sbc distributor shaft diameter

[Belgian1979]

I was planning on using a vortec distributor with cam sensor so that I can use it as a cam sensor for the sequential injection. Untill now I've always used msd distributors. Turns out that the shafts on the msd's are .500 and the vortec one is .425". Any issues with using the vortec with the thinner shaft in combination with a HV/HP oil pump ?

[JWRE]

Just for comparison, a 302 SBF only has a .250" oil pump shaft and they hold up fine. I've seen a few break, but only because debris locked up the oil pump. And even then, they usually twist and very rarely break apart.

[Slowpoke_70]

FWIW the shaft diameter for points and large cap HEI is .490 so the MSD is actually slightly oversized.

GM used the .427" shaft in the small cap HEI from '85-'00, including the 454. The stock 454 oil pump is already more taxing on the shaft than the stock 305/350 pump. Whether or not the standard BB pump is tougher to turn than an HP/HV SB pump, I have no idea.

[cgarb]

I would be more worried about the small roll pin holding the gear from turning on the shaft than the shaft itself.

[Belgian1979]

I would be more worried about the small roll pin holding the gear from turning on the shaft than the shaft itself.

I intend to use the msd rolled pin, which holds up just fine.

[JWRE]

I would be more worried about the small roll pin holding the gear from turning on the shaft than the shaft itself.

I see his point though. I mostly do Fords which press on and use a roll pin so I completely forgot about how the Chevy gears just slide right on. That's actually a great point, no matter what pin you use it will still be the weakest link. And if you were to step it up a size, that would just be more material you've taken out of the original shaft in question. Just go with it man, I've never heard of anyone having problems with them.

[dirtracr5]

Just for comparison, a 302 SBF only has a .250" oil pump shaft and they hold up fine. I've seen a few break, but only because debris locked up the oil pump. And even then, they usually twist and very rarely break apart.

Thats debatable. Seen quite a few broken ones.

[Belgian1979]

FWIW the shaft diameter for points and large cap HEI is .490 so the MSD is actually slightly oversized.

GM used the .427" shaft in the small cap HEI from '85-'00, including the 454. The stock 454 oil pump is already more taxing on the shaft than the stock 305/350 pump. Whether or not the standard BB pump is tougher to turn than an HP/HV SB pump, I have no idea.

The distributor is off a Vortec engine, I think from 1996 and up so that could be correct. I think in volume that would be comparable.

Will just use it with the rolled pin of msd and see how it does.

[JWRE]

Just for comparison, a 302 SBF only has a .250" oil pump shaft and they hold up fine. I've seen a few break, but only because debris locked up the oil pump. And even then, they usually twist and very rarely break apart.

Thats debatable. Seen quite a few broken ones.

True, but no matter if they're broken or twisted it was caused by a locked up oil pump or some other unforeseen problem causing the damage to the shaft rather than the shaft causing the damage. And for some reason the owner refuses to believe their pump temporarily locked up because when they pulled the distributor and checked it, it turned fine. I used to have the patience to explain things to them, but eventually I just agreed and said, "yea, you're exactly right. I've always wondered how the teeth on the distributor gear somehow have the exact same lifespan as the oil pump shaft" .Anyway, we're getting the OP's post off track. I think he get's the point though, at least I hope we helped him out.

[wyrmrider]

put another roll pin inside?

[Belgian1979]

Just went over things some more and was planning on installing the msd rolled pin

Vortec item


MSD



The metal between the flat piece going into the oil pump drive is really thin compared to the msd due to the hole for the pin.

[cgarb]

Where can the metal go? Remember it has the gear around it. Think of it as a distributor shaft girdle.

[Belgian1979]

Where can the metal go? Remember it has the gear around it. Think of it as a distributor shaft girdle.

Well, the oil pump and the shaft tries to force them to turn in opposite directions if you will. The split pin has to take up that force, but it works against the flanges of the holes. so in essence the force works on the thin section imo.

[cgarb]

Well put them both in a vice and see how much torque it takes to break it...lol. I think it would be fine but its not my motor. I also don't use high volume pumps either. Every motor I've raced had a Z-28 pump with the high pressure spring in it. I haven't had any trouble. I built one for my stepbrother that had the BBC oil pump in there. He hasn't had any trouble either. Way more mild of an engine than mine, so who knows. I hope it works out for you one way or the other.

[Schurkey]

The GM TBI LO5 Caprice engine 12513151 crate engine replacement uses a TBI-small diameter distributor, along with a "high volume" oil pump. GM seemed to trust it.

Now, this "high volume" pump doesn't have the high-pressure spring inside, and there may be some debate on how "high" is "high volume"; but the point I'm trying to make is that I have no expectation that the distributor shaft/roll pin is likely to be a high-failure item.

For that matter, all the TBI big-blocks used that same distributor, and they didn't seem to fail when twisting the BBC oil pump.

I'd call it a non-issue.