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Discussion Starter #1
Well, I have an 89 18 horse Onan. It runs great and has plenty of power. The only thing wrong with it is after it warms up it smokes. It doesn't smoke all the time, just when I give it more throttle, then it'll blow out some smoke.

Now could this be valve seats or what?
Thanks.
 

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No,worn valve SEATS would reduce compression, valve SEALS or worn guides and stems can cause smoking at idle or upon de-acceleration--usually smoke under a load or while throttling up is oil passing the rings or piston ,but some engines tend to do that "normally" to some degree,including Onans and other horizontally opposed twins...also an over rich mixture can cause some black smoke to be belched out under acceleration ,again,some engines do that anyway ,especially after being run many hours..

As long as the oil isn't being used up rapidly (keep a close eye on oil level on the dipstick),I'd say not to be overly concerned about a puff of smoke once in a while ,if it starts smoking constantly or out of the crankcase breather,then its probably going to need a rebuild soon..some engines prefer a heavier,straight weight oil,many do not "like" multi-weight oils..best to stick with SAE 30 or SAE 40 in air cooled engines ,use the SAE 40 weight in hot summer weather...
 

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Discussion Starter #4
Thanks guys. It doesn't use a lot of oil. It's still good between oil changes so I aint too concerned with it. Just wonderin why it was doin it. Thanks!
 

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No,worn valve SEATS would reduce compression, valve SEALS or worn guides and stems can cause smoking at idle or upon de-acceleration--usually smoke under a load or while throttling up is oil passing the rings or piston ,but some engines tend to do that "normally" to some degree,including Onans and other horizontally opposed twins...also an over rich mixture can cause some black smoke to be belched out under acceleration ,again,some engines do that anyway ,especially after being run many hours..

As long as the oil isn't being used up rapidly (keep a close eye on oil level on the dipstick),I'd say not to be overly concerned about a puff of smoke once in a while ,if it starts smoking constantly or out of the crankcase breather,then its probably going to need a rebuild soon..some engines prefer a heavier,straight weight oil,many do not "like" multi-weight oils..best to stick with SAE 30 or SAE 40 in air cooled engines ,use the SAE 40 weight in hot summer weather...

Tractor-Holic must be a carpenter and a good wrench since he hit the nail on the head with this one. :fing32: :fing32:
 
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