In a message dated 3/22/2008 4:21:34 P.M. Pacific Daylight Time,
tr3driver@ca.rr.com writes:
differ from a 3/8" bolts shank? Is drill rod fractionally
> larger or is a bolt shank thinner?
Yes, exactly. If you take a micrometer to a 3/8" bolt, you will find that
the shank is always somewhat smaller than .375". It actually varies from
bolt to bolt, but .368" is probably typical. Frequently they are even
several thousandths out of round. There are various reasons for this, but
basically it doesn't hurt anything (in 99.9% of all applications), and makes
the bolts much easier to manufacture (meaning cheaper) as well as to
install. But, being .007" undersize means the gearbox can be out of line by
as much as .014" (plus whatever other tolerances stack up), which is
definitely enough to be a problem.
However, the drill rod is ground to a precise diameter. The rod I used is
specified as being between .3745" and .3755". This isn't quite as good as
an actual alignment dowel (3/8" nominal is .3751" - .3753"), but I believe
it's "good enough".
I actually tried to start with a long alignment dowel, but they are
delivered already hardened and my tooling just wasn't up to cutting threads
in a RC40 surface. The drill rod comes annealed, so is much easier to cut
(and IMO strong/hard enough to use as-is, without further hardening).
And since that Stag had already broken it's equivalent of the rear plate
(it's an alloy casting on a Stag) without the dowel bolts, I feel that
Triumph/BL had a good reason for switching from a standard alignment dowel
to a custom (and expensive) "dowel bolt". Perhaps it's less critical on a
TR6 with a steel rear plate, I don't know. But I've also had the
bellhousing flange break (on a TR3A) and I know the factory took a lot of
other steps to strengthen this area, so ...
Randall
_______________________________________________
Randall,
I was just a little bit involved with this issue with Herman when he
developed his conversion kit.
He spent a lot of time and money to make sure those dowel pin holes are
located accurately relative to the center of the crankshaft. The attachment
holes
for the bellhousing to the engine block are large diameter and relatively
loose tolerance holes. I say "relative" compared to the dowelpin holes. His
design, like the factory design depends on the tight fitting dowel pin holes
to
properly align the transmission. A likely problem will be clutch failures if
it is not accurately aligned.
Mike Moore
**************Create a Home Theater Like the Pros. Watch the video on AOL
Home.
(http://home.aol.com/diy/home-improvement-eric-stromer?video=15?ncid=aolhom00030000000001)
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