Timing Belt Eating Itself??

[downforce22]

I recently rebuilt this engine with custom ross pistons and an s52 crank to make a 3.0 stroker. I drove the car about 50-75 miles before this incident happened and I am trying to figure out what, how and why it did. Here is a summary of what happened.

I had gone about 10-15 miles and everything was going great. Then all of a sudden as I'm merging to the highway exit I felt as if I had no throttle. I downshifted and I felt the usual engine braking before I tested the throttle again and still, nothing. I couldn't tell what was happening so I moved to the shoulder and coasted to a stop. I initially thought it was a clutch or something but that obviously wasn't it as I could still shift gears. I didn't hear any pop or noises like metal contacting metal. It was then that I realized the car was not running. I tried starting it only to hear a buzz coming from the starter, but no engagement. The engine was not cranking. I popped the hood to see liquid dripping out under the car and some fluid on the top of the valve cover that looked like it had sprayed out from near the firewall. I touched the fluid leaking underneath to see oil and coolant. Long story short I got a tow back home until I could look at it in the daylight.

--After I had some time to look at it I check the oil. It is slightly dirty, but not cottage-cheesy which tells me coolant did not mix with the oil, so HG should be ok. There were no visible leaks or problems. Next up was the timing belt. I found a couple bits of what looked like belt and feared the worst. So I pulled off the timing cover. Here is where it gets weird.

--The belt is still intact and tensioned. It was a new belt and new tensioner installed during the rebuild, but it looks like it has come off track somehow. The right side must be where the belt shavings came from.

--I then checked the valve cover to find no broken rockers. Retaining Pin still in place, too.

--No broken rockers. I would expect atleast one broken rocker at 3000 rpm. I need to pull the fan to check the timing belt did not shred, but why would it strip the belt?

--I believe I found the coolant leak out the back of the head. But how the hell would the belt get off track to begin with? and then what the hell happened when I was driving-about 75 mph,or 3000 rpm?

Keep in mind I have stroker pistons with large valve reliefs. Could that possibly have saved my head? (intake: 0.22 in clearance and exhaust: 0.175 in clearance)

Here are pictures.

[downforce22]

I had a chance to dive in. Check this out.The belt was rubbing on the lower timing cover. Maybe that is why the coolant temp was about 50% on the cool evenings I drove it. I figured it had to do with the stroker kit and higher compression ratio.

Here are some belt strips found in the engine bay.



Next I pulled the bottom cover off and the belt was somehow rubbing on the metal cover. I don't know how it would get off track like that, but it wore a groove in the metalprobably a half cm deep.

You can see the damage to the belt and that silver line is the groove I am talking about.



Here is the belt. It is still intact and tensioned. Keep in mind this was a new belt about 75 miles ago. I will remove the tensioner after I check the timing marks are still lined up to see if something could have pushed it off track. Either way this could be a blessing in disguise; I may have dodged a bullet when the belt would have finally snapped.

[e30trooper]

at least you caught that early.

[E30-325iS]

Looks like you have a pressed metal intermediate shaft gear, might be a good opportunity to replace it with a sintered one.

[nando]

Looks like you have a pressed metal intermediate shaft gear, might be a good opportunity to replace it with a sintered one.

I was going to say the exact same thing. same with the main cam gear.

[downforce22]

Thanks guys, I was not aware of this. Is the int shaft bolt and washer the same?

[jeffnhiscars]

I was going to say the exact same thing. same with the main cam gear.

Ditto

Thanks guys, I was not aware of this. Is the int shaft bolt and washer the same?

The Intermediate & cam gears are different although they use the same seal. I didn't see your cam gear but I just replaced my intermediate and the dealer was $21 when the cheapest online price I found was $35. If you need the cam gear I'd try the dealer for that too.

[downforce22]

Thanks guys, the head was not stock so the cam gear is the correct later model and I am not sure about the int shaft gear.

If you look in my picture above I have a theory as to what happened. The int shaft gear bolt must not have been tight enough and worked its way out after a few miles until it was only held in place by the timing cover. This caused the int shaft gear to rock off center since it was only held in place by the key way. With the gear loose/able to rock it allowed the belt to rub on the lower timing cover and start to shred. Somewhere along the belt was loose enough to skip a few teeth as the timing was off by 10 teeth, which bent some valves and shut off the engine.

I also found the coolant leak in the hose from the heater core to the head. I plan on changing the cast gear just make sure and locktighting the gear bolt in place. I believe the only way to tighten it is to use the engine as resistance only AFTER the belt is on and tensioned (or with a torque gun, which I don't have). Thinking back I don't remember doing that...

As they say, Hind sight is 20/20...

[jeffnhiscars]

It's better to use an old belt held on the gear with a pair of vicegrips jammed against the water pump (or whatever is close). You really do not want to subject a new belt to that especially since its easily avoidable.