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in situ valve spring compressor, air supply question

Mr Whippy - 20/9/12 at 07:47 AM

I really need to change the landys valve stem seals as it smoking on start up so much it is going to struggle through it's next MOT, really can't be arsed taking off the head as the valve seats are fine and the gaskets good

I see Burton have these spring compressors and it comes with an air hose connection for the spark plug to pump the cylinder up, not used this myself and am wondering how much air this would need as my compressor isn't all that powerful being quite small. How much air tends to leak past the piston rings? could even a smallish compressor keep up?

any ideas?

Thanks

adithorp - 20/9/12 at 08:14 AM

Not a lot.

While you're taking the spring off and changing the seal etc, the hissing/whining does tend to do your head in. Just make sure the cylinder is at TDC when you decide to disconnect the air-line. The pressure has been known to slooowly push the piston down; Guess how I know?

Mr Whippy - 20/9/12 at 08:56 AM

Thanks, that sounds promising if a tad annoying, I can lock the piston by just leaving it in gear and the transmission brake on.

owelly - 20/9/12 at 09:45 AM

I use a piece of cord stuffed down the plug hole at bdc, then slowly wind the engine over by hand until the cord is squished up under the valve head.

adithorp - 20/9/12 at 11:06 AM

quote:
Originally posted by owelly
I use a piece of cord stuffed down the plug hole at bdc, then slowly wind the engine over by hand until the cord is squished up under the valve head.

I stopped doing that when the cord managed to tie a knot in itself and wouldn't come back out. VERY unlucky but don't want the hassle twice.

britishtrident - 20/9/12 at 12:03 PM

In reality it is easier to lift the head

Canada EH! - 20/9/12 at 04:48 PM

I used to carry a length of 3/8" rope in my 66 corvette 427, was always breaking valve springs, luckily it had a damper spring as well so the valve didn't fall and hit the piston. I could change springs at the side of the road with a few onboard tools.