25thredrs

iTrader: (2)

I have been noticing blue smoke on deceleration lately so I was thinking rings or valve seals so I did a leak down test. Please look over my procedure and results and lend me your comments. thanks See sig for build specs
BTW: I used a MAC tools leakdown tester with 2 gauges. It look approx 40 psi to zero the first gauge before starting the test.
Procedure:
1) pulled all plugs
2) Pulled valve covers
3) Removed Rockers
4) Blocked open throttle blade
5) Pressurized one cylinder at a time and recorded percentage leakdown.

Results:
Drivers side front to back: 1= 30%, 3= 28%, 5= 88%, 7=86%
2=20%, 4=22%, 6=24%, 8=22%

could not hear any major air escaping through intake or exhaust, also no bubbles in coolant. #5 and #7 plugs were also BLACK. But all the plugs had a little bit of oil around the threads.

Any help or direction would be greatly appreciated.

TT632

iTrader: (3)

Those are not very good numbers. Very low #'s on adjacent cylinders are usually indicative of a head gasket being blown betweeen those cylinders; you would be able to hear the air escaping through the intake or exhaust on the adjacent cylinder if the rockers were on the heads if this is the case. Your valves are sealing well if your not getting any air past them. Either way, your poor leak down #'s all the way around indicates you need a to re-ring the engine at the very least.

bww3588

iTrader: (49)

not so. anything 20% or below is acceptable. the 88% leakdown is out of the question.

my question is, why did you remove the rocker arms? you should have left everything alone, VC's excluded, this makes it easier to hear air going through the crank case/valve seals, brought each piston to TDC on compression then did the leak down.

25thredrs

iTrader: (2)

i was under the impression that this was a fool proof way to ensure all valves were completely closed.

racecar

It's real simple, your engine is trashed. I had a leakdown of 11% on one cyl, it had bad rings and the cylinder was scored. With the numbers you have, I'm surprised the motor will start or run. That engine is dead. Remove and replace with a fresh engine.

eallanboggs

iTrader: (1)

You can hear air at the tail pipe, dipstick tube(stick removed), throttle body(plenum removed and throttle blade open). I agree that your leakage is excessive. How much vacuum are you making at idle and snap?

NBM-LS1

iTrader: (7)

Did you do a wet leakdown?

Tony Mamo @ AFR

iTrader: (13)

You should hear a BUNCH of air escaping somewhere with some of the weaker holes you reference. It should be so much so that its easy to listen to exactly where its coming from (past the rings or past the valves). You cant lose that much air and not be able to track down where its escaping.

I'm questioning whether the leak down is being done right if you cant easily trace that much of an air loss.

I wouldn't throw in the towel just yet....more digging is certainly in order

-Tony

25thredrs

iTrader: (2)

thanks for the replies...I recently removed the heads to check pistons, cylinders, valve seals etc. I can't find anything noticable. Cylinders and pistons look good. Only thing I can see is excessive "GUNK" around valves in #5 and #7 cylinders.

ZHAWK154

iTrader: (1)

i bet if u pop out #5 & 7 pistons, they would be broken in ring lands. been there. good luck on shortblock build!!!

69LT1Bird

iTrader: (1)

Did you take the pistons out or are you just looking at the top? I broke the rings lands between the compression rings and oil rings last year and showed 85% leakage on 5 and 7.

Just pull it all apart and rebuild it.

25thredrs

iTrader: (2)

thats kinda where i'm headed. I'm thinkin a twin 66mm forged 408ci.

crainholio

iTrader: (2)

You want to put each piston on TDC before pressurizing it, throttle blade position doesn't matter (you WOT it for compression testing), and it doesn't hurt to tap each valve with a rubber mallet just to ensure it's fully seated.

None of this would account for your results, though, so good luck w/ the rebuild.