RKD in OKC

Cruising from OKC to the Dallas 1st Saturday breakfast my drivers side cam broke. More specifically the cam gear broke off.

In the 3 years I've owned this car the Toothed Belt light has come on several times.

Right after I got the car it came on a couple of times while I was sitting idling at a drive through waiting patiently for my burger. Turned out the tensioner itself was loose. Tightened it up and refreshed the oil in it and all was well.

Next the light came on during a high speed cruise. At speeds over 140, occasionally the light would come on. Not every time just once in a while. If stayed under 140 it would not come on. Checked tension and was exactly where it was set 5000 miles earlier. Checked tensioner and gears, etc all looked okay.

Continued driving and now after 3 or 4 runs up over 140 toothed belt light comes on. Stay under that speed, no light.

Go on trip. First part of trip many different speeds including runs over 140 and no light. On the way back tensioner light starts coming when lifting off throttle to slow after running up to only 130. Slow down and stop at Sean's in Dallas. He finds nothing wrong and refreshes electrical connection to tensioner warning. Continue driving to get home, run it up over 130 and light comes on, keep it under 120 and no light. Have local mechanic check it out again, no problems found.

Was told by both mechanics not to worry about it, some of these GTSs just do that.

Take another couple of long trips, do not take the opportunity to go over 120 and no light for 1000 mile trip.

This morning make drive to Dallas, cruising along at speeds between 90 and 110. After about an hour I hit 110 and the toothed belt light comes on. Slow down to 80 and plan to call and stop at Seans to have him check it over. After another hour the light comes on at 80. Slow to 60 and call Sean. After 10-15 minutes get Sean on phone and while on phone with Sean car slows like it has gone into limp mode, then toothed belt light comes on and car dies. Coast to side of road and wait for Sean and wrecker.

Get the car to Seans and find timing belt is not broke, but loose, cams are in time (not jumped a tooth) and driver's side cam is broken off at the cam gear. Borescope and find nice shiny crescent marks on tops of pistons. Don't have leak down tester that doesn't require crank to be turned.

JET951

This is less common on the twin cam per bank engines as opposed to the 4.5L & 4,7 L single cam per bank engines , but the principle remains , and that principle is }

When you have a single retaining bolt (only) going through an alloy cam gear , this single bolt must be re tensioned at every cam belt replacement and again half way through the next cam belt interval , this will always maintain enough tension / grip of the allow cam gear to the relatively small contact area where the alloy cam gear butts up against , this is especially true with the single cam per bank engines ( 4.5L & 4.7 L ) where the cam gear will noticeably crush ( over time) where it buts up against the circular machined cam shaft end boss end stop ( which in comparison to the 5.0L & 5.4L engines is much less)

Remember, on the twin cam per bank engines 5.0L onwards , the woodruff key plays no part what so ever in retaining the alloy cam gear securely in its correct position on the cam boss ( cut out for key in alloy gear is much wider to allow cam gear indexing/ valve timing ) , so if the bolt looses just a bit of tension ( alloy gear crush) then its just a matter of time until the gear slips ( very badly indeed) ,much life a jack hammer, with devastating consequences .
And the reason why it breaks just there is because its just behind the gear and that part is the weakest because the machined / threaded bolt hole is there within the cam ( hollow) and its just cast metal = break / snap
Easy to prevent , just torque the bolt ( one per gear as mentioned above )
I have been telling as people as would listen to this for the last 27 + years

Arnoud

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).

blown 87

I bet the gear were worn and the belt was not set to spec, or was set with something other than a 9201, IE the light kept coming on and it just kept getting set tighter to keep the light off.
The cam gears do not wear all over the same, they become eccentric, and that will just beat the living hell out of everything as the engine rotates.


Sorry this happened.

heinrich

If you need, I have valves and GTS cams.

olmann

Damn Richard, sorry to hear that.

Imo000

Let's not start speculating without any proof.

hacker-pschorr

You must be new here

NoVector

At least the car's at Sean's and not a dealer or Lone Star Auto Repair. Marks on the pistons... oh boy. Keeping fingers crossed.

ALKada

Cars' in good hands. Sorry to hear that after you made that long drive down.

blown 87

More of a warning to folks that think cam gears do not wear.
But we know with out a doubt that something was not right or it would not have broken.

SeanR

I think it was last year that Richard brought the car down and we checked the tension. It was loose so set it and it was good for almost a year.

When we were doing the tear down what I found amazing was the drivers cam gear was still riding on top of the exhaust cam and in proper rotation with every thing else. Was able to rotate the crank (belt all intact) and both cam gears lined up to TDC with the crank. Took a pry bar and nudged the cam gear on the broken cam and it all came apart.

The first thing I checked when the cam gear cover was off was how tight the torque was on the gear retaining bolt, the gear wobbled when we turned the engine over. The torque was w/in spec. Belt was very loose though and it is my thought that the extra belt slap caused extra stress on the cam. It's possible that the gear bolt had too much torque on it in the past, but these were the original cam gears. The car only has 60k miles. Both cam gears have wear but not to the point it would cause a loose belt like has been going on. Have not torn it all down yet (will be a couple weeks, too swamped to get in to this one just yet) but if I were to guess, bushings on the arm. The oil pump gear appears to be just fine. Oh, and the belt is a Conti, so that should tell you something.

As for going forward, we have several options. RKD has been wanting to go with Colins cams or GT cams, pop in some S4 exhaust cams with GTS intake, or just going the fastest way and put in a nice, used GTS cam. Of course the heads are coming off once the engine is pulled and will keep a record of how things progress. We've got a set of GT cams at a nice price and will most likely go that route but there is a couple weeks to think about it.

So, as always, if your belt warning goes off, and if a single retention check doesn't fix it long term, get it tore down and find out what the issue is. What might take a few hundred to take care of then can save you $10k later. The saving grace on this one, Richard is just forced to get that extra power out of his lump a bit sooner than he planned on.


Some pictures





All four cylinders in the drivers side look like this, so there are at least 8 valves that hit.





Ignore the time stamps, I've not set the clock on my boroscope.

OBehave

Sorry to see this happen to my GTS' 5spd brother. We're pulling for good outcome!
Ed

jcorenman

Aww, crap! Richard, I'm really sorry to hear this, the good news is that the car is in the right hands!

namasgt

How old was the T-belt job? Miles and year?