Hey all,

Need some opinions. Road racing (which is all I do with this engine) at 6K RPM and my exhaust valve on #1 let loose with the valve head going through the piston. Obviously a rebuild is in order but what could cause this type of failure?

Valves: Manley Severe Duty Pro Flows
Springs: CC Dual Spring 155 seat pressure with Titanium retainers
Rockers: CC Pro Mag 1.6
Pushrods: Don't remember but hardened with guides
Cam: CC 236X242 about .590 final with 1.6 rockers. Ramp rate was not the most aggressive they made. Went middle of the road there...for this reason!
Heads: AFR 190 ported and rebuilt with probably 50 hours total on the assy.

Thanks,
Ben

 

Sorry for your loss, Ben
Maybe the titanium retainer let go on cyl no 1. or did the valve stem break?
Can you inspect the remaining valves to determine their actual condition? You could probably tell if the failure was about to repeat in another clinder.

 

Ricardo,

I have not pulled off the heads yet. The failure was seen through the piston below and the exhaust port. Agreed that a complete inspection of both heads needs to be done. Amazingly, the rotating assy seems to be undamaged less a few nicks here and there. Most worried about the cam and and block. Parts of the valve damaged the lower portion of the cylinder wall. No idea if the upper part was scored very badly. Will seen when heads off next week. I hope I can repair as I had $1500 in machine work done to that block!

Any suggestions on where to go to rebuild heads that have had catastrophic failure with serious damage?

 

Sounds like some serious carnage.
Dont mean to be a jerk but I am guessing you have at least a bent rod in that rotating assembly and probably crank damage too.

 

That is why we let experts that do this stuff all day look over these things. I am only guessing the rotating assy is OK.

 

Really would need to see the parts or at a minimum pictures of the parts before making any kind of comment about the cause of failure, it could be many different things. Any good race motor shop around you should be able to repair any damage to the cylinder head, if not AFR I am pretty sure offers repair service.

 

Machinist, Thanks but how about repairing scoring of a cylinder wall? I think that may be an issue.

 

The cylinder can be sleeved if it's really bad and then you can go to the next oversize piston.

 

Forgive my ignorance but why would one need to go to the next oversized piston if the cylinder is being sleeved?
I had a similar catastrophe years back with a 327 and lost the exhaust valve which bounced around in the cylinder, exited out the cylinder wall and head. Had the crank checked, sleeved the cylinder, new piston, rod and head. This motor only had 600 miles on it.

 

I would prefer to stay 30 over on all the pistons as I currently have. Machinist, did you mean go 40 over if not that bad but if deeper, then resleeve and go back to 30 over?

 

He may have meant either or not both. If it's only slight scratches you may get away with only a rehone of the cyl. (not likely). If they're deeper, then boring to the next over size may be necessary, finally, if it's real bad, then sleeving would be required, or a new block.
You can run an engine with only one of the 8 cyls. over bored. I personally would over bore all the cyl. the same, if I had to do just one.

 

When installing a sleeve it distorts the cylinders next to it, and to make those cylinders straight and round again you may end up going beyond the recommended clearance. If you started out with .003" clearance and with a single repair sleeve are able to hone the cylinders to .005" that would be ok, rattle at startup, but ok... any more than that and you want to go to the next oversize.

So the usual procedure is to fix the bad cylinder with a sleeve and then bring all the cylinders up to the next oversize.

 

Thanks for clearing that up. I had the repair done 40 years ago and it was a new GM short block. everything checked out so the sleeve was bored to standard. I guess I got lucky.