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Old 6th Aug 2019, 08:17
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PEASACAKE
 
Join Date: Feb 2008
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Originally Posted by RVDT
Motoring the engine to cool it will do SFA wrt to coking and only promotes rim cracks as per the quoted CSL.

Change to a better oil - Mobil Jet II is marginal at best - works in some engines but not all - try 254.

Is your scavenge strut clean? Have a really good look - it is not round in shape but has 2 flat sides and 2 radius sides.

Low scavenge flow does not help. How many hours has your gearbox and pumps done? There is a procedure to test the scavenge performance from memory.

Flooding of the space will cause build up on the lab seals. I think there is a check valve in the pressure side that works to shut off the oil as the pressure drops below a certain value on shutdown. This check valve can leak. May be wrong as it is about 30 years since I worked on a 250 but hey................

Scav filter will clean the lumps out and is worth every cent.

It's a classic old engine - pay attention to the details though and they work fine.
We swapped a fleet of at least 20 C20B from Jet II oil to Jet 254 in the eighties, the trouble we had from carbon coming loose and blocking the torquemeter orifice in the gearbox, it was unacceptable, we were pulling engines out all the time to open the gearboxes and clear the orifice.

BUT, we never had carbon problems after that.

In hindsight our company sShould have fitted a Facet scavenge filter kit to all aircraft before changing oils, but hindsight................ and costs.
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