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Sunstar CH-20 valve seat

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I had what I thought was a collapsed lifter as the rocker arm jumped off the exhaust valve stem LB. After thinking the engine was on its last legs, I was ready to part it out. I took the engine apart yesterday and found this:


Any one else have a similar problem? I have a machine shop close to me and a going to see if I can get the seat swaged down.


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This is something that happens on occasion. The usual culprit is excess heat making the head expand and causing the seat to fall out. I think there is a new seat available with a slightly larger OD to help prevent this from happening again. Don't quote me though:D

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There was an "everlasting thread" on this problem/issue a few years back; a CH-20 with a dropped valve seat. The guy ended up just buying a used head off of the "auction" site. As Kenh mentions, there might be a way to machine the head for an over-size O.D. valve seat, but with current machinist labor rates plus parts, going with a known good used head might be the best choice (that is if you plan on keeping the engine/tractor). Failure is usually due to overheating/clogged cooling fins. Staking the seat back in results are not that great for the long term.

Tom (PK)

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When you put it back together, new head bolts or studs. Kohler recommends replacing the bolts (prevailing torque). The studs only require new nuts.

Also use the new style head gaskets. They are less prone to blowing out due to backfire.

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