This is a fresh rebuild, and you are only getting 95PSI on most cylinders, and 65 on three of them? Right there is your problem. If you are below 100PSI on a new motor..... something in the reassembly didn't go quite right.

Was the block bored? Checked for taper? Roundness?

 

That was my concern as well, but the leak down on even the good cylinders was 5% or less. We were thinking that maybe the rings havent been quite broken in yet. It only has 26 miles on the motor. Motor was bored .030 due to wear. Brand new heads put on as well. Only thing NOT new on this motor is the block, and the intake manifold. I will be calling my builder today to find out what's going on. AF gauge will be here today.

 

Re do the test this way.

Remove all the spark plugs
Relax all the rocker arms, this will eliminate possible pushrod length issues/bad lifter's and let the valves close 100%, well it should.

Next run your tests again.

If the numbers improve then there is a timing, pushrod length, possible cam or lifter issue.

If I had comp numbers like that on a fresh rebuild I would not be happy at all. They should be high not low. If it is found to be the builders fault I would bill him for R&R time for sure.

 

When i did the leak down, i took out all spark plugs and completely removed rockers. Let sit for 15 minutes and then test. I will definitely be calling the builder today, and if it is on him, i'll be taking the truck to him so he can pull it out and fix it.

As for pushrod, cam issues, we only put in a mild .480 cam, and i got pushrods and springs from hi-potek. The builder did tell me he had to grind down the heads slightly to seat the valves, so maybe that is the issue.

 

Heres a thought, with the .480 cam, what should the pushrod length be? Stock is 6.915, Hi-potek has 6.750 as a replacement.

 

I would think those would be too short, if anything.... not opening the valves all the way might (iffy) influence compression test numbers, but, not that significantly, I should think.

 

+1 To short, go back to stock length but in a hardened rod. I would still like to see a comp test done with the rockers relaxed.

 

That's what i thought at first as well. I may pull one out to make sure they are proper length, but i have hardened stock (or so i ordered) rods in there now. My builder said when he sank the valves, they were right in his spec sheet. He's lost as well as to what the hell is going on. He told me to loosen the rockers and run another compression check. Here's what i got on the cylinders with 0 leak down.



It's got to be somewhere in the heads.

 

Are you propping the throttle all the way open?

Ok, zero leakdown? At what pressure?

I would consider pulling the timing cover, and checking cam timing.

 

Zero leak-down and 90 psi, that makes no sense.

What head gaskets are you using? Just one per side right?

What pistons are in this motor?