[s-cars] sheared crankshaft-gear key

Thu Jan 22 09:36:38 PST 2009

 Again Scott, I think you know I respect your opinion. For those thinking this is an argument, I beg to differ... this is good natured debate.

I suppose if I were operating a shop and repairing other people's cars all the time, I would do the same thing. After all, it is cheap insurance that your customer is paying for.

Perhaps I will change my mind if I have one fail. However, as stated before, I've got 26 years of experience with the exact same setups, and haven't had a failure yet.

I guess I'll choose to think of it like this:
Insurance... the concept of paying a small amount of money on regular intervals to eventually cover for the big event *if* it ever happens. You have selected to have yourself or your customer pay $100 at each event to prevent the "large" failure.

I have chosen to not pay on my policy, and deal with the big failure "out of pocket" *if* it ever happens. If I were to count the number of times I've either done a timing belt or removed the gear to swap a cam etc... I would conservatively estimate it at 100 occurrences during 26 years. 100 x $100 = $10,000.? Even *if* this failure ever bites me, I'm still a solid $8000 ahead of the game.

Component failure is all about statistics, that's what I do for a living. I don't disagree that the failure *can* happen, I disagree with the rationale of replacing those parts at each maintenance interval, because the frequency of failure doesn't justify it... if the job is done properly, and the parts are carefully inspected prior to re-installation. I *have* replaced each of those gears on some occasion... but they looked like Dave F's picture, and the disaster never happened because the clamping force kept the gear stationary.

If I had a preventive maintenance engineering client with a fleet of Audis (that'll never happen!) I would not advise them to include replacement at each interval as a part of their PM program.? The cost is higher than the benefit.

Again, this is something that each person has to evaluate for themselves.? My engine is currently torn down... I'll be happy to tell you when I have my first failure.

Dave

-----Original Message-----
From: qshipq at aol.com
To: forgied at shaw.ca; s-car-list at audifans.com; Djdawson2 at aol.com
Sent: Thu, 22 Jan 2009 8:22 am
Subject: Re:   sheared crankshaft-gear key

 Dave, Dave et. al.

DF, your photo is the way I see most of them....? Best case scenario.? And that crank bolt *is* definitely a "torque to yield bolt", which by definition means it's a one time use, and if you are luck will take a couple proper torques before failure.? Here's one that didn't take the 3rd torque to spec - about 50lb/ft short to be exact.? 

http://pictureposter.audiworld.com/37342/scrankbolt.jpg

BTW, I own all the proper Audi tools to do timing belt procedures on 10 and 20v I5's - and I'm absolutely most anal about Timing Belt R&R, it's the most expensive fix to the I5 - really any audi motor.? I won't take the risk on this R&R, it's not worth it. ? The Ingersol Rand air tool isn't a valid argument IMO, assuming you lock the crank, it doesn't add failure to the crank-pulley key, in fact, I'd argue it lessens shear-risk on removal.? I've found failed keys on second round timing belts that *I* did the first round!? My own experience leads me to the opinion/conclusion that it's the reuse of the stretch/hardened crank pulley bolt that causes the key to be stressed.? Read (IMO/E): The key will live a longer life if you replace the crank-pulley bolt every timing belt change.? I also encourage everyone reusing the crankgear to remove it from the pulley and inspect it carefully.? Some of those hairline cracks are hard to see.

I also support my experience and opinion by claiming this is exactly the reason Audi went to the Timing Belt procedure ala the v6 - leaving the crank gear and bolt in situ - remove serpentine pulley from the crank-gear only.

DD, I've lost count of the I5 timing belt jobs I've done over the last 15years.? I've seen key and bolt failure many many times - the key once on my watch was all I needed to believe.? I've also had to figure out how to lock the crank when the key sheared trying to remove the bolt.? You can disagree with my opinion, doesn't bother me.? You see your very first failure, you won't ever take the risk again, btdt.? Bolt and gear is 100 retail, much cheaper than pistons and valves out of time.? Mr. Librarian is welcome to put this in his reference material.? 

My .02

Scott J

-----Original Message-----

From: David Forgie <forgied at shaw.ca>

To: s-car-list <s-car-list at audifans.com>

Sent: Thu, 22 Jan 2009 12:11 am

Subject: [s-cars]  sheared crankshaft pulley

I case you want to know what a sheared crankshaft pulley (key) looks like, go to 

this post:

http://forums.audiworld.com/s4s6/msgs/252125.phtml

I agree with Scott.  Replace with each timing belt job.

But would add the obvious, avoid impact wrenches and tighten with a proper 

torque wrench (and/or extension as per Bentley).

Dave F, 

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