TomZ

My 502 decided to run like hammered crap two weekends ago. I did a compression test and found bad numbers across the board. The season before with fresh heads I had 150 psi on all cylinders. Backing off the rocker bolts brought compression up on all cylinders so I figured that after three head jobs (two previous to me and then mine last winter) I thought maybe too much preload so I bought a stud kit to convert to adjustable valvetrain. Each was strong after that until I got to #7. Dead. I noticed that the exhaust valve wouldn’t hold adjustment. Today I measured and found the valve was about a 1/8-inch stuck on return to seat. I smacked it with a dead-blow and it popped back up. Repeated attempts at cycling the valvetrain caused the same thing. Something is f’d in there and it has to come apart.

At this point my season is done and I might as well concentrate on doing the AFR head swap a little earlier. My question... what do you all think may have caused this? When I smack the spring stack, it snaps back into place. Anyway, just curious on a root cause. I’m thinking the header might have leaked and the stem got corroded. Or a broken spring (if it’s spring I can salvage that in the boat). It’s odd how it snaps back into seating.

It was running fine previous to that.

2020 can kiss my a-s-s.

sutphen 30

were the heads rebuilt?pull the 7 plug,does it look lean?lean,water,leaking/rotted valve guide or to tight of guide is your problem,time to see what it is.
it sucks

TomZ

Yes, the heads were rebuilt At the beginning of last season. I rebuilt the heads because 7 and 8 showed water intrusion. The headers were pressure checked with no leaks found. All the plugs came out black (assuming because of low compression). There was no sign of any water damage on the plugs.

Since it has to come apart anyway, I’m going to pull the header and then pull the spring to see if maybe the inner spring is damaged.

The rebuild has probably 25 hours on it. Wouldn’t a guide issue been evident from the beginning? This came out of no where. It ran great a few weekends ago, and when I went to start it up to prepare for going out the next day, the valvetrain had a major tap. The tap went away after warming up a little. Maybe a seat issue?

getrdunn

iTrader: (7)

I'd think the guide or bent stem or a "corrosion issue". Did you rotate the valve and see if it continued to hang up.

TomZ

I have not gotten the spring off yet. I may work on it tonight a little.

Interesting observation... with the rocker backed off but with enough to provide lift, I would get compression but intermittently. Sometimes the valve would seat on its own, other times it would hang.

F-2 Speedy

iTrader: (6)

might have a bent stem

mike tkach

iTrader: (3)

if you have a broken valve spring the valve might have made contact with the piston,once that happens the valve gets bent and cannot seat properly.i would not run the engine again untill the valve is replaced along with all the valve springs.add in,at this point a valve job needs to be done by a shop that you know does good work.

TomZ

Agreed, I'm not going to run it until I have it all figured out. One of my buddies was saying to button it back up and run it for the rest of the season. I had to school him on what happens when the valve train decides to let go.

I have an inspection camera that I'll stick down in there to have a look also.

sutphen 30

did you replace he valve guides?if not,corrosion will come back and cause the valve to hang up.and from the sounds of it,head of the valve is bent.seen it many times.

TomZ

I know the guides were replaced when the heads were done but I do not have the details in front of me.

If the valve head was bent how would it occasionally have compression or be able to snap back into place?

It’ll be interesting to see what it actually is when it comes apart.