<VV> attaching pressure plates to flywheels

[djtcz at comcast.net]

snipped and bottom posted

-------------- Original message -------------- 
In order to address my excessive pressure plate finger compression, it was
suggested that I put washers between the pressure plate and the flywheel.
So I put .10" thick washers under the six legs and reinstalled the assembly.
Now, the fingers move approximately 11/32", nicely within Larry Claypool's
recommended range.  So now my question is, given that the early pressure
plate already has small hexagon-shaped "feet" (washers welded on flywheel
side of the legs), should I use slightly longer bolts to attach the pressure
plate?  The number of turns before the bolts bottomed out was noticeably
less with the washers installed, so it has me wondering if there is enough
thread contact.

Also, does the fact that this suggestion worked indicate that my pressure
plate is defective?  Should I delay reassembly and see if I can try another
pressure plate?

Thanks,

Steve Brennan 


I think you got a later model pressure plate meant for a stepped flywheel.

I would worry that standing a pressure plate up on washers would allow some amount of centering change from inherent and inevitable thread clearance.

A part is balanced while it is spinning around a particular axis.
A 10 lb (4540 gram, 160 ounce) clutch spinning on a "new" axis offset 0.010 inch is now 1.6 ounce-inch or 45 gram-inch out of balance.  If one 164 CID Corvair connecting rod had a big end 5 grams heavier than the others (A reasonable high performance spec, although some shops pride themselves on working to 1 gram or less) the result would be 5X2.94/2=7 gram-inch

A pressure plate (or any component)  needs to be consistently centered on a flywheel just like it was during balancing to maintain its balance.
This means at least 2 dowels or pins must fit snugly thru the pressure plate and the flywheel.  Screw threads are NOT useful centering features. 
Lots of foreign cars used 3 equi-spaced dowels to accomplish that centered location.
The standard for American cars was to use bolts with shoulders 
http://static.summitracing.com/global/images/prod/large/arp-130-2201.jpg
that fit snugly in three of the pressure plate holes, and engaged fairly snug counterbores in the flywheel. 
http://images.hotrod.com/techarticles/p116390_image_large.jpg

Back when I worked in a balance shop it looked to me like Chevy did not provide a reliable means of Corvair clutch centering. That's confirmed on Fig 7.1 in the 1965 chassis shop manual that shows only threaded sections of the clutch bolts engaging the flywheel.  We used to pin Corvair pressure plates to the flywheel with an offset pattern and balance the pressure plate on it's flywheel.


Dan Timberlake