Dennis Wilson

Just discovered that the drivers side cam on my 78 was broken inside the gear. This is on a 17 year old crate engine that was installed in 91. Tom Charlesworth (PCA guru and Tulsa mechanic) indicated this is the 3rd cam to go this summer in the Tulsa area. The timing belt had never been overtensioned in the 8 years I've owned the vehicle. All the rollers, tensioners, etc were in good shape. Metal fatigue? Is this unique to this area and if so, could it be the water?

Dennis

Jim bailey - 928 International

The cams are quite brittle and surprisingly easy to break.... usually it is the drivers side with the longer unsupported snout... We have sold a LOT of cams over the last 20 years ...

Kevin Michael

Happened to me last year.

Dennis Wilson

Jim,

I had a brain f@rt. It was the drivers side. Did Tom order the replacement from you?

Dennis

Dennis Wilson

Sterling,

You'll have to ask 928 Intl about that. All I have is a copy of their invoice to a PO. I had checked the tension since the last belt change and it always came up on the loose side of the notch on the JK tension tool.

Dennis

Dennis Wilson

Discussed the 3 Tulsa area broken cams with Tom today and there were 2 common factors in all three breaks. 1} All were older engines with the halfmoon woodrift keys/cuts and 2) all were using Mobil 1 in the new low zink formula. He has also seen a broken shaft on a GT's oil pump which was using Mobil 1. Over tensioning was not a factor.

Dennis

dprantl

Are you saying that the use of Mobil 1 engine oil may be a cause of the breaking of spinning metal shafts?

Dan
'91 928GT S/C 475hp/460lb.ft

Dennis Wilson

I'm saying that it could be the deeper cut for the woodrift key or the Mobil 1 or a combination of both.

Dennis

Fabio421

Don't tell Kibort!!!!!

GMS

I've seen broken cams in the 80s, mainly on 2v engines, sometime before Mobil-1 was around.

WallyP

Dr. Ed just had a broken cam on a 32 v engine...

heinrich

Oh give me a break Dennis ... LOL ... oil cannot be the cause here unless the engine was run dry!!

heinrich

Woodruff depth maybe. But without imbalance and undue tension on the cam, or MORE LIKELY some sort of impact at some point, it seems unlikely a cam would break. Many thousands of cams run many quadrillions of miles with no issues, and we're looking at what ..a sample of 3? 10? 100? Out of how many cams, thousands...

FBIII

x2 on oil being the cause. Maybe we need to ask what brand antifreeze was being used.

Dennis Wilson

I do know that the bearing for the drivers side cam is at the end of the oil supply chain. My oil pressure has been good and and I've always kept fresh oil in the beast. When I tore it down the belt was still tensioned, the cam gear was still in place (checked the timing marks) and all the other rollers, tensioners, etc were in good shape. There was a little play on the waterpump roller but no sideways movement or wobble. The cup on the tensioner was still intact and it had plenty of oil in it. When the cam went, there was no knock or any type of noise, it just started missing less than a block from my house.

Actually, the jury is still out on what caused it but I will be changing to a high zinc oil on all of my cars, especially the 928 and 931.

Dennis