Stu
Joined: 23 Oct 2008
Posts: 8
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 Posted: Thu Oct 23, 2008 1:22 pm Post subject: M14P Missing Oil & Hydraulic Lock |
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Greetings fellow Yakmeisters. I have been lurking around this list for sometime, now have a Yak and seek help.
Our M14P has about 870 hrs. Recently, after the airplane sits for a week or two, it has been prone to hydraulic lock in the no. 6 (lower left when viewed from the front) cylinder. Another puzzling phenomenon started at about the same time: when cold, the reservoir oil level (as indicated by the dipstick) may read several litres lower than after the last run. After running the engine again, oil level mysteriously returns back up to where it ought to have been.
Our mechanic reports this problem is probably related to a faulty checkvalve in the oil pump assembly. This valve is supposed to prevent oil from backflowing out of the sump back into the crankcase when the engine isn't running. In higher time engines, the valve is prone to leak, allowing oil to drain back through the pump into the crankcase and lower cylinder(s). That explains both the missing oil and the hydraulic lock.
Apparently the fix is either a rebuild of the oil pump and associated check valve or a separate new check valve retrofitted between the pump and the sump. The new valve is less troublesome than a pump rebuild, but still costs about $1500 installed (the valve itself is around $500).
Because accumulation of too much oil in the crankcase may affect other components, the mechanic recommends doing something soon. In the meantime I presume the approach should be to pull it through more than normal to get excess oil from the crankcase back to the sump.
Any comments on the diagnosis, fix or what to do in the meantime?
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Stewart Nicholson
Yak 52 N122GC |
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