New valvetrain and still failing leak down test
08-23-2017, 12:20 PM
#1
Registered User
Thread Starter
New valvetrain and still failing leak down test
As a final attempt before I pull my hair out and roll my Z down the street, id like some feedback as to what you guys may think is going on.
I have a boosted Z that I rebuild the engine (for the second time) about 500 miles ago, full rebuild, machined, forged pistons rods, the whole 9 yards. lapped stock valves. Broke her in without boost and was on the way to the dyno when I jumped timing. It wasnt a sudden death, just limped off the highway and it idled like crap. Towed it back home and performed a leak down test. can remember the exact numbers but was around 10 on all but two cylinders. The two bad cylinders had something like 50 %... so I pulled the heads and noticed where almost all of the valves had made contact with the pistons, none of them were drastically bent, I could just notice where the valve at cleaned off the carbon from the piston in a little spot. So I broke the bank and ordered Ferrea valves, Titanium retainers, and BC springs.
The Ferrea Exhaust valves I received were not undercut and the stem actually made contact with the guide before the seating surface. Talked to Ferrea and they had me send the valves in along with my valves. I had used some layout fluid and marked where they were making contact. I originally thought I had dropped a valve but that was not the case. Ferrea sent me a new set of valves with a straight cut stem and they fit fine now.
I had someone look at my seats and they thought they were fine to just be lapped. So I just lapped them with coarse and fine and put it all back together, new head gaskets, etc.
Performed a leak down test today and numbers were all across the board. So bad that I went and got a new leak down tester hoping that was the issue. The numbers were 45, 20, 40, 50, 15, 35 or somewhere close to that on each cylinder. I have timed a VQ enough times to be pretty confident but i hope thats all it is. Even though wouldn't the entire bank have a high leak down? and not just one cylinder? or did I just do a really shitty job lapping the valves?
I have so much money tied up in this POS and I havent even been able to beat on it yet.
I have a boosted Z that I rebuild the engine (for the second time) about 500 miles ago, full rebuild, machined, forged pistons rods, the whole 9 yards. lapped stock valves. Broke her in without boost and was on the way to the dyno when I jumped timing. It wasnt a sudden death, just limped off the highway and it idled like crap. Towed it back home and performed a leak down test. can remember the exact numbers but was around 10 on all but two cylinders. The two bad cylinders had something like 50 %... so I pulled the heads and noticed where almost all of the valves had made contact with the pistons, none of them were drastically bent, I could just notice where the valve at cleaned off the carbon from the piston in a little spot. So I broke the bank and ordered Ferrea valves, Titanium retainers, and BC springs.
The Ferrea Exhaust valves I received were not undercut and the stem actually made contact with the guide before the seating surface. Talked to Ferrea and they had me send the valves in along with my valves. I had used some layout fluid and marked where they were making contact. I originally thought I had dropped a valve but that was not the case. Ferrea sent me a new set of valves with a straight cut stem and they fit fine now.
I had someone look at my seats and they thought they were fine to just be lapped. So I just lapped them with coarse and fine and put it all back together, new head gaskets, etc.
Performed a leak down test today and numbers were all across the board. So bad that I went and got a new leak down tester hoping that was the issue. The numbers were 45, 20, 40, 50, 15, 35 or somewhere close to that on each cylinder. I have timed a VQ enough times to be pretty confident but i hope thats all it is. Even though wouldn't the entire bank have a high leak down? and not just one cylinder? or did I just do a really shitty job lapping the valves?
I have so much money tied up in this POS and I havent even been able to beat on it yet.
08-23-2017, 12:33 PM
#2
Registered User
Thread Starter
Also ill add that I don't have my intake back on yet. I only have the timing covers on and just did the leak down to make sure everything was good. So I am able to see down in the runners and look at the top of the valves. One of them that has 45 or so percentage loss I can visibly see the air shooting by the intake valve because of some run off assembly lube on the valve. It is bubbling up and spitting out. But the other valves seem to all be exhaust valves that are leaking. It could also be that the engine assembly lube that ran off is not allowing them to seat properly.
