Leakdown shows 0% on just #5

Chris Lovell · 10-20-2003, 05:30 PM

Does anyone have any experience with a beautifully running 3.2 that has a leakdown of 0% and compression test of 25% on just one cylinder? After every cylinder came through well, #5 bombed completely. We assume a burnt valve or broken rings. Does anyone have any other ideas? Stuck valve, head gasket, etc?
Thanks.

john walker's workshop · 10-20-2003, 06:03 PM

leakdown of 0% is virtually unheard of. usually they're 3-4% for excellent and 20% on up for a cylinder with issues. what is 25% compression? do you mean 25lbs? if you think it runs beautiful now, wait until it's fixed.

Sonic dB · Sonic dB's Garage

Quote:

f you think it runs beautiful now, wait until it's fixed.

ouch

Chris Lovell · 10-20-2003, 06:12 PM

John,
I just read 25 off the pressure test report and translated to 25% based on the leakdown result. Whoops. We were also stumped with the 0% leakdown. Seems weird. Do you have any thoughts on any other tests or what might be going on with #5? Any way to confirm valves or rings? Any real danger in driving this car? Honestly, I can't feel the miss at all.

Rot 911 · 10-20-2003, 06:13 PM

John, I think he means 100% as in #5 will hold no pressure. Chris, have you been following the posts on my engine rebuild over the last week? '86 Carrera's must have a #5 cylinder curse. My #5 had compression of 60lbs and 100% leakdown. Tore the engine down and the exhaust valve has 3 big splits on it. There are pics on my threads. You are looking at least at a top end rebuild.

Chris Lovell · 10-20-2003, 06:15 PM

John, I just reread your response. We have no pressure at all in #5. Maybe the leakdown my guy uses calibrates differently. Maybe hould be 100%. Ugly.

Rot 911 · 10-20-2003, 06:16 PM

Chris my '86 was running just fine, but using a lot of oil.

Chris Lovell · 10-20-2003, 06:17 PM

Kurt,
How soon for the rebuild? The '88 runs great now. I guess it may be a matter of luck but I don't want an internal meltdown.
Thanks.

Chris Lovell · 10-20-2003, 06:18 PM

Kurt,
Thanks. I have exactly the same situation. Using oil, running fine. I'll check your post.
Thanks.

john walker's workshop · 10-20-2003, 06:19 PM

well, the recent pic of kurt's burnt valve comes to mind. check that both rockers are still in place, and also check the valve adjustment on both of them. just see if you can detect some clearance by moving them with your fingers.

Rot 911 · 10-20-2003, 06:22 PM

Here is a pic of my #5 exhaust valve. How comfortable would you feel knowing that valve could self destruct at any time?

Chris Lovell · 10-20-2003, 06:27 PM

Good advice from all. I am just in the final negotiation for this car and am factoring in a top end rebuild. Thanks again.

Chris Lovell · 10-21-2003, 05:41 PM

We agreed to a reduced price covering a top end. All parties are happy. Maybe now I will have a reason to buy Wayne's rebuild book.
Per the bad cylinder, my fabulous tech thinks we may have a ring break. Leakdown "exhaust" was passing back though the oil box and not out the tailpipe. He could hear this. Interesting...

Rot 911 · 10-21-2003, 05:46 PM

Chris that is not so good news. I would rather have a burnt valve. Broken ring could have scored the cylinder. I personally would not buy the car as you described unless you are getting enough of a deal on it that you don't mind spending $3000-$7000 on an engine rebuild depending on what is needed and who is doing it (yourself or paying someone else)

Chris Lovell · 10-23-2003, 08:17 AM

Kurt,
$3=7K still works. You advice is much appreciated.

Superman · 10-23-2003, 08:32 AM

Ummm, if I were to buy new P&Cs for a 911, I'd view it as an opportunity to increase displacement and install "proper" (non-emissions) pistons. A 3.4-Liter, 9.8:1 engine would be quite fun to drive. Don't forget to replace the rod bolts.