3.0 Compression Results Advice

[911gilley]

Hello all,

I am currently looking for a 3.0 engine for my project car. This past weekend I went to look at one (an '82 3.0 with a reported/documented 77K miles, Carerra tensioners, turbo valve covers) and did a compression test on it. The seller said engine has been sitting for approximately 1 year. The results of the test are as follows:
#1 175
#2 165
#3 40-50 (highest after 3 tests)
#4 145
#5 158
#6 135

Seems like left bank higher and better but with #3 very bad, as opposed to right side lower but within 15% of each other.

Tested #3 3 times, after first time shot small amt of oil into cylinder and results did not improve.

I have an idea of what the very low #3 may mean, and can anyone explain why the drastic difference between left and right hemispheres/banks?

I would appreciate any views on what people think of the general condition of this engine.

Thanks

[911gilley]

bump

[MotoSook]

Why was the car sitting? Did the owner have problems and couldn't afford to fix it then let it sit? Does it run?

I don't think compression numbers from an engine that sat so long are reliable. Others will chime in, but that engine has to be run (car driven) for a bit before any compression or leak down numbers would be of any value. Right guys? And compression numbers will still be debated over their worthiness.

[911gilley]

The owner bought a front-end collision targa as parts car, used some parts for his '83 SC coupe, parted out rest.....this is the engine from that car, and is out of car.....drivetrain to heat exchangers intact.
Without starting the engine, is there any way to know if this is a viable engine? He is asking slightly under the going price for engine.

-Ed

[MotoSook]

My guess is that you'll have to take your chances. A 3.0 rebuild at home may still make the package a good value if the price is low enough. You can always doa "field" rebuild. That'll probably put you right back to what you think you're getting. But don't start a debate on the value of a "field" rebuild (i.e. a Motormeister rebuild)

[911gilley]

Souk,
I think I understand what you are saying regarding the reliability of the numbers due to the engine sitting so long in that things tend to shrink and loosen up, and everyone knows that a warm running PCar engine is a different animal than a cold one. So the numbers will not be reliable unless the engine is run, but if I cannot run the engine, can the current numbers be used as any indicator of the health of this engine?
What bothers me is that there is such a major drop in pressure in cylinder #3 that how could there not be a mechanical problem...ie valve guides, split valve, broken ring, etc. in that area. I guess that one possiblity is that there is some carbon or something stuck in a valve seat from the cranking over during the compression test that maybe running the engine may push out.
-Ed

[MotoSook]

Well, you've got the idea. The lone low cylinder is a concern, but it could be anything fron a bad valve, bad valve seat, bad valve adjustment, broken ring, carbon...you understand. I'd be more worried about the potential of a bad rod or crank. Those you can't tell from the compression numbers. If #3 has bad rings, it'll be a topend rebuild, but if you have to split the case it'll be costly. Of course you can then build a motor with some bragging rights.

Like I said, if the trans and engine can be had for a low price, it'll be worth it.


Try posting in the rebuild forum. Those guys can spit more than I know about these engines, but I figure someone should speak up.

[911gilley]

Thanks for the pointers, Souk
-Ed

[MotoSook]

Good luck. With 2 911's, you should be prepared for the worst already, so just weigh the worst case against the cost of the package.

Personally, if I could pick up a worn but rebuildable 3.0, I'd do it. The cost of a good education is ..well..it's priceless.