Compression Test Data

[niall]

Hi

Just had compression tests carried out on a 3.0L SC engine by the seller of the engine.

The engine is already out of the car on a pallet, so the tests were carried out with engine cold and out of car.

The figures range from 165psi to 170psi from cyliners 1 to 6.

Does anybody know out there if these are good pressures?

Thanks
Niall

[MBEngineering]

HI Niall
How many miles has the engine covered??, if it is high mileage , thay are not bad for a cold engine and even, was there any noise when the engine was turning over to indicate a leak through the headjoint?? what year is the engine.

regards mike

[Porsche_monkey]

Sounds fine to me, at least they are all in the same range.

[niall]

Unfortunately the mileage cannot be verified by the seller and I am told that the engine was a good runner before removal.

I think he just turned the engine over cold with the starter motor to get the pressure readings on the gauge.

I was sent photos showing each individual reading on the gauge 1 to 6, detailing gauge read out and connection of gauge to each spark plug socket.

[Porsche_monkey]

So you were not present for the test?

[MBEngineering]

HI just where is the engine?

regards mike

[niall]

No, not present.

But the photo's show each test with gauge attached to the plug sockets numered 1 to 6, clearly showing gauge reading.

[Porsche_monkey]

Compression is something I would want to confirm in person, unless I knew the seller.

Are you picking the engine up or having it shipped? Maybe someone from this board could go see the engine for you?

Getting stiffed with a bad headlight or a floor-mat is no big deal, you want to be more careful with an engine.

[niall]

Yes I get the point.

Its from a breaker who came upon a crashed unit over here.

I was just going to get it shipped, he offered a 1 month return if the engine was faulty.

[ianc]

All cautions aside, those compression results sound fine for a cold engine.

ianc

[Crashly]

The numbers sound great for a cold motor. The only question that wouldd be in the back of my mind would be " did he put oil in the cylinders before he did the test". If that trick was done then it can really mask leaking rings. If he will stand behind the warranty simply get the motor home and do another compression test on it using your own Gage. The test is extremely easy to do with the motor out. Before you do the test you could check for oil residue by simply putting a white rag on the end of a dowel rod and put it down by the spark plug hole while turning it over. If there is any oil residue it will show up. If the compression test checks out I wouldd be overjoyed to have those compression numbers. FYI while it is out it wouldd be a good time to do a valve adjust and check out the head nuts/bolts. Good luck. PS how much did the motor cost?

[Porsche_monkey]

The oil in the cylinders point is valid. And a one month return guarantee is fine provided you can get the engine to your shop, installed, and tested within a month.

If it were me I would want a bit more time. I don't get much done in a month.

[David E. Clark]

Those numbers are fine. From my experience, the most important factor you are looking for in a compression test is consistency between cylinders. There should be no more than 10% variance between cylinders. In your case, assuming the test was done properly, your low cylinder is 165 psi and your high cylinder is 170 psi. Roughly 3% variance which is excellent by any standard! If you are really worried you might request that your mechanic (or the seller) do a leak-down test. This test measures how much "pressure" (PSI) is lost in the engine while the compression test measures how much "pressure" (PSI) the engine can produce. It is generally accepted that the leak-down test is more indicative of engine health than the compression test.

I agree with the advice of the other members that you watch the seller perform these tests; or, even better, learn to do them yourself - it's not hard! Not necessarily because you think the seller is a crook but because with these old cars it's always helpful to learn as much as possible. Good luck.

[Porsche_monkey]

There's an idea. Re-do the test the day you receive the engine. If the numbers difer from those you were given send it back.

[tcar]

Will the breaker (wrecker over here) pay shipping both ways if not as he represents?

That can be a significant number, depending on how far away it is. You can't just put it in the boot of your mini and take it back.