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120SF Exhaust valve?

Old 04-24-2023, 04:13 PM
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Join Date: Oct 2005
Location: Grand Rapids, MI
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Default 120SF Exhaust valve?

I was given a fun airplane ("Jerry's Big Boy") that came with a YS 120SF engine. Once the regulator was cleaned out, it ran great - a really nice combination. However, I've had the exhaust valve stick (or drop down) twice. A friend straightened it and lapped it in the first time - that worked for a handful of flights. Happened again, though.
I'm now looking for a new valve. CKAero doesn't appear to have parts for this old of an engine. The PN is YS0535-120SF, and the valve head measures 14mm diameter. The part CKAero has - YS0535 - is for a 12mm valve. (I've got one of those, that I can't use - anybody need it, get in touch.)
Anybody have the 14mm valve part? Any other options?
Old 05-04-2023, 04:03 AM
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Do you by any chance run fuel with castor in it?
If so, chances are you won't need a new valve once you start using Synthetic oil.
Because a valve that works fine after cleaning and lapping, to me indicates "fouling", not "defective".

If you are allready using fuel with synthetic oil, then it is time to look further, but it still could be an issue with cooling and/or lubrication.

Last edited by 1967brutus; 05-04-2023 at 04:05 AM.
Old 05-04-2023, 06:01 AM
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Join Date: Oct 2005
Location: Grand Rapids, MI
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The first time, the valve was bent - took some work to get it straight enough, more than just cleaning

Latest valve failure - more than just cleaning!
. This time it is bent to around a 45 degree angle. It hit the piston, the engine stopped dead suddenly.

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