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RE: TR6 Distributor: Advance Springs

To: Triumphs Mailing List <triumphs@autox.team.net>
Subject: RE: TR6 Distributor: Advance Springs
From: Randall Young <ryoung@NAVCOMTECH.COM>
Date: Fri, 8 Feb 2002 11:34:40 -0800
> How easy should it be to twist the ends of the distributor shafts (in
> opposite directions) to feel the advance mechanism working?

One direction it should turn fairly easily, for maybe 10-15 degrees.  Then
when you let go, it should return at least most of the way to the stop under
it's own spring pressure.  Sounds like your point cam is bound to the dizzy
shaft.  Disconnect the springs (carefully, don't want to distort or lose
them), remove the screw under the rotor, and the point cam _should_ just
lift off of the dizzy shaft.  If it's rusted on, it may take more force <g>

> However, in my distributor, one of the springs appears to
> be a much lighter spring than the other.  One spring is made of
> heavier wire with a larger coil diameter, and as I look at it right
> now it is coil-bound.  (the coils are touching each other)  The other
> spring is of lighter wire and a smaller coil diameter and the coils
> have plenty of space between them (not coil-bound).  As I look at the
> mechanism, I cannot think of any reason why these springs should not
> be identical to each other.

The reason is that the advance curve is not a straight line, as you would
get with two identical springs.  The heavier spring is actually slightly
loose, so it does not come into play until higher rpm, after the advance
mechanism has moved some amount under the control of the lighter spring.
The result is an advance curve that starts out rising rapidly, then rises
more slowly from roughly mid-curve to maximum.

> What does this all have to do with my cracked rotors?  Maybe nothing.
> But could it be that a problem with the centrifugal advance mechanism
> could create a situation that causes the rotor's orbit to expand
> enough to touch the terminals inside the cap only under certain
> circumstances?

The springs and weights shouldn't have anything to do with this, but if the
point cam were loose on the shaft it could.  Or, perhaps if it were rising
on the shaft.  Which brings up another possibility, how's the distributor
end play ?

Randall

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