Putting together a 400 sb short block for an '87 IROC when I ran into a major issue. Block is a '76 .030" over splayed, running a forged Scat crank w/ a 3.75" stroke, and rods are Scat Pro Comp I-Beam 6". The short block came together perfectly, but as soon as I started rotating the crank , there was one spot in the rotation where the crank seized. After careful thought and observation, I found that the side of the connecting rod was actually hitting the bottom of the cylinder. This was the #1 connecting rod hitting the bottom of #2 cylinder. I took #1 and #2 pistons out, and checked the other rods/cylinders. Although the casting on #2 cylinder is larger than the other cylinders, the clearances on all the other cylinders/rods are merely a couple thousandths. Has anyone else encountered this problem? I haven't seen any other posts addressing this issue, which is why I'm posting this. I was thinking of filing the cylinder bore in the problem areas myself or having a machine shop do it, or even filing the connecting rods themselves, but I'm afraid that would throw off the balance. Any suggestions or help would be greatly appreciated!

 

Happens all the time.

Gotta grind the block where the interference occurs.

Use a tie-wrap as your guide for clearance, throughout the engine. (~ .030")

DO NOT touch the rods except as an ABSOLUTE LAST RESORT; which, doesn't sound like you're anywhere close to that.

 

Yeah it's very common on longer rod 3.75" and up stroke engines. (383, 400, 406, etc)

It's also the main reason GM used a short 5.565" rod in the 400.

Like sofa said, grind/clearance the block, just do not grind more than you need off.. Go slow and take your time. Sofa's tie wrap trick is a good one, I thought I was the only one to do that but guess not lol.