What are good leak down #s for a fresh (never been fired) engine

DW SD · 11-14-2005, 11:10 PM

Met up with a friend tonight to do a leak down test on his 3.6 which is has been rebuilt, but not fired. What are good leak down #s considering that the rings have not seated nor has it been heat cycled? Far as we can tell the numbers are all over the map.

Engine has new bearings, been re-ringed and has a fresh 3-angle valve job by AASCO machining here in CA. Valves have been adjusted.

Leakdown %s range from 30% to 95%. All but the one are 70% or higher. The one low cylinder had a leak at the exhaust, which was obvious at the header collector. The rest, in the 70s leaked into the crankcase.

How much better do the numbers get once the rings seat?
Are the results of this test valuable at all given the fact that the engine hasn't fired?

Thanks,

Doug

Joeaksa · 11-15-2005, 12:15 AM

With new P&C and rings, why do a leakdown check anyway? Unless its to find out if there was something put in incorrectly, cannot figure out a good reason why. Rings have not seated so you know the value will be low.

Did you try tapping the exhaust valve to eliminate the air pressure from bleeding out of the exhaust? Might try turning the engine over a few times and run the test again, or pulling a cam cover off and tapping the valve to make sure that its seated.

Otherwise fire that puppy and let the rings get bedded in, THEN do a leakdown check IMHO.

JoeA

DW SD · 11-15-2005, 06:17 AM

Joe,
Good advice. Wouldn't you think the leak down #s would be fairly consistent, even without bedded rings? IE maybe all 80s?

Didn't try tapping on the leaking valves. How would I do that - a plastic headed hammer?

Doug

KNIGHTRACE · KNIGHTRACE's Garage

Leak down test isnt very accurate on a cold new motor. The rings take about 3k miles to seat.

Dan Owens · 11-15-2005, 09:37 AM

Isn't it kind useless to do a leakdown before you run the engine in to seat the rings. Once you seat the rings everythings gonna change. I'd just break it in and then run a leakdown if you're want to know what the accurate numbers are. Prior to that point who cares? Just my opinion.

Jeff Alton · 11-15-2005, 10:27 AM

Well, I was curious about this same thing after putting a 3.2 together in the summer, so I tested it. It leaked between 7-9% while it was still on the stand. All of it through the rings. It is not a worthless test however as it would reveal poor sealing valves or a leak in the head to cylinder seal as well, it is not too useful in determining whether or not the rings will seal however.

cheers

DW SD · 11-15-2005, 10:44 AM

Quote:

Originally posted by catca
Well, I was curious about this same thing after putting a 3.2 together in the summer, so I tested it. It leaked between 7-9% while it was still on the stand. All of it through the rings. It is not a worthless test however as it would reveal poor sealing valves or a leak in the head to cylinder seal as well, it is not too useful in determining whether or not the rings will seal however.

cheers

Thanks Jeff!

Consistency is something I was kind of expecting, not necessarily perfect numbers like 2% to 4%. This is a good point of reference.

Thanks,

Doug

Jeff Alton · 11-15-2005, 11:47 AM

I am not sure why I bothered really, just seemed interesting at the time! I also measured actual valve lift on that motor to see how the reground 964 cams compared to the actual specs..... Just too curious I guess! After being broken in, that motor showed around 2% leak.

Cheers