RKD in OKC

The belt light NEVER came on while racing. Only after cursing for an hour or more and then at speeds where the RPM were above 4000. And then not every time.

namasgt

The bolt could have been re-tightened by the free rotation of the cam gear it self after the exhaust cam nose broke. Exhaust cam stopped rotating after breaking, cam gear continued rotating along with the rest of the rotating assembly, tightening the cam bolt.
I do not think the steel triangular shaped thing Greg mentioned could have been the problem, last time a failure like that was mentioned here the engine sounded like an old Diesel tractor. It would have been obvious before the cam broke.
The problem must have been the cam gear being loose itself for a while causing the multiple belt warning lights.

Another possibility could have been either the bolt itself being too long from the factory or the threaded hole in the cam nose not having been machined deep enough for the bolt.

I would have questioned the whole timing belt job after finding the tensioner bolts loose!

In either case, a belt warning light should not be taken lightly, specially when it happens multiple times, I find it rather unusual for both mechanics to say that 'its Normal for the GTS belt warning light to come on', because its not normal...

heinrich

Ali, in my experience, when a timing belt warning comes on, it should be considered something that must be taken care of. That light comes on for valid reasons only. Whether the gear was loose; or (as I would guess) the whole set-up was just too sloppy, timing off, worn shoulder bolt / stud; gears worn, tensioner needing oil, too much play in the entire belt train ... whatever the reason, the light coming on, was a warning that conditions existed that were going to cause this. I am really sorry for this failure, no-one deserves this.

Imo000

This woud only be visible just before the cam snaps.

RKD in OKC

The mechanic that found to loose tensioner is very reputable and familiar with the 928. He checked everything when he fixed the tensioner. He also checked it all over again and couldn't find any cause for the light at extended high speeds. When I called him to inform him of the failure, his comment was it must have been a part defect that caused the failure.

namasgt

That's possible, a defect in the casting, your engine is reasonably young.
I wish this had not happened, I love your GTS. You will be back on the road soon and now have performance upgrade options, bigger cams, ect....

GregBBRD

You guys are trying to make this way more complex than it is.

Rust in a otherwise non-rusty area....forms from cracks and loose parts.

The bolt was loose. This allowed the triangular piece to "work" on the camshaft and crack. This allows the key to work in the cam, starting a crack at the base where the cam is machined down, from the gear. When the cam actually breaks, the break isn't square, so the pieces rotate until the bolt is tightened by the two pieces "climbing" on top of each other. It's a simple thing. Seen it several times, now...always the same.

Sean.....knock the "broken" piece out of the cam along with the key and the pieces from the triangular drive piece. These pieces will be "beat" from them working against each other. The only way that can happen is if the bolt is loose.

Lizard928

If he was truly a 928 expert he would have known the cause of the light was the conti belt, and he would have insisted on changing it to a gates. In this he would have reset the cam timing and problem possibly avertted. IMHO.

Tommy5543

Ouch, sorry to read this RDK! Repairable however, and now a good time to think which cam's to put back in there?

Good advice from JET951, now added to my yearly maintenance check list while checking upon the correct timing belt tension (= also re-torque cam gears bolts).

RKD in OKC

Again, every time the "Conti" belt was checked, it was not loose. That is why Sean redid the spade connector on the belt warning after I pulled in from a belt light event.

andy-gts

RKD,

I have cams left over for the gts if you want them....but I bet you are eyeing some better ones....any way , they are yours for the asking.
I dont mean to be selfish but we all want you to get this bad boy back on the road , cause you are giving the drivers ed at the ocic , I hope that is still on!!!

andy

SeanR

Here's a closer look at the cam gear. Obviously the bolt has been loose in the past otherwise the key wouldn't be torqued like this. I find it odd though that the bolt had good torque on it when I checked it the other day. Makes me wonder if it was found loose like this in the past, re-torqued w/o a proper inspection. This is not due to a cam shaft defect.



There is a slight bit of rust, but not at any of the break points on the retainer. Just the mating surface between retainer and cam gear.



We can all speculate as to the cause, until I get the engine torn down we won't know for sure. There is a chance the parts are fine with the tensioner arms/bushings/belt/pump and Greg is correct about this gear/bolt.

Lizard928

Richard I understand this, but every conti belt that I have ever seen on a 928 with the warning system has had this problem.
Switched out to a gates/porsche belt and problem disappears. The Conti belts stretch under load and heat.

RKD in OKC

Well, guess I got a previous owner gripe with the conti belt then.

Yea, the Driver Tech for March 10th is still one whether I have my car or not.

Waiting for more info on the damage before deciding how far I will go on WYIT upgrades.

AO

RKD-

So sorry to hear about your troubles. But it doesn't sound like the damage is catastrophic. It'll be back up and running in no time.