LLLosingit

iTrader: (4)

This is a copy and paste from another thread that is pretty much how I do mine but since our balancers are marked you'll have to verify that it's on TDC>


Here’s how I do it,
I remove all the plugs,
I put the hose in the cylinder being tested and turn the motor over with a wrench or socket until air comes out of the hose on the compression stroke.
I then look at the balancer and turn the motor to the 90 degree mark that corresponds the TDC for that piston. I never turn it backwards, always in the motor running direction.
I zero the leakdown tester by putting it on and off the hose. Relieving the air pressure each time. Each time zeroing the regulator when off.
When I’m happy it’s at zero each time it’s removed, I put it back on and record the leakdown.

If you put it on TDC for that cylinder it will never spin the crank. If it spins, you’re not at TDC and the piston is c*cked over and the rings are not sealed.

Hope this helps. I’ve been doing it this way for 35 years and it has worked every time for me.

Frank O'Brien

After I filled engine with oil and installed oil filter I began to use starter to achieve oil pressure. Once that was confirmed I began doing compression tests. The lifter for that 1 valve then corrected and intake valve seated. After that all leakage recorded during leak down tests had come from the rings. Tests were done at TDC as well as off TDC at far as I could go till an exhaust valve opened then I back the piston towards TDC. That enabled me to get better numbers (less than 10%)confirming wear on the cylinders. I also rolled the flywheel back and forth about 2 teeth in each direction while piston was at TDC to give the Rings the best shot at sealing. I believe tests were done as correct as could be. I also for ***** did a leak down test cold on my 02 Miata with 110,000 and came back with 6%.

Che70velle

iTrader: (6)

I thought he meant that he rolled the engine over on the stand....not with the starter.

StorminMatt

kingtal0n

iTrader: (1)

the problem is running the engine, is like owning it. Theres no difference between saying "oks lets put it in and test it and see if it improves" and "ok I will take the engine and pay for it". Even with a warranty it still means double labor, which costs more to some than the engine itself. I have to strap a 20year old hoist to a boat to keep it from pulling over the 5.3+4l80e, taking it in and out sucks I don't know about for you. If you have a team of people and three lifts full shop equip then obviously you can swap an engine multiple times per day.

If you are unhappy now, you keep checking next engines.

In my first experience with JY LS engines, I was wayyy to picky. I tried to get the perfect engine onthe first try for next to no cost. Now that I realized my mistake, in the future I would be far less picky and just count new heads as part of the cost of the engine. You really want to take a look inside there anyways, if you plan to drive it 10k+ without pulling the heads again anyways.

StorminMatt

Che70velle

iTrader: (6)

Leak down tests are far more telling, than a simple compression test.

StorminMatt

But even a leakdown test will be inconclusive on a sitting engine because the rings and valves will likely not be sealing properly. An engine that has been sitting for any period of time will show excessive leakdown, even of it is good. Only after running the engine will either a compression or leakdown test yield conclusive results.

Che70velle

iTrader: (6)

Your right, but your missing the point.
A leak down test should be used to find the sealing ability of ALL cylinders, to find a possible problem with one or maybe two of them. Doesn’t matter how poorly they seal after sitting for a period of time. All your trying to do is find one or two that might have sealing issues compared to the rest.

LLLosingit

iTrader: (4)

How is that information going to help you if the poor sealing is due to sitting? Perfect example was a 6.0 that I tested before it was pulled, results were good considering the engine had 154,000 miles. Fast forward a couple years and I have a buyer who wants to test it, Now it's showing 5 leak less than 10% one at almost 25% and the last two were down nearly 30%. I told him to install the engine and get it running and test again. If it didn't test good I would give his money back plus whatever he spent for fluids to do the install.
I ran into him at a car show a few weeks later and he was driving the car and said he it tested fine after running it for a few minutes.

Che70velle

iTrader: (6)

Depends on how long it’s been sitting. The longer it sits, the more crap you’ll have build up on the valves/seats that are open. Depends on the environment it’s sitting in also. Lots of variables here.

kingtal0n

iTrader: (1)

^^^ thank you

it doesn't matter what number shows up on the test equipment. 10% or 80%, run the test identically and compare cylinder results. The actual number only starts to matter for compression under special circumstances where exact cranking speed and air velocity is known, variables you cannot directly measure in the garage easily.

Some engines give strange result; i.e. 180 170 180 170 180 170 A recently 2.6L RB series gave me. Twenty years old, runs fine. We must attribute this to something, it could be manifold or oil/pcv related, perhaps oil is getting sucked into 3 of the 6 intake runners and those cylinders read higher because oil raises compression.


For leakdown it is easier to listen and use judgement sometimes than rely on the test equipment. It depends on the quality/resolution of the gauge. If you have a very nice gauge then yes, pay close attn to the leakdown number and write it down. Everytime you test the engine write the new numbers down and compare them. this is how you keep track of engine health, like physical checkups at the doctor. Use decimans 3.4% 5.5% get numbers with respect to differential of piston position, test with piston #1 all the way up then all the way down. You are looking for places in a cylinder wall that are deformed or where the ring deforms at lowest temperature while engine parts are cold. Sometimes it leaks more if you stop the piston going up rather than descending at the time. There are an infinite number of position you can try but most people do not hold the engine still so it typically pushes to BDC which I feel is acceptable for most routine tests. Make sure each piston moves down and the valves should be closed. Rotate to make sure you are not in overlap, which all cams have. The cam card is showing 0.050" of cam timing and people say "no overlap" but truly there is overlap between 0.000" and 0.000" of cam lift, which could be miniscule (1%? Can you hear it?) So this is just a word of caution to check the rockers if you are not sure about overlap or rotate the engine 360 to check the other side.

without a good gauge its all ears. Listen carefully, find ALL exits for the chamber, and I also do the same exact test for the crankcase, put a psi or two in there and find ALL the exits.

StorminMatt

This may all be true, but the REAL issue here is SITTING ENGINES. Sitting engines are just plain weird, and individual cylinders very frequently give lower numbers than others for reasons other than the cylinder(s) in question being bad. All of this clears up after running for a little while and warming up. So only after running for a little while can a compression/leakdown test be conclusive on an engine that has been sitting.

kingtal0n

iTrader: (1)

alright so what can we do if we get an engine thats been sitting and it gives us a couple poor compression results. The first thing to do is realize that was a mistake.

The first thing you do to a sitting engine is take a look at where the valves are. Hopefully you have not turned it yet, and nobody has for 10 years. Look at which valves are open. Those are the highest chance to give us poor results. If you mark down that cylinder 1, 3, 6 were open at the time and those three also give me poor compression I can attribute that to stuck valves or gooped up valves. this is called pre-conceived valve notion.

The next thing is signs of oil. Take all the plugs out and really spin that motor good and fast with oil in it. Look for oil splashing out of cylinders. Any sign of oil coming from the cylinders is a sign of bad rings/relatedpiston sort of problems. Thats called a clean spin.

Any cylinders which are low compression, not initially depressed, and have a clean spin, you can put oil in them. If the oil improves their compression back to the other cylinders then guess what. thats from the factory service manual to check ring behavior.

StorminMatt

If you REALLY want to be on the safe side, you can only buy an engine that has good numbers. Although doing this might mean that you pass up LOTS of otherwise good engines, you will be guaranteed an engine that gives good numbers AFTER is has been run.

turboal1

I bought a 2011 L9H 6.2 38000 MI
from a JY for 4K with a warranty.
PNP complete eng. and it was perfect. we
dropped the pan checked lower end
then put in a cam and kit. runs like a
scalded Rabbit.