Crankshaft gear (nearly) falls off!!!

[Paul.Heneghan@bbc.co.uk (Heneghan,Paul)]

My Avant is obviously reading this list and getting ideas on how to make me 
spend my money fixing it.  I am sure someone reported recently that
his crankshaft gear had come loose and destroyed itself - well so has
mine.  It started loosing power a couple of months ago - I found the
timing marks were no longer aligned and readjusted and tightened the
cam belt which was a bit loose.  The car ran really well for a week
or so, but my waterpump made a racket which I duly ignored.  

Then over the last few weeks, the car lost power until, it could only
manage 0-20 in about 20s.  I bought a new waterpump and belt and
stripped it down last night.  When I tried to remove the large bolt
in the middle of the crankshaft gear, it started turning at a torque of 
 about 20lbft - so much for the 300lbft and loctite mentioned in the manual.

Now for the bad news:  the crankshaft gear doesn't use a woodruff key, 
 instead, it has a lug which engages with a cutout in the crankshaft.  
 This lug had broken off and had partially disintigrated - there were a 
 lot of iron filings in there.  I have ordered a new crankshaft gear 
 (UKP25) but I am a bit worried about the crankshaft - one edge of the 
 cutout (slot) is very rough.  I don't think the new gear will provide 
 an interference fit anymore.

What should I do?  Is there any compound I could use to shim the cutout 
 (slot) in the crankshaft?  Can I rely on 300lbft to ensure gear 
 doesn't move relative to crank any more?  I really don't want to put a 
 new crankshaft into this engine (I am intimidated at the prospect of 
 removing the engine, buying a crankshaft, replacing big end bearings 
 etc) as it has only done 138,000 miles.

I think the reason all this happened is that the shop where I had the 
 belt replaced when I bought the car (at 90,000 miles) didn't tighten 
 the crankshaft gear nut to the correct torque - it then worked loose 
 and allowed some movement between the gear and the shaft.  The lug on 
 the gear wasn't designed to cope with this constant mechanical shock 
 and eventually broke off.  The moral of the story is:  do your own 
 maintenance.

Paul
paul.heneghan@bbc.co.uk
1984 Audi 80 quattro
1983 Audi 100 Avant (not feeling very well at the moment)

p.s. how do you arrive at the figure 300lbft from 258lbft and a 12" 
 extension?