Boring Block but getting conflicting advice

I have my 70 Evinrude block at

I have my 70 Evinrude block at the machine shop to be bored out. Previous owner: overheated…bad pump…bad warning horn and didn’t have Service Bulletin updates for cooling issues that scored 2 cylinders. Here is the issue; the machinist said he likes to have the pistons before boring. He is going to micro the groves and then tell me what size pistons to purchase. I’ve been told by others to just bore it out because the newer pistons are manufactured with very close tolerances. It was suggested that I bore it out 30 over and be done with it. The machinist also wanted to know the piston-to-wall clearance. I'm confused of what to do….can somebody help me out?

"Find a machine shop familiar

"Find a machine shop familiar with outboads. Many dealers have the capacity to do this work in-house, or have shops they use on a regular basis. Find out who your local dealers use and take your block there. He needs to check the original bore size by checking the engine spec. information, then add .010, .020 or .030 depending on how deep he needs to go to remove all scores. I have been out of the outboard business for 10 years, but at one time you could buy pistons as large as .044 oversize.

Good luck
Rick"

"[url=""]www.outboardrebore.co

"www.outboardrebore.com"

The shop is correct in wanting

The shop is correct in wanting the pistons first but they also need to tell you the size that will be needed.
If they say .20 will do then order the pistons but make sure they understand that they own those pistons if the parts are not correct.

It doesn't make sence to just over bore the block to .30 if .20 will do.

Either you trust the people doing the work or you don't.