Dear FOTers
I've been researching crankshaft problems with 4 and 6 cylinder TR racing
engines.
I'm trying to find out the most reputable 'racing' Triumph crankshaft
manufacturers (and suppliers) on both sides of the pond in the hope of
developing recommendations for the most effective and reliable crankshafts
'by experience'. My research obviously has to centre on a 'use within rev
limits' and 'with the right damper' formula to give accurate guidelines
and to be fair to manufacturers.- I would appreciate your recommendations
on leading Stateside crankshaft people.
Obviously the one single equation that will almost certainly ensure crank
failure (sooner or later) is to over rev the engine above design
recommendations. Whilst on the 'sooner or later' angle, however, I know of
three TR3 full race engines with 'stock' but race prepared cranks that rev
regularly to 6500 and over. One driver ALWAYS uses 7000 RPM and over. He's
raced the same engine once a year at the Manx Classic for the last seven
years (7 races) and other events with no problems (all three engines use
crank dampers). Similarly Hardy Prentice in the States uses 7200 RPM with a
stock nitrided crank.
My initial research over here has uncovered the fact that stock but race
prepared 4 cyl cranks have given some quite incredible racing service. It
must also be born in mind that many of the stock cranks used for racing
have, more often than not, done many thousands of road miles before being
converted to race units. - Rather like preparing an old age pensioner (like
Bill Dentinger) to take part in the London marathon!!
I know of special 4 and 6 cylinder Triumph cranks designed specially for
racing with 'dummy mains,' and hollow pins with a half inch drilling
through each. These cranks are lighter and more overall weight is moved
nearer the centreline of the crank allowing a higher rev limit. They have
been used for about five years with great success over here with
'recommended' rev limits of 7500 for 4 cyls and 7000 for 6 cyls (with
dampers). These cranks are, of course, expensive but they're machined from
solid billets (which takes about a week of man hours) in Nitroy EN 40B
steel (used for F1 cranks).
Best wishes
Paul
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