Building a 347
 

I'm putting a 347 together and running into some small clearance problem's where the crank and pistons meet at the bottom of the stroke. I believe all pistons will need to be clearanced. The couple I have checked touch in two or more places but the motor will still turn. Is it ok to just barely clear, a few thousanths, or do I need to really remove a lot of material. This is not a street motor, it is a full race 9000rpm blower moter, billet crank, oliver rods and JE custom pistons. The last motor used wiesco pistons and cleared the crank. I am doing this myself, please don't recommend another shop to assemble. Every one we have used in the past did something wrong. A LONG list.

9000 rpm sounds like on hell of a motor. I am no pro but I think it is strange that you are having that problem. My 347 had plenty of room and I would think that all rotating assemblies would be checked for that before sold. Are you running the basic 3.4 stroke crank, 5.4 rods and a 30 over bore? or is this a custom setup? Do the pistons pop out past the deck over spec? Maybe you got the wrong pistons, or the pip height is not correct. Like I said I am no pro these are just my thoughts.
As far as grinding on the piston skirts I would think that if you did that you would need to get it reballanced especially if you spin it to 9000rpm

If your assembling the 347 from your existing 302 block, you can run into issues where the rods will knick the bottom of the cylinder walls. You will have to grind down those spots and you will be fine. If they dont touch you should be fine.
Derek

This is an R-302 block and already modified for clearance. We are touching the crank throws when the piston is a bottom dead center. The Wiesco pistons used last time had less piston skirt so I believe we are going to do a little grinding with a template we will make from those pistons. This is not a kit. Everything is custom and high dollar. So far we have ran this combo into the 8.50 range at over 160MPH with a 3350lb. car. If we could just make it hold together a little longer this time:)