I have a question for you engine builders, and machinists. I have 2 360 blocks that a few of the main caps are loose in the register. I always thought they were to have an interference fit. Any remedy to this? Or are the blocks junk? Or am I wrong in the interference fit issue? Thanks - Andy

I freshen a few during the winter months and id say yes (Junk) simply because there has to be a way to index them if that's the proper term. Clearly the main bolts or studs do not center them so if it were not from the register step what would?

Maybe 10 years ago I had shop 4 bolt a block for me and it came back with what looked like one big wide chisel mark near the step and my take was this was to move a little material over prior to align boring.

I would think if you mixed and matched caps to get that oem fit where it takes a block of wood and a thump with a light hammer to set them you could have one (align) bored/honed and be ok. Would I use the bfh and a chisel, no, but it seemed to work on my block as it had a long service life and sits on the shelf for future use.

But im sure others will have some good input as to ways to correct this.

Do not use those as is. They have to fit tight and no you can not mix and match them to get them right either. Each cap is fitted to one saddle and that is it. If you mix and match them to get them tight then you will need it line bored and honed.

we machine our caps to have a .002-.004 interference fit. if the register is wider in the block we can custom machine a set of caps to fit. it would be good to have a machine shop measure what fit they want or we can provide the caps oversize and machine shop can custom fit them. definitely don't use as is.

Thanks for the info. I didn't think it was good that they are loose in the register. Heck my old 408 had over 400 passes on it with nothing but a set of ARP main studs in it and the registers were still tight when it came apart. I'll have to let my machinist look at those blocks, and see what his recommendation is.

Over heating a block will make the caps loose like yours They need to be held tight in the main webs from being fitted correctly I have seen a lot of SB and BB Cevy have loose main caps and the owners thought that was okay