I've always leaked my engines cold and normal range is 6-10%. My current engine is an all aluminum 632 with small ring pack. I started leaking it and the 1st one had 29% seemed to be coming through the carb, second cylinder was 18% and sounds like exhaust. This is my 1st full aluminum engine and with small ring pack. I wonder if I need to warm the engine with this setup? I made a mistake and didn't leak it when fresh. It has 249 passes since freshen up. I was planning to run another season 125-150 passes but these numbers have me re-thinking it.

With skinny rings you should warm the engine up....Also (especially with gas ports) put the tester on a cylinder and use a long torque wrench or breaker bar on the damper bolt and give the wrench a little tug/jerk to load the rings. You should see a dramatic improvement in leakage..as far as valves leaking use a good size rubber mallet and smack the top of the rocker arm. Not stupid hard just enough to make it "pop" out the headers or intake...lots of dust and rust can collect in between the seat and valve so just do a little blow off to get accurate readings....if none of this helps it's time for a freshen up.....I like to see 10% max but if all 8 cylinders are the same 10-25 I run it...shoe polish corrects moderate power loss nicely...

If you have air coming out of the intake or the exhaust, it is leaking past the valves. If it is going past the rings you would hear it in the crankcase. My aluminum small block with .043 rings would leak down between 4-8% cold.

All aluminum Hemi. Leak down between 3 and 7% most of the time. I have had all aluminum engines since 1990 and all had good leakage unless Bad valve of hole in piston. Now hole in piston will leak a lot.LOL

Isit running good? If yes ship all leak down test! You are wasting your time!

If you still need to do one, if the motor sat for any length of time and you have steel seats, light rust can cause leaks through the valves, intake leak noise from the carb and exhaust leak Nosie in the headers. Noise from the valve cover, blow by. Unless the performance is off, 99.5% of the time you are looking for consistency from cylinder to cylinder, don't get caught up in the actual numbers.

FYI, I switched to an AL block about 8 years ago, same internals and there was no difference in crankcase vacuum. Besides the honing process, the next most important thing to do is don't idle a new/fresh motor long, use break in oil and load the motor to break in the rings! Idling long can kill the break-in process. Much easier to do on the dyno but you can in the car too.

Valve lash cold? Could be holding the valve open slightly ??

quote:

Originally posted by BP758:
Valve lash cold? Could be holding the valve open slightly ??

That would be my guess

[QUOTE]Originally posted by inferno camaro:
I'll warm it up and re-check. I'll also try the tap with a mallet.

I does sound like most is coming out either carb or header, not much through valve covers.

It's maybe off .02-.03 from fresh and .75 mph but I am running a different trans this season so not 100% sure.

Thankfully no holes in a piston as far as I know

I take the rockers off when I leak it so I don't have any chance of a valve being partially open. I can't get it to not turn over when I put air to it if I don't back them off.

Obviously, you have to have the cylinder your testing at that moment on it's compression stroke...And when you put air pressure to that cylinder it is always going to push the piston all the way down. Thats one reason why you have to turn the crank slightly to push the piston upward so the rings can flex to get their sealing edge against the cylinder wall...The crank only needs to rotate a few degrees to accomplish this

So even with valves backed off I should rock it with a breaker bar?

My all aluminum blower motor was always 0-6%, .043, 043 gapless top ring pack with lateral gas ports and no warm up. even with all the plugs in except the cylinder I was testing my son had to hold the blower with a long breaker bar to keep the engine from turning when I hit it with 100psi

When I do a leakdown, if the piston is exactly at TDC, the piston isn't pushed down. Off by 5-10 degrees is a different story. The numbers on my balancer help me get it right where it needs to be. Take care. Tom Worthington

quote:

Originally posted by Big Steve:
My all aluminum blower motor was always 0-6%, .043, 043 gapless top ring pack with lateral gas ports and no warm up. even with all the plugs in except the cylinder I was testing my son had to hold the blower with a long breaker bar to keep the engine from turning when I hit it with 100psi

It won't turn if you have that cylinder at TDC!

Gapless top rings also will give you good static leak down numbers, but this test is just that, static! A running engine could be a good deal different. If gapless top rings always made more power, no one would make anything else. Good Ring seal comes from getting the hone right and correct break in.

I never use to remove my rockers but really struggle to get this one not to turn when putting air to it. What procedure do you use to get it TDC on each cylinder?
I turn it over until both rockers are loose (seems tough to do with large overlap cam)

This message has been edited. Last edited by: inferno camaro,

quote:

Originally posted by inferno camaro:
I never use to remove my rockers but really struggle to get this one not to turn when putting air to it. What procedure do you use to get it TDC on each cylinder?
I turn it over until both rockers are loose (seems tough to do with large overlap cam)

I use the balancer degrees - I have an ATI so it's accurate, just need to ensure your timing pointer is aligned with TDC.

I would hope you would know that you have accurate TDC established or leakdown could be the least of your concerns..
I don't like to put the piston on dead nuts exact TDC..
#1 It's a pain in the ass to get each TDC..
#2 I like to load the rings to get what I feel is a more accurate measurement of leakage..obviously, you can't move the piston up a few degrees to load the rings if the piston is as far up as possible already..rings now days are .0 to thin floppy so I think putting some amount of compression against them is a more real world test..JMHO

I certainly thought I knew how to find TDC but it wouldn't stay there. So I thought maybe there was a better way.

quote:

Originally posted by imakehp:
I would hope you would know that you have accurate TDC established or leakdown could be the least of your concerns..
I don't like to put the piston on dead nuts exact TDC..
#1 It's a pain in the ass to get each TDC..
#2 I like to load the rings to get what I feel is a more accurate measurement of leakage..obviously, you can't move the piston up a few degrees to load the rings if the piston is as far up as possible already..rings now days are .0 to thin floppy so I think putting some amount of compression against them is a more real world test..JMHO

Maybe I'm mis reading it. But I think he means all the other pistons except for 1. If I get more than a couple degrees off tdc for each, It's tough to keep it from spinning. Big bar helps, but don't turn your back on it

With the other valve rockers/springs on it, that helps hold the motor in position. I don’t know if your cam has as much as ours? Leaking at piston TDC is not an issue.
287/314 118.5 .557 lobe with a 1.87.

Our billet alum blocks leak at 1-3% cold.
Not gapless.


I agree somethings not right…

This message has been edited. Last edited by: BP758,

If I’ve figured correctly we have 97 * overlap.
That’s on the 636 and 650 motors.