at 5 degrees past TDC, that sounds good. Since you know how to check that stuff, when does it open? Anywhere from 30 to 0 degrees before bottom should be okay. It’s easy to check, so start there.

You say you got the value for the spark timing from a book? I’ll go out on a limb here and say the writer of that book was smoking something strange. Give it 10 degrees, rather than 45 degrees.

If everything doesn’t work nicely after that, try to restrict the incoming air. The mixer was made to run at rated speed and horsepower with full air flow through the venturi. You may have to get tricky to compensate for slower speeds and less load.

– Can you richen it up enough to make it smoke? If not, check your fuel system and check valve.

Whenever you have that much advance on your ignition you will get an eight-stroke effect. Cut it down to 5 degrees, or even less, as long as the engine is not laboring. Also, check your exhaust valve spring tension, because if it is not strong enough, it will cause eight-stroking, as it may be sucked open and give a lean mixture. This can be imperceptible to the eye, but does happen.

After these suggestions, the engine owner responded:

– Timing is on my list of things to troubleshoot again, but your thoughts on the exhaust valve are going to be checked first. It is a new spring, as are all the springs on the engine, but there just may be something wrong with the tension.

– I had a few minutes to tinker this evening and I think I spotted the problem. It appears the governor is out of adjustment. I can’t believe I hadn’t noticed it before. As best I can tell, it is completely shutting off the butterfly. It doesn’t appear to be moving the throttle a lot, but when it closes the butterfly it is causing the eight-cycling I am seeing, or at least that’s my current theory.

As we heard no further on this one, we can only assume that adjusting the governor cured the problem.

Engine enthusiast Helen French lives in Leicester, England. Contact her via e-mail at: Helen@insulate.co.uk

You can join the Stationary Engine List on the Internet at: www.atis.net

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