Ok I feel like Im losing my mind. Im reinstalling the motor mounts on my LT1 to put back in the chassis. Ive literally done this like 8 times before doing rebuilds for my racing career. I bought new factory motor mounts because im putting the race car back to factory. I have used ARP 3/8th inch bolts all these years. For some reason the new passenger side engine mount bolt holes are 1/2 inch big. The ARP bolts will slide all the way through this size hole. Looking online mounts from other manufacturers also look like they're 1/2 inch. And looking at new motor mount bolts they are all saying they are 3/8". Of course I already threw away the one I took off so I cant compare. What the hell am I missing? Thanks -

 

The bolts that secure the mount to the block are 3/8-16 x 3/4.

 

Right! So whey this mount has 1/2" bolt holes blows my mind when the other side mount has 3/8" holes to match the bolts, you could bolt this mount on very crooked. The fact that the head of these ARP bolts slide right through this hole means if I just put a washer on it to make it work then the bolt head isnt even pressing on the mount, its pressing on a tiny slice of ~1/16" washer. Doesn't seem safe. I looked around for the original bolts and it looks like they may have been large flange headed bolts. Anyone know this? These would at least put pressure on the mount and make some sense. I think this is what I will go to.