What PSI should the cylinder be for valve stem seal replacement?

[Davidf]

Originally Posted by LightlyToasted

I think he's asking about the pressure for the leakdown tester to keep the valve from falling into the cylinder when its spring is removed.

I don't know what the recommended pressure is, but I recall it being enough pressure to hold the valve in place but not so much pressure to cause the engine to turn over.

This is an interference engine. Therefore, if the cylinder being worked on is at TDC then the valve cannot drop into the cylinder.

[Scott ZHP]

Originally Posted by Davidf

This is an interference engine. Therefore, if the cylinder being worked on is at TDC then the valve cannot drop into the cylinder.

The valve stem can drop far enough into the guide that fishing it back up will be a major hassle. You need pressure on the valve head to keep it closed in order to R+R the retainers. Been using oiled cotton clothesline stuffed into a plug bore and compressed by the piston for years.

[byM5]

Originally Posted by Scott ZHP

The valve stem can drop far enough into the guide that fishing it back up will be a major hassle. You need pressure on the valve head to keep it closed in order to R+R the retainers. Been using oiled cotton clothesline stuffed into a plug bore and compressed by the piston for years.

I did start to lose a valve as I was not careful enough to compress the spring while staying off the valve. Fortunately, it didn't go down far. But I wasn't evaluating how far it might drop either.

I believe you both are correct.

If the cylinder is not TDC, then it will drop lower.

If the cylinder is TDC, the valve is long enough that it won't drop much in such a way that it is retrievable with a magnet or needlenose.