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mroman59

White smoke update - now what?

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mroman59

In previous thread I told about oil consumption and white smoke on my tractor which has a 27HP V-twin , Model CV740S, Spec CV740S - 0024 engine. Manufacture date 12/2004.

A member suggested that I may have a blown head gasket and start with checking plugs and compression.

Here are the results.

Right spark plug - appears brownish (normal) with little black carbon on threads, compression 150 psi.

Left spark plug - all black carbon build up both on plug and threads. No oily residue. Compression 170 psi.

There appears to be oil on the frame around engine, but no fresh oil. This oil mixed with dirt from cutting grass. Not sure of source yet as I would have to start taking engine apart for further inspection. Oil could always be from seepage around oil filter or perhaps or drain tube. Not sure about around head gaskets until I start removing parts.

The difference in compression confuses me. The spark plug that appears as it is burning correctly has the lower compression.

Instructions require that the throttle has to be wide open and choke closed during a compression test. Anyone know why?

My compression test was a dry compression test. I have heard that some people do a wet compression test also. Would it help me in this case to do a wet compression test and what should that tell me?

So far, it appears that changing head gaskets would be the least thing I could try. I can pick up a leak down gauge this weekend and attempt to perform that test, if you think it is necessary in this case.

Thanks,

MR

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Kenh

IMO the leakdown is the better of the two tests. With that said your compression numbers are pretty good. I always used 10% difference as a go/nogo between cylinders. Others may disagree but you will be in the ball park. The bad thing is compression and leakdown, doesn't really tell you the condition of the oil control rings.

The cylinder with the higher compression is suspect to me. The black on the insulater of the plug indicates oil consumption which in my mind contributes to the higher compression as the rings will have a bit more oil on them. Sort of like an ongoing "wet" compression test on that cylinder. You could try a wet compression test on the other cylinderand see what you have. If they even up, I would suspect the oil control rings. Pulling the heads will let you get a look at the cylinder and check for scoring.

For what it's worth I have the same engine as you with about 600 hours on it. The pressed on timing gear on the crank split. No more cam shaft operation. I have a new crank and cam for it. If push comes to shove it could be for sale.

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Willy

I would change the plugs and try it for awhile.

sounds to me like you have a plug misfiring and

causing the carbon build up.

It's cheaper than tearing things apart and finding

you have a bad plug.

unburned fuel can also show as a white vapor.

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mroman59
quote:Run some seafoam with the gas and burn out some of the carbon that has built up on the valves.id="quote">
id="quote">

Thanks, I will look into this seafoam, but I never heard of it. Can you buy it at your local autozone store?

MR

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