[Robby23]

i would just take the heads off to inspect and go from there. you are just brainstorming at this point.

[s346k]

removing the cyl head won't tell the *whole story if it's a ring/ringland issue. i witnessed disassembly on a motor with 0 compression on a couple cylinders. pistons and cyl wall looked fine, but the lands and rings literally crumbled when we took the piston(s) out. i found it...interesting.

[cmitchell17]

Ok so I got a leak down tester, hooked it up to the problem, #7 cylinder, turn the regulator up to 60 psi and the combustion chamber is only reading about 7psi so large leak, I can hear hisses. Opened the PCV valve to valve cover hole and no leakage felt. Hear leakage at the throttle body but also hear leakage at the exhaust pipe so I am kind of confused.

But I am kind of relieved as I think this kind indicates its a sealing issue, and its not a ring issue (I would have pressure in the crankcase), but has got to be a valve sealing issue but I don't think its common to have both intake and exhaust sealing issues? It also doesn't completely rule out hydro locking which I am still afraid of.

Is it rare to burn both an intake and exhaust valve at the same time.

I also hooked it up to cylinder #5 for comparison, and its tight no leaks even heard and only about 1 psi differential.

[cmitchell17]

Ok, maybe it is just the exhaust valve and not the intake. I hooked it back up to the #7 and forced the throttle body closed and sprayed soap around the edges and I couldn't see bubbles forming, although not sure if the throttle body edges are sealed enough to make bubbles, but I didn't see any bubbles form but when I put my ear next to the TB opening I can hear the air filling up a metal tank noise and when I try to put my hand inside the TB I can't really tell if I feel air or not.

I can hear the air filling up metal tank noise down by the header though, the noises are just so faint its hard to tell if its coming from the regulator on the leak down tester or what.

If it was a broken ringland issue, I think I would have pressure coming out of the dipstick and valve cover that I could feel with my hand?

[cmitchell17]

Now I am thinking its a bad lifter again, I pulled the intake manifold and #7 intake port has considerably more oil on the walls than the other ports, when I turn the motor over with the starter it backfires and hisses out the intake on the #7 with a puff of mist, so I am thinking its a lifter or maybe a bent pushrod even though I saw the rocker arms seemed like they moved normal on #7.

You can hear the hiss/puff/backfire noise on the #7, I could also hear it when the engine was running:
https://photos.app.goo.gl/jcSQkzcVeFd4HWdk9

[cmitchell17]

My best guess is that both my intake and exhaust valve have burnt or have sealing issues. The backfiring out the intake valve is just because the intake valve is not sealing. At the same time I can feel both intake and exhaust rocker arms on the #7 and they are both loose, so the valve springs are pulling them shut as far as they can since pressure is off the rocker arm. It still only builds about 7 psi in the chamber though, and I think I can hear it at the tailpipe hissing.

At this point I guess I need to start ordering head gaskets, but I want to use this as an opportunity to upgrade and check piston to valve clearance at the same time. I want more compression since I run E85 100% of the time, my heads are supposed to be milled .030 which I have calculated that I should be around 12.25 but I want to see how much more I can get checking PTV and maybe trying a thinner head gasket. Anyone else out there running a thinner gasket on the LT1?

[Scottyz]

Bent valves maybe from floating at high rpm.

[95 imp]

A collapsed lifter or a bent pushrod would mean the valve isn't opening or is partially opening. If you're getting backflow thru the intake valve and it's closed, you have a bent valve/seat issue.

You wouldn't be leaking with a bent pushrod/collapsed lifter either...

I'd pull both rockers and double check the leak down just in case they are in the overlap area on the cam.

[cmitchell17]

It almost looks like I took apart the motor for nothing haha. It almost looks like the #7 had a slight opening on the intake valve, but you can't really see it in the pictures.


So I tried to compress the spring and the retainers are stuck in there, I tried to bump them with a rubber mallet and they are still in there.

I am using a cheap chineese spring compressor, I have 2 and one dosen't fit, does anyone know of a good reasonable one? I didn't want to pay $200 for the special LT1 one for just a piece of steel and aluminum with some threaded bolts haha.

These PAC springs are extremely hard to compress I had to use a pipe to put on the wrench and I have no way of holding the head down now since I took it out.

[cmitchell17]

I think I found the problem, and I have never seen anything like this:

So apparently some carbon or coked up oil is lodging itself in between the valve and the valve seat, the picture is looking through the intake port and I put a flashlight up under the head and let it shine through the intake valve I have no pressure on the valve so the valve spring is trying completely to pull the valve back up but it can't.

Anyone ever see anything like this? What's so weird is how is it staying there, with as violent it is in the combustion chamber and given the extreme heat you would think it would blow itself out and fix itself?

[Tim M]

Are you sure it is not bent?

[s346k]

no marks on #7 piston, i take it?

[cmitchell17]

So I have been trying to get the locks and retainers off the valve and valve spring for the last 2 hours. I have tried bumping them with a rubber mallet to try to loosen them and have been trying to stick a pick in between them while compressing the spring but they are wedged in there really tight and they aren't moving.

Is there something I'm missing on these? I have the PAC .660 dual springs with the PAC integrated seat and seal. Once I can get these off I can pull the valve out and check it and try to check the guides as well.

That being said, how would I have bent valves without visible piston to valve contact damage? I mean if there was float I would think the pushrod would bend long before the valve stem would.

[L78toLT1]

Find a deep socket that is slightly smaller than the spring retainer, place it on the retainer and smack the hell out of it with a hammer. That will usually break the retainers loose.