Replacing valve stem seals in the car using compressed air

[Haroon]

I was watching the video titled “How To Remove Valve Springs In The Car” (the one using compressed air to hold the valves in place), and had a few questions before I try to change the seals:

1. Rather than using a compression tester hose with the schrader valve removed, would a leak down tester also work? Is there any particular reason not to use that instead? Just curious – I do have both.
2. Should it be set to any particular PSI on the compressor?
3. Does it matter if the compressor isn’t that big? It’s 50L/3HP, and I wouldn’t want it to suddenly run out of air half-way through the procedure. I also have washing line as an alternative if that’s less risky.
4. I plan to join a narrow neodymium magnet to the end of a cord and have it ready in case things go wrong. Are there any better ways to pull the valve back up?

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[Richard Kirshy]

1. Rather than using a compression tester hose with the schrader valve removed, would a leak down tester also work? Is there any particular reason not to use that instead? Just curious – I do have both.

As long as you can maintain enough air pressure with in the cylinder either will work.

2. Should it be set to any particular PSI on the compressor?

I should think anything above 80 PSI will do.

3. Does it matter if the compressor isn’t that big? It’s 50L/3HP, and I wouldn’t want it to suddenly run out of air half-way through the procedure.

I also have washing line as an alternative if that’s less risky.
That will work also, but a bit more work.4. I plan to join a narrow neodymium magnet to the end of a cord and have it ready in case things go wrong. Are there any better ways to pull the valve back up?

If you want to minimize the risk of dropping a valve into the cylinder …
I would suggest when you remove the spark plug that you bar the engine over to bring that specific piston to the top of its travel.
In most cases your dealing with an interference engine in which case the valve itself will only drop a minimum distance, if the worst happens.

[Author]

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