Whats up guys I have a Benson sleeved b16a2 that is o-ringed at the top of the cylinders, I am wanting to rebuild it and go from 83mm to 84mm but am wondering what happens with the o-ring groove? Boring it would put the cylinder diameter about halfway into the groove leaving a little step...so what is the machine shops procedure for this? It was already decked once it doesn't seem like a good idea to deck it again all the way until the groove is gone? ...Any info is helpful thanks!






Chris

 

First, are you sure 1mm overbore will over run the Oring groove?
Secondly why move up 2 sizes? why not 83.5mm?
You could always consider custom pistons with a custom diameter and not move up a full size.

Youd have to mill .020~.030" to shave off the groove. That would put your pistons out of the hole.
To compensate you'd need to move the wrist pin up or run extra thick head gasket. yuk

 

Thats a good idea about custom piston diameter that would solve the problem for sure, really didnt want to ditch this block.. it has a lot of boosted miles on it and is smoking now so I was thinking it may need 84 to clean up but I guess I wont know until its measured. .5mm is pretty small after looking at my caliper maybe there is room

 

if your looking for a clean up .5 should be fine that's pretty much the norm... clean bay by the way!!!

 

Depending on piston forging and power level, you can sometimes just purchase another piston. This is one of the many reasons why I suggest running 4032 forging first then switching to 2618 later on (assuming it is honable). Most people end up wanting more power than they originally thought anyways...

 

Interesting concept. Most ppl dont plan on having to rebuild though.

 

With age you tend to learn to plan for the future... hehe.

Either way, the OP needs to do some measurements before any speculation is done. If the O-Ring groove was cut properly to begin with there should be adequate clearance to go 1mm over is need be.

 

Beat me to it. Was just thinking this while reading the OP.

There "should" be more than enough room for over-boring on an o-ringed block if it was originally cut properly and the OP has owned the block from the time of sleeving. UNLESS the block was previously owned and o-ringed at 81.5 or 82mm and has been over-bored already before the OP acquired it.

Pictures of said block deck surface will tell 1000 words.