duraspark distributor gear shaft sizes


Active Member
Dec 11, 2003
hello i am using an 82 duraspark distributor and i don't know the size of the shaft. i tried to put my 91 tfi gear on it and it was too big. how many different sizes of shafts did they have on duraspark distributors.
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Can't quote the sizes, but you can find them here somewhere.

There are 2 sizes for the small block. The smaller one is the most common 302 type Duraspark size. The larger one is the same as a 351W, and is used in the roller cam engines, I think. Either works if you have the right cam gear. The Ford FRPP catalog has a list of them, and the gears, and the website should also have it.

I think the 351w also has a larger oil pump drive shaft.
I hate to dig this old thread up, but is there any reason WHATSOEVER that a distributor with the larger shaft would NOT fit in an '86 roller-cam H.O. block where a distributor with the smaller shaft had been?

I swapped out the bronze distributor gear and turned it on a lathe to size to adapt to the bigger shaft. Now the #$!*&er appears to not fit through the block at the first ring on the housing, like it's 1/16" too wide.

I don't think it's hanging up on anything inside, as I can pivot it on the housing, and by measurement I haven't even hit the oil pump shaft, yet.

I am open to suggestions.
Thanks, puter. What's got me is the actual housing, the rings where the dizzy goes into the block. I just mic'd mine (I'm at my shop, now) and the old one is 1.490" and the new one ("should drop right in there," says the guy at the Ford Parts Counter) is 1.569". It don't go into the block. At all.
Interesting stuff to know.

Only guess is that they are different because 302 and 351w dists are not supposed to interchange?

Aren't the oil pump drive shafts different between these also?

Have not fooled with a 351 yet, much, so I don't know. But I do have a 351w, 351/400M and a bunch of 302/255 dists laying around.
These are both 302 distributors, at least, according to the Ford parts guy. I just called him and he said that it's impossible, that they have to be the same size. I think I'm going to go in there with both housings and my micrometer and show him.

My only recourse at this point is to dismantle this one and put it in the old housing. . . . another lunch hour spent at the bench . . . . :mad:
I dunno if it's remfg'd but I just said f--- it and turned it down to 1.49" on a lathe in our machine shop at lunch. The larger shaft wouldn't fit in the smaller housing.

It's all back together again and (hopefully) ready to drop in. Fingers crossed that this was a 302 dizzy and not a 351. The shaft lengths looked identical; I laid them side by side before I started surgery so I'm hoping I won't have problems with oil pump shaft clearance.

I have the most custom distributor I could ever want: machined housing, bronze gear, Pertronix ignition, and the freakin' advance plate busted off the shaft when I was removing it from my old one so I hand-filed the advance curve on this one, opened it up to 20 deg from the stock 10 deg. Old-school shadetree engineering. :nice:

My old distributor literally came apart. When I opened it up, my mechanical advance was shrapnel. My carbs were shooting flames higher than the top of the car whenever I'd drop it in gear. A stock distributor does have a limited lifespan, FYI. And when they go out, they REALLY go out!

EDIT: The gears are the same OD -- they have to be, to engage the cam -- but there are two different ID's. I was of the impression that different distributors for 302/5.0/289 had varying shaft widths but I wouldn't think Ford would be so stupid as to change the size of the hole in the block between years. That's just asinine. And yet, poking around on other boards, I'm finding stories of people who have had exactly this problem.