huh... guess I should have read further into my email list. However, it still
seems strange to me... the cam is in a fixed location (i.e. held in place by the
cam towers), so it is not pulling the chain tight. Seems like at any time you
could pull the chain all the way to the "evil" L, it would be problematic...
what
stops that from happening while the engine is running... oh wait, maybe I
answered my own question... hydraulic pressure on the tensioner from the oil...
which would not be there when the engine is not running. Still, seems weird to
me... but I learn something new every day... Smoke Yunick as a resource
though... hummm. If he became a Yunick, he can't be that bright (or lucky
perhaps?)
Greg Burrows
Gordon Glasgow wrote:
> Not surprising. The forces on a camshaft are not symmetrical. Think of the
> resistance from a single valve and spring. As the cam is opening it, the
> spring is resisting, essentially pushing back against the cam, in effect
> trying to rotate the cam backward. Once the peak of the lobe is passed, the
> force of the valve spring is trying to rotate the camshaft forward.
>
> Now put all eight lobes into place and you can see that the camshaft lives a
> very frustrating life, constantly being subjected to conflicting forces.
> Smokey Yunick claims to have done studies with high-speed strobe lights that
> show that camshafts actually reverse their motion briefly at points in their
> cycle.
>
> So don't worry about that specific phenomenon. The correct way to check
> timing chain slack is to rotate the crank backwards (opposite engine
> rotation) enough to put slack in the manifold side of the chain, then check
> for contact with the L-bracket.
>
> Gordon Glasgow
> Renton, WA
> www.gordon-glasgow.org
>
> > -----Original Message-----
> > From: owner-datsun-roadsters@autox.team.net
> > [mailto:owner-datsun-roadsters@autox.team.net]On Behalf Of Cohen, David
> > M
> > Sent: Wednesday, March 26, 2003 10:56 AM
> > To: datsun-roadsters@autox.team.net
> > Subject: strange timing change discovery on my '68 2000
> >
> >
> > Hi all,
> > I have a very strange problem. When the motor is cold, the top timing
> > chain is tight on all the rotation except when the #1 cam lobe is in the
> > 2 o'clock position. At that point the chain loses enough tension to
> > pull the chain all the way into the L-bracket. Once the cam passes this
> > position there is tension on the chain again. Any ideas what the problem
> > is or is this normal?
> >
> > Regards,
> > David Cohen
> > 510-354-4005
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