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Earlier today another member contacted me by e-mail with a few questions regarding a 69 big block which he is restoring. I did a little research on the subject and I thought that I'd post the info on the board in case it might be of interest to others. Be advised, though, that big blocks are not a particular area of expertise for me. All my big block experience was with Chevelles during the 66-68 time period. That was enough and the reason why, when I ordered my 69 Corvette, I decided to go with a small block. It must have been a good decision and a perfect match because I've kept the car for almost 30 years now. Anyway, enough. Here goes:
1- The member was having problems with an exhaust manifold bolt kit which he purchased from Paragon. Seems that the manifold end bolts were "bottoming out". He was also wondering if 69s BBs had washers on the manifold end bolts and whether the end bolts might have had flat washers. In addition, he wondered whether or not french locks were used on 69 BB exhaust manifold end bolts.
1969 big blocks originally used exhaust manifold end bolts GM # 3909821. This bolt is 3/8"X 1-3/16" and it is still available from GM at a list price of $1.45. I believe that these bolts were used with the thick, flat washer at the end locations regardless of what some sources might contend. To test this theory would be relatively simple. Since GM # 3909831 is still available, obtain one and try it at the end bolt location. If it "bottoms out", that might be a pretty good indication that these bolts were originally used with washers. Incidentally, I checked the 1969 specification for 3909831 and it is the same as today's part so it's not as if today's 3909831 is different than the 1969 version of that part number.
All of the original "center" bolts for 1969 BB were GM part # 3736035. This bolt is 3/8"X 1-1/4" and is still available from GM at a list price of $2.75. The end stud for cars with power steering was GM #3928905. This stud was 3/8"-16--5/16"-18X 2-5/32". It was discontinued quite some time ago and replaced by GM # 14103124. I do not know the configuration of the new part number.
Regarding french locks for the 1969 BB exhaust manifolds, I do not believe that any were originally used and this is consistent, I believe, with "conventional wisdom".
2-The member was having problems with the accelerator return spring. He had purchased a reproduction "orange" color-coded spring which was supposed to be correct for his 69 3X2 carb installation.
1968 Corvettes with 3X2 427s used accelerator return spring GM #3937913. This spring was color-coded "yellow" and had a free-length of 3-5/32" with 10 coils. This spring was installed so that one end attached to the upper eyelet of the center carb accelerator lever and the other to the center carb fuel line(yes, it was kind of hoaky). The accelerator cable bracket attached to the left rear mounting stud of the rear carb was GM #3921613 and this bracket was not used as a mounting point for an accelerator return spring in 1968, as far as I know.
1969 Corvettes were apparently originally scheduled to have this same set-up but, before production began, the design was changed. In the new design, the rear accelerator mounting bracket was originally the same as for 68(#3921613)and this bracket was used with a new spring. This spring, GM #3939748, was color coded "orange", had a free length of 4-3/8" and 14 coils. As far as I know, the spring was attached to some point on the rear accelerator mounting bracket and an eyelet on the lower part of the center carb accelerator lever. However, I am not sure of the spring mounting locations.
Later on, the design of the accelerator return system was changed again. Bracket #3921613 was replaced by bracket GM # 3972629. The accelerator return spring was changed to GM #3972631. This spring was also color coded "orange"(a really dumb thing to do), but had a free length of 3-25/64" and 19 coils. This spring attached between an eyelet on the bottom of the center carb accelerator lever and a hole on the bottom of the 3972629 bracket.
At about the same time as the above occurred, another change was made which is very poorly documented in the assembly manual. Apparently, an additional bracket was added. This bracket was GM part # 3960647. I know very little about this bracket or how it was mounted because the available AIM is incomplete. However, I did find a listing for this bracket in a 1969 GM Parts manual. It is described as "BRACKET, spring". I expect that this is the bracket sold by reproduction sources like Dr. Rebuild.
1- The member was having problems with an exhaust manifold bolt kit which he purchased from Paragon. Seems that the manifold end bolts were "bottoming out". He was also wondering if 69s BBs had washers on the manifold end bolts and whether the end bolts might have had flat washers. In addition, he wondered whether or not french locks were used on 69 BB exhaust manifold end bolts.
1969 big blocks originally used exhaust manifold end bolts GM # 3909821. This bolt is 3/8"X 1-3/16" and it is still available from GM at a list price of $1.45. I believe that these bolts were used with the thick, flat washer at the end locations regardless of what some sources might contend. To test this theory would be relatively simple. Since GM # 3909831 is still available, obtain one and try it at the end bolt location. If it "bottoms out", that might be a pretty good indication that these bolts were originally used with washers. Incidentally, I checked the 1969 specification for 3909831 and it is the same as today's part so it's not as if today's 3909831 is different than the 1969 version of that part number.
All of the original "center" bolts for 1969 BB were GM part # 3736035. This bolt is 3/8"X 1-1/4" and is still available from GM at a list price of $2.75. The end stud for cars with power steering was GM #3928905. This stud was 3/8"-16--5/16"-18X 2-5/32". It was discontinued quite some time ago and replaced by GM # 14103124. I do not know the configuration of the new part number.
Regarding french locks for the 1969 BB exhaust manifolds, I do not believe that any were originally used and this is consistent, I believe, with "conventional wisdom".
2-The member was having problems with the accelerator return spring. He had purchased a reproduction "orange" color-coded spring which was supposed to be correct for his 69 3X2 carb installation.
1968 Corvettes with 3X2 427s used accelerator return spring GM #3937913. This spring was color-coded "yellow" and had a free-length of 3-5/32" with 10 coils. This spring was installed so that one end attached to the upper eyelet of the center carb accelerator lever and the other to the center carb fuel line(yes, it was kind of hoaky). The accelerator cable bracket attached to the left rear mounting stud of the rear carb was GM #3921613 and this bracket was not used as a mounting point for an accelerator return spring in 1968, as far as I know.
1969 Corvettes were apparently originally scheduled to have this same set-up but, before production began, the design was changed. In the new design, the rear accelerator mounting bracket was originally the same as for 68(#3921613)and this bracket was used with a new spring. This spring, GM #3939748, was color coded "orange", had a free length of 4-3/8" and 14 coils. As far as I know, the spring was attached to some point on the rear accelerator mounting bracket and an eyelet on the lower part of the center carb accelerator lever. However, I am not sure of the spring mounting locations.
Later on, the design of the accelerator return system was changed again. Bracket #3921613 was replaced by bracket GM # 3972629. The accelerator return spring was changed to GM #3972631. This spring was also color coded "orange"(a really dumb thing to do), but had a free length of 3-25/64" and 19 coils. This spring attached between an eyelet on the bottom of the center carb accelerator lever and a hole on the bottom of the 3972629 bracket.
At about the same time as the above occurred, another change was made which is very poorly documented in the assembly manual. Apparently, an additional bracket was added. This bracket was GM part # 3960647. I know very little about this bracket or how it was mounted because the available AIM is incomplete. However, I did find a listing for this bracket in a 1969 GM Parts manual. It is described as "BRACKET, spring". I expect that this is the bracket sold by reproduction sources like Dr. Rebuild.