Boring question...

I'm a bit of a newb when it comes to engine mods, but a friend and I were batting around a few ideas the other day.

So, the question is... When boring out the cylinders, do you need to go with oversize pistons or can you just get rings to make up the difference?

 

And the boring answer is. . .
Most likely you would end up with lots of piston rock. (or slap)
Machinists bore the cylinders to the exact size needed and measure the piston going in the hole.
A hone and re-ring in the original size would be way better than trying to go up to the next size and use the original pistons.

A quarter MM is ten thousanths inch extra clearance. That would rattle.

 

MaximumX: You cant Bore out the cilinder walls and get away with just adding new rings to your stock pistons. The reasons for boring a block, or in our case the cylinders is
1) you either have a lot of wear and scratches (scratches big enough for your finger nail to get stock on.)

2 you want to increase the size of your engine.

You may be able to get away with just HONING the cylinders IF your scratches are not too bad and then you can add new rings to your pistons. This is what I call a RE-Conditioning,this is not a rebuild.

I have not doen one of these on a bike, but on trucks with 4 cylinder engines I have done it and they have lasted years.

If you bore the engine out you WILL need new over sized pistons.

If you hone, make sure you do a cross hatch pattern.

 

I guess this is where I come in. I'm an automotive machinist, and I do this stuff all day. Yes, you need new pistons to bore the block. Oversized pistons are available for the XJ's, and one interesting tidbit, the cylinders are the same between the 650's and 750's except for bore size, so if you get the 750 crank, rods, and pistons, you can turn a 650 into a 750. I actually have all the stuff to do it, just haven't had the chance yet.

And yes, if you're just trying to re-ring the motor, most of the time you can get by with just honing the cylinders.

 

If you can Hone the Pitting or Scratches out ... you can go with Over-sized Rings.
If available.

If the damage requires an Over-size Bore ... you need Over-sized Pistons and Rings.
If you can find them.

Ask our resident Parts Department Manager what they got!

 

Maybe a quick email to Len is in order... Thanks guys!