G'day Tom, all
I thought the cause was also related to a sudden change of revs.
eg missing a gear (something I never have done in the heat of a race (er
maybe) or picking 2nd instead of 4th which is not so difficult in racing if
you are used to a wider gate and have developed lazy habits in positioning
your hand.
What is your thought Tom, maybe he wasnt just sitting there at the light
but dropping the clutch at 6000 revs. I have heard of the problem happing
in this small place with non race as well as race engines.
In the context of an engine rebuild the mod is probably $60 - very cheap
insurance compared with engine damage.
If it is any sort of competition engine I would recommend it too.
Regards,
Howard
Aussie
-----Original Message-----
From: Thomas Walter [SMTP:walter@omni.sps.mot.com]
Sent: Wednesday, 9 February 2000 3:35
To: datsun-roadsters@autox.team.net; gboone@sisna.com
Subject: Re: U20 Jackshaft Mod
On the Jackshaft modification:
By installing a stud into the jackshaft, you can provide
some extra support to the front "nose" of the jackshaft.
The double timing chain gears on the front of the jackshaft
will induce bending moments. This load, when extreme due to
high rpm, will induce a crack around the portion of the
jackshaft nose where it goes from a smaller diameter to a
larger one (the front bearing support).
By installing a stud, which will reach further into the
jackshaft, it will keep that front portion of the nose
under more compression, lessening the chance for a crack
to start at the portion.
Usually the only time I have heard of the Jackshaft
modification being needed is on high rpm engines. Ones
that are usually taken to 8,000 rpms. So I didn't recommend
such a fix for street engines. One roadster snapped the
jackshaft while waiting at a stop light! Really odd time
for it to fail!
So it is a worthwhile modification, after all! Still the
failures are fairly rare events, not one I loose sleep over.
Sincerely,
Tom Walter '67 2000
Austin, TX '68 2000
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