Compression test while on engine stand?

[EagleTalonTim]

I am finishing up my engine build and wanted to see how well the compression was in each cylinder to see if there was a noticeable difference between cylinders. I tried to connect my compression tester to each cylinder to see what I could get when spinning over the motor with a 1/2" breaker bar as fast as I could (which is not that fast ). Hopefully this is not a bad thing to do.... After 3 full compression rotations per cylinder, I was able to get all 4 cylinders at 80 psi. Does this sound reasonable for hand cranking or am I just wasting my time?

 

[rlacasse1]

You're wasting your time.

 

[EagleTalonTim]

Ok, I kind of figured. Just worried my MLS head gasket may not seal. Everything was done by the books though.....

 

[YZFR1]

If you want to find out how well it's sealing right now, do a Boost Leak Down test.

The best way to do it is to remove the cams but if you already have them intalled just make sure that both cam lobes are on their "base circle" for the praticular cylinder you are testing. This way the valves are as closed as they can be.

Before i brocke the motor in my nubers were all around 13% which is normal for a brand new engine. Now, that i put 180 miles on the engine, i took it all apart and put it back together, did a test on it the other day, getting a 6-7% seal on the engine stand.

 

[rlacasse1]

What all did you do in this build? Cause if you touched the piston rings then there is absolutely no point in trying to do any sort of compression test or leak down test. The rings will not be seated yet, so those tests are pointless. You need to get it in the car first and run it.

 

[BogusSVO]

On the stand testing will not tell you much. But it will tell you if you are sealed, and seing 80 psi of compression, it seams that you are sealed.

I know builders that will stick there finger in the spark plug hole and have some one spin the engine over on the stand, just to make sure it is makeing some compression, and that the mech. timing is good.

 

[hotrodssnova]

Not to mean any disrespect, but that made me spit my coffee out! Like bogus said, I used to do that with a helper on my sbc, thumb over hole, and spin the crank. I'd say you are good to go also.
Great visual, btw.

 

[flawlessTSI]

If they all are at 80a on a stand by hand,i say that is good because 1. Its geeting good amount of pressure for how you are doing it and 2. They are all about the same number.

 

[YZFR1]

Even on a fresh engine a leak down test can be usefull in my opinion. If you are sticking a 100 psi into the cylinder, it is expected that the rings are not going to seal well before they are brocken in. However, you can still see if the headgasket is sealing and if the valves are sealing especially while still having both intake and exhasust manifold off the head.

You can get a tester for about $40 and spinning the engine by hand isn't going to tell how well the headgasket is actually making a seal once it actually sees some pressure.

 

[EagleTalonTim]

Lol.. glad you got a good visual from that since I would probably laugh at myself if I watched me do it on video! Maybe I should record that and put it on Youtube "How to start a 4G63 engine out of the car..."

Thanks for the info everyone! I guess I will wait till I can get it in my car and have the rings broke in to do a real compression test.

 

[BogusSVO]

What method will you use for break in?

 

[EagleTalonTim]

Probably the same way I have done my others.. Drive it nice and easy, mostly staying out of boost for the first 500 miles. On first heat cycle (cold - hot - cold) check torque on head studs. Continue to 500 mile mark, change the oil and filter and cut open filter to see any metal shavings etc...

Is there a better way?

 

[miguelmcv]

I am agree with some of you saying that a Leak down test will be good to see if the valves and head gasket are sealing good, That will give a good relief.

 

[WES_393]

Probably the same way I have done my others.. Drive it nice and easy, mostly staying out of boost for the first 500 miles. On first heat cycle (cold - hot - cold) check torque on head studs. Continue to 500 mile mark, change the oil and filter and cut open filter to see any metal shavings etc...

Is there a better way?

That's the exact opposite of what you want to do. Here's the guide I followed:

Use regular 10W30 oil.
Before you fire up the engine, remove the MPI fuse and crank the engine several times to build oil pressure.
Put the MPI fuse back, start the engine and immediately take it to 1.5-2K to maintain the oil pressure so the lifters fill with oil and the cams bed properly.
No matter what you do, don't let the engine idle.
When the engine warms up and the coolant temperature is normal, bring the RPM to 3K and hold it there for 20-30 minutes.
Let the RPM drop, adjust the idle and timing.
When done, shut the engine off, check for any oil/coolant leaks, change the oil and the oil filter and let the engine cool down.
If everything checks out OK, take the car for a spin and several 30-65-30 mph pulls at stock boost level.
At this point, the engine is fully broken in, but you might want to take it easy for a few more days and keep an eye on oil/coolant leaks, loose bolts and hoses, etc.
Change the oil/oil filter at 500 miles again.

There's absolutely no need to drive 500 miles under 3K or 1500 miles without boosting. As a matter of fact, you can tune the car and race the engine the same day you install it.

 

[awdtalon4451]

Curious to know what method you would use bogus?

 

[BogusSVO]

I use something about like the motorman method.

Build pressure and get the rings pushed into the cylinder walls.

Pull the fuse, get the oil on the head, fire it up, check for leaks, a few intown stop and go miles about 10. Pull over give it another go over for leaks, and up out on the interstate for about 20 or so miles, 10=15 psi of boost, run her up to about 80mph, and decel in gear down to about 40,
Hit boost in every gear, and decel.


WES... the middle part of the method you posted, 3000 rpm for 20-30 min, is old school for mating the cam lifters to a hyd/solid,non roller cam. I know it as 2000-2500 rpm

Since the 4g is a roller cam, that is not needed, even with new cams in a new build.

But if it what works for you.... rock on.

 

[WES_393]

The 1.5-2k part is meant to break in valvetrain and warm up the engine. I see the 30 minutes of 3k as seating the rings.

Regardless, the overall point is to break it in by running it normal, not babying the engine or letting it idle for long periods.