AMC 401 Ground off

I have a friend that bought a long block from a reptable machine shop, so I've been told. :-| Th block has the "401" casting ground off the side of the block. The internals are 401, but we don't know if the block is 390, punched or resleeved 360, or what. I thought the 390 had a different deck height and the 360 has different journals. Plus, isn't a 390 worth more than a 401? So why grind off the "401" casting? Is there another way to tell what the block is? If there were no problems with this motor, I wouldn't be asking, but it overheats when towing and he has detnonating problems. He runs regular gas, but with an 8.5:1 compression, that shouldn't be an issue. New radiator and the timing is right on, and even had the tranny checked out to see if that was an overheating issue. Help guys.

It could be a factory service block. They were cast with no displacement # on the side. They were cast so they could be finish bored to either a 360 or 401. What's the casting number? It's on the bellhousing web on the left side.

68/69 390s do have a shorter deck. 70 390 and 401 are identical bore blocks, only the crank and rods are different.


Bob
tufcj

It's installed in a 89 Grand Wagoneer so I'm not sure if he can get to the numbers. I'll have him check though.

What year did they change the headbolt size. He has the small headbolts.

70-up had 1/2" head bolts. 66-69 had 7/16" head bolts.

If it's a 68/69 block, the casting # should be 3190806, a 70-up would probably be 3195528. If it is a 390/401 the standard bore will be 4.165". A 360 has a 4.080" bore.

Bob
tufcj