Leak Down Test With Unseated/New Rings
 

Hi.

Hoping for some help.

Can I do a leak down on an engine that has rebuilt heads and new rings? I am guessing that the unseated rings would produce significant blow-by.

I am about to remove the heads. one needs repair due to improper installation of an exhaust valve. I am trying to determine more information about the engine before I take the heads off.

Thanks for any help.

James

Probably should have mentioned that the engine is on an engine stand.

Your rings are going to blow by.
Your valve job should have pressure tested the sealing of the valves.
Valve problems on one head? You didn't back down the piston from top center?
Bruce

Thanks Bruce. I appreciate your response. I know you are an engine builder.

I have a valve guide boss that has had been damaged. Possibly from the rebuild of the head.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/947355-964-exhaust-port-not-looking-good.html

Are you recommending that I back it down "counter clockwise" after TDC and then lock in place (actually it was a friend holding the crank with a wrench)?

That said, is the test redundant when the valves are not seated?

Not an expert in the slightest...

But, you can pour oil into the cylinder to seal the rings artificially. Any leakage on leak down left would be from the valves...

My motors on a stand to... I was sure my leakage was from my valves as I heard some hissing from the exhaust. Well, not so much. Put some oil in the cylinders, and leakdown was near perfect even in the two sub par cylinders ...

This little test can help...

Good luck...

You should expect less than 5% leak. Test is pointless if valves are not seated.

Thanks for the replies. I think that the oil in the cylinder would test the valves.

Jeff. ..this engine has not been run since the new rings - do you still think that unseated rings would leak around 5%?

it should not matter, but the distributer in not in it, perhaps i am wrong. It is 964 engine.

Thanks for the replies. I tried the test on two cylinders. Valves seated. Lots of blow by.

If your intent was to check the other heads, judging that you have more than one with an issue, I'd consider all of them suspect and send all to a reputable rebuilder for test/refurb.

You wanted to evaluate your valves, but were worried about unseated rings screwing up the test, correct?

Pouring oil into the cylinders takes the valves out of the equation. Any cylinder that leaks, has bad valves.

Isnt that what you were worried about?

Bo

Thanks again for the help.

I am getting a baseline before I pull the heads off of 1, 2, and 3. If the only fault after inspection is the boss, I will assume that the all the heads are OK. I may change the plan as I go. I am sending them to a fairly local factory (in Germany) trained mechanic.

Thanks again to all who replied.