B
Bingo002
Guest
I've been running a Texas Speed 427 (LS7 head castings) in my car for a year or so now without issue until I noticed it started to burn oil. I'll eventually make a separate thread about that entire saga but it wound up being valve seals. Well, I screwed up the spring compressor tool and side loaded one of my valves to the point where I just pulled the heads and had Texas Speed go through them again for peace of mind. I threw the heads back on and fired it up...it did not go well. I remember hearing a loud "pop" like something metal snapping as soon as the starter rotated and when the engine fired, it sounded pretty bad. Video below, the engine was only run like this for ~10 seconds. It would idle, but it only ran on cylinders 2,4,6,7. I learned not long after that that I couldn't simply re-use the old pushrods after having the heads decked and new valve guides installed. When I measured for pushrod length at zero lash, I found they needed to be 1/10" shorter...whoops.
So this brings me to now. I've had the heads back off and didn't see any obvious piston/valve contact. I installed the correct length pushrods, checked all the valve springs, checked and randomized all the (Johnson) lifters, and cam lobes look perfectly fine. The engine still will not fire on 1,3,5, and 8.
Next I compression tested it. 1-7 were all fine at ~220psi, but #8 was completely dead, 0 psi, and you can hear it on the starter. I then popped the rockers off #8 and leakdown tested it where It held 57 out of 60 psi. So I know there's nothing wrong in the bottom end, and the valves aren't bent or unseated.
Soooooo I can't figure out what would cause this. My leading theory is the engine jumped time with the old pushrods due to that excessive force trying to hold the cam in place and that "pop" I mentioned earlier was it shearing the pin on the cam gear. But that would mean all 8 cylinders would be out of time, though maybe it's just right on the edge of being an issue for the other cylinders? I'm really not sure. I just want to get some more opinions before I go through the effort of pulling the timing cover because of how awful that job is...but hey I've done it before.
Video link:
Continue reading...
So this brings me to now. I've had the heads back off and didn't see any obvious piston/valve contact. I installed the correct length pushrods, checked all the valve springs, checked and randomized all the (Johnson) lifters, and cam lobes look perfectly fine. The engine still will not fire on 1,3,5, and 8.
Next I compression tested it. 1-7 were all fine at ~220psi, but #8 was completely dead, 0 psi, and you can hear it on the starter. I then popped the rockers off #8 and leakdown tested it where It held 57 out of 60 psi. So I know there's nothing wrong in the bottom end, and the valves aren't bent or unseated.
Soooooo I can't figure out what would cause this. My leading theory is the engine jumped time with the old pushrods due to that excessive force trying to hold the cam in place and that "pop" I mentioned earlier was it shearing the pin on the cam gear. But that would mean all 8 cylinders would be out of time, though maybe it's just right on the edge of being an issue for the other cylinders? I'm really not sure. I just want to get some more opinions before I go through the effort of pulling the timing cover because of how awful that job is...but hey I've done it before.
Video link:
Continue reading...
