Your views please, did I kill my car or was it suicide?

Earlier today I was happily driving around and upon finding a nice quite stretch of road I decided to try and practice some fast launches (I’m in practice for a 1mile sprint start – don’t ask)

I managed two good starts, both around 1900rpm, lift the clutch, floor the accelerator – nominal spin was arrested by the Quaife, I was very pleased. At the third attempt I lifted the clutch, and heard an almighty noise from under the bonnet, I instantly switched off.

After opening the bonnet, I saw the remains of the crank ancillary drive wheel along with the anti vibration wheel happily sat next to the fuel pump! With the ancillary drive belt resting on the lower engine cover. At first I assumed the worst, after calling out the VW OnCall service a friendly VW mechanic came and had a look at what I had done. He found that I had sheared all four bolts that hold the anti vibration wheel to the crank pulley wheel, the noise would have been generated by an out of control anti vibration wheel bouncing around the engine bay.

The car was taken to my faithful VW dealer, who happened to have a spare anti vibration wheel in stock (it’s a first for them to have the correct part in stock ) it was changed, along with a new belt and guide wheel. The crank pulley wheel was removed and checked for damage and finally replaced with a new belt.

Thankfully not a great problem, the anti vibration wheel and belt did not cause any damage – apart from the odd paint scuff.

While I know what triggered the failure, I’m on two minds as to the real cause behind the failure. On the one hand the car is a 90hp engine tweaked to 150hp which I am fully aware will induce more than normal stresses. On the other hand the car has done over 180,00 miles..

Your opinions ladies and gentlemen, was it fair wear & tear, or am I guilty of abuse.

Sorry to hear about that sooty. Didnt you have the crank pully and main large central nut/bolt replaced at one point. To replace that you need to remove the 4 bolts that came loose or broke. Seems to me like those bolts may not of been put back to the right torque or something. Powerout put doesnt effect those 4 bolts anyway. They just drive the water pump, alternaler and powerstearing on the A3 i believe.

Plain and simple, too much TDI abuse.

Court fines you 50 pence and sentences you to repeat this abuse once more at the 360,000km mark to make sure this was not a fluke! lol

Sheared all four bolts?

Sounds like the vibration damper was loose.

Des, the dealer did it by the book, the crank wheel bolt was replaced when I managed to warp the crank wheel pulley, but the original ancillary wheel bolts went back on. With hindsight it seems silly not to have replaced them but they are meant to be reusable.

All four bolts had sheared, it’s not as if one or two had worked loose then fallen out causing extra stress on he remaining bolts! When they started to strip it down I wondered if one of the ancillaries had seized or locked up somehow, but all are fine and rotate freely.

I think I’ll start to have extra checks made when it goes in for it’s next service, re-torque all crank related bolts may be on my list, it is concerning me a little as it’s the second time now, it may have been a coincidence but…..with be planning on adding propane soon I want to know for sure.

I have the bolts and will be dropping them off to a friend of mine who’s a metallurgist, hopefully he should be able to help with a conclusion.

Skypup if it’s all the same I’ll try not to repeat it, at least the bolts breaking up that is

Hello Sooty! I saw the results of a situation much worse than yours at a VW specialty shop mnot long ago. We (my wife and I) went to pick up our car after work (we hadn't met the mechanics) we asked to pick up the green Passat diesel, a grim expression came over the face of the guy behind the counter. He called out the name of the mechanic the did the work on our car and the mechanic told us the engine was shot! He walked us over to a big box of shreaded parts and told us that the rubber in the damper had deteriorated over time and started to vibrate, which in turn...da dat da daa,you know the rest! This was not our car though! After a big laugh and a sigh of relief from my wife we talked for a second. When the mechanic saw two people come in to pick up a green diesel Passat, he thought we were the ones he had to break the bad news to. He went on to tell us that more and more now they are seeing this vibration damper failure in veicles over five years old and we need to keep an eye on the crank pulley from time to time and at the leist bit of wobble the rubber must be repleced! The pully assembly is a three piece unit and they can replace just the rubber for about $120, Canadian. A far cry from $600, the dealer wants for the whole unit! Just thought I'd pass that along.

Hmmm ... we'll file that in the memory bank along with all the other things to check when fiddling around with the timing belt.

If you use the high power output on a regular basis then it could have something to do with it, because power delivery to the crankshaft doesn't happen continuously but rather one cylinder pulse at a time, and if the engine is running high boost (= higher cylinder pressure) and high power output, the crankshaft speed is bound to be more uneven.

At least it didn't smoke the timing belt.

Brian P.
'96 Passat TDI mit UPsolute

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Sooty:
1900rpm, lift the clutch, floor the accelerator – nominal spin was arrested by the Quaife, I was very pleased. At the third attempt I lifted the clutch, and heard an almighty noise from under the bonnet<HR></BLOCKQUOTE>

So at the instant that you lifted the clutch, the thing failed.

It seems to me that what will put the max strain on a part like this is a sudden change in RPM.

I guess that when you lifted the clutch the engine would very suddenly get sort of stalled as it instantly decelerates from 1900rpm down to some lower figure.

All of the ancillary components and the pulley will then also have to decelerate too, and this requires some force.

It sounds as though this force was greater than that which the bolts could take.

The deceleration must be greater due to the quaif too. My car would not be capable of slowing the wheels / trans / motor that much as it would simply break one tyre off of the tarmac instead.

I would have thought that if they were already loose that the thing would have made a horrid noise for a little while before it actually failed. So it sounds as though the bolts just snapped. Though they could have been weakened from being reused maybe and from previous hard use.

I've always thought that hard acceleration in gear, foot to the floor, is nothing compared with the forces on the trans / drivetrain / motor when the clutch is dumped for a quick start.

Personally I try (but sometimes forget) to get the car moving with the clutch out and then floor it. It's obviously a lot slower but easier on the car. With the Superchip I'll still get wheelspin even doing this,m but at least no sudden change in rpm.

If your trying to drag race though, then that's simply not going to work I know.



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SuperChipped 96 Passat TDI wagon
See my Peugeot / Passat site

Your injector pump is driven by the timing belt, so I can't understand why 150hp would put any more strain on the accessory drive shaft and related hardware than 90hp. All it does is drive the water pump and oil pump. Extremely high rpms would obviously put more strain on those parts, but TDIs aren't capable of generating "extremely high rpms."

I think the general thrashing caused something to break that was on the verge of breaking anyway.

-mickey

Johnny, last year the anti vibration wheel was changed along with the crank pulley wheel, it had done less than 25,000 miles.

All I can think of is that fatigue over time caused the failure, the bolts may not have liked been disturbed last year when the crank wheel went. Last time the crank wheel bolt was bonded in place, this time the whole lot has been bonded just in case.

Christi, I’ve got into the habit of lifting the clutch quickly but not completely, this lurches the car to about 3-4mph with the revs dropping down to about 1700 then I simultaneously floor it and lift off the clutch. I still get a small amount of spin, but it is reduced greatly. When this happened I was working close to home and had a little spare time between calls, so I changed my front wheels from my normal Goodyear F1’s to my Avon ACB10’s which are a road legal race tyre (they only last 500 miles max but stick like glue) which is why I can keep wheel spin down, so your point about reduced rev shock may hold some water, although I think Mickey may have summed it up with:

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
I think the general thrashing caused something to break that was on the verge of breaking anyway.
<HR></BLOCKQUOTE>