1965-67 L79: is GM bolt #3733130 (trans mount bracket) same as exh. mfld. end bolts?

[Scott S.]

I'm trying to figure out the correct exhaust manifold fasteners for a 1967 L79 with C60. The '67 AIM (UPC C60-C1) calls out a specific stud for RH exhaust manifold bolt hole #1, and a specific bolt for RH exhaust manifold bolt hole #3 (the first of the two "center" holes, longer bolt than normal to accommodate A/C bracket support 3878222).

If I understand correctly, the other (regular) RH "center" bolt, and both LH "center" bolts, should be GM 3733134.

That leaves the remaining seven "outer" or "end" bolts (RH #2, #5, #6 bolt holes, LH #1, #2, #5, #6 bolt holes). Are these 7 bolts all GM #3733130, the same bolt used on the transmission mount bracket, located at UPC 6-B6, Item 8?

[Joe L.]

Re: 1965-67 L79: is GM bolt #3733130 (trans mount bracket) same as exh. mfld. end bol

I'm trying to figure out the correct exhaust manifold fasteners for a 1967 L79 with C60. The '67 AIM (UPC C60-C1) calls out a specific stud for RH exhaust manifold bolt hole #1, and a specific bolt for RH exhaust manifold bolt hole #3 (the first of the two "center" holes, longer bolt than normal to accommodate A/C bracket support 3878222).

If I understand correctly, the other (regular) RH "center" bolt, and both LH "center" bolts, should be GM 3733134.

That leaves the remaining seven "outer" or "end" bolts (RH #2, #5, #6 bolt holes, LH #1, #2, #5, #6 bolt holes). Are these 7 bolts all GM #3733130, the same bolt used on the transmission mount bracket, located at UPC 6-B6, Item 8?

Scott-----


Yes, they are exactly the same bolt.

By the way, the GM #3733134 bolt used for the center small block exhaust manifold bolt positions is also used for the transmission linkage-to- bracket center bolt. These bolts sometimes crack after long service; check yours.

[Scott S.]

Re: 1965-67 L79: is GM bolt #3733130 (trans mount bracket) same as exh. mfld. end bol

Scott-----


Yes, they are exactly the same bolt.

By the way, the GM #3733134 bolt used for the center small block exhaust manifold bolt positions is also used for the transmission linkage-to- bracket center bolt. These bolts sometimes crack after long service; check yours.

Thank you Joe.

If I understand correctly, there are 1/8" thick "spacer" washers (not shown in the AIM) normally used with the eight (or 7, with RPO C60) regular exhaust manifold "outer" or "end" bolts (GM 3733130), but not used with the four center bolts. I have two of these "spacer" washers that survived, but one is a bit misshapen. While trying to figure out the correct bolts, I tried the good spacer washer in different places.

I suspect that for the LH exhaust manifold, the 1/8" spacer washer should be used on all four of the outer 3733130 bolts, same as a car without C60. For the RH exhaust manifold, it seems like it would be different, but I think it ends up the same (again) as a non-C60 car on the RH exhaust manifold too. It appears that the spacer washers would be used on the RH #2, #5 and #6 bolt holes (counting from the front of the car toward the back), same as standard.

I thought it would be different with regard to the stud in the RH #1 bolt hole. However, in order to make the 3878222 Support bracket align without rubbing against the side of the exhaust manifold, I inserted the 1/8" spacer washer between the exhaust manifold and the "nut" portion of the Stud in RH #1 bolt hole (order: exhaust manifold, 1/8" spacer washer, stud, support bracket, end nut). This seems to align the support bracket perfectly, with NO 1/8" spacer washer on the bolt at the rear end of the 3878222 support bracket (RH exhaust manifold #3 bolt hole, special bolt 3841724 called out for that location in the AIM).

This configuration ends up with the 1/8" spacer washers at the following exhaust manifold bolt holes:

LH exhaust manifold (#1, #2, #5, #6, just as a non-C60 car)

RH exhaust manifold (#1, #2, #5, #6, again, just as a non-C60 car)


Does this sound correct? I can post pictures showing the bolts through the manifolds tomorrow, top-down view to show exposed thread-lengths on the head-side and the alignment of the 3878222 support bracket, if that would be helpful.

[David L.]

Re: 1965-67 L79: is GM bolt #3733130 (trans mount bracket) same as exh. mfld. end bol

Scott,

Pictured are the bolt, stud, and nut that came with a 3878222 support that I bought at a swap meet many years ago, original source unknown but my guess is a 1969 Corvette because of the nut w/threaded nut. Part numbers are from 1966, 1967, 1968, and 1969 assembly manuals.

Bolt: GM 3841724, head marking unknown because of serious rust pitting, 3/8"-16 X 3 11/16" effective length, 1 1/8" thread length.

Stud: could be GM # 3841723 but more likely GM # 3932448, 3/8"-16 X 2", thread length 1 1/8" on engine side; 3/8"-16 X 1 11/16", 5/8" thread length; 9/16" hex, 3/8" width of hex; total length = 4 1/16"

Nut w/distorted threads: GM # 9422297; 3/8"-16, flat on one side, "rounded" on the other side with 6 "dots" (or very small "bumps), one at each corner. The 1966-1968 Corvettes used nut # 120377.

Dave

[Scott S.]

Re: 1965-67 L79: is GM bolt #3733130 (trans mount bracket) same as exh. mfld. end bol

Scott,

Pictured are the bolt, stud, and nut that came with a 3878222 support that I bought at a swap meet many years ago, original source unknown but my guess is a 1969 Corvette because of the nut w/threaded nut. Part numbers are from 1966, 1967, 1968, and 1969 assembly manuals.

Bolt: GM 3841724, head marking unknown because of serious rust pitting, 3/8"-16 X 3 11/16" effective length, 1 1/8" thread length.

Stud: could be GM # 3841723 but more likely GM # 3932448, 3/8"-16 X 2", thread length 1 1/8" on engine side; 3/8"-16 X 1 11/16", 5/8" thread length; 9/16" hex, 3/8" width of hex; total length = 4 1/16"

Nut w/distorted threads: GM # 9422297; 3/8"-16, flat on one side, "rounded" on the other side with 6 "dots" (or very small "bumps), one at each corner. The 1966-1968 Corvettes used nut # 120377.

Dave

[Scott S.]

Re: 1965-67 L79: is GM bolt #3733130 (trans mount bracket) same as exh. mfld. end bol

Here are a few pictures of the 3878222 Support bracket on the RH manifold. With a 1/8" thick spacer washer on the Stud in #1 hole, the bracket appears to align correctly.

Edit: last picture has 1/8" thick spacer washer on #1 hole with equivalent of 1/8" spacers (2 x 1/16th) on #2, #5 and #6 holes.

[Scott S.]

Re: 1965-67 L79: is GM bolt #3733130 (trans mount bracket) same as exh. mfld. end bol

Here are the measurements showing how much of the bolt thread extends past the inner face of the RH manifold in the following configuration, with 3878222 AC Support bracket mounted:

GM 3841723 Stud (#1 hole, front of AC support bracket)
GM 3733130 outer or "end" bolts (#2, #5, #6 hole)
GM 3841724 Center bolt, rear of AC support bracket (#3 hole)
GM 3733134 Center bolt (#4 hole)

1/8" thick Spacer washer (or 2 x 1/16" thick washers to make an equivalent 1/8" spacer washer) on all four outer (or 'end') bolts.
No spacer washers on the two middle or center bolts.

[David L.]

Re: 1965-67 L79: is GM bolt #3733130 (trans mount bracket) same as exh. mfld. end bol

Scott,

What is the casting date on your 3878222 support?

My 3878222 support has a circle logo, a large "D" (9/32" high), then below that a large "1" (9/32" high), screw, "191", screw, then a large "+" sign. The casting date is the 191st day but of what year? I think it is 1969 vintage because of the 9722247 nut w/distorted threads that was used in 1969. I believe that the large "1" indicates the form number where it was cast. I believe that the circle logo & large "D" are for the vendor as I have seen this same logo on 63 and 64 master cylinders which also just have the 3-digit day of year without anything for the actual year.

Dave

[Scott S.]

Re: 1965-67 L79: is GM bolt #3733130 (trans mount bracket) same as exh. mfld. end bol

Scott,

What is the casting date on your 3878222 support?

My 3878222 support has a circle logo, a large "D" (9/32" high), then below that a large "1" (9/32" high), screw, "191", screw, then a large "+" sign. The casting date is the 191st day but of what year? I think it is 1969 vintage because of the 9722247 nut w/distorted threads that was used in 1969. I believe that the large "1" indicates the form number where it was cast. I believe that the circle logo & large "D" are for the vendor as I have seen this same logo on 63 and 64 master cylinders which also just have the 3-digit day of year without anything for the actual year.

Dave

I'm not sure if mine is dated, or if it is, what the code means. It doesn't have quite the same markings as yours, it's missing the screw outlines and has a different logo-letter combination. One side has "3878222" over "GM", and the other side has what looks like a "B" (or possibly an "8") inside a circle, with the number "18" to the right.

The car was built January 11, 1967. The majority of parts are dated November or December 1966, getting fewer as you go back until August of 1966, which I think is the earliest date that I have found on a part. At the other end of the spectrum, the 'newest' parts are from January of 1967, the tire tub (dated Jan. 6, 1967) and the steering column dated 005 7 (January 7th).

If the number on my 3878222 support bracket represents the day, that would mean either the 18th day of 1966 (unlikely) or the 18th day of 1967, about a week past the production date. Do these markings explain anything, one way or the other?

[David L.]

Re: 1965-67 L79: is GM bolt #3733130 (trans mount bracket) same as exh. mfld. end bol

Scott,

I would say your 3878222 support was probably made by GM since there is a GM casting. Your support has the casting number where the numbers are "raised" while mine has a casting number where the numbers "sink in". I do not have the "GM" casting.
I believe that my 3878222 was made by Delco-Moraine because of the circle logo and "D" which are the same as on the 1963-1964 Chevrolet & Corvette master cylinders.
Thanks anyway,

Dave