I bought an used LS1 engine from a forum member, it was supposed to be in working coindition. The engine looked good and I did a leak down test. Only cylinder 1 registered 5% leak down. All the cylinders registered 30% to 70% leak down. Most of them are leak from the exhaust port and some are leak into the crank. Since the engine was shipped dry, I squirted some motor oil into the cylinders and turned the motor over a few times but I was getting the same result. The engine is drained of fluids when it was shipped. Is there something different I must do on an engine that was crated and shipped?

Please help


[Modified by benelliwang, 9:32 PM 6/19/2003]

 

Are you sure the valves are closed? Undo all the rockers and let us know...

 

Rockers arms are taken off before the test.

 

You have problems. Sorry to be the bearer of bad news. :cry

 

Looks like your in for some new rings. Did you check the upper drive train, springs, pushrods, etc? Sounds like some valves aren't sealing, along with some rings. It could be any # of things. Maybe you should be asking the CF member you bought it from? I bet he knows!!! :boxing Maybe it was too much nitrous? :smash: Sorry to hear about it, good luck...

 

how are you doing your leakdown test?

 

Engine on crate, valve covers off, rocker arms off, squirt some oil into intake, each cylinder turned to TDC and perform leakdown test...

 

:) what constitutes the 'leakdown test' ? ARe you pumping it up to 120psi then doing a static check over 1 minute?? Or are you cranking it over to develope your pressure then let stand for 1 minute? ??
Whoops, my bad...you're probably not cranking the the motor over since it is OUT of the car!!!


[Modified by rwj383, 2:58 AM 6/20/2003]

 

Don't freak out yet. How long are watching the gauge? It can't hold pressure for ever. Does it hold it for a moment and then slowly bleed off? Many times the valves need to close suddenly to seal. The rings need to heat up at to seal. I'm not saying that it should be exceptable for it to burn oil until it heats up. You could access the oil pump drive and bring the oil pressure up with a drill, I used to do it while starting freshly built motors. The motor should be up to temputare for this test. If not up to full operating temp atleast warmed up some. The rings do expand with heat. That's why some motors do burn oil a little in the morning. The valve stems heat up and expand too as well as the entire aluminum engine.

But, if it's not in a car yet, now is the time to go through it anyway. Pull the heads, look at the cylinder walls for burns, plastic gauge the bottom end and throw a new head gasket on it. There are somethings that you can't do with the motor installed. It's easier to do it now anyway. Take advantage of it.

Tommy

 

I haven't pull the heads yet because I want to make sure at least the bottom end is holding pressure. If I pull the heads, is there a way to check and make sure the bottom end is good? Also, someone please describe what plastic gauge is? thanks

7 cylinders are not holding the pressure... Almost all of them are leaking through the exhaust. Could it be related to long term storage of the engine. It was pulled off the car months ago...

Also, the rocker arms seem fine and the pushroad are straight


[Modified by benelliwang, 7:21 AM 6/20/2003]

 

I see some strange answers here. I have never seen a motor that could hold cylinder pressure for a minute, even half of that. Anybody here ever leak a motor down that way or is this just speculation? Only kind of leakdown testers I've seen use a constant flow regulator and a bleed-off valve. They keep putting pressure into the cylinder and bleed off an amount determined by the manufacturer. I doubt there is any standard for the amount bled off. It seems different brands of testers give different readings. They are only good for comparisons between motors tested with the same brand.

One thing I've seen leaking down motors is that the valves often show some leakage when first putting the tester on. For that reason, I leave the rockers on and turn the motor with a wrench. When a valve cracks open, it blows the seat clean and when it closes again, it usually seals fine. On a short cammed street engine, I never set pistons to TDC, just hold them against the cylinder pressure near BDC. They can't spin the crank that way, and it's much faster to leak an engine. It also shows up a crack somewhere down the cylinder by filling the whole can. Only things I wouldn't do this way are a race motor with so much cam that you're fighting to hang onto the wrench or a real old motor that could have a noticeable amount of cylinder taper. Whether you measure high or low, try the trick with leaving the rockers on. I've had a bunch of low readings come up by turning the motor over one rev with pressure in the hole.

 

Well, they were leaking the moment I connected the tester. It went immediately to 40% leak to 60% leak. I didn't have to wait for a minute or so. Here is the break down:

cylinder 1: 5% leak down.
cylinder 2 to 8: 40 to 70% leak down the moment I plug in the air hose and the tester.

I've done the leak down test to my car while it was not driven for 2 days. Never turned the engine on to warm it up and it worked. The only guess I have is that the engine was off for a while and the oil pan is bone dry. Should I fill up the oil pan and try to crank it up with a drill or something to lubricate the internal parts?

But does it matter if almost all of them are leaking from the exhaust port?

 

Could be carbon on the exhaust seats. Try putting rockers on & turning with a wrench like I posted before. Hard to believe all exhausts would be burned or bent. Intakes usually bend before exhausts.

 

Ok, I've emailed and owner and he replied. I still believe he is a stand up guy and this engine is good. The engine was pulled several months ago and it did sit outdoors and saw rain for two days. That could be the reason why exhaust weren't sealing... It may have rusted. I am gonna get my own heads freshened up and swap them in. I will do the leak down test agin.

I don't care if the heads are junk as long as the bottom end is good...

I thank you all for the help and please keep posting your thoughts here.

 

If it is leaking that much you should be able to hear where the air is leaking from. Check the exhaust port, intake manifold, PVC hole, or water manifold and listen for air coming out. This should telll you if the leak is from the exhaust valve, intake valve, rings, or head gasket.

 

As I stated above, they are leaking from exhaust port. :)

 

Plastic gauge is a peice of plastic band that you use to check the clearence of your crankshaft bearings and your rod bearings. It's a simple way to check the bottom end of your motor while it's not in the car hopefully on an engine stand. It can be done while in a car, probably not a C5. You take the oil pan off and take a main or rod bearing cap off. You put the plastic band on the surface of the crank then put the cap back on and tighten it to torque specification. Then take the cap back off remove the plastic band that has now been smahed flat and measure it. The gauge to measure it with comes with the kit. This will tell you without a doubt whether the motor is blown or not. There shouldn't be too much clearence between the two surfaces. This is how oil pressure is built. The maximum clearence will be in the shop manual.