Oversize case bolts

[neilca]

I was at the shop last night looking over a case I will be using for my first race motor. I don't have the through case bolts for this case and was wondering what to do. With the type IV motors it is common to increase the through case bolts to 1/2" fasteners instead of shuffle pinning. The six cylinder (3R Case) holes are strange. On the inside near the bearing the hole has a 12 mm diameter, on the outside the holes are 10.5mm. I am thinking of boring the outside to 12mm and using 12mm through case bolts.
Any comments on this?

Thanks,
neilca

[ChrisBennet]

The case though bolt holes double as oil passages to feed the piston squirters so the stock ones leave room for oil around them. I've never heard of through bolts failing but I don't get out much.
-Chris

[Eagledriver]

The oil passages also feed the main bearings so you can't block them with a bolt that fits tight. I've heard that the factory did something like this with a bolt that had a "fat" section where the case halves met. This was to act like shuffle pins. They also made some kind of provision for the oil to get by. Something like a groove in the case or bolt might do it.

-Andy

[adomakin]

someone was saying that ARP were looking into making the fatter case through bolts to act like a shuffle pin setup but with a groove machined in the side of the bolt where needed to allow the oil past

[neilca]

I didn't know oil went through this space! Glad I asked.

Thanks guys,
neilca

[Wayne 962]

Yup - bad idea here, but good thinking. In general, you don't want to cut any material from the case anyways, as that would make it even weaker...

-Wayne