brandon_6667

iTrader: (3)

I am working on an lq9 I bought a while back out of an escalade that was in a roll-over. I decided to do a compression test (dry test). Im only getting 30-40 psi on each cylinder and there is one cylinder that I get only 10 psi on.

I then removed all the rocker arms so the valves would all be closed and used 120psi of compressed air to check and see is its the valve seats that are leaking. When i connect the air to each spark plug hole the air starts escaping the exhaust port on 6 of the cylinders and the intake port on 2 of them. The leaky intake valves leak just enough to make a pretty loud whistle noise out the intake port but most of the leaky exhaust valves are blasting the air out the exhaust ports pretty hard.

the crank turns a little each time I compress a cylinder so i'm guessing/hoping that the piston rings are fine and its only the valve seats that are leaking. What would cause it to have bad valve seats?? am I doing something wrong when checking this? ? I also noticed that on a few of the valves I can actually grab the spring and spin it by hand they arent super loose but if i try I can turn them about an 1/8 of a turn. i dont know if this is normal or not, but could it maybe just be worn valve springs or something? the motor only has 80K on it and I don't understand how the valve springs OR seals could be bad. Any help would be appretiated!

swift700

iTrader: (3)

Are you turning the engine over with the starter while doing the compression test?

Some will probably leak through the valves at a lower pressure setting like that. When I did my valve springs they all leaked with compressed air except for a couple of cylinders which were exceptionally tight. I did a comp test though and they were all around 150 psi.

You say that air is coming up through the valve seals. Do you mean around the valve SEATS? It's possible that the valve face or seats have become corroded from sitting in a damp environment but I think that what you've decribed is fairly normal for a set of factory heads with factory springs.

If you are worried about it, you can take the springs off, remove the valves and try using a bit of lapping compound to freshen up the contact surfaces.

brandon_6667

iTrader: (3)

its on an engine stand and im turning it by hand with a breaker bar on the crank bolt. and yeah I meant valve seats ill edit the post. The air thats escaping is coming out the exhaust ports and the intake ports ( i currently have the intake manifold and the exhause manifolds off)

AKlowriderZ71

iTrader: (22)

You can't possibly spin the engine fast enough by hand to do a compression test.

brandon_6667

iTrader: (3)

so do you think I shouldnt worry about it?

AKlowriderZ71

iTrader: (22)

How long ago was the engine pulled out of the rollover? Has it been sitting outdoors? There's a lot of things to think about here. Was the engine running while the vehicle was upside down? If so, there's probably some internal engine damage from oil starvation. If you have it on a stand already, I'd tear it down. Clean it up, repair whatever is needed, do a simple valve job, freshen it up a bit.

brandon_6667

iTrader: (3)

I bought it from a salvage yard. The engine had sat in the corner of the shop for about 4 months the guy said. It had some decent surface rust on a few places on the outside of the block and a lot of oxidation on the aluminum so maybe it was a damp environment and the valve seats built up corrosion? I don't know if it ran upside down at all

AKlowriderZ71

iTrader: (22)

I'd pull it apart. In my mind, I'd have to assume that it had run while upside down. I'd also guess that it was stored outside in the elements for some time.

Or, you could roll the dice!

brandon_6667

iTrader: (3)

damn, and i already spent a good amount of money on the cam, springs, pushrods, new water pump, gaskets, etc. was hoping i was almost done but looks like I will be needing new head gaskets and bolts along with some head work. Where should I go for the new bolts and gaskets for the best price?

swift700

iTrader: (3)

I don't think the engine could be in too rough of shape by sitting for that short a time.

Oil starvation probably wouldn't affect the heads but sure might have affected the cylinders. To do it right, take it apart and have a look.

I'd bet that the heads are in near-perfect shape. The leakdown you described is quite normal.

To do a compression test properly, the engine needs turned over by starter with normal lubrication in the cylinders. It's best done after the engine has been run recently.