Timing chains - tendency to break

[Mike Wattam <MikeWattam@domain.elided>]

Hi Joseph

Standard vs 'German' timing chains, hmmm controversy, controversy.

I had a 'German' timing chain on my Dolomite (tuned TR7 motor) for a long
time, it did over 60,000 miles and still no noise, then I sold the car (I
realised I was driving behind rather a lot of rusty metal) to somebody who
appeared to want to eat the rust.  The motor was always run up to 6,500 rpm
and generally abused, it was as fast/faster than a standard Sprint but
regularly chewed up single-rail gearboxes.

The original standard timing chains on my Stag lasted less than 25,000
miles with some hard use - in retrospect I think I was lucky they did not
let me down and were a tribute to the assembly standards at Triumph at the
time - not.  

The second set were also standard chains and I changed them at 75,000 miles
as I lost my courage.  When I took them out there was barely perceptible
wear with the hydraulic tensioners still well back in their housings - I
still have them all in my garage.  By the way I nearly burst into tears
when I found I had spent money and time unneccesarily. 

The current set I fitted are again standard, and have done a moderate
amount of miles so nothing to report yet, except that  they are still 'as
fitted'.  In case you think I drive my Stag in cotton wool, I still
regularly rev the Stag to 5-6,000 and use it up to 110 mph  or so (in
Germany of course!).

However, despite the above I have never been able to establish the
difference between the standard and 'German' timing chains.  There is no
difference in hardness of the links.  The person who originally introduced
them said they had bushings in the links so were heavier duty and they were
at the time purchased from Renold Chain the well known British manufacturer
of load-carrying chains, but imported by them from their German company.  I
have also heard it said these chains are 'pre-stetched' but have no
evidence to support this either.  Having spoken to Renold on the phone
today, they have no knowledge of the 'German' timing chains any more.

It may well be that regular oil changes allow the chains a longer life as
the tensioners may not score and wear - however they do depend on good
lubrication with good main bearings retaining the oil pressure - as do the
chain links which only receive drip from the tensioners.  Perhaps the
chains and tensioners wear out due to lack of good oil.

However, I have seen Stag engines with broken small screws in the camshaft
sprocket with disastrous consequences.  When I look at these screws, I see
they are marginal in design and in my view could actually be the cause of
all the problems.  I have fitted new high quality screws each time I have
renewed the chains and been very careful not to hammer over the locking
tabs, but to bend them over with pliers.

BTW John Clayton is absolutely correct about accuracy of torque wrenches at
low settings.  A 5lb inaccuracy doesn't matter at 100, but at 7 to 9 lbf ft
it's lethal!

So, my own opinion is;

 - the standard chains have been fine for me when correctly fitted
 - no actual evidence to support the German chains being any better/worse
 - only hearsay available on difference with German chains
 - if there is a problem, this may actually be due to the camshaft screws,
renew them with good quality ones
 - or possibly lack of decent lubrication

So what IS the point in 'German' timing chains when they are more expensive
to buy?

BTW I have broken timing chains once - on a competition Mini with a duplex
chain.  Reason - operating beyond design capacity!

IMHO - Mike Wattam
Chairman - Triumph Stag Register