6066 (1960-1966) GMC Truck Club

Hello Rod,

Will see if I can get a good picture when the weather clears.

Buick distributor is in and running, great mod. It was static timed and fired up as soon as I turned the key. Used to have to choke it fully and pump the gas peddle, but not this time, 1/2 choke and it was running before I got a chance to hit the peddle. When I got the light on it I was only off by a few degrees, static put it at 11 degrees and I run it at 8 to 8.5 degrees.

Mod was easy, but during the study time a important detail showed up I had not read about. This might help someone who finds the mod not working as described in the other writings.

GM's small block (which includes the Buick even fire V6) has a interesting difference as compared to GMC's big block V6.

The GM distributor uses up-thrust to position the star wheel correctly to the pickup. This is controlled by the thrust washer you will find between the top of the drive gear and the bottom of the distributor housing on the Buick factory distributor.

Now the cam for the points in the GMC big block V6 is positioned so the rubbing block of the points rides in the center of the cam by down-thrust, which pushes the distributor drive gear down against the engine block. You will notice that there is a flange on the bottom of the distributor drive gear you should also notice that the bottom of the drive gear is polished like a mirror when you remove the distributor.

Now if you will take the new Buick distributor remove the cap and rotor push up on the gear and while doing this inspect the star wheel and the pickup pole pieces you will see how the distributor manufacturer aligned the star wheel to the pole pieces. Remember what you see, we will come back to this in a minute.

Question is how to convert the Buick distributor from up-thrust to work in a GMC big block down-thrust application? Answer not a big problem it just takes a little fussing around.

By now you should have noticed that the old points distributor has a huge amount of shaft end play.

Things that you should also pay attention to, watch the oil pump drive rod depth in the gear, the Buick shaft may be a little to long and reduce the depth of the drive recess when the gear is correctly installed.

So, now you have the drive gears off the old and new distributors. Throw away the Buick drive gear, thrust washer, and roll pin.

The GMC drive gear should be a nice slip fit onto the Buick distributor.

This needs to be turned into a light drive fit. Take a center punch and raise a few burrs around the shaft where the gear is going to end up (the space between the top of the old gear and the bottom of the new distributor housing will be a little less than 3/16 in.) Start the gear onto the shaft and rotate where you want it in regards to the flattened end of the shaft, then drive it on until there is about a 3/16 in. gap between the top of the gear and the bottom of the housing. Now take it to the engine and install it (Use the hold down clamp). Now don't worry about timing, just get engaged in the cam gear and oil pump drive. Remember the relationship between the star wheel and pickup? Hope so, as this is where we come back to it.

Inspect the star wheel and pickup pole pieces, the star wheel should be standing tall! Now use a 3/8 drive socket to protect the top of the distributor shaft and a small hammer and tap the shaft into the gear until the star wheel is where it belongs in relationship to the pickup pole pieces.

Carefully remove the distributor from the engine (not moving the shaft and gear setting) and drill a hole through the old gear and new Buick shaft and install a new roll pin, use red lock tite on the roll pin.

You have now converted a up-thrust distributor to a down-thrust distributor. When installed and timed the star wheel and pole pieces will line up just like they did in the Buick engine.

Glenn