Pin on Distributor keeps breaking at gear
 

Hi Guys,
I have broken two pins so far. I am tempted to just buy a new distributer. I'm not sure if my old distributer is just worn out and has some slop in the shaft.
Someone told me that there is a stronger pin available....does any one know what they are talking about?

Thanks for your help.

This is on a 1964 Thunderbird with the stock rebuilt 390, may have a high volume oil pump, lots of oil pressure at the gauge, original Ford distributer.

Steve

I drilled mine out and replaced the pin with a chebby pin. I forget the size but it is a larger diameter

Have you changed your gear or are you putting the old gear back with a new pin? You have to change the gear. Once the hole in the gear gets a little slop in it it can shear pins.

Make sure you dont have a rough spot in the distributor either. Does it turn freely all the way around.

No, didn't change the gear. I will check for a rough spot. I suspect that the 47 year old is worn out.

do you have a high volume or high pressure or both oil pump?

Dwight

gear pins will shear if some debris gets picked up by the oil pump, the slightest particle will cause a momentary shock to the pumps vanes and the shear pin will let go. if you have done any engine work, like gaskets or the like. this may be the source. the most common is the umbrella valve seals when they get old they become brittle and flake off particles. putting in a new gear is certainly a good thing but if it happens after that then a oil pan removal may be needed to look for dirt

What kind of pin are you using?
 

Steve V Steve what kind of pin are you using?? It should be a spring roll pin. Some of the guys go up one size for more strength. I am running a stock MSD pin. I also have a HPHV oil pump with 100 psi spring in the pump. Cold pressure is 135-137 at idle until motor warms up. Solid pins will not work. I will look and see if I can find a company that sell the correct one for you. Rick L.

Yup. It's a Ford thing. Never heard of it happening on Chevy motors, but I've only been building them for 40 years. I replaced one in a friend's 289 and was surprised how tiny the pin was. Those dinky pins work fine until you add a HV/HP pump.

Tim O'Connor can probably get you any parts you need for your distributor. He rebuilds and restores Ford distributors and has nearly any hard to find part you can think of (other than some of the bushings which can be tough).

Give him a call. Great guy.

http://428cobrajetcars.com/home

Chevy pin. Period.

Just drill it out and put a larger one in, doesn't need to be from Ford, Chevy or Dodge. Roll pins are roll pins and you can get them at hardware stores. I put two in mine after I snaped my original one, (+). Just make sure you drill the correct hole so it's super tight.

I s'pose you're right...any ol pin will do.

Course, out on a cruise and for some reason ya hafta change gears or sumthin...all ya got to do is remember it's a Chevy pin instead of some specific size.

...just sayin

The shear pinis the weak link in the system. It's designed that way on purpose. When the system gets near it's breaking point, the pin shears, and the engine quits before any damage can be done.

You can always put in a stronger pin. Put in two pins. Heck, you could just weld the gear to the shaft. Or, you can figure what's putting all that strain on the system, and change that. For example, if you have a HV/HP pump and use straight 50 oil, maybe that's not such a good decision.

Coiled Roll pins
 

Ford distributor gears are supposed to be a press fit. Once its spun its probably too loose. A new gear will fix it. A new gear and a Chevy pin will fix it forever.

Define forever

does that mean trouble free from now on or

Does that mean the engine will keep running after the oil pump drive shears off which will finish the engine off forever?

If the hole is worn in the original distributer gear the gear should be replaced. MSD uses true roll pin rather than spring pins . A little tougher. I/8" x 3/4" as I remember. Got mine through Summit. Drilling for a larger pin weakens the shaft. The oil pump drag is usually the problem. Thick oil, high volumes, and or high releif presure. I was worned that I should not get carried away with RPM until the engine oil temperture was showing at least 140° Think of that pin as a fuse, a built in weak point. It will only take so much. A larger for pin hole will weaken the shaft and or move the damage further up the line like twisting the drive shaft, if the oil pump stalls or such. They make a FE truck pump with a larger hex drive 5/16" as to original 1/4". And they make better material drive shafts with 5/16" hex shaft with 1/4 tip to fit the car distributer shaft tip. As it was shown to me most wear of the oil pump drive line was at the female hex socket in the oil pump end rather than the distributer. Under normal cercumstances, the original 1/4" hex drive and 1/8" pin worked just fine, but add higher volume oil pumps at higher releif presurses the throw in cold oil and something has to give. But when the oil pump is stalled the the distributer drive pin breaks the distributer stops , the engine ignition imediatly stops and the engine coast to a stop. If not at high RPMs usually no damage and is caused and it only takes another pin and about an hour to repair.
It has been mentioned in past postings on this subject that the shaft outside and gear inside measurments may varry causung anything from a rattle to a press fit.

Jerry, I suppose that would depend on what OP drive he's using. Is it a newer high strength piece or is it the original glorified linguini that came with the motor from Ford? If the OP is HV/HP and he's using the linguini then it's toast either way. If on the other hand its stock everything and the pin is shearing then my first look would be to the pin and gear. Way too many people have performed this simple mod with total success to poo poo it based on what? Nostalgia? I've got 2 motors with that mod myself right now. One is a Windsor block and the other an FE. The simple truth is that if the OP does lock up that sudden and hard then the motor probably has more problems than that anyway.

Steve

The original Ford design had the pump shaft twist like a barber pole & then break once the pump inhaled junk. The pin was stonger than the shaft. We fix that with better drive shafts since an HV pump is harder to spin, and now the pin is the weak point. The pumps used to get locked up from pieces of umbrella valve stem seal and plastic timing sprocket - not many of those in our newer builds.

I have never seen a distributor shaft break from an oversized pin hole. Not any real load up above the gear with electronic ignition, and the gear/pin/shaft area is pretty short and well supported.

Update, I went to Napa, got a new (rebuilt) distributer, the original 47 year old unit was still in the car. If it shears again, I will look deeper. The HV oil pump is unknown as the engine was rebuilt before I bought it.
Thanks for all the information here. It's amazing the debate stirred up by a $.99 part.

Thanks again.
Steve