Joe944

Hey I know I must be getting repetitive but I just did a leak down test and came up with 80% loss in cylinder #1. Could hear it from both the intake valve and the exhaust faintly.

Hole #3 showed less than 20% loss (went down as i turned up the pressure)

compression test results were pretty similar though

#1- 150ish#
#2-155#
#3-160#
#4-160#

what should I do? I think the results pretty much indicate that the head needs to be freshened up.

edit forgot the 1 's in front hehehe

User 41221

Does your car even run? Wow... my '84 with 300k miles on it posts 155#'s pretty much across the board. Don't ask me about my 951 tho... lol

Regards, ...Scott

BartW

How certain are you that the valves were in the closed position when you did the leakdown?? With such good compression results I think you may be just a small twist of the crank off on that cylinder.

iloveporsches

What should normal compression be?

Joe944

I'm 99.999% sure the #1 cylinder was on TDC when I did the leak down test. I bumped the ignition with a tissue in the hole to find tdc and I tried it 3 different times... same results with each test.

L8 APEKS

Sounds like you weren't @ TDC. 80% leakdown but 150+ compression really sounds like the valves were open.

MHT

each individual cylinder must be at tdc for the leakdown test. Leakage of more than 5% indicates a problem. There is so little overlap on the cam that you can do 2 cyls at a time. You can do 1 and 4 together, rotate the crank 180 degrees and do 2 and 3. Use the timing mark on the flywheel for no 1 and use the balance shaft timing notch for no 2. If the piston is not at tdc then your numbers mean nothing.

User 41221

Ya know, I feel REALLY stupid now (and for those of you who know me and are saying to yourselves "why now?" ... shuddup! lol)...

When I ready your original post, for some reason, I saw 50#'s, not 150#...

Nevermind me...

Regards,

Joe944

yeah i forgot the 1 before the 50's earlier hehe... anyways.. i did test each cylinder for being at tdc before I did the leak down test so I'm pretty sure they were.

User 41221

Hey, I suddenly feel less "dumb"! lol I'm sure its just a passing thing, tho...

Out of curiousity, is there a particular reason you were doing the comp/leakdown tests? If you measured those kinds of pressure losses during the leakdown test, I would think you'd also see it in a compression test. Since your compression tests look good, it puts me in the "something wasn't quite right when you did the leakdown test" camp.

Regards, ...Scott

D. Autry

I'd redo the leakdown.

I get app. 160#'s across the board on an '86 8v with (20th street auto told me) app. 80k on it. I have to believe them as I'm at app. 9500 ft. so my compression should naturally be less than those at lower elevations.

I think 160 is REAL good for being up here. My 911 only see's app. 135#'s.

BTW, Typically you'd leak through an exhaust valve and not both. I agree with several others, with compression like that I'd redo the leakdown.

Joe944

Yeah I'll try redoing it. I think the leak down tester itself might have been on crack.

L8 APEKS

Make sure you're putting at least 130 psi into the leakdown tester. I've been told 150 psi is a good pressure for leakdown tests, but my compressor barely reaches 125-130.

What are the correct specs for "good compression" in a 951? For example, the Bentley manual for my VW Corrado states something like 115-170 psi with a variance of no more than 10 psi between cylinders is OK.