Distributor Housing Bottom Slot -- purpose ?

[Wayne M.]

Surveying the 7 or so ignition distributors I have (C2-C3 era) I notice the slot cut into the bottom of the machined "boss" at the bottom of the oil annulus [see housing on right in the picture]. Is this for oiling of the camshaft driven gear washer & shim stack ? All are in the same position with the following exceptions: Slot does not exist on the 1111263 racing distrib on the left (for big block reverse rotation cam), and I notice that on '65-6 BB units (ie. the 1111093) that the slot is relocated to the opposite side, so as not to interfere with the fully machined section face on the annulus. Colvin's Chev '65-9 book shows GM drawings with the comment that the slot is optional (1111240 and 1111267). A revision comment on the '240' drawing indicates that on 8-4-67 "oil annulus revised". y

[Clem Z.]

Re: Distributor Housing Bottom Slot -- purpose ?

Surveying the 7 or so ignition distributors I have (C2-C3 era) I notice the slot cut into the bottom of the machined "boss" at the bottom of the oil annulus [see housing on right in the picture]. Is this for oiling of the camshaft driven gear washer & shim stack ? All are in the same position with the following exceptions: Slot does not exist on the 1111263 racing distrib on the left (for big block reverse rotation cam), and I notice that on '65-6 BB units (ie. the 1111093) that the slot is relocated to the opposite side, so as not to interfere with the fully machined section face on the annulus. Colvin's Chev '65-9 book shows GM drawings with the comment that the slot is optional (1111240 and 1111267). A revision comment on the '240' drawing indicates that on 8-4-67 "oil annulus revised". y

my guess since that slots cuts into the dist seal area of the lifter gallery it is to allow some oil to flow thru to the cam/distributor gear interface. with after market distributors i would machine a .015 X .015 slot in that area to get extra oil to that interface when we use hi pressure oil pumps because of the extra load on the gears

[Joe C.]

Re: Distributor Housing Bottom Slot -- purpose ?

That design/configuration makes the oil delivery volume very dependent on distributor height/location and therefore deck height/cylinder head depth.

Surprising that the design wouldn't have called for a small hole to be drilled vertically through the lower annulus instead of the slot cut. Sound's like a stretch that machining the slot would have been cheaper than drilling the hole.

[Clem Z.]

Re: Distributor Housing Bottom Slot -- purpose ?

drilling a small hole requires a small drill bit and this means breakage. i have seen holley metering bodies with broken drill bits in the emulsion holes

[Joe C.]

Re: Distributor Housing Bottom Slot -- purpose ?

drilling a small hole requires a small drill bit and this means breakage. i have seen holley metering bodies with broken drill bits in the emulsion holes

That makes sense......................in the days before EDM.

They could then have cut a shallow vertical groove across the surface to the lower annulus to accomplish the same thing. Again, oil delivery rate would no longer have been dependent on distributor installed height.

[Tom D.]

Re: Distributor Housing Bottom Slot -- purpose ?

I plan to run a test with this housing, in a 67 427. We don't think this part was made by GM. Possibly from an aftermarket supplier?

[Clem Z.]

Re: Distributor Housing Bottom Slot -- purpose ?

do those machined slots line up with the the distributor/cam gear interface when the distributor is in the correct position in the engine ??

[Kenneth B.]

Re: Distributor Housing Bottom Slot -- purpose ?

my guess since that slots cuts into the dist seal area of the lifter gallery it is to allow some oil to flow thru to the cam/distributor gear interface. with after market distributors i would machine a .015 X .015 slot in that area to get extra oil to that interface when we use hi pressure oil pumps because of the extra load on the gears

The slots are cast in & not machined. You can see the parting line on the one that dose not go all around. I do beleave like that it is for oil.
KEN

[Wayne M.]

Re: Distributor Housing Bottom Slot -- purpose ?

Just to make sure we're not confusing the terms, I attach the Colvin GM view drawing of the slot (optional). Looks like it was make with a cutting tool in the closeup of an actual 1111267 that I have.

So we're not talking about the recessed annulus -- at least not for the moment .

[Clem Z.]

Re: Distributor Housing Bottom Slot -- purpose ?

The slots are cast in & not machined. You can see the parting line on the one that dose not go all around. I do beleave like that it is for oil.
KEN

the cast in recess is so the oil can get thru to the passenger side lifter oil gallery. i believe the distributors with the partial cast in recess was done to cut down on internal oil leaks in the BBC.

[Timothy B.]

Re: Distributor Housing Bottom Slot -- purpose ?

I guess the finished housing top and bottom of the annulas fits snug but allows oil to leak above and below. Above, to get to the oil hole in the distributor and below to find the machined slot Wayne is talking about for oil to the cam/distributor gear, correct..

[Clem Z.]

Re: Distributor Housing Bottom Slot -- purpose ?

I guess the finished housing top and bottom of the annulas fits snug but allows oil to leak above and below. Above, to get to the oil hole in the distributor and below to find the machined slot Wayne is talking about for oil to the cam/distributor gear, correct..

also the oil in the lifter valley will run into the hole drilled into the dist. housing

[Tom D.]

Re: Distributor Housing Bottom Slot -- purpose ?

Clem: Three of the lower slots I looked at today were "cut" almost directly behind (180 degrees around and higher up) the vacuum advance attaching point. One such distributor still has a tag w/ Delco Remy no. 1111293, for a 1968 427 application. I found one (See my housing pictured above with the partial annulus) that has a slot cut directly under the tach drive cable attach point. This is the housing that I believe is "non-GM".

Also, I reviewed a small group of aluminum, non-tach drive units. None of those had such a cut slot.

[Clem Z.]

Re: Distributor Housing Bottom Slot -- purpose ?

Clem: Three of the lower slots I looked at today were "cut" almost directly behind (180 degrees around and higher up) the vacuum advance attaching point. One such distributor still has a tag w/ Delco Remy no. 1111293, for a 1968 427 application. I found one (See my housing pictured above with the partial annulus) that has a slot cut directly under the tach drive cable attach point. This is the housing that I believe is "non-GM".

Also, I reviewed a small group of aluminum, non-tach drive units. None of those had such a cut slot.

if i read you right the "cut" is oposite of the vacuum can and that would put the cut in the area of the cam gear and distibutor gear interface for extra oiling.

[Wayne M.]

Re: Distributor Housing Bottom Slot -- purpose ?

Here's some more meat to chew on: First two thumnails are from the '65 interim shop manual, or '66 Chevrolet Overhaul Manual -- same dwgs). Those with access to the '67 OH manual please report if the dwgs differ in the critical area of the rear cam bearing, with the '351' block.

3rd and 4th thumnails are shots down the distributor hole in my 396 May '65 #3855961 block, which should be the same as the L78 '962' and the 1966 '842' block, insofar as the oiling design uses both use a grooved rear cam journal and bearing. Notice the copper wire I threaded thru the passenger side lifter(s) oil header hole. I've circled the two holes that are exposed to the oil annulus in the distributor housing. In the last pic, I shone a light up the oil pump drive shaft hole, with the two block oil annulus holes again circled.

Next, we have to figure out which of those two holes are blocked/restricted by the partially filled annulus of the disr. housing, and its effect on the left/right lifter oil headers.