the jack shaft breaks from two forces one is sherload form the timing chains
and the other is toque from change in engine speed. The drilling and
installing of the stud solves the sherload problem but not the torque this
causes the jack shaft to break behind the first bearing .. the torque
problem is only for high rpm race motors that have lightened engine parts
and are capable of quick changes in engine speed ... To solve that steel
jack shafts needs to be installed $450.00
Roadster Restoration
3730 Todrob LN.
Placerville CA. 95667
Ph.# 530-644-6777
Fax# 530-644-7252
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-----Original Message-----
From: Thomas Walter <walter@omni.sps.mot.com>
To: datsun-roadsters@autox.team.net <datsun-roadsters@autox.team.net>
Date: Wednesday, February 09, 2000 6:30 AM
Subject: RE: U20 Jackshaft Mod
>> 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.
>
>Howard,
>
>I think you are correct. In reality the jackshaft was ready to break,
>due to high revs, but probably had the last little bit holding it on.
>Damage was already done, and just picked that moment to fail.
>
>A friend was really upset as he had loaned a dirt mulcher (turns up the
>dirt for a flower bed) to a neighbor. The engine self destructed while
>she was using it. He felt "she broke it, she should pay for it". Obvious
>the neighbor didn't want to pay $400 for a broken mulcher. Once I stated
>looking at it, you could find the crank shaft failure started long before
>she borrowed the machine. Stress point, and lots of "beaches" across the
>crankshaft were clear... New engine was $150, and she offered to pay half
>if she could borrow the mulcher every spring. Kept them on good terms,
>rather than "She broke it!" and having them made at each other.
>
>So sometimes when things fail, they failure had started long before
>you realize. Good idea to also have those jackshafts magnafluxed for
>a race engine. If they snap at 8,000 rpm... enough momentum to keep
>those gears and chains moving and doing all sort of damage to softer
>aluminum. For the fellow who had it fail at a stop light... no engine
>damage, as it killed the engine immediately (both distributor AND oil
>pump will stop turning).
>
>Cheers,
>
>Tom Walter
>Austin, TX
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