I`m in the process of trying to do a leak down test and not having a lot of luck. 350 with long tube headers. Had to remove the headers to get a couple plugs out and be able to hook up the tester. Now I learn the motor should be @ normal temp before testing. My question is will it harm the motor if I run it like it is or would it be better if I put the stock manifold back on first, no down pipes just the manifold or can that harm it also ?

 

You don't need to get the motor up to any temperature

You do want to test every cylinder at TDC and have a good supply of airflow to maintain the 100 psi input

 

I agree with gkull. Never heard of any requirement to have it at temp.

On mine before the rebuild I saw much different results depending on how far down the piston was. At TDC the results were decent, but halfway down the leakdown was massive as my cylinder walls had more wear there.

 

The instructions that came with the tester say warm the engine, but it is also using only 30lbs of air pressure. It was cheap. Just ordered a better one. Thanks for the info.

 

Yeah, that sounds like a weird tester. Standard is 100 PSI.

 

Definitely test at true TDC and at 100 psi steady pressure, or you will show high leakage. The piston will rock in the bore more if it’s not at TDC, thus creating more leakage.

 

I own this one:
It works great. Use a socket on a breaker bar to hold the engine at TDC as it may move with 100psi of air on it.

Great tool and a must for any repair guys box. I use it actually more for the vintage bikes I work on, Rhino's, Dirt bikes etc........
Last summer I hooked one up to a 180 Johnson V6 outboard after my buddy went to three marina "mechanics"......it found the problem immediately as loose carbs and reed block. Awesome troubleshooting tool.

Jebby

 

I ordered that one this morning from Summit Racing about the same price after shipping. I tested three cylinders with the first one and showed 0 leakage I felt something was wrong. I also did a compression test with a different tool and it showed 170 to 175lbs on each cylinder but I dont know if that is low or not. Its a ZZ4 or a ZZ3 dont really know the difference. It was produced between 1986 and 1994.

 

That is on the money.

Jebby

 

You have any ideal if the compression listed is OK

 

It is what I was referring to....

Jebby

 

Thank you.

 

Yes, that is problem with leakdown and compression tests as they should be done with the engine close to operating temperature but I don't know of anyone that can get their hands and hose in there with hot exhaust manifolds. That is because warm pistons and rings will seal better giving a more accurate indication. But even though cranking pressure will be lower and cylinder leakage will be higher you should still get a relative good indication of cylinder leakage and pressure.
FWIW 175psi cranking pressure would be a good number for even a high compression engine.

If you really wanted to be obsessive and compulsive about engine temperature you could rig up your household water heater to your engine's heater hose and warm the engine that way. But most of us will settle for the results while engine is cold.

Nice effort and now you know the health of your cars engine regardless of it's mileage.

 

Got the new tester this morning and did the test. My results are as follows. #1, 12% #2, 5% #3, 4% #4, 4% #5, 5% #6, 6% # 7, 5% #8, 7% It looks like #1 is the worse and the air, I can hear with a stethoscope is coming from where the push rod goes through the head. So that would be the crankcase. am I right ? Compression is good, Oil pressure is at 60ish on cold start 40 after warm goes up some when driving. Very little smoke if any. but I do see a lot of blow by when running on left side. What condition would you say the engine is in. What started all this is the ticking coming from some where, I havent been able to pin point it. Then all of a sudden the engine has started vibrating, a lot. I wanted to make sure it wasnt a cylinder dying before I look at the flexplate. Which I will have to buy a transmission jack. I`ll be 72 in a couple months and getting down under is not something I look forward too. Am I going about this right ?

 

12% leakage is not bad. Its definitely worse then the other by a good bit but...nothing I'd be overly concerned about, especially if its still cranking 170 psi cold. Your leakage is going past the rings, but its normal, you'll always have a little seap by the rings as there is gaps/clearances in the rings. Your noise is likely a lifter going bad...Some blow by through the breathers at idle is also fairly normal, especially on a used engine. I'd be looking for the tick honestly. If it has a dead cylinder, pull the plug wires off one by one when its running and see which one does not affect the engine tone. Then you know which cylinder is having the problem

If its making a noticeable ticking sound and its missing, I think I'd be pulling the lifters out for an inspection. That'll cause a tick and a miss if a lifter is going bad. Hopefully its not eating up the wheel on the lifter and the cam.

Keep investigating, you'll find it.

Definitely check the torque converter bolts for tightness. That will make a sound similar to a rod knock. But it usually doesn't vibrate, although I'm sure its possible. The torque converter bolts are an easy check, I'd do that first just to eliminate it.