BB distrib housings; '65 to '69

[Wayne M.]

I'm trying to make sense of the service part # changes throughout this early Mark IV period and correlate to the physical appearance of the housing, and how it relates to the lower annulus oil groove.

Picture is of two cast iron distrib housings: the one on the top is (supposedly, per eBay seller) removed 20 years ago from a '66 Chevelle 396/325hp w/manual trans. Band 1111109 dated 5_G_7 (July 7th 1965). Must'a been one real early '66 Chevelle, as the 5 assembly plants producing '65 Chevelles worked until early to mid-August. This distrib was probably installed in a 3855961 cast #, 2-bolt block.

The one shown on the bottom is from a '66 L72 Corvette (VIN unknown) with band 1111093 dated 5_J_20 (Sept 20th 1965).

Focusing on the Corvette housing, which is our main interest here, the only difference I can see is the tach drive. The Chev parts catalogs P&A30 show the following listings under the group 2.362 "housing", and the service parts history of the same.

For the '093' distrib, the part # in the July '65 revision of the parts book lists #1965974, but by Oct'65 (in the first issue of the '66 P&A30) they're calling this '974' part # the 1st design, for the '65 396 Corvette alone, and adding (2nd design implied ?) # 1966654 applicable (again) to '65-6 Corvette distrib's 093, as well as '66 Corvette distrib's 1111141 & 142, the latter two for '66 L36 without/with K66.

The July '69 parts history shows # 1965974 was replaced in service by 1966654 on 11-66, then switches back again to 1965974 on 5-68 (huh ?).

The Jan '69 P&A30 says # 1965974 for all BB Corvettes; no caveat about installing in the '65-6 with grooved rear cam:
1st line for '65-7: 1093, 1141, 1142, 1240 1247 1248 1258 (ie. for distrib's originally w/partially filled oil annulus, as shown in my pic ?)
2nd line for '68-9: 1111293/1294/1295/1296/1111926/1927/1928/1950 (ie. for TFP that never had, nor needed, a partially filled oil annulus ?)

Any insights welcome.

[Tom D.]

Re: BB distrib housings; '65 to '69

Did 1965974 and 1966654 look alike w.r.t. the annulus? What is TFP?

[Clem Z.]

Re: BB distrib housings; '65 to '69

the early big blocks because of the rear grooved cam journal had a internal oil leak because of the large area involved so the partial groove in the dist. housing was used to try and cut down on the internal oil leaks. if the dist groove was 360 degrees there was more area for the oil to leak out between the lifter oil gallery and the dist housing. once GM in 67 changed the rear cam journal there was no need to try and cut down on the oil leak around the distributor housing. GM most likely over reacted about the internal oil leaks on street engines. i do know that 65 and 66 BBC corvettes would see oil pressure drop at the end of a 1/4 mile drag strip because the excess oil upstairs was not returning to the oil pan fast enough and to prevent this we would run the pan 1 quart over full. i think most of this problem was caused by the use of piddle valve lifters which allowed more oil upstairs than the edge orifice type lifters.

[Tom D.]

Re: BB distrib housings; '65 to '69

Clem: Any problem with this 1966 "partial cut" housing in a 1967 390 HP 427?

Machine shop says back when mine was redone, they "most likely cut a by pass groove". They say "That's our usual practice". What do they mean?

Thank You.

[Clem Z.]

Re: BB distrib housings; '65 to '69

Clem: Any problem with this 1966 "partial cut" housing in a 1967 390 HP 427?

Machine shop says back when mine was redone, they "most likely cut a by pass groove". They say "That's our usual practice". What do they mean?

Thank You.

no problem since you can't install the dist the wrong way with a vacuum advance installed. my guess the "bypass grove" is a groove put vertically on the bottom of the dist housing to allow oil to be sprayed onto the cam gear,dist gear interface from the passage around the dist housing.

[Joe L.]

Re: BB distrib housings; '65 to '69

my guess the "bypass grove" is a groove put vertically on the bottom of the dist housing to allow oil to be sprayed onto the cam gear,dist gear interface from the passage around the dist housing.

clem-----

I think so, too.

[Bill W.]

Re: BB distrib housings; '65 to '69

Wayne , I checked the dist. from 16120 it is a 093 with a 5G8 date and a cast # of 110 . It has a groove that goes all the way around . I also have the orig. from 17346 but its not at home .

[Clem Z.]

Re: BB distrib housings; '65 to '69

no problem since you can't install the dist the wrong way with a vacuum advance installed. my guess the "bypass grove" is a groove put vertically on the bottom of the dist housing to allow oil to be sprayed onto the cam gear,dist gear interface from the passage around the dist housing.

notice groove in the lower part of the dist housing to pressure oil the gears. just use a triangular file.

[Wayne M.]

Re: BB distrib housings; '65 to '69

Clem, others --- is this the factory "notch" that you refer to for shim pack and gear teeth oiling ? Did they not also use this to retain a "tang" on a special washer for aluminum housings so the shim stack would not eat the softer metal ?

Interesting that on the '66 BB Corvette (left) with partially filled oil annulus, they had to move the notch away from the filled section, or else the oil might not leak enough. The distr on the right is off a 1970 small block; I aligned the tach drives so we can see the relative positions of the part-filled annulus and the tangs.

Out of the 8 or so distrib's I have, there are only two further exceptions to the slot configuration/location; ie. NO slot in the 1111263 ball bearing/partially filled annulus/reverse gear teeth for reverse rotation cam; and a 1964 distrib (full grooved annulus) that is about 90 degrees off what would be expected.

[Clem Z.]

Re: BB distrib housings; '65 to '69

Clem, others --- is this the factory "notch" that you refer to for shim pack and gear teeth oiling ? Did they not also use this to retain a "tang" on a special washer for aluminum housings so the shim stack would not eat the softer metal ?

Interesting that on the '66 BB Corvette (left) with partially filled oil annulus, they had to move the notch away from the filled section, or else the oil might not leak enough. The distr on the right is off a 1970 small block; I aligned the tach drives so we can see the relative positions of the part-filled annulus and the tangs.

Out of the 8 or so distrib's I have, there are only two further exceptions to the slot configuration/location; ie. NO slot in the 1111263 ball bearing/partially filled annulus/reverse gear teeth for reverse rotation cam; and a 1964 distrib (full grooved annulus) that is about 90 degrees off what would be expected.

i would guess it is used to allow oil to flow to the dist gear dist housing interface since the pressure on the gear is upward against the dist housing.

[Tom D.]

Re: BB distrib housings; '65 to '69

Wayne: Another NCRS member here in MI suggested that some tach drive housings like the '66 version might have been produced or at least sold by non-Delco or non-GM parts suppliers. Do you believe this might have happened?

[Wayne M.]

Re: BB distrib housings; '65 to '69

i would guess it is used to allow oil to flow the dist gear dist housing interface since the pressure on the gear is upward against the dist housing.

Clem -- well then that would explain the lack of oil feed "notch" on this particular ball bearing distrib (pic below, on left), because (as I understand it) the thrust on a reverse rotation cam driven distrib gear would be downward.

My NOS 1111263 is on the left; I've heard that there is at least one other version of this same part # (from member Mike Zamora) including annulus open/distrib driven gear with helix teeth like all other Chev distr's (ie. w/chain driven cam).


c

[Clem Z.]

Re: BB distrib housings; '65 to '69

Clem -- well then that would explain the lack of oil feed "notch" on this particular ball bearing distrib (pic below, on left), because (as I understand it) the thrust on a reverse rotation cam driven distrib gear would be downward.

My NOS 1111263 is on the left; I've heard that there is at least one other version of this same part # (from member Mike Zamora) including annulus open/distrib driven gear with helix teeth like all other Chev distr's (ie. w/chain driven cam).


c

yes the thrust is downward on the gear drive cam dist

[Wayne M.]

Re: BB distrib housings; '65 to '69

Did 1965974 and 1966654 look alike w.r.t. the annulus? What is TFP?

Tom --that's what I was hoping others could tell me; ie. did early 396's (say, VIN 13000 thru 15000) not have a partially filled annulus ? And did the change from the first to the second part # reflect the modification to the annulus to solve an oil starvation problem to the valve train ? I've heard that the early 396's were prone to "swallowing a valve". One of the fixes was to change the rocker ball (add slots ?). I would have thought there would be a Chev Tech Bulletin on this subject.

P.S. TFP = typical factory production (ie. configuration of the part that would have been installed at the assembly plant) --- what the judges look for, of course only on parts that are visible during judging.