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Points Cam & Stop Plate Surprise

turbine68rt

Turbine Bronze Member
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So I was at the yard today for a replacement radio for the wife's Jeep and took a look through the old section where there was a 62 Belvedere 4 door I saw a few times before. Still had the original poly 318, no mods. I took out the original points distributor to compare the cam measurements with mine. This one was .994" point to point. Mine is .990". I wondered why I had to have only .012" gap to get 30° dwell. The weird part was the stop plate that had a #8 stamping, for 16° mechanical advance, which would allow 18-20° initial with no modifications. I wasn't even aware that these plates came like this originally. Mine has a 15 stamping for 30° mechanical, but I use an FBO plate in order to get 18° mechanical. The $2 the yard charged me was nice too.
20210905_163615.jpg
 
I'll be curious to see what people say it is from. If aftermarket or original.
 
So I was at the yard today for a replacement radio for the wife's Jeep and took a look through the old section where there was a 62 Belvedere 4 door I saw a few times before. Still had the original poly 318, no mods. I took out the original points distributor to compare the cam measurements with mine. This one was .994" point to point. Mine is .990". I wondered why I had to have only .012" gap to get 30° dwell. The weird part was the stop plate that had a #8 stamping, for 16° mechanical advance, which would allow 18-20° initial with no modifications. I wasn't even aware that these plates came like this originally. Mine has a 15 stamping for 30° mechanical, but I use an FBO plate in order to get 18° mechanical. The $2 the yard charged me was nice too.
View attachment 1163484

OUTSTANDING FIND AT $2.00. Its very likely that the distributor is an early model Prestolite (maybe not).....but is it a dual point distributor? Remember that a 318 Poly engine's distributor rotates in the opposite direction from that in an R/RB engine. The early engines could tolerate more innitial advance to achieve a shorter mechanical advance (smaller length slots) and different springs to get the same overall total advance. The breaker plate for an "A" engine looks like it will fit an B/RB Prestolite Distributor (it will physically fit, but the points will not be in the same orientation and take different points...opposite hand). I believe you've mentioned you have a Prestolite dual point distributor in your Dodge. The rotor may interchange as well as the cap and condenser. The 0.004 difference is not significant and the effect could be adjusted out, but the key slot on the cam plate may be in a different angular position. Just points to ponder....
BOB RENTON
 
OUTSTANDING FIND AT $2.00. Its very likely that the distributor is an early model Prestolite (maybe not).....but is it a dual point distributor? Remember that a 318 Poly engine's distributor rotates in the opposite direction from that in an R/RB engine. The early engines could tolerate more innitial advance to achieve a shorter mechanical advance (smaller length slots) and different springs to get the same overall total advance. The breaker plate for an "A" engine looks like it will fit an B/RB Prestolite Distributor (it will physically fit, but the points will not be in the same orientation and take different points...opposite hand). I believe you've mentioned you have a Prestolite dual point distributor in your Dodge. The rotor may interchange as well as the cap and condenser. The 0.004 difference is not significant and the effect could be adjusted out, but the key slot on the cam plate may be in a different angular position. Just points to ponder....
BOB RENTON
Robert, I had the identical thoughts and concerns you had as well re: rotor position, etc. I just finished swapping out mine for the 62 small block, and everything was identical to mine such as stop plate to rotor position. All that was needed was resetting the dwell, then getting the initial to 20° and it runs excellent. I'm very curious as to the reason behind limiting the mechanical timing so much on the early poly engines. I guess because it was before the CAP of 68. Also, both distributors are Chrysler single point units.
 
Robert, I had the identical thoughts and concerns you had as well re: rotor position, etc. I just finished swapping out mine for the 62 small block, and everything was identical to mine such as stop plate to rotor position. All that was needed was resetting the dwell, then getting the initial to 20° and it runs excellent. I'm very curious as to the reason behind limiting the mechanical timing so much on the early poly engines. I guess because it was before the CAP of 68. Also, both distributors are Chrysler single point units.

Thank you for your email and reply... re limiting the advance on a poly head engine....perhaps because of the shape of the combustion chamber (poly spheric) and possible location of the spark plug and ultimate "quench" area affect the flame propagation, and possibly cam timing to the point the engine can tolerate more innitial advance. I've not used a Prestolite single point distributor b4. However, I've used a Prestolite dual point distributor, in lieu of a single point distributor in a LA 318 with good results. I've purchased a Prestolite dual point distributor for an RB engine at a Mopar swap meet for $20 because I convinced the vendor it had a bent shaft. It would only rotate about 300° of rotation before stopping, either direction....the fix was to remove the points screw that fell in the centrifugal weights causing shaft to stop.....nothing wrong with the shaft. Its one of my three spares for the GTX. AGAIN.....OUTSTANDING find....enjoy your car....
BOB RENTON
 
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I stole a 9 out of a slant six tug tractor we used at the airport for work for my 71 Bee distributor many moons ago

18 Mechanical was just about perfect with my 383 Magnum
 
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