Hi,
I got a couple of queries recently about the differences between TR6
crankshafts (early vs. late), so I thought I'd post to the list.
As you may know, TR250's and early TR6's used a different crank than the
later cars. I have no idea when the changeover took place, but it was most
certainly before the 1970 model year.
The primary difference between the two cranks is the length of the "tail",
which is to say that section on which the rear seal rides and to which the
flywheel attaches. On the early crank, the "tail" is longer. Because of
this longer tail, the early cars use a different flywheel than the later
cars. This difference in the flywheels should be noted if you intend to
hop up your early TR6 motor, because there are few options for the early
style setup (although you can cut-down an early flywheel to save weight or
you might be able to buy a special "ally" flywheel from one of the
suppliers in the UK.
At any rate, just how much difference is there? Or, put another way, how
can you easily tell the difference between an eary and late crank.
The early crank "tail" measures in at 1.750" when measured from the
flywheel interface to the thrust flange face (actually, it's the back side
of the thrust face). The late crank measures in at about 1.125".
There are probably other differences, but the flywheel interface and tail
length are the big difference.
Speaking of flywheels, how do you tell which is which. If you lay the
flywheel on a surface with the friction surface facing down, the early
flywheel ring gear will be flush with the surface. Conversely, the late
flywheel will wind up with the ring gear off the surface (not suprisingly)
about 5/8". That's pretty much it.
Which crank is better? If you have a choice, go with the late
crank/flywheel for several reasons. One - you pretty much cannot buy an
early crank and the flywheels (as mentioned) come from precious few
sources. The oiling is better with the late crank (which is cross-drilled)
(although it's pretty hard to tell from a visual inspection that there's
any difference at all). The big plus is that all the "new" options
available are all the late style, so your decision is pretty much made for
you. By "new" options, I mean NOS, brand-new or billet. Believe it or not,
there are brand-new NOS cranks still out there, although they do seem to
be getting harder to find.
regards,
rml
TR6's
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