lq9 cranking compression

[l92Firebird]

Got a 2005 LQ9 with 110,00 miles from LKQ to start my conversion project. Threw it on engine stand and did a cranking compression test. 270 - 300 psi. WTH!!! I was expecting 190-210. My first thought is user error, but how could i screw up a cranking compression test? Is there something wrong with this engine? I am tempted to return it now. I don't want to install it and have it not work. Any thoughts?

Thanks

[BR3W CITY]

Did you do it on all cylinders?

[l92Firebird]

yes. 270,270,300,300,300,300,290,280

[clinebarger]

The only thing that could cause that is a Timing Chain that jumped a couple teeth, Problem is...I have never seen a LS engine jump time.

I question either the tool, Or the procedure your using, 4-5 seconds cranking on each cylinder is good. The objective is not to keep cranking to get the highest pressure...But to see if the cylinders are within a close percentage of each other.

A leak down test is the only REAL test to see if a engine is healthy or not.

[BR3W CITY]

You didn't happen to have the fuel rail on (and possibly full?). Only reason I ask is that wet motors will give high results.

[l92Firebird]

Engine on stand. Intake off. All spark plugs out. I am going to get a different test gauge and try again. Also it was suggested on another forum that the lifters might have bled down from sitting causing valves to stay closed longer. That would increase dynamic compression.. so they say.

[solidaxel]

Watching this one !!

[Wasted Income]

Seems way high. With a decent size cam, and LS3 heads, mine was round 150-160ish.

I agree with Cline...a compression test is a quick and dirty way to tell you have big problems, but a leak-down is the right way to do it.

[l92Firebird]

Sorry it took so long to retest the motor, but here are the results.

I first hooked up a mechanical oil pressure gauge. Spun the motor and no oil pressure. I did put oil in filter prior to screwing it on. So I spun the motor for 20 seconds four times and got 30 psi pressure while cranking. I then repeated the compression test and found 230-250 psi on all but number 8 which was 210. I did get another compression gauge and it read about the same as mine. I guess there was something to the theory of lifter leak down and higher dynamic compression as the compression is now down to what is expected.

I made a leak down tester (using a dampener plug 0.25"x0.040") and got 93-98% all cylinders but 7 and 8. They were 90%. Sounds reasonable right? I used a HF inspection camera to inspect the piston tops ( actually I was using it to ID TDC). and saw the apparent marks in the tops of pistons 7 and 8. Is that my imagination or does that look like the valves kissed the piston?






The leak down and compression tests are ok so should I be concerned? I know that this is a salvage yard motor with 110K miles. I don't want to take it back to LKQ and ask for a different motor unless needed. I most likely won't be able to start the motor til spring to see how well it runs.

Thoughts?

[boostedc10]

Looks like they may have kissed a valve, the marks are in the right spot.

The damage on the piston side looks minor, however I would pull the heads and take a better look at it and the valves. You will be able to tell right away if this is what happened.

I would also take a look at the timing chain when you tear it down. Worse case is you do a chain and some junkyard heads.

[boostedc10]

Actually if I tell you its scrapped can i pick it up for free?