[William Miller]

My pop off valve has had an intermittent air leak that has been driving me crazy for the last 2 years. It hold's tight when idling so it wasn't until recently that I found the actual problem.

The hinge pin worked it's way out so only one arm was holding it in and the spring pressure was causing the flapper to close off center at times. This happend mostly at moderate acceleration when ther was little manifold vacuum to hold it closed tight.

I fixed the hinge pin and found it still leaking intermittantly. I realized that the flapper may have been permantly tweeked a little preventing a good seal. The spring on the flapper is pretty weak so I installed a heavier spring over the existing spring. (The spring came from a standard Victor Rat trap!)

This is keeping the flapper shut.
I can't help but think that part of the problem is that the o-ring that seals the pop off valve is getting pretty old and probably getting hard. When I removed it and cleaned it I can see permanent indentations where the flapper seals against the o-ring.

I think if I replace it I will solve my problem long term.
I took some measurements last night.
The diameter (thickness) of the o-ring is 4mm.
It's hard to measure the inside diameter of a rubber o-ring so I measured the base of the pop off valve where the o-ring sits.

The ID of this channel is 44 mm and the OD is 55 mm.
That's a 11mm spread and the o-ring takes up 8mm (4mm x 2)
So there is some room for the o-ring to move arround. Or maybe it has shrunk?

I found a source http://www.mcmaster.com/
I have used them for hardware before.
They sell (in packs of 25 for about $10) two sizes that are close.
44mm Id x 4 mm dia.
45mm ID x 4 mm dia.
They also have 44ID x 5mm but that might be too thick.

Does anyone have a new pop off valve to double check these measurements.

Has anyone had this problem before?
The normal parts sources do not sell the specific o-rings for the pop off valves seperatly.
Does anyone have another source for these?
If we can figure out the right size I'll buy them and pass the out to who ever wants them!

[Parenn911]

Hey Bill, you are welcome to check out the pop-off valve on my 79 SC, it is somewhat new.

[William Miller]

Thank Pari I hope i will have some time in the next few days.