What do you think of these numbers?
 

Cylindar 1,2,3,4
Compression 150,150,135,140
Leakdown 3%,1%,5%,5%

Are those numbers reasonable for a 2.7 liter sleeved 951 engine with 4000 miles? or do I have something to be concerned about? Thanks.

Minh

I think that's right about on for a 2.5(ins't 155 about the norm?), how about some dyno figures?

Minh,

Everything I have read states that the cylinders should all be within 10% of each other.

Your cylinder #3 is on the ragged edge.

You can see differences on a motor during the break-in period, but after 2,000 miles everything should be seated.

I would be concerned with those readings on a motor with 4,000 miles.

It would be my guess that your motor idles and runs ruff, due to the fact that #3 is not pulling its weight. I would also venture to say that after 2,000 miles it will not get better, only worse.

We just put a remanufactured engine in our
Ford Aerostar and had the same problem. It ran rough and at 1500 miles the shop did a compression test and one cylinder was low. The engine remanufacturer said that if it was not within specs after 2,000 miles they would replace it. The engine gets pulled tomorrow.

I forgot to mention. After driving 50 miles to the shop, my car was off for about 45 minutes (turned on and idled here and there for a few minutes at a time) before running the compression test and about an hour and a half before the leakdown. Could the results be skewed because the car was not at operating temperature? Thanks.

Minh

The car lopes a little at idle, but nothing too bad.

Most likely the piston rings didn't seat properly. When you rebuild a street engine you usually need to run dino oil for a few thousand miles so that the piston rings can seat properly. Typical wisdom is that synthetic oil doesn't allow enough friction for the rings to seat. If this is the case, replace the synthetic with dino oil, then give it a few 10 second bursts of full throttle on the street. Let it cool to ambient and repeat this two more times. Do a compression check. If it looks good, switch back to synthetic oil. This is similar to the procedure I used to break in my two stroke kart motors which made about 330 hp per liter and had a static compression of about 16:1, only in my case changing the oil was as easy as changing the gas.

When cars roll out of the factory they usually have some additives in the oil which aid in engine break in.

'86 951
-Steve