What's the distributor housing groove deal?

[Chuck R.]

I keep hearing about the groove around the distributor housing being either all or partially around the housing?

Is this a small vs. big block specific design?

Can big and small block distributors interchange

I'm assuming it's either an oil flow or oil pressure reason for the groove.

I'm shopping out another distributor for my 350 project and don't want to purchase a boat anchor.

Thanks,

Chuck

[Michael H.]

Re: What's the distributor housing groove deal?

Chuck,

The distributor housing with the partially filled slot is/was used for 65-69 big block only. At that time, it even had it's own listing and part number in the parts book. Eventually, the original number was discontinued and the small block housing serviced both small block and big block.

As far as it's actual function/purpose, you will probably hear several theories on this tonight but I don't know if any of us actually KNOW the reason these BB housings were that way. I've even questioned a few of the engineers on the big block project and most had no good explanation, although a few had several good guesses. I've never seen any GM paperwork that describes or explains this housing.

A fair guess would be that it had something to do with the 1st design 65-66 cam with the grooved rear journal??? There are lots of possibilities and I'm sure we'll hear of several tonight.

[Wayne M.]

Re: What's the distributor housing groove deal?

Here's what the 2 variations look like -- ignore the reverse rotation driven cam gear on the left (1111263 ball bearing distr.).

"How to Hot-Rod BB Chev's" (1971) has this to say. [although it doesn't mention the relation to the distributor configuration, IMO, in production, the grooved rear #5 cam bearing coincided with the non-continuous groove in the distr. shaft].

"1965-66 big blocks require a grooved rear cam journal and a grooved rear cam bearing. The combination was used to provide valve lifter oiling on these early models. In 1967 and on all subsequent BB models, the lifters are oiled through an annulus groove behing the rear cam bearing. If you have to use a grooved cam with a '67 or later block, remove the rear cam bearing. Solder the hole closed and redrill with a 0.060 inch drill. Reinstall the bearing. Any attempt to use a grooved cam in a '67 or later BB without this modification will create a massive internal oil leak which can affect oiling system performance".

But then again, elsewhere I've read that it doesn't make any difference (can't locate this article). Don't believe this is a small block issue (ie. oil starvation with non-continuous annulus -- BB and SB distr's can interchange), but maybe others can provide insight.

If you come across one without the full groove, you can probably trade for 2 of the others.

[Chuck R.]

Re: What's the distributor housing groove deal?

It may very well have been oil flow related. It makes sense.

Sounds like either one will work with my 350 then.

Thanks for getting back to me Mike.

Chuck

[Chuck R.]

Re: Well you know Wayne

I tore down a burnt up 427 and tossed the distributor housing under the bench.

Hmm, two for one huh? I like the sounds of that

Like I stated to Mike, it sounds like sither one will work with my 350 project.

Thanks for getting back to me Wayne,

Chuck

[Terry F.]

Re: What's the distributor housing groove deal?

Wayne, I am slowly gearing up to pull my 390hp out of my 68. I had it rebuilt years ago, started it and turned it off. My engine never developed any significant volume of oil to the rocker arms. It would show up to the rear half of the engine slowly and real slowly to the front half. At the time, The engine rebuilder mentioned something regarding the oiling issue and the rear cam bearing. I am nearly certain he goofed it badly. I never took it back to him because I never trusted him after that. I used the guy because I assumed he knew what he was doing. I have since found a very, very good engine builder that is eager to find what the problem is and has done great work on another engine I had done. In all, I think the situation is with that rear bearing and the camshaft. As I recall, I have the right camshaft but I suspect I have the wrong bearing in there and I am starving the top end or I have this so called massive internal oil leak. I wish I had a copy of that origial article. Terry

[Phil P.]

oiling for early 283 and 348/409 *NM*

[Mark #28455]

sounds like restrictors were used

Same thing happens when the roller cam oil restrictors are used in the rear oil gallery holes - some drag race engine builders like that stuff.
Mark