what are good leak down #s for a (rebuilt) engine which has never run

DW SD · 11-15-2005, 07:19 AM

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?

Even if the numbers are low, shouldn't they be consistent?

Thanks,

Doug

****note, sorry for the cross post. I realized this is a better forum for this question.

john walker's workshop · 11-15-2005, 08:05 AM

don't bother. put 1000 miles on it and then do it when it's hot. you already found out about high readings on a dry engine. you should see 3-4% then.

stevepaa · 11-15-2005, 09:13 AM

I had my heads done twice because I was concerned about the numbers when cold and never run. Didn't change. I'll get new numbers when I run it.

DW SD · 11-15-2005, 09:17 AM

Steve,
Thanks! just so I understand, you had the heads redone for a second time and the cold leak down numbers didn't change from first valve job to the second? What were the #s (roughly)?

Thanks,

Doug

RiskyBusiness · 11-15-2005, 09:59 AM

Crankcase leaks are not suprising: That's a function of the rings. It will change when you run it as stated above. I would be concerned, however, about the valve leak. I would not expect valve seating to change considerably after break in. Its not unusual to see an exaust valve with a bit of carbon under it... but not on a fresh rebuild. You could try hand lapping the exhaust valve and see if that makes the mystery valve seat better.

stevepaa · 11:33 AM

I was blowing air out of the valves, so much so that when I sprayed brake cleaner on top of the valves it sprayed it back at me. I think I had at least 20-30%.

Before the rebuild I had less than 5% on good cylinders on 160k engine. The bad was 70-90%.

Hopefully I'll have it running again in a few weeks and then remeasure.

KobaltBlau · 11-15-2005, 01:39 PM

DW, is this an engine you are considering buying? If so, perhaps forum members can give some ideas on how to determine whether the rebuild was done right, given that the 0 mile leak down is not going to be useful.