Opinions Needed: Compression and Leak Down Test Numbers

I know of a good black on black euro tr for sale in san jose. I think its 139k, 15km just had serviced done. I saw the car and it was Nice enough...as far as compression definitely would worry about it... maybe u can negotiate


Sent from my iPhone using Tapatalk

 

I was just discussing Leakdown/Compression numbers with my good friend, and Ferrari tech, over this weekend.

Though I gave him a hypothetical 8 cylinder as an example (360 Modena), his thoughts were that within 5-7/8% you are looking at a driven, well rounded car, that with appropriate service records, in good chronological order, he wouldn't advise against a purchase on.

As the numbers grew past 10%, his concern grew higher, and to him, you are working with an engine that is in the "not if, but when" time frame for a rebuild. #12 on the car you mention, would have me asking for a very in depth "tour" of that cylinder, and I'd likely walk.

Keep in mind, he's very picky, and an absolute perfectionist, but shouldn't all people who are hands on involved in a VERY expensive engine (if it goes KABOOM)?

Just my two cents.

 

https://mobiloil.com/en/article/car-maintenance/car-maintenance-archive/how-to-do-a-leakdown-test

"Reading results
No engine will have perfect sealing with 0 percent loss. Five to 10 percent loss indicates an engine in great to good running order. An engine between 10 and 20 percent can still run OK, but it’ll be time to keep an eye (or ear) on things. Above 20 percent loss and it may be time for a teardown and rebuild. Thirty percent? Major problems. The percent of leakage should also be consistent across the cylinders. Any great differences indicate a problem in that cylinder."

Cheers,
Vincenzo

 

Any cylinder leakage above 10% with corresponding low compression figures bothers me.
But if the car has not been driven for a while, the test is not valid. After a service and 500 miles of hard driving, the figures may come up. The car should also be at operating temperature when the test is done. Also the coloration and carbon build-up or lack there of on the spark plugs is a good indicator of the condition of the engine. Even plug coloration indicates good fueling and lack of carbon show no oil usage.

 

this both is a. MUST

 

Its funny when I read that the engine needs to be hot and all this criteria met. It doesn't. Running an engine prior to testing will clear out a chunk of loose carbon on a valve seat whether its been sitting for decades or not but with one cylinder suspect theres a problem hot or cold. The new 512M crate engines I bought were last run on a dyno in 96 then boxed up. I did a leak down test right out of the crate and they were no more than 7% loss on all 12, one was 5% on all 12. With the above example, your ears are your best friend to reveal if its a valve or a ring issue. Yes a hot engine will close ring gaps but not make a dramatic difference if its a good engine.

 

on a 4 cylinder opel engine 1,6 ltr with about 100.000 km, laying around about 10 years the compression has been in cold condition before I put it in the car between 7 and 9 bar ( of course cold condition ). after installing in the car and about 1000 km driving I tested again and the compression has been in cold condition after valve adjustment between 8 and 10 bar, in warm condition between 9 and 10 bar. so there is a little difference between cold and warm condition, but nevertheless if you test in warm or cold condition, the difference between the single cylinders may be nearly equal.