Distributor Won’t Go in, 351M Ford
filed in 1966 Mustang
Question: I have a 351M Ford truck engine.
I’m replacing the distributor* (which is the one vacuum-advance type). I removed the old distributor, and now I’m trying to insert the new one. That’s the problem. The new one won’t go in. And I can’t even re-insert the old distributor, even with the gear removed.
I can’t tell what the distributor is getting hung up on, but I suspect the shaft is not seating properly on the hex shaft that comes up from the oil pump. Or maybe the hex shaft is supposed to seat in something itself.
Has anyone had this problem and worked his or her way out?
* The truck wasn’t giving much power and acting like it was out of time, but it wasn’t. When I removed the old distributor, I could see the gear at the bottom was loose; the roll pin holding the gear in place was broken and only half there.
Answer: You should not be able to remove the drive shaft from above. It should have a tinnerman nut on it so it dowsn’t fall out and land in the oil pan whenever you pull the distributor. So put a drive socket on it, and gently turn it until it fits back in to the oil pump. If the oil pump is in good condition, it should turn pretty easily, so don’t let that fool you. Turning it fast enough to create pressure takes some work, though. When you think it’s in, apply a 1/2 drill motor, and turn in reverse until you get oil pressure, or you can see oil in the distributer hole. Now you know everything’s in place.
Place the engine at TDC on the compression stroke. Lube up the distributer gear, shaft end, and O ring area. Be sure and give the driven gear and shaft end a good coat of white lithium grease. Drop the distributer in as far as it will go without forcing. With the spark plugs removed, use a wrench and socket to turn the crankshaft in it’s normal direction of travel. Usually, within 1/4 turn and the distributer will drop in to place. Now turn the engine over twice with a wrench, and remove the distributer. Check the pattern in the grease on the driven gear. If should be pretty much centered in the gears. If it isn’t, you’ll have to move the gear up or down a little to make it match. Also, check the hole at the end of the shaft. There should be only grease visible in the bottom of the hole. If you can see steel in there, that means the drive shaft is bottoming out in the hole. Then you have to pull the pan and pump, and shorten the drive shaft. If everything looks good, you can go back to the beginning. Install the distributer as above, and set static timing. Start the engine and set actual timing. Whenever I install a new distributer, I always go through the above steps. It sounds time consuming, but it really only takes about 10 minutes. And, I have to admit, I’ve never had to modify a distributer to correct any problems. But the first time I don’t check………. I have seen broken rollpins before – and then seen jammed oil pumps shortly after. I would be dropping the pan, pulling the pump, and checking it carefully in the near future – just for peace of mind.
And no, I am NOT recommending changing parts just for the sake of changing parts. If the pump seizes it can ruin your day – particularly if the pump shaft has twisted a bit already (before breaking the first roll pin) and it snaps next time INSTEAD of shearing the rollpin. Don’t ask how I know
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