Leakdown check results

[drobin8]

Been rebuilding my sons 420a 97 but a 96GST fell in my lap so swapping parts over that will and am now building it.. When I got the car I noticed it smoked a lot after some checking it appears several seals are leaking (139000 miles). Also the valve cover has been removed before and apparently was put back on with no new gaskets just RTV because it is leaking oil pretty badly also some of the bolts weren't finger tight. I got it to my garage and i'm looking to tune it up and replace seals. Thing is I did a compression leak down with the results being at 90psi the cylinders only had 5psi drop or less on three cylinders and 7.5psi on the #2 cylinder at running temps. Is this within tolerance. I have never worked on a 4g63 so im not sure if this is ok. 8% leakoff at worst doesn't seem to bad. Any help Is greatly appreciated.

 

[jayson427]

90 psi is below the service limit so it will need a bottom end rebuild at the least. Might get away with new rings and still use stock internals. It depends on the cylinders needing a bore or just a hone.

 

[drobin8]

Sorry I didn't clarify. I didn't do a compression check I did a leak down where I put regulated air (90psi) into the piston and watched the amount of loss. 3 of the 4 cylinders read between 85 to 87psi amounting to a 5psi loss the cylinder 2 was at 82.5psi which was more but is less than a 10% loss which is what im used to being an indicator for a rebuild. All air loss on the cylinders were into the crankcase but I figure the rings are not total seal so this is expected. By my calculations that 6 to 8% drop which if I had an N/A engine I would probably let ride.

 

[jayson427]

1. Less than 5% - You either did something wrong or have one hell of a nice tight engine.
2. 5% to 10% - Great to good. You should have no worries.
3. 10% to 20% - Your motor may still run ok, but it isn't at it's best. Parts may be starting to wear out....keep an eye on it and test it more regularly.
4. 20% to 30% - It may be (and probably is) time for a rebuild.
5. Greater than 30% - You have some major engine issues that need to be addressed.#

 

[drobin8]

Compression check was 163, 160, 165, 165 at WOT.

 

[jayson427]

Those are great numbers for an engine with that many miles! Looks like you found a good car. Little bit of matenience and she will be good to go. Is it all stock?

 

[Phantom DSM]

Compression check was 163, 160, 165, 165 at WOT.

Nice results sir. Lot of people would be happy with under 10 psi differences between cyinders, but these are dead on equal results Good healthy motor and not much loss on leakdown.

 

[jayson427]

Here's a great link you should read that will help you out. You're definitely on the right path.

Tech Guide: 2G 4G63t Upgrades - DSMtuners

 

[drobin8]

What I have noticed so far is, AEM fuel rail, underdrive pulleys or so they seem, definitely not stock. Greddy side mount and piping, SAFC2, Eibach springs and KYB shocks, Greddy blowoff, also the turbo is aftermarket but cant tell what yet, probably is some eBay turbo cant see any embossed numbers on it yet. Only thing that really bothers me is it dies if im up in speed and depress the clutch in and leave it RPM's just drop to nothing. Hope its not this crankwalk I hear about. Also thanks for the replies its really appreciated.

 

[jayson427]

No one likes the horrible crank walk at all and people hate seeing others suggest it right off the bat. It's something you should read more about and there's a way to measure the tolerance on the crank with everything in place. I'll see if I can find the write up for you

 

[jayson427]

Check his link and post your measurement.

http://www.dsmtuners.com/forums/new...-check-crankshaft-end-play.html#post151703279

 

[drobin8]

Thanks for the links. I will break out the indicators tomorrow and see what I got.

 

[okcummins]

If it dies when you push in the clutch. Make sure the bov is recirculated in to the intake pipe. You may also want to do a boost leak test.

 

[drobin8]

blow off valve is recirculated already. Rechecked leakdown and compression cold and got different readings but not horrible. Then did it with the engine at normal run temps and got almost same results again so if feel good about that. Didn't check for crankwalk but did build a boost leak tester and will try it when I work off again. Puzzling thing is I boroscoped my cylinders and saw good crosshatching except for some straight up and down grooving on the front side of 3 and 2 cylinders. I assume since my compression readings are good they aren't deep but look sketchy. I would upload some shitty pics but I old and don't know how to.WTF

 

[emcee]

My readings are 175 168 170 172 Anyone know what the original spec is?

 

[miliman13]

120ish is service limit. Your good.. Like real good.