Timing Belt Failure After Only 150mi!! WTF!?!?

Hello All,

Over the winter, my 308 QV motor was painstakenly rebuilt from the ground up and I was looking forward to a spring full of driving enjoyment. The motor was running absolutley fantastic during the first 150mi, and I was accellerating (not excessively) at about 4000rpms. Without any notice or warning I heard a sound fwap fwap fwap fwap comping from the engine compartment. Immediately, I let off the throttle & reached for the key. Just as I was turning off the motor, I heard ting ting ting ting and coasted to a stop. Sorry for the bad sound effects, but although I had never heard these sounds before,, I knew what it was immediately and my heart sank.

I know that many will suggest that the belts were installed incorrectly, my cams may have not been spinning freely, my tensioner had failed, but I can assure you that all the usual suspects do not appear to have caused this disasterous failure. I am positive that the belts were at the propper tension & all was well up to the moment of the failure. What seems so strange is how the belt "broke" it looks like it started unwinding along its direction of travel. Equally as strange is that it appeared to continue to keep correct timing for several seconds after it broke, and the narrow "good strip" of belt couldn't keep up with providing the force to open the valves for long. The belt teeth are stripped off only off the narrow part where the belt was wrapped around the lower pulley when the notor came to rest (while attempting to open cyl 6's exhaust valves).

Has anyone else experienced something like this? I purchased these belts from Ron Tonkin in OR and the tensioners are new & still spin freely. Serial numbers on belt are 05243133-05243136. I have already contacted them and, as expected, they gave me the usual "you must have done something wrong" response. If I did, then fine, but I really don't think so and need to get to the bottom of this before the time and expense is taken to repair all the damage. Has anyone ever seen something like this before? Flaw in manufacturing maybee? Any input would be greatly appreciated.
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It appears as though the belt is still continuous. Did the engine jump timing or did you have a little luck left over and the motor is fine?

As for the belt I would venture to guess a manufacturing failure. Parts normally fail within a very short period of use or they will run their useful life without failure. It appears as though this one was destined to fail and I would doubt that there is any installation issue here. The timing belt install on the 308 is a pretty foolproof procedure and any problems would have shown themselves immediatly after starting. Blame the belt.

 

Wow . . .that bites.

I was analyzing some 308 tensioners a while back and I noticed that the stamped piece was bent on one of 'em which might of made a belt track to one side . .. also on another one the nut had been way overtightened and indented the aluminum piece making the bolt possibly not perpendicular with possible same outcome . .. another one had one of the aluminum legs cracked all the way thru but you couldn't tell when it was installed . .. from the pic's though it doesn't look like the belt was rubbing against the flanges . . . just a thought.

The tensioner with the aluminuum indentation on the back side also would not tension the belt properly because the flange of the locking bolt did not slide smoothly along the aluminum surface . . . it was binding up in the indentation so really no tension . .. possibility?

Was the engine running okay before the service? Just curious if anything else was touched.

Sounds like you stopped it just in time right?

Sean

 

OMG!!

Sometimes the gods just don't like us.

So very sorry.

 

Oh...that is disheartening...the whole frikin thing need to come aparts again

I wonder if something got into the cover to cut the belt? tha't all I can think or a defective belt.

 

Having read the original post more closely (well written BTW) it appears as though the pistons may have contacted the valves. Lets hope it is just bent valves and nothing more.

 

Read your first post in more detail . .. if you're saying the entire motor was tore down who did your heads? Do you know you're valve guide clearance is correct? If someone else did 'em something to be suspect of.

Just a thought.

 

No such luck, it kept time for about 2-3 seconds after it broke, then I heard the "tinging" of the valves hitting the pistons. I couldn't shut the motor off fast enough. If you look at the second photo, all the teeth are gone where the skinny remaining part of the belt is wrapped around the lower driving pulley. I guess it could have been worse. The relative timing between the intake and exhaust cams stayed correct, so the valves didn't hit each other. A quick leakdown test wtih the cams now removed now shows that cylinders 5, 7, & 8 are still holding 97% at 80psi and cylinder 6 is at 10%. Exhaust valves on #6 are bent for sure....other damage, I won't know until I pull the head.

 

The heads were fine and were completley redone from top to bottom by a VERY trusted local machine shop with lots of Ferrai experience. I painstakenly spent three days adjusting valve clearances to be 100% spot-on balls all around. Plus, this motor was rebuilt again this winter due to a manufacturing defect in one of the pistons & all 8 pistons were replaced in this last rebuild. The heads were redone the previous time, and have about 2000mi on them since they have been compltely overhauled. I have studied every inch of the cams, bearings, lobes, and shims under magnification to look for ANY signs of problem and there are none.

 

Sorry to see this, unfortunately it's always one of the possible outcomes.

It looks like it will all have to come apart but at least everything is clean and you will remember where all the bolts are.

 

This is tragic...and my heartfelt sypmathies go to you and your engine. There are 3 possibilities. 1 = manufacturing flaw in the belt. 2 = incorrect installation. 3 = something that compromised the belt's construction, like a mark, scratch, or gouge. Looking at the pictures, I would lean towards something like a cut or gouge, or maybe even a foreign object that found it's way in between the belt and pulley, or belt and timing belt cover. Timing belts are very tough as long as they are without any flaws like nicks, gouges, etc. But once a belt gets gouged or marked, or mishandled in some way (overly twisted or creased) to cause damage...their life is significantly shortened.

An observation, when changing the timing belt on my Audi, the timing belt covers are installed very close to the belts, so close in fact that if the belt were to ride up onto the pully teeth, the extra height would not pass and the covers would try and force the belt back down into the proper mesh with the pully teeth. I don't know what would actually happen if this occured....maybe enough "scuff" would occur to weaken the belt...I don't know. It's just something I observed and may not have any bearing on your problem.

I would definately look at over everything for any signs that something "external" may have been involved. Are there any sharp edges or protrusions on the inside of the timing belt covers? If so, could installing the belt covers have dragged this across the belt anywhere? Could road debris have been kicked up into this area? Could any misplaced or forgetten item (bolt, nut....I've seen this happen!) on top of the motor have made it's way down into this area?

I'm very sorry this happened to you....please post whatever you find....

 

I had the exact same thing happen to mine, but the belts were 5 plus years old. stripped the teeth, etc.. made the same noise... the engine shut off all by its self.

bent every valve, and put smiley faces on all the pistons. I think mine was the result of oil on the belt surface, or engine cleaner... I do feel for you.

If you see my thread "belt broke anyone wanna help" it was about 2 years ago, it may be helpful... I had a ton of belt dust on the covers? so I think it was wearing for quite a while. took about 3 months to get it all back together... ran fine then I sold it!

 

Disheartening indeed....and thanks for the condolances. I thought of this too, but does not seem possible. The hoses that run under the plennum to the bottom of the airbox (for exhaust air injection and oil vapor revoery) were routed in a way to "block" anything that could have tried to get into there. Plus, I was very anal about stuff like that and spent an hour making sure every nut, bolt, and washer was present and accounted for. I even studied the breakage point to look for contact marks or clues of any type.....nothing whatsoever.

 

It looks like the belt was cut or something. Look how the belt is still connected to the pully and the tear is in a straight line just like if you'd cut it with a razor. Maybe far fetched i know but the tear looks pretty straight.

What does it look like where the two sides came apart?

 

The break looks kind of rounded to me, like a washer or something got in there and punched a hole in it. Whatever happened it really sucks.

 

Isn't there supposed to be a flat plastic cover on the backside of the timing belt covers to help keep debris and foreign objects out?

Your post says "308QV", but your profile shows a 308i-2V -- what do you have?

 

Really sorry to hear about that.

It seems to me that there would never be a chance of NO damage. The other bank keeps running so it's going to continue to move the pistons up and down on the bank with the broken timing belt and there's no position for the camshaft when all valves are closed (out of the way) at the same time.

 

Timing belts are indeed different between the 2v and 4v cars. The belt shown in the picture, 111334 (96r254) is a 4v belt. A proper 2v belt would read 107833 (101r254).

Same number of teeth, but different length; they are not interchangeable. Is it possible the incorrect (too tight) belt was installed on a 2v car?

 

He said QV in the OP.

 

I understand that he said he this was a QV motor (and the camcover in the picture is a QV) -- my point is where is the flat plastic cover (and that he should update his Profile -- either 308QV or 1981 308i with QV engine)? With the belt in place (even in pieces) shouldn't the flat cover be captively trapped and appear in the photo?

 

From what I could tell through looking at parts manuals, I think they did away with the rear (backside) covers in the 70's.

This failure was on the 85 308 GTS QV. I also have an 81 308 GTB 2-valver.

 

On the other belt (the one that looks still to be intact) as it rides over the cam pulley, there appears to be a linear witness mark on the surface, just above the last line of printed text "096 R 254 MADE IN". It looks as if something has rubbed against the belt in the direction of its length. I wonder if the other side / belt (the one which failed) has the same mark? Is it possible your belts are rubbing against something (eg, belt covers, debris stuck to the contact surface of the tensioners, etc.) ---- might be worth investigating a bit...???

 

Ahhh... that sounds better.

 

Steve, you're right some people doesn't realize the important of this back plate it is indeed for keeping foreign objects from getting in,

one little tiny pebble can cause a Tbelt to break. Even if you have the backplate on, the bottom drive gear is still expose, so it's possible

something got in there. After all he said the bearing is still spinning freely so it can't be that nor over tighten. The breakage of the belt seems

cut not torn so my theory is probably debris.

 

Thanks for the reminder...done. My profile now reflects both my 81 2V and the 85 QV.

I will look at the breakage point again with fresh eyes this evening, now that has been completley removed, & see if I can lean anything new about what could have caused it. I will also take some close-ups with an SLR camera if I find anything of interest. Maybee something mysterioursly crept in there, got kicked up from the road, or the million other scenarios that can be dreamed up. Some guy at the parts warehouse could have put an engine block on top of the belt for all I know. it appears that until (or even if) I can find more evidence....speculation is the best answer I will be able to get. I appreciate all the good feedback & ideas though....and yep....it sure does suck.

I just double-checked the parts manual for 85, and indeed there is not supposed to be any type of cover for the back side of the timing belts. Now it seems really clear that having one might just be a really good idea. If not for stopping the rare occurance of something getting in there, but also becasue of an earlier mention of things like engine cleaner, water, & grime. This is such a critical component in the system, causing such destruction when it fails.......a HUGE acheilles heel.