Re: Grade 7 bolt
Now for some information on the big block crankshaft snout bolt:
As I mentioned previously, I was previously unaware that the big block crankshaft snout bolt was a GM-290-M grade bolt (SAE grade 7). However, some photos of original bolts from big block applications clearly demonstrated that it was. Curiously, those photos seem to have disappeared from this thread which, I suppose, means the posters deleted them. I cannot figure out why. However, Mike Browning included in post #13, above, the bolt from his 1965 L-78. I have no doubt this is the original bolt although it differs somewhat from the bolts previously pictured (but now deleted). The things that both bolts have in common is that they are GM 290-M, 1/2-20, phosphate finished, and 1-1/2" in length. However, the bolt pictured in #13 above is fully threaded while the bolt previously pictured had 3/4" un-threaded shank.
GM never specifically cataloged a crankshaft snout bolt for a big block. I searched high and low and, basically, came up with very little. Even, big block engine assembly manuals do not specify a particular part numbered bolt. But after a lot of further research, I finally came up with it. It's a very old part number dating back to the early 50's and was originally used for a completely different application. However, I believe it's the bolt used for most big blocks although likely not as early as 1965 as post #13 demonstrates.
Attached are photos of said bolt and it's identical to the bolts pictured in the now apparently deleted posts. The one pictured is an NOS example, maybe the only NOS example left in the world [not for sale]. This bolt was discontinued by GM in 1981.
DSCN4372.jpgDSCN4374.jpg
Now for some information on the big block crankshaft snout bolt:
As I mentioned previously, I was previously unaware that the big block crankshaft snout bolt was a GM-290-M grade bolt (SAE grade 7). However, some photos of original bolts from big block applications clearly demonstrated that it was. Curiously, those photos seem to have disappeared from this thread which, I suppose, means the posters deleted them. I cannot figure out why. However, Mike Browning included in post #13, above, the bolt from his 1965 L-78. I have no doubt this is the original bolt although it differs somewhat from the bolts previously pictured (but now deleted). The things that both bolts have in common is that they are GM 290-M, 1/2-20, phosphate finished, and 1-1/2" in length. However, the bolt pictured in #13 above is fully threaded while the bolt previously pictured had 3/4" un-threaded shank.
GM never specifically cataloged a crankshaft snout bolt for a big block. I searched high and low and, basically, came up with very little. Even, big block engine assembly manuals do not specify a particular part numbered bolt. But after a lot of further research, I finally came up with it. It's a very old part number dating back to the early 50's and was originally used for a completely different application. However, I believe it's the bolt used for most big blocks although likely not as early as 1965 as post #13 demonstrates.
Attached are photos of said bolt and it's identical to the bolts pictured in the now apparently deleted posts. The one pictured is an NOS example, maybe the only NOS example left in the world [not for sale]. This bolt was discontinued by GM in 1981.
DSCN4372.jpgDSCN4374.jpg
Comment