Evaluation compression - is it the one? I want it.

[shawn908]

Deliberating a mid 70s 911
3.2 transplant:compression 1/150, 2/175, 3/175 4/166 5/170 6/170
with a leak down result of 35% on cylinder 1
No rust. No leaks.
Given the caveat that numerous variables can affect compression, should these numbers cause concern? The leak down can (I'm told) be corrected with valve adjustment and valve cover gaskets.

I am on the cusp, 911 gravity is pulling me in, I don't think I can be stopped...
Is there logic that can stop me?

[Jeff NJ]

Are you paying top dollar, or is the price commensurate with the possible work needed? Don't assume that the leak down issues are an easy, cheap fix. They could be, but then again, it may need a top end rebuild.

For the right price, do it!!

[shawn908]

Thanks Jeff. I agree it's a balance of risk vs price paid. The car drives very well, engine sounds only good. But the leakdown is a remaining concern.

[techweenie]

The leak down is not affected by valve cover gaskets or valve adjustment. It can be affected by bits of carbon in the combustion chamber. A second leak down test -- even if only on #1 is a good idea, after the car has been driven a bit.

I should add: if the discrepancy in compression is really 25 lb. after a second test, you are looking at a top end overhaul in the relatively near future. Something to factor in.

[Tspringer]

Before doing the leak down test again, try this. Get the car up to full operating temperature. Then spray a fine mist of water into the air intake while revving the engine. Use a sprayer that puts out a fine mist - do NOT pour water into the intake. (I mention this because of a post from a guy who had read about this trick but did not understand that you were supposed to spray a mist of water - instead he poured water into the intake and busted a rod).

The mist of water turns to steam and does a great job of cleaning off carbon deposits. I have used a bore scope to look into a combustion chamber at nasty carbon gooked up piston domes then done this trick resulting in clean carbon free domes.

[jwasbury]

It could be a piece of carbon preventing the valve from sealing, but it may also be something like this:

40% leakdown, car will run great, no smoke, etc. But it is broken, needs fixing, and stuff like that ^ is not cheap. Proceed with caution.

[shawn908]

Thanks to all for insight - the technician cited that...38% leak down on the exhaust valve. Most likely cause is carbon build up on the exhaust valve or on the valve seat. Can be addressed with valve adjustment. Its cited as a 6 hr job with valve cover gasket set as parts. The technician I believe knows the car and also has a career as a P mechanic - like 30 years experience. No reason I can think to not trust his judgment. Still that image above does illustrate what cannot be seen or readily diagnosed.
This car just looks so right, I drove it and the transmission and gear shift so tightly, engine starts in two seconds from cold, no smoke. etc. it suggests well taken care of car. Its kind of a "survivor" with a 3.2....
Thanks again for thought/insight. Appreciated.

[WANNA930]

38% Leak down on the exhaust valve? Sure you got that right?

leak down tests are not that easy to do correctly. They are also open to operator error and reading the gauge used. I think if you Google "leak down test" there is great article written by Hot rod or maybe Car Craft that really explains the numbers and what they mean. A good read.

I am going to assume there was air leak heard through exhaust at that cylinder?

[Tt surgeon]

Exactly, if not at tdc, numbers will be aberrant.

[shawn908]

I bought it.
Got the valve adjustment which included replacing two rocker arms + shafts (out of tolerance).
Could I sleep? Not until second opinion so took it to independent Porsche shop and had a Post-Purchase Inspection.
Got it back today: 175-180 compression and <3% leak down on all 6 cylinders. Relieved. Needs new front strut inserts, but otherwise clean bill of health.
Now, start to drive it.

[Jeff NJ]

Nice!!

Congrats and where are the pics??

[pmax]

Congrats !

So the leak down test can be affected by valve adjustment.

How much did the repair cost ?

[Matt Monson]

Sometimes rolling the dice comes up in your favor. Congrats.

[pmax]

I roll the dice everytime I drive the Carrera.
Life's too short to worry about broken studs, leakdown numbers etc etc

[COLB]

Originally Posted by Matt Monson

Sometimes rolling the dice comes up in your favor. Congrats.

Craps is a hellacious fun game, so long as you have the bankroll to afford it.

Sounds like OP hit the hard six.

Nice!

[shawn908]

For the record...this is the one.
Not original color (was copper brown metallic), but it looks like velvet red metallic (?)
I don't know how the valve adjustment and rocker arm replacement affected the prior leak down, if at all. Maybe I could second guess the validity of the initial result?
Having the independent inspection by a trusted/unbiased P mechanic was worth it. Next time (if there is one...) it will be "pre" vs "post".
Work done cost $900. about 50% was labor cost.
Driving this is the goal.
Currently trying to exceed the goal spending time behind the vintage Raid steering wheel.

[bri450sl]

Congrats. Beautiful 911.

[Matt Monson]

Great color.