Compression test, VS Leak down. ?

[PARADOX]

Taking my good old CMI headers off for testing, form 525's.
Don't see any issues, but if I do a compression test on the cylinders, which is a lot easier then a leak down, and the compression is OK, Can I assume that the motors are OK? Or do I have to do a leak down also to be sure that motors are OK.
Is there anythingI can discoonect on the 525 EFI's when I do the compression test so I won't get a spark?
Or just remove all spark wires.
Thx
P

[Chris]

Compression tests are good to tell you if you have a problem- one cylinder being different than the other. Leakdown is only truly useful if you started early in the engine's life and recorded your results. It allows you to track deterioration. If tou see anything out of the ordinary, I'd go to leakdown.

When I do leakdown, I do measurements at TDC, 90 and 180. I had a circlip come out once. Scratched the cylinder wall. But below the TDC range there was no flaw. Had I not done what I did the engine would have definitely been severely damaged.

[PARADOX]

Thanks Chris.. I will do the compression, and hope all is well. If I have a problem, I will have to do the leak down, but I assume that if the compression is OK.. then I'm good to go.
Taking these headers off is a pain in the behind.

[MikeyFIN]

I do only leakdowns and with a warm engine.
A WTCC/ STW Audi back in the day had 18% leakdown cold and was a bottle hot...

I don´t do the 90 degree test but I compare BDC and TDC leakdown #´s just for the fun of it.

[PARADOX]

I do only leakdowns and with a warm engine.
A WTCC/ STW Audi back in the day had 18% leakdown cold and was a bottle hot...

I don´t do the 90 degree test but I compare BDC and TDC leakdown #´s just for the fun of it.

YOu think this is FUN? C'mon over and do it for me.. Let's see how much FUN you'l be having.
It's will turn into fun when I have no problems.

[MikeyFIN]

YOu think this is FUN? C'mon over and do it for me.. Let's see how much FUN you'l be having.
It's will turn into fun when I have no problems.

Believe me I think it fun to wrestle around in the engine compartment.. or go places people smaller than me couldn´t get to.

Did I tell you I almost always sparr with heavyweights also ?
Because after that a pound for pounder is mincemeat...

But hey thats just me, when you tell me not to work on the boat/racecar I get ****ed really fast.

So where´s my plane tickets?

[MOBILEMERCMAN]

Once the headers are off it is easy.. Heck a couple Sutphens I worked on you could not stand in the bilge. Pull the center manifolds off and it became tolerable.

Peter the comp test will give you a good idea what you got. If one is low a leak can help tell you why. You don't have to take the headers off to pressure test.

[PARADOX]

Once the headers are off it is easy.. Heck a couple Sutphens I worked on you could not stand in the bilge. Pull the center manifolds off and it became tolerable.

Peter the comp test will give you a good idea what you got. If one is low a leak can help tell you why. You don't have to take the headers off to pressure test.

Two is out, two more to go. I have to get the tail pipes off to get new flappers in the tips. So I figured mind as well take off the headers.. look into the exhaust ports. (so far so good, no rust.) Easier to get to the plugs and do the comp. test, I have some bilge cleaning to do and one of my bilge pumps strainer is off. Can't get to it with the headers. So it just made everything easier. New header gaskets are not that costly. Better safe then sorry. More bilge time in the AM.

[imco offshore]

Two is out, two more to go. I have to get the tail pipes off to get new flappers in the tips. So I figured mind as well take off the headers.. look into the exhaust ports. (so far so good, no rust.) Easier to get to the plugs and do the comp. test, I have some bilge cleaning to do and one of my bilge pumps strainer is off. Can't get to it with the headers. So it just made everything easier. New header gaskets are not that costly. Better safe then sorry. More bilge time in the AM.

peter make sure you get exhaust gaskets with the metal shims in them,? i spoke to imco yesterday and they have everything to switch its over to sc or scx,,

[PARADOX]

I got the standard Merc. gaskets.
Thanks George. Will talk on Monday.
P

[YoungPerformance]

Paradox,
I generally do a comp. test if I don't think anything is wrong and I just want to check it out. What I look for is equality from one cylinder to the next. If I see a difference of more than 10 psi from the highest to the lowest, then I will leak the lowest hole. Make sure you do not have any liquid (gas, water, etc) in the cylinders because it will give you an inflated comp. reading for that hole. Good luck.
Eddie

[Sydwayz]

Send the headers back to CMI. I am told for $150/pair they will check the headers and polish them. We are doing this to a couple of ATs this winter.

[WeaponX]

Compression tests are good to tell you if you have a problem- one cylinder being different than the other. Leakdown is only truly useful if you started early in the engine's life and recorded your results. It allows you to track deterioration. If tou see anything out of the ordinary, I'd go to leakdown.

When I do leakdown, I do measurements at TDC, 90 and 180. I had a circlip come out once. Scratched the cylinder wall. But below the TDC range there was no flaw. Had I not done what I did the engine would have definitely been severely damaged.

That's a good idea I've never thought of that.

You must have a long breaker bar or a strong arm.

[MOBILEMERCMAN]

At 90 degrees its much easier with two people.

[ROGUE]

The fun part is getting them hot and THEN trying to get the headers off fast enough to do a warm leakdown test. Better off pulling them and doing it on a stand.

[WeaponX]

Headers off??

Never done it that way.

[MILD THUNDER]

Headers off I believe helps to pinpoint if the exhaust valve is leaking, although I'd imagine you can hear a small leak with your ear at the tailpipe in a quiet shop??? Not sure.

[Lee]

At 90-180 degrees ATDC I would think that the intake valve would be off of the seat resulting in 100% leakdown, unless you completely loosen the rocker arms.
But I could be wrong.

[ROGUE]

Headers off??

Never done it that way.

32" centers you cant get at the center plugs unless you pull headers.