Would grade 5 or grade 8 motor mount bolts be necessary on my 67 BB? I'm not concerned about replacing them with GM NOS, just a high-quality bolt from ye-olde-hardware store.

I heard that one had better sheer strength and the other had a better tensile strength...

I use L9 but I am fairly certain a grade 8 would be fine. American made of course.:yes:

not sure what grade they are but if it has a big cam i would use the blue one's, any farm copo would have. atwoods is a good place for bolts they have three different grade amd they sell them by the pound , that what i like about them, and their peanuts and pickles are a GOOD DEAL

I used grade 8 on mine.

At least grade 8, made in the US of A.

Grade 8. Do yourself a favor and grind the ends to a point. It will make lining up the holes MUCH easier.

If you used grade 5's and the motor mounts would hold you could lift the whole car by the engine. The shear on a good quality grade 5 bolt in 2 places at the same time to make it fail would be some huge torque numbers. Typically the part that always fails here is the mount itself. 8's will work also . Like they said use USA hardware and you'll be fine.

Good luck trying to find USA made hardware! :sad:

Any idea what the factory bolts are?

Any idea what the factory bolts are?

I believe original bolts are grade 8.

As others have said, try to get "made in USA".

I have had several foreign made bolts, marked as grade 8, fail.

Some of them are being laboratory tested at this time.

Verle