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Date:  7-2-2011
Number of Hours:  3.00
Manual Reference:  
Brief Description:  Adjustable Oil Pressure Relief Valve

Since I purchased the engine, I've had trouble with oil pressure. Most recently, I was using a Lycoming P/N 11713 11 lb spring and two washers, and seeing 110 psi on on cold startup and as low as 20 at idle when hot. On the Lycoming forum, it was suggested that a relief valve lapping tool be made by welding a relief ball onto a steel rod. I pulled my relief valve and closely inspected the valve seat and there was some pitting. I lapped the valve seat using valve grinding compound. Next, I replaced the fixed oil pressure relief housing with an adjustable one, P/N SL77808, and put in a new relief ball, P/N SL1028-B using the same spring. I adjusted the adjustable housing so that it the spring height was slightly lower (and looser) than the current configuration. I wanted to change to an adjustable relief valve, as the plenum on my baffles makes it fairly laborious to add or subtract a washer, requiring an upper cowl removal in addition to removing the plenum. I also figured out how to remove the valve without removing the right rear baffle - some wood shims are placed between cylinder #5 and the baffle which pushes the baffle out far enough the clear the valve. I center-punched a spot on the baffle where, if necessary, I could drill a hole to pass a 1/4 inch socket extension and engage the adjustment nut with a 9/16 inch socket, which would be put on the extension via the cabin heat outlet. The hole could be covered with a metal cap plug when not in use. This will allow me to adjust the oil pressure by simply raising the right cowl lid, removing the cap plug and cabin heat duct and applying the socket and extension. Much simpler. After changing the valve (and oil hoses), my max oil pressure cold was 90 psi and my min pressure hot was 35 psi, within Lycoming limits.
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New, Old and Lapping Tool.

New, Old and Lapping Tool.

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Oil Pressure Relief Valve Seat - some  pitting visible.

Oil Pressure Relief Valve Seat - some pitting visible.

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Adjustable Oil Pressure Relief Valve.

Adjustable Oil Pressure Relief Valve.

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