Leakdown Test Results

[dereklola]

As some may remember I race a NA Stage II in a formula car in vintage road racing. After last winter's engine rebuild things were good this summer. Just checking things before winter storage - leakdown was 6% on five cylinder and about 20% on #6 - leaking out of the exhaust. Started up the engine and ran it for a few minutes in case that dislodged some carbon on the valve or seat - leakdown improved to about 16%.

So what now? Need Buick experts to guide me!

I assume 6% is OK. I assume 16% is not a bent valve but it still needs attention. Two suggestions have been made by friends - 1 - remove the valve spring and spin the valve (chucked in a battery drill) with light pressure on the seat and - 2 - started up the engine run it for 10/15 minutes then squirt some water from a squirt bottle into that intake (it's a Kinsler intake with 6 stacks) - that will "steam clean" the valve and seat and should do the trick. The friend who suggested #2 also said #1 won't work!

So what do you guys think?

And can anyone suggest how to compress and remove the valve spring (they are double valve springs with a flat 'friction spring' between) without the removing the head. I have such a tool but it only works on single springs. Is there a lever type that works on Buick V6s?

Thx for any help - Derek

 

[karolko]

Just some more food for thought, I had a similar thing happen to me. however I believe I bent a valve ever so slightly and had 20% leakdown. I attribute it to old springs and I revved up to 6300 on my last pass and I believe the valve chattered thus causing a slight bend.

If you are going to take the valve spring off, I would check the spring tension on it.

Adrian