[Grady Clay]

OK, here is my diagnosis (just a guess because there is lots of other I would like to see):

Spring bind. The first clue is the failure of the rocker-to-cam surface. The rocker is under extreme duress when the cam is trying to open the valve and it won’t open any farther. Another clue is the comment about aluminum valve spring retainers. With the spring(s) bound solid, the retainers are taking the full force.

The aluminum retainers probably bent first so the engine would turn over on the stand. There must have been only very minimal bind or the builder couldn’t have timed the cams. Since the valve springs were always at, or just short of bind, this caused some springs to break. Any spring bind is disastrous.

I think the chain ramp damage is from the incredible forces necessary turn the engine over through spring bind. It also can be as a result of the failure. Were both sides damaged?

Of course once there was a broken spring, the keepers and retainer came off. This allowed the valve to drop into the cylinder and all hell broke loose. Everything appears to be the usual carnage except I have never seen a piston turned over.

The additional things I would want to see are to look at the spring installation on the other cylinders. How close is it to spring bind? I would want to see how many spring shims were used on the #3 valve that failed compared to all the other valves. The builder could have simply misread the gauge or miscounted shims.

Another issue is the contact of valves-to-pistons on the earlier engine. I would want to know the initial clearance, which cylinders, and the clearance after the failure. This might be related to the failure. It might be a separate issue that hadn’t caused a failure – yet.

I can think of several other possible scenarios: Valves hitting the piston and initiating the failure sequence is the next most likely. His site postings aren’t exactly clear.


I don’t think this failure had anything to do with it being a racing engine. This is an example of the degree of care that must go into a modified engine. If you stuck a vacuum gauge in this guy’s ear, it would peg the meter.


Another interesting point is to look at the degree of effort and expense that went into the unusual bore/stroke. A custom ground crankshaft. Custom rod bearings. Custom rod length and big-end diameter. I assume stock P&C but how did they determine deck and valve clearances? Well … maybe not.
I think single plug was mandated by the rules. Look how far the plug is from center with that 102 mm diameter. That combustion chamber is screaming for a second plug.


Thanks for posting this. While none of us like to see broken Porsche stuff, it is very instructive. I have always helped others solve their problems so I didn’t repeat them.


Best,
Grady