I had the same problem with my 77 F-150 with a 390, it would occasionally shear the roll pin and start backfiring, then just die. I never did find why, but it seemed to disappear as I got more miles on the combination. Number dummy is very correct in pin selection, the solid ones are usually mild steel where the roll or split pins are a high carbon heat treated steel. They are more brittle ultimately, but stronger in shear which is the way they are loaded. Make sure the gear isn't loose on the shaft as that will shear the pins as fast as you install them. What kind of oil pressure are you running? I have seen FE engines shear the pin on cold starts as the oil pressure spiked.

 

since i bought the truck it has always had around 60 psi cold, then around 45 when warm and cruising. i run full synthetic oil. i am hoping that the roll pin that busted was just an inferior piece (procomp distributor, kinda cheap). like i said the pump turns freely by hand and i can hear it sucking oil. i went to lowes to find some of the hardened roll pins(split) and put one in. it cranked right up, oil pressure is still the same, all seems to be back to normal. the distrubtor was only in for 2 days before this all happened.

 

I have had this problem with every aftermarket distributor that I have put in one of these 335 motors. I have gotten to the point that I save the roll pin out of every factory ditributor that I end up tossing. I put the factory roll pin in place of the aftermarket pc and have not had a problem since.

Steve S.
To many to list

 

Hi guys. I hope I'm doing this posting thing right.
After reading dozens of stories about broken distributor roll pins and having my own problems I am beginning to think there is just a design flaw in the system. Here's my story:I Bought a '79 bronco with 400 auto which was a good deal because the dist. roll pin was broken and the guy's mechanic said it would cost $1200 to replace it and the oil pump which was thought to be the problem. So I replaced the pump and the pin and it ran great. For a few days, then it broke again.Did the pin again. Same thing. I then decided there must be something wrong with the distributor, so I bought a brand new one.Same thing again. So I thought there might be too much slop in the timing chain. So I replaced that. Same thing again! I then decided that the engine must be the problem somehow (misalignment of the dist. bore or something maybe?)So I replaced the engine with a used one from a 76 LTD which ran good and had never broken a dist. pin to the knowledge of the previous owner.Guess what? Yup, same thing again. So I took that engine and put the new dist. the new oil pump and the new timing set on it. Do I need to say it? yep, same thing again!! So now I'm grasping at straws and wondering if there could be something else causing it The only thing I can think of is that the trans shifts a bit wierd. it slips or something between shifts, allowing the engine to rev up for a split second between shifts. maybe this shocks the roll pin? I know, I'm grasping, right? Anyway my next solution is this. I'm gonna put a 428 and 4 speed I have in another truck in it and if it throws a roll pin after a few days I'm gonna set it on fire and push it over the bank out back. That'll learn it.