Bennie -

Looks like we are both trying to replace the center bolts in our front motor mount. Mine is a '54. I could not find 7/16-20 carriage bolts standard or hardened anywhere. They may be available only as salvage from another engine. The best choice I could find is ...
> 7/16"-14 x 2-1/2" Zinc Finish SAE J429 Grade 5 Round Head Carriage Bolt
or
> 7/16"-14 x 2-1/2" Plain Finish SAE J429 Grade 5 Round Head Carriage Bolt

MPC specs for washers for the two center motor mount bolts:
> GM #352282 7/16"ID X 13/16" OD 0.062' Thick

Also MPC specs for the washers for the two outer motor mount bolts:
> GM #365685 3/8"ID X 1-1/4"OD 0.187" Thick

Hardened hex nuts or lock nuts, washers, and the carriage bolts are all available from Fastenal. They also have Grade 5 3/8-16 carriage bolts for the two outer bolts. 3/8-24 carriage bolts are not available.

Now the big question - - -
Are you replacing the 7/16" carriage bolts while the engine is in the truck? If so, please tell me how. I don't think that I can get them through the front plate while the engine is in my truck. < CLICK > to read my current post on Stovebolt.

- Lonnie
My '54 3104
Photos that I have shared on Stovebolt via PhotoBucket are no longer available. Please contact me if you want a photo from an old post.
lonniecook [at] aol [dot] com. I sold my '54 3104 12/12/2017, but I still visit Stovebolt.

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