[bmw] re: timing chain breakage

[jkerouac <jkerouac@xxxxxxxxxxxxx>]

John,
    Cutting the chain is taboo.  Besides difficult.  Also begs the 
question about metal shavings falling down into the oil.  The method I 
learned and used on many big blocks was to open the master link of the 
old chain, attach the new chain to that link, turn the motor manually 
causing the old chain to rotate out, bringing the new chain in place, 
remove the link from the old chain, reclose the master link on the new 
chain.
    Always a good idea to replace the cam gear at the same time.
The real error could have been improper replacement of the master link, 
or in improperly bleeding the chain tensioner.
Was the tensioning rail also new?  Was it well worn or damaged too?  Cam 
gear securely bolted in?
If the chain was off by a tooth there would have been __noticeable 
running problems.
   Based on experience doing expert witness reports and testimony for 
BMW cases in a past incarnation, I can suggest that hard evidence, such 
as cam gear bolts showing flattened threads, for instance, will make a 
strong case.  Claiming the shop touched it so the failure must be the 
shop's fault but without producing a 'smoking gun' will likely not be 
successful.  If you can get an expert inspection done, look to see if 
there are retaining tabs bent over the heads of the cam gear bolts.  
They could have been omitted on reassembly.  Did the chain open at the 
master link or is the master link intact and a regular link fail?  Take 
pictures pictures and more pictures of every bolt and part removal along 
the way as you have the top end removed and torn down.
The chicken or the egg is important here too.  Was there a valvetrain 
failure leading to the chain failing when piston/valve impact occured?  
Of did the chain fail causing pistons to hit valves where they were left 
sitting?
    Single row or double row chain and gear?  Single row could 
conceivable snap, never heard of a double row chain failing.  Might 
there be impact marks inside the cam gear cover or front cover?
    In any dealing of this type, approaching the shop with honey, not 
vinegar, can go a long way in getting their cooperation.

Guten Lucken,

Barry
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