SeanR

Yup, exactly.

Leon Speed

Ah. Duh.

danglerb

Sad to hear it.

I'm curious about how long the Conti belt is now, how much it stretched.

blown 87

They stretch during use, like a rubber band.

RKD in OKC

Sean checked the torque on the cam gear and it was correct.

M. Requin

Two things: 1. I would really like to hear a reply to Bruce Buchanan's comments; 2. Damn, NoVector, where are you getting those avatars? (RDK- just missed your last post while I was cogitating- sorry!)

GregBBRD

I've seen this a few times.

The triangular cam drive sprocket cracks right at the key, after the key gets loose and "wallows" out the "key way" in the cam. Eventually, the cam will break off whenever this happens. The crack originates from the base of the damage in the "keyway" and progresses across the front of the camshaft, where it is machined down. If you look at the picture of the broken cam drive sprocket, you can easily see the rust where the crack has been "working" and has "stained" the aluminum gear.

Whenever you see rust, in situations like this, that is where two pieces have been "working" against each other. Two pieces of steel or cast iron that work against each other will produce a "powder" that rusts fairly quickly.

When I was much, much younger and worked in the garage at a major grocery distribution center, you could tell a loose or cracked tractor rim 20 feet away, once you knew this. Rust around lug nuts only means one thing.....the nuts are loose.

whatudrivin

Such crappy luck Richard. Very strange indeed. I was riding with him when it all happened. Was pretty much w/o warning too. Even if we would have pulled over and done a timing belt job this probably wouldn't have been found, and then just happened later....and probably with a worse outcome.

I don't know how you kept it together so well Richard. I would have been really upset, but **** happens at times. And once done you kinda just have to go with it. I'm hoping there isn't any more damage that we have seen thus far.

That was my first trip down to meet the Dallas guys. Must say that despite not making it to the breakfast and having this happen to the car, I did enjoy myself. Was very nice to meet Rodger and Sean. There were some other guys that showed up but I do not remember all the names and who all posts here. I learned a bit and got some insight into my car. I can't wait till I can come down again. Hopefully next time things will go smoothly.

JET951

Some more info on the subject of the 928 cam breakage just behind the alloy cam gear , I have been working on Porsche cars for the past 35 years ( give or take a few months) and have noticed }

A ) have never seen a steel cam gear on a 944 ( be it single cam or twin cam) loosen and move on the end of the cam which naturally would cause the same catastrophic failure of the hollow end of the cam as the 928 , the reason is quite simple = The 944 ( single cam & twin cam use steel cam gears , so it being steel is far less susceptible to crush over time where it buts up against the cam boss end stop , meaning the holding force via its single bolts remains for a much longer time period if not permanent , because we check these on a regular basis during service intervals , but never find they ( centre bolt for the steel gears on the 944) low on torque value

However this can not be said about the alloy cam gears retaining bolt on the 928 , we have found far too many perilously low on torque value

Remember a cam gear (on any engine) has to remain firmly in its locked position , so if a cam gear ( say on a 928S / S4 / GT / GTS ( which are alloy ) move even just a fraction of a millimeter , then this movement will be in both directions from the shock waves from the operation of opening the valves/ double valve springs etc , meaning anyone who has operated a complete 928 or 944 cylinder head fixed in position on a work bench and try turning the drive gear by its 17mm headed retaining bolt ( within the centre of the alloy gear) with a spanner 360 degrees will know what I mean , its very harsh ( back and forwards kick back through the spanner ) , so naturally once the crush / holding force releases even so very slightly the alloy composition , being softer than steel takes little incentive to just slip / move ( be it fraction of a millimeter ) however when this event occurs then its now only a matter of time because the forward / back jack-hammering will / must make matters worse untill the very large cutout in the alloy camgear( 5.0L onwards) finally makes contact with the woodruff key( in a very smashing way) and the result is assured = failure

However its easily cared for , just torque these bolts on a regular basis

Subnote } I remember the first time I came across this 928 cam break thing , I was working at a Porsche dealership , the year 1986 , the car a 1985 928s 4.7L ( we didn't get the quadcam 5.0L in Aus untill 1986) the 928s in question had very lowish Kms ( less than 10,000kms from memory I can still remember the colour combo) , the car was idling in the workshop and I along with the workshop foreman could make out an unusual ticking type of sound emanating from just behind the timing case on cylinder bank 5 - 8 , we had no idea what it was , we had never heard of this issue at all , the 928 was parked in the workshop that night and started the next morning only to find it didn't run for long because the cam end broke off just behind the alloy cam gear , remember this car was only a year old , we very quickly found out what had happened but took more time to piece the events together ( meaning why ? )
All it ended up being was that one bolt was not torqued correctly at the factory , very rare , but some strange things happen on a production line ( particularly in 1985 when the production of the 928 was flat out ) , all worked out well , covered by new car warranty etc etc
But that was the first time & from that we / I thought it might be wise to at least check these bolts torque value at cam belt replacement intervals or even more often if one thinks it wise , after all its just tightening a bolt

Brent

Yes sir, the Texas gang are some of the best, I'd be kind of lost without them.

Richard, I read your post early yesterday morning and did not comment, not knowing what to say. The whole thing just makes me kind of sick, so I can't imagine how you must feel. This scenario should give many of us plenty to think about and add a few more things to the check list. Sounds like everything is going to work out though. Good luck to you and Sean.

Cosmo Kramer

Sorry to hear this Richard, but seeing that you were looking to do upgrades this just expedites the process!

I guess with the use your GTS sees the Gates belt would have been better choice, but back when this TB job was done the Conti was still being used by many.

I wonder it the Conti belt had anything to do with it? Could a slightly loose stretchy belt cause undue strain on the timing gear or cam?

heinrich

Guys ....

I have owned 22 Porsches, about half of them being 928's. And Godzilla has run for 12 years of excellent performance, on Conti belts. YES the Gates belt seems a better belt, but seriously ... Conti belts do not break cams.

Herman K

Richard I’m sorry to hear about the breakdown of your car and my sympathy to all that you will have to go through to get it corrected.

I believe that “JET951” offered the correct analysis about what more than likely has caused this to happen (human error when the last timing belt or cam timing was done).

Comparing the facts that my original cam gears where replaced with a new set and the old ones came off without incident, no case history of the belt tensioner light coming on in a frequent fashion at 140K versus yours at 60K makes me believe that during the previous belt replacement cam gear timing service interval an error was made by the PO’s mechanic.

Since my last change of cam gears and T-belt I have done just about another 15K miles and now that I have learned what you are going through it’s a good time for me to do a belt, cam gear and torque check on all the relevant items.

I wish you and the car a good outcome.

NoVector

Was thinking the same thing as with a PorKen tensioner, there is no light warning--it's defeated.

dcrasta

Ditto :

Wondering if a visual inspection of the Cam belt through the inspection holes during idle would have revealed this issue? (Like a wobbly run/tracking belt.)