Pressure relief piston confusion

[donbecker1234]

79 930 CA motor.

Light on documented history, first engine drop and I'm trying to not miss anything. I'm not pulling the heads or splitting the case, but nearly everything else within reach.

Wayne's 911 engine book mentions that the updated style pistons and springs (w/hex cap) are REQUIRED if the oil bypass was done, else you'll get no oil pressure when starting the engine.

He also mentions that the factory started doing the oil bypass modification in mid-1976....however I have the flat/slot, older style caps.

Does anyone know if the older flat/slot caps are compatible with the upgraded pistons and springs required for engines with the oil bypass?

I had no issues with oil pressure and the engine seemed to run okay before I removed it.

It looks like I have a bunch of oil around the lower/bottom pressure cap, so I figure I can replace the caps/pistons/springs while it's out and use a new sealing washer too.

[Flat6pac]

Factory went to the 15 mm hex about 1980. Definitely easier than the old style
Bruce l

[donbecker1234]

Originally Posted by Flat6pac

Factory went to the 15 mm hex about 1980. Definitely easier than the old style
Bruce l

Hi Bruce,

So if the factory started using the new style spring/piston in mid 1976, but switched to the hex caps in 1980, I likely have the new style spring/piston with the old flat caps.

Thanks!

[Walt Fricke]

Leaving aside the issues with turning the old style caps, just take yours out and compare the two and look for the presence or absence of the little guide tube which goes inside the longer, newer one to prevent it bending sideways. Easy with the engine out and drained of oil, at least if you have it up on a stand. Would give you the incentive to purchase the hex caps while you are at it. Otherwise this stuff doesn't seem to be much of a wear item.

But it should have the newer style, if you aren't too worried about that. It would be very strange indeed if someone put the old style springs in at some point. No incentive to do so, and every reason not to.

[donbecker1234]

Originally Posted by Walt Fricke

Leaving aside the issues with turning the old style caps, just take yours out and compare the two and look for the presence or absence of the little guide tube which goes inside the longer, newer one to prevent it bending sideways. Easy with the engine out and drained of oil, at least if you have it up on a stand. Would give you the incentive to purchase the hex caps while you are at it. Otherwise this stuff doesn't seem to be much of a wear item.

But it should have the newer style, if you aren't too worried about that. It would be very strange indeed if someone put the old style springs in at some point. No incentive to do so, and every reason not to.

Thanks Walt, I have a bit of oil around the bottom one, so I figured with the engine out and oil drained I might as well replace the springs and pistons and switch to the hex caps and use new sealing washers.

[304065]

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