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RE: Flywheels: them big, round, heavy frisbe

I spent an evening last week examining the flywheels from both an
1983 TQC and an 1987 5000 TQ to see if there are any differences.
>From a quick glance they are indentical. Both heavy, didn't weigh
them, with a stepped edge to the surface where the clutch disk contacts
the flywheel.

The 'stepped' flywheel gives more 'flywheel effect' with less mass Vs just making the entire flywheel thickerer at the same total weight, or more flywheel-effect with lower weight/mass, the real goal.
Gotstah be very carefull when resurfacing these flywheels to grind the 'step' the same amount as the clutch surface to maintin the same relative dimension - grinding only the clutch surface (a surprisingly common mistake) will increase this dimension, reduce the clamping force and results in a rapidly toasted clutch.  :(

On the clutch side, there are 3 locating pins for the pressure
plate and then two longer pins close together on this raised step.
Both flywheels had these pins. Looking over my 1989-91 200
Bentley manual, these 2 pins are shown as being magnetic engine
test pins, or some such description. They aren't used for normal
operation, but for some diagnostic test, which I haven't found a
description for yet. They appear to be in the same location on
each flywheel.

Hmmmmm. Perhaps this is the REAL answer to the two 'mystery pins'!

I don't think the 0 mark location is really the TDC mark on the flywheel
as this places the  ref mark pin roughly 92-94 degrees from this mark.

Then what is the TDC mark, if there is one?

      5000/200 ECU and ignition system, the 5000 ECU is expecting to see
the ref mark pin signal in a different location by one tooth. So this
would imply that my resulting timing would be retarded by 2.6 degrees
at every speed. I am thinking of just changing the timing maps in my
ECU by this amount to compensate for this bias. I know people have
said before that this is well within the range for the knock sensor timing
adjustment( ~7 degrees), but if I want to eek out that last bit of timing
advance I probably need to adjust the ECU map. Suggestions? Thoughts?

Might be easier to simply drill a new hole and move the pin to the 'correct' location. 
Guess it depends on if you are 'fix it in HW' or SW guy.    :)

More than anyone ever wanted to know about turbo flywheels....

Dave Lawson  dlawson@ball.com

Not hardly, thanks!