Getting wet feet....junkyard TBI

[Shannen Durphey]

If you are going back to mechanical timing to diagnose a
problem, you're using the wrong approach.  


The fewer the number of cylinders, the larger the distance
between cam lobes.  The larger the distance between cam
lobes, the greater the potential for change in velocity of
the cam.  In a system with a camshaft driven distributor and
anything other than "zero tolerance" crank/cam drive system,
this will result in rapid changes in the velocity of the
distributor shaft.  For your worn, tired, low rpm, can't
seem to get enough fuel to burn, 360 test mule, the changes
may not be very pronounced.  For something like a 2.5 liter
4 cylinder, the changes are so dramatic that the ignition
has to be set by averaging the pulses from the coil wire.
This is factory procedure, BTW.  The fluctuations in timing
at number 1 cylinder are large enough to make a very
difficult job of getting accurate timing readings.  For the
gentleman who started this thread, a 6 cylinder camshaft has
the potential to create significant changes in the
distributor shaft velocity, which would cause problems with
rotor and timing trigger movement.  It is good advice _not_
to "temporarily" disable your advance mechanisms.  If you
are concerned that you may need a mechanical distributor,
carry a spare.

Shannen

WEG1192 at aol.com wrote:
> 
> In a message dated 5/30/2001 2:17:22 PM Eastern Daylight Time,
> bob at tecmark.com writes:
> 
> << Can you prove that it doesn't on a AMC dist, without a Butt-O-Meter as the
>  test device?    And then prove that it *still* doesn't with a GM HEI, as
>  the original poster is using?    >>
> 
> I can tell you that it doesn't seem to effect my truck and thats all I care
> to say about it. I'm the one running my trucks this way, so I think I've
> proved what I said. If you want to dispute what I claim, then back up your
> comments with some positive proof that the springs alone can't keep the rotor
> gizmo from out running the distributor shaft gizmo during deceleration or any
> other time.
> 
> As a possible compromise, you could drill a hole down thru both gizmos and
> then wire the two together to prevent relative movement. This would allow you
> to reverse the mod and put it back to mechanical advance if you wanted to,
> which I have had the need to do on occasion to verify that the timing was not
> the problem on a troublesome truck of mine. JW
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