The Stovebolt Site Forums The Shop Area Engine Shop Breaking Distributor Gear

The '39 shut itself down a couple weeks ago as I approached my drive and I towed it up the hill to the house. I have a 1955, 235 cu.in. engine in my 1939 that has about 2000 miles on a professional rebuild. Upon checking, long story short, the distributor gear had sheared off 3 teeth and lost ignition. I turned the engine over while looking at the cam gear and it appeared to be in good shape. I replaced the distributor gear with a NOS one, lubed up the distributor good, I got the engine to TDC, and reinstalled the distributor, I cranked the motor and it fired off for maybe one revolution and wouldn't hit again. Pulled the distributor and the gear was sheared off again. Valves are opening and closing, I can see the cam turning down through the distributor hole. What could be doing this? I will be pulling the pan again to see if I can determine anything but wanted to see if anyone has had this happen to them. I was thinking last night in my slumber before falling asleep that it has to be that the distributor gear is being held fast as the cam continues to spin and take out the gear. Have oil pumps been known to lock up and cause these symptoms?

For what it's worth, had it happen on a small block once. After eating several distributor gears, we determined that the distributor shaft (on a purchased rebuilt distributor) had a slight bow in it. How or why or where the bow came from, we never figured out. We took the shaft out of the housing, put it in a lathe and put a dial indicator on it. And there was a slight in and out runout on the shaft. Wasn't enough to really see with the naked eye, but it was there. Replaced the distributor and never had another problem.

Would be odd you've run it for 2000 miles, and then something like this just show up though. Just speculation on my part.......................

You can use a long screwdriver to turn the oil pump and see if it turns smoothly. Or use your distributor without the gear to check it.

Agree ^^^^^^^^^^ sounds like the oil pump is jammed or seized ??????

Am I missing something? The distributor gear is only held to the distributor shaft by a roll pin, which should have given up long before the teeth broke off.

Panic, the stock gears are held in place by a solid steel pin. The gear on the 55 and up distributor is cast. I just broke a gear driving the pin out during a rebuild and I was not really hammering on it all that much. Was a bummer, the gear was in usable shape. The nos GM replacement gears generally have a new solid pin but you really do need the right equipment to peen the pin correctly. In the early GM parts catalog (mine is through 59), the pin is specified as a solid pin. The same GM part number now gets you a roll pin. The GM replacement roll pin is the same length as the solid pin, but since you don't necessarily peen the pin over, it ends up a little long sticking out on either side of the gear when its installed. I generally have used Ford roll pins which are shorter. You can safety wire the pin or counter sink the gear just a little and peen the pin a bit. I have seen it done both ways, and I do it both ways, depending on the application, when I am rebuilding a distributor for these motors.

I have never had an oil pump on one of these early 6 motors actually seize but that certainly could be the cause of the issue. I will be curious to hear if the pump was the cause.

Check the oil pump- - - -I'll bet you find some sort of foreign matter jamming the gears. If the strainer screen gets a hole in it there's nothing else protecting the pump gears from ingesting something big enough to jam them up.
Jerry

the oil pump probably has the piece of gear stuck in it, broken off due to a bent distributor shaft in the first place. Just a guess though. I spend a lot of time at work finding really weird things wrong. This last week was like an episode of the twilight zone.