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Bill Boyle
Horse Feathers (Charter Member)

5056 Posts

Posted - 05 Apr 2018 :  08:02:40 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Bizarre behavior of weights during testing of a Summit Racing 850001 SBC HEI distributor.

My friend with a 77 Corvette was using his stock Delco Remy unit in his car. There were so many problems with that old piece I recommended he purchase a new unit. That's what he did and he delivered it to me for testing and possible mod to the curve.

After removing the cap and rotor the unit was mounted on my Sun Distributor machine and I began to log the base line advance numbers. When I got to 3000 rpm I backed it down to idle and discovered a design flaw in the way the weights are situated on the pins.

What happened? The weights jumped the center plate and got stuck in the advance position (weights were flung out) and the springs could not retract the stuck weights. I had never seen this behavior before so I started over again. The problem continued.

As a result I called the Tech department at Summit and explained what I was seeing to Ken Selleck. The tech had never heard of this happening. I asked him how many customers have a Sun Distributor machine that can test the action of the weights off the car with the rotor off. Few he replied, or words to that effect.

After conversing for 15 minutes, we started talking about the rotor and the ribs in the rotor. It was thought that the ribs just might prohibit this bizarre behavior. After getting off the phone with him I retested the distributor with the cap on so now I could not see the weights. As it turned out the rotor when in place prohibits this action from happening. This was verified by watching the amount of advance going up to 3000 exceeding it and watching the advance decline smoothly as rpm changed. The springs were retracting the weights smoothly.

Why was this bizarre action happening with the rotor off? The pins where the weights are mounted have a shim that the weights rest on. OEM distributor have no shim. So the weights sit almost flush and align evenly with the center plate. When looking at the weights and the center plate, the weights are already above the center plate. As the rpm increases the force kicks the weight over the center plate and it was lodging agains the center plate pins. I do not like this and consider it a design flaw. Testing this Summit Racing HEI for SBC was a new experience and Summit tech, Ken "Tom" Selleck knows about it.

To conclude, the distributor was not returned to Summit. It was installed last night in my friend's Corvette engine and it works great.

Note: Summit Racing Pontiac HEI distributor--I have not seen this problem with them.

"Dedicated to keeping the classic Pontiac engine alive."

400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.


5424 Posts

Posted - 05 Apr 2018 :  10:09:27 AM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I went through 2 summit hei SBC distributors, one the post broke off during the dyno break in and flew through the cap, broke it. Second one, the weights were loose on the posts, and clacked at idle like noisy valves. This was in the last year.
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