Oil Pressure Relief Valve Cap Leak

How to keep the Cessna 170 flying and airworthy.

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bjoness
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Oil Pressure Relief Valve Cap Leak

Post by bjoness »

Does anyone have any tricks to stop an oil leak from the O-300 oil pressure relief valve cap? No matter how many times I change the AN900-14 gasket, the new gasket always seems to leak. I've even tried applying Loctite 592 Teflon PST Pipe Sealant IAW TCM SIL 99-2B, but even that doesn't seem to help.
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Bruce Fenstermacher
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Re: Oil Pressure Relief Valve Cap Leak

Post by Bruce Fenstermacher »

I would check the nut or cap for a crack as well as the accessory case. After thatI might also try two crush washers though doing so will slightly lower the relief blow off pressure. I wouldn't be worried about the lowered pressure but if you found it worked the pressure could be restored with a washer the thickness of second crush washer placed in the cap under the spring. Of course two crush washers and the washer under the spring are not specified anywhere.
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GAHorn
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Re: Oil Pressure Relief Valve Cap Leak

Post by GAHorn »

It sounds as if there may be a crack that the plug is opening-up when torqued....or there is a rough seat where the AN900 gasket sits.
If neither is the case, you might try a neat bead of Permatex Oil-resistant RTV gasket-maker ("Ultra-Black" at NAPA.)
'53 B-model N146YS SN:25713
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