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Tach Drive Distributor Mainshaft Question

fine69

Well-known member
Joined
Dec 12, 2004
Messages
975
Location
Maryland / D.C.
Corvette
'69 Convertible Vette; '72 Z28 Camaro Rally Sport
I finally started the restoration of a used tach drive distributor that's been sitting on a shelf for some time now.

With the distributor completely disassembled, I noted that the cam on the top of the mainshaft has an area on each lobe that is worn and shiny. It should probably be replaced, no? I've seen replacement mainshafts included in kits, and Wilcox offers a kit for $70.

I read in an article that there were 38 different mainshaft cams in tach drive distributors from 1962 to 1972. The mainshaft I have now is stamped "208W" - of course this is used, and I'm not sure what it was installed in.

Does anyone know which mainshaft should be used for a 1969 350/350?

Thanks.

Ralph
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
I wouldn't be concerned about the shiny spots on the edge of the cam - that's perfectly normal, and not a sign of wear unless the tails of the weights have actually "indented" the surface - have never seen one like that.

I'd go ahead and use the mainshaft you have, if it isn't scored in the bushing areas and the tach drive gear is in good shape; it doesn't matter much which one you have, as it should be set up with the proper curve and rate in a Sun machine anyway. GM had lots of them, as the parts were picked from bins and assembled without any testing, in many combinations of mainshaft cams, autocams, weights and springs, to fit LOTS of different advance curve maps, "out of the box". There are only two mainshafts available in the aftermarket anyway - GM discontinued them many years ago.

Don't forget to re-shim the drive gear-to-housing gap - .010" works best, and make sure the "dimple" on the drive gear is facing the same direction as the tip of the rotor when you install the roll-pin. :)
 

fine69

Well-known member
Joined
Dec 12, 2004
Messages
975
Location
Maryland / D.C.
Corvette
'69 Convertible Vette; '72 Z28 Camaro Rally Sport
I wouldn't be concerned about the shiny spots on the edge of the cam - that's perfectly normal, and not a sign of wear unless the tails of the weights have actually "indented" the surface - have never seen one like that.

Thank you, John. I will go-ahead with the restoration.

Are you going to be at this Carlisle?
:beer
Ralph
 

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