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DMedal

valves too tight

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DMedal
ok, this is one of those basic questions a guy would be embarrassed to ask if he were young enough to have a bunch of pride left. I bought yet another Onan. I can't seem to keep a spare engine on hand for my 3 "runners". Anyway, the seller (a professional mechanic who I know to be honest) says his guess is the valves are too tight. What does that mean, and how does one fix it? Would that make a compression reading misleading? (no reading taken yet) thanks for your experience, Don

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BLT
My two cents worth. If the valves are tight, the only thing holding them back is the valve guide bores. I would think the can be reamed. Compression reading will tell you, valves not seating or worn rings. Either way heads would have to be removed to be confirmed. Removing valve springs would confirm how tight the valves are in the bores. Does Onan have a valve stem to tappet clearance dimension, say .005 - 007" intake and .009-.011 exhaust?

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UCD
Tight valves is when the valve clearance is out of spec (not enough clearance) Loose valves are when there is to much clearance. To tight and the valves don't close. To loose and they dont open or open enough. Dirty guides and/or valve stems cause the valve to stick. (open)

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MikeES
Keep in mind, when we talk about tight valves is that the valve stem clearance is not enough. So the valve are probably closing completely with a cold engine. As the engine heats up the valve stems grow by a few thousands and this takes up the slight clearance and now the valves do not seat. So the symptoms are that the engine seems to loose power as it gets warm up or hot, or hard starting when hot, but starts fine cold.

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Brettw
I don't know if there is an inspection cover on the Onan. There is on the Kohler K series, and therefor you don't have to pull the head, etc. You could start by checking the clearance first, if there is an inspection / adjustment cover, and then proceed further if necesary.

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