Need some info on "how to do a compression test and leak down test, on an LS1/ HELP!

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Mar 19, 2007 | 01:18 PM

regorih383

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From: Pasadena Tx,

Need some info on "how to do a compression test and leak down test, on an LS1/ HELP!

Ok, I have an LS1 with 124,XXXmiles and I would like to do leak and compression test to see how healthy my motor is. The motor dose not smoke or is gives me any problems. I already did a search but, could not find any direct information that would give me a step by step procedures on how to do both test. If anyone could direct me to a link of some sort I would appreciate it.
Thanks
Roger.

Mar 19, 2007 | 02:05 PM

brad8266

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From: Watertown, NY

Forget the compression test and go straight to the leak down test. leak down does the same thing as the compression test except it lets you know what the worn parts are.

1. Rent or buy the leak down tester and compressed air source.
2. Warm the car up to operating temp.
3. Turn off car.
4. Pull all spark plugs.
5. Thread leak down tester to into a spark plug hole.
6. Connect comprerssed air to leak down tester. (90 PSI is good enough)
7. Turn hand crank engine until cylinder you are threaded into is at TDC on compression stroke. (TDC will be the point where leak is the least amount on the gauge)
8. Record percentage of leak on that cylinder.
9. Find source of leak. Take off oil fill cap off and feel for air coming out of the oil filler neck, if air is coming out here your piston rings are worn. Listen and feel the tailpipes for air coming out the exhaust, this indicates leaking exhaust valves. Pop your airlid off and listen and feel for air coming out of the intake manifold, this indicates leaking intake valves.
10. repeat again for all cylinders.
11. Fix sources of leaks.

Google "leak down test" and you will gets lots of articles with pics on this too.

Mar 19, 2007 | 02:07 PM

Halloran

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Do you want to pressure test the heads? If you're looking to pressure test the heads for leaks and compression, the best way to do it is actually to pull the heads, turn them upside down and pour some solvent (i.e. gasoline) into the bowls. If the gasoline leaks through to the other side of the ports then you may need new valves or valve stems. Either way a valve isn't seated properly and the heads either need to be ported or buy new heads. If you want to do it with a pressure guage I would just take it to a machine shop and have them do it for a nominal fee. You'll get numbers on paper but if your car isn't giving you any problems use the old engineer's creed "if it ain't broke don't fix it"

Mar 19, 2007 | 02:08 PM

brad8266

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^^ Thats a waste unless you are going to pull the heads anyway. Leak down is the way to go when the engine is assembled.

Mar 19, 2007 | 05:24 PM

Halloran

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Absolutely, if the engine is staying in the car then listen to Brad. Mine is completely apart at the moment so I just thought I'd throw out my 2 cents on what I did with the heads out.

Mar 19, 2007 | 08:09 PM

mzoomora

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I also agree on the leakdown. The only thing a compression test would find that a leakdown wouldnt is a flat cam, which was pretty common on 80's small blocks, and there were easier ways to find that. These cars have roller cams so having one go flat would be rare.