Dead motor, but why? Need investigators

[2mAn]

A few weeks ago, I was my usual self driving my M20 like a getaway car when suddenly it died on the freeway and wouldnt start again. After towing it back to my house and cursing the car as I walked away for the night, I eventually discovered a busted timing belt. This timing belt was only a few months old, so I was incredibly shocked and gutted... I couldnt understand what happened.



The car is now fixed and rocking a full SuperETA longblock with the 'I' cam and dual valve springs swapped over and its running on the same 173 chipped ECU and intake goodies that powered the previous M20B25. I definitely feel the torque difference and am overall happy with the outcome, but still bewildered as to why this happened. So here I am, asking the R3V detectives to help me figure out what happened. Obviously most of the evidence has been trashed but I have a few "scenes of the crime" and some firsthand witness account of the tragedy.



First, lets look at the belt, or what was left of it anyways:



Shreds of the belt that were removed from the timing cover and general area...





and yes, I couldnt resist doing this with the shreds....because R3V







This was an interesting image. Looks like the belt had been rubbing and collecting rubber "dust" inside the pulley.






Heres the money shot. Outer part of the belt half shredded all the way through into the cogged belt area. Also note the inner timing cover and the rubber groove that had been rubbing on it.







and now onto the 885 head carnage....



Hard to see here, but we have several broken rockers, a few areas of the rocker shaft mounts are also broken. a dead 885 head for sure... RIP







I have a few theories in mind, but Im curious what you all think.

[kronus]

guess 1 - bent cam nose caused the cam pulley to waggle the belt off
guess 2 - belt tensioner lock bolt wasn't locked, tensioner was held by the spring only

sorry to hear about the carnage

[LateFan]

Is this the blue car? Bummer.

Belt was definitely off center on the wheels for whatever reason. Something was canted to walk it off like that. Was there any noise?

[2mAn]

Originally Posted by kronus

guess 1 - bent cam nose caused the cam pulley to waggle the belt off
guess 2 - belt tensioner lock bolt wasn't locked, tensioner was held by the spring only

sorry to hear about the carnage

Originally Posted by LateFan

Is this the blue car? Bummer.

Belt was definitely off center on the wheels for whatever reason. Something was canted to walk it off like that. Was there any noise?

Yup, a very Happy Holidays for me! ....

Tensioner was good & tight, that was my initial thought too

Basically, trying to figure out what could cause the belt to slide over and rub on the inside. No recognizable noises prior to this happening.

yes, this was on my Cirrusly Blue daily driver. The Roadster was serving as a daily for a few weeks... a fun experience doing open top freeway driving in the SoCal winter mornings haha

It also fully derailed the 2.8L M20 build so Im hoping this SuperETA motor is up to the task, as I will show it no mercy

[LateFan]

It's jealous of the roadster and threw a snit.

Could the tensioner have been tight but not seated flat??

[uturn]

Just bad luck....
Could it be that old style stamped idler puller? Pull it and see if it's fatigued and cracked.

[jgilber0]

That SUCKS. Sorry!

Might be a good idea to look inside the cover with a boroscope from time to time. Justification to buy a new toy?

I wonder what the typical failure mode is on these belts - shred or snap?

Jon

[2mAn]

Originally Posted by uturn

Just bad luck....
Could it be that old style stamped idler puller? Pull it and see if it's fatigued and cracked.

Anyone have more info about this pulley? I recall hearing about its issues, but not sure what trouble it causes...

also, fun fact: I heard a belt squeal today when I started the car and nearly had a heart attack #PTSD

[MrBurgundy]

looks like the idler froze up and ate the back of the belt

the culprit it the thingy muhhh bobbber the back side of the belt touches

[zaq123]

clean up all your pulleys, tension spring, spring guide and tensioner pulley and post their pics. My guess is something to do with the belt tensioner issues. Stamped sprockets do fail but it would be very obvious

[2mAn]

I will be back to where the block is probably next weekend and will clean it up, take pics and start to strip it. The 2.8L build has to start somewhere

[TobyB]

looks like the idler froze up and ate the back of the belt

Yeah, or the bearing inside it came apart, with the same results. Including new angle...

My money's on a failed idler, too

Because quality control is NOT job one for replacement parts these days.

t

[2mAn]

What is a sign that the idler is frozen/ dead?

[MrBurgundy]

Originally Posted by 2mAn

What is a sign that the idler is frozen/ dead?

the bearing is probably seized based on the pics.

If you hold the pulley in your hand and pinch race of the bearing with your fingers and try to spin the pulley and it wont turn, or is super hard to spin

[zaq123]

Originally Posted by 2mAn

What is a sign that the idler is frozen/ dead?

can you spin it with your hand? idler pulley is a part of the belt tensioner on these, it is actually a tensioner pulley.
Your belt is shredded only on 1/2 of its width. How does the pulley look? If its bearing failed and it was cocked to the side when frozen, that would explain why only 1/2 of the belt with was worn. Again, no need to guess here: clean all parts and they will speak for themselves. Tensiner pulley would have one extremely polished spot on it if it was frozen