I picked up a spare tach-drive distributor on eBay and am planning on sending it to LARS for setup. In looking at it, it appears the cam is worn and I am sure it is not the correct advance plate for my engine. I looked at Corvette Central and LICS for replacements and they do not show any.

Does anyone know where I might find a replacement cam/plate if it turns out I need one? I understand there were around 30 different types based on engine & drive train combinations.
Thanks, Roy

 

Paragon has them - called "cam and plate" on their website; not shown in their catalog. Have no idea which one it is, but it doesn't matter - just have your distributor set up in a Sun machine with the curve you want.

 

I'm gonna just throw this out there and wait for the flack...

When the main shaft is replaced it is extremely important to use a shaft that has the same cam brazed onto the end. GM used (38) different main shaft cams in tach drive distributors from 1962 to 1972.This cam is fundamental to the centrifugal advance curve because it determines the shape of the curve as well as controlling other functional characteristics (see article “All TI Distributors Are Not Equivalent” THE CORVETTE RESTORER Vol. Twenty-One, Number One, Summer 1994). If an identical main shaft cannot be found, the original cam should be removed and brazed onto a good shaft. One should be careful to orient the cam in the same angular position (with respect to the roll pin hole) as it was on the original main shaft. Caution: It is possible that substituting a main shaft with a different cam will have a detrimental effect on the performance of the vehicle.

http://www.tispecialty.com/articles/article6.htm

 

Roy, Good luck and would you tell me more about LARS as I need to get my d/p '62 done. John Z got me streight on the parts, but I have no access to a Sun Machine.
Tom454, Can't speak for others but, I for one am always appreciative of data concerning our favorite cars. Without others' knowledge, most of us would not get past first base.


Earl

 

The cam 67-427ci is requesting is the points cam (8 lobe cam that the points ride on to open/close). The cam that is ref. in the above quote is the cent. advance cam that is brazed to the top of the main shaft (2 different cams).

However, the cam 67-427ci was requesting was probably used on several different engines (according to the Chevy Parts Manual), and may or may not be the same as what Paragon has to offer. From what I can determine, the main difference in the various cams is the length of the cent. advance slot. Since most of our engines need to have the cent. advance recurved for today's fuels, it does not matter a whole bunch.

Plasticman

 

I didn't read it that way..... I interpreted it differently... that their comments were for all tach drive distributors in general... not specific to the TI unit. But you may be right... flack accepted.

 

Tom,

Not saying it has anything to do with TI or non TI (although TI dist. would not have the 8 lobed cam).

The ref. quote is for a different cam! And it applies to all point operated Delco distributors (Tach drive or not). That cam that is brazed on top of the main shaft operated the cent. advance wgts., and will vary greatly from one dist. design to another (and must be indexed correctly when replaced).

The cam 67-437ci is asking about is the point cam. This is the 8 lobed cam that the points ride on to open and close the points.

Plasticman

 

"Does anyone know where I might find a replacement cam/plate if it turns out I need one? I understand there were around 30 different types based on engine & drive train combinations."

I guess... I dunno...

The lobes wear on the points cam, and the profile wears on the advance fingers.

Who's on first?

Edit:
Go to the web site above...

They name two parts... main shaft cam (controls the advance curve)
weight base/cam (contains the cam that runs the points).

Pick one?

 

Thanks John, I gave Paragon a call and the cam & plate is on back order for at least a week. I'll send the distributor to LARS for his evaluation of its condition.
Roy

 

Roy
i believe Willcox may have it in stock, and their price is a few $$ less than Paragon.
Bill

 

You can use the cam plate out of any GM distributor with clockwise rotation. There are a lot of different configurations on these plates, since they have a lot of different advance slot hole sizes to tailor the advance curve. But this does not matter if you're having the distributor custom curved. When I run and set them up on the SUN machine, I always end up altering the length of the slot to fix the curve length, so it really doesn't matter which plate you start out with. Most of the plates have a slot that's too long, producing a very long advance curve. I like to see a centrifugal curve about 20 degrees long for most mild performance applications. This allows setting the initial timing at 16 degrees while maintaining 36 total.

Likewise with the cam on the mainshaft referred to above: Yes, the shape of this cam alters the curve shape, but you can work with any cam shape when you're setting up a distributor by playing with weight size and shape. I have found for most performance applications that the exact shape of the curve is not as important as making the curve come in smoothly and as consistent as possible. With a fast advance curve, a performance engine does not spend much time in the middle of the advance curve - you transition throught the curve very fast. The important aspects become setting it up to produce a repeatable and steady initial timing, a smooth and steady rise to full centrifugal advance, and making that full advance come in at about 2500-2800 rpm with about an 18 to 22 degree long curve, depending on application (shorter curve for bigger cams and vice versa).

It's not often that I see a distributor with the actual points cam worn: The hardened steel cam is much harder than the points rubbing block, so the cam generally will not wear. But if there is damage or wear to the cam, it must be replaced, since any damage or wear will produce inconsistent dwell and timing from one cylinder to the next.