So just finished a timing chain set swap on my 75 f100. Have also just replaced dizzy, coil, fuel pump, plugs, and wires. Once I put the new timing chain and gears in and pieces everything back together she started up and ran amazing. Drove her about 30 mins to work, had it off for about 30 mins then went to start her again and she cranked for a lil then a loud grinding/screeching noice came from the block. After some trouble shooting I noticed that when the the dizzy rotor gets to a certain spot it’ll lock up and produce the grinding noise. If I hand turn the motor just a lil bit past that spot, it’ll try and crank again, and the grinding noise will stop. Then when the rotor points to the spot directly 180 degrees from the original sticking point, it’ll do it again.

my first guess was that the dizzy wasn’t lining up properly with the oil shaft, thus not engaging it, thus producing the grinding noise from lack of oil been pumped.

now discovering that there is two sticking points directly 180 degrees from each other has got me thinking it might be something else.

any ideas or trouble shooting steps? Could it be timing chain related sense I just put a new one on? The truck has got a 390 in it. I’ve checked the gears on the dizzy and they look fine. what doesn’t make sense to me is how it drives perfectly for a day, then after sitting for 30 mins it becomes problematic. Actually now that I think about it, I’m not that surprised judging how this restore has been going.

 

The distributor really can't lock up, something has to give and that usually is the distributor gear or pin .

The first thing you need to do is pull the distributor gear and see if it's stripped or if you really do have a timing set issue. if the gear looks good check the pin, if it looks good turn the engine as see what's turning.

 

If the oil pump shaft was not turning the oil pump you may have spun a rod or main bearing. Oil pump rods will some time lift up with the distributor and fall into the oil pan. Trust me on this. I had this happen and heard the rod fall because the retainer washer had slipped down which let the rod come up enough to drop.

 

That's possible but normally if the oil pump stops so does the distributor. so I would be mindful of it but not worry too much yet.

All it takes is a piece of gasket or silicone getting trough the pickup screen to lock an oil pump. since you were just inside the engine I'd be very suspect of it.

 

So I think I have found the culprit. I went to see if I can prime the oil pump by turning the oil shaft manually. I tried what I’ve read is the correct size of 1/4 inch well socket to go around the hex portion of the oil shaft but the socket was to small. I tried the next few sizes up until 5/16s. 5/16s was to big to fit into the hole where the dizzy sits and mates with the oil shaft. The dizzy oil shaft female mating hole is verified 1/4in. I’m starting to think that my older dizzy was the correct size and the new one worked for a short time before it became unable to grip the oil shaft. Any thoughts? Do oil shaft rods come in 5/16s for fe 390? I’m going to go home now and see what size my old dizzy oil shaft hole is.

 

You should buy an oil pump priming shaft to perform this test. Be sure to go counter-clockwise. At this stage you should have already inspected the dizzy gear and retaining pin. If all this is OK, look at the part of the cam shaft that drives the dizzy.

 

Checked old dizzy today when I got home and it had a matching 1/4 in oil pump shaft drive to my current one. I’ve had the truck running and driving good intermittently with both dizzys, using the current oil pump shaft. I’m trying to understand why I can’t get a 1/4 in deep well socket attached to the shaft if it worked for both dizzys.

 

I don't think any of them are less than 5/16 but I'm not sure.

that still wouldn't explain why your distributor was messed up that would only account for the oil pump.

 

Measure the O.D. Of the old distributor lower shaft and the O.D. Of the socket, you may have to grind the socket down to fit in the bore.

 

are you confident it isn't a damaged flywheel/starter drive scenario?

 

It pretty much has to be something that's attached to the crankshaft. That would at least explain why you're getting it twice during a distributor rotation. At 180 degrees apart, that's one full rotation of the crank for each dragging point. Same spot each time basically.
So to my mind that would mean it's not related to the cam, valvetrain, distributor or oil pump. Has to be something in the main rotating assembly. Like was said, a flywheel bolt, or rod or something.
Did you make note of where in the crank rotation the binding occurred? About the only way I can think of that it might be cam related would be if a cam gear retaining bolt was hitting two separate places on the cover at 180 degrees apart. But which engine is this? 302? If so, it's just a single centered bolt (correct?) so would not normally be hitting something in rotation. Just be spinning on the timing cover.
Which engine is this? Is it possible for a fuel pump arm to hit anything other than the cam eccentric in there? Like the crank gear perhaps? I don't think so, but really don't know how much clearance there is in there between the two under normal circumstances.

And after all this, I did not read anywhere that you rotated the engine after removing the distributor. If you did, what happened? Same scenario with the two rubbing points?

Good luck.

Paul

 

Does anyone have the stock measurements of what the dizzy oil pump shaft hole is supposed to be? Im still trying to wrap my head around why both of my dizzys have 1/4inch shaft holes but my oil pump int shaft is 5/16....idk a whole lot but I’m sure these are suppose to match lol

 

I don't think I've ever seen a 1/4 drive on any distributor.

If you distributor actually has a 1/4 hole and your shaft id 5/16 you never would have gotten the distributor installed. unless the distributor is too short and wrong for the application in which case it shouldn't have run at all, or if it did you weren't turning your oil pump and now you have big problems.

 

Maybe the recommendation was for a 1/4" drive ratchet, so that the proper socket to fit the shaft would still fit into the hole? If you're using 3/8 drive, that's probably why the sockets are too thick.

I've used long-stem Nut Drivers before and that worked slick. No worries about dropping a socket.
Speaking of which, not sure if it was mentioned, but taping the socket to the extension is highly recommended unless you relish taking the pan off again!

Paul

 

So I’ve decided to go ahead and replace the oil shaft drive to eliminate the problem of the shaft not properly fitting in the dizzy. Me not being able to get a 1/4in socket on the top of the oil pump shaft has got me thinking that it’s either a 5/16 hex on the shaft that’s not able to fit in the 1/4 inch dizzy (might of had enough friction to turn oil pump intermittently, explaining it working before) or the oil shaft hex has been stripped in some way. I’ve been meaning to go ahead and pull the engine to replace some gaskets and clean it up. Was thinking about replacing oil pump, oil screen assembly, oil pan gaskets, and throwing my new flowtech long tube headers on while I have the engine out. Anything else I should replace or take a look at while I have the engine out? I will also be pulling the intake manifold off to clean, repaint, and put new gaskets in while I’m at it.