HondaCB650

I've had a few 650's and someone Once said I can't get overbore pistons.....

So I have 66, 64.75, 62, 61 and 60mm piston sets I have modified for the 650.
Most for stock cam, 1 set for turbo, 2 550 sets, and 1 set for a lumpy cam. 9 useable sets in total.
Cb750, kz650 and kz750 pistons are the easiest to mod I have found in abundance.
The piston pots and mill fixture are made by me.


L8r

That's a skill I would like to know about. I'm sure some other non-machinists would love to see a write-up with pictures on how you modify pistons for another engine! Are you a machinist by trade?

Yes I am a machinist. Trained in '98/'99 been in the trade ever since. Lots of repair shops, manual machines, and vtl lathes. I'm CNC functional.... more a fat finger at the console programmer than a mastercam user.
(mastercam writes the program for you once you draw the part in 3-d in mastercam)


I first got the idea of modifying pistons when I saw what NOS piston sets cost, and I found 1 overbore set that sold on ebay for over $600.
I was told there is no way to getting a 650 overbore for a fair price on a few honda cb forums.
At the time my 650s motor was starting to smoke(slightly stuck ring or two)

So I ended with the first useable set I could get rings cheap for.
A 76?77?... the first year of the cb750 hondamatic.
It has a higher dome than any other cb750.
Thats the first piston pot I made. 61mm. Shortly after, piston pot for stock 59.8mm pistons.

Turned only a little off of them in the manual lathe, I think it was the skirt mainly.
I basically copied a cb650 skirt length, deck height.

That first set, I set a manual mill up, and angled the head and positioned the valve pockets by mimicking where they were on a stock set.
And now I had 2 piston lots, 59.8mm and 61mm.

The piston pot is basically a thick walled aluminum sleeve with a custom bolt that goes through the wrist pin bore to hold the piston while machining it in a lathe.
In a mill it was a challenge to be able to get both valve pockets in the exact position in 3 axis, without 2 setups.
But I came up with a fixture I could set a hardened steel pin to center a cnc z,y,x on, and run 2 programs, one for the intake, one for the exhaust valve pockets.

had to use a manual mill to make the aluminum fixture, but I now have a fixture that fits a common good quality vice in most machine shops.


Been a while since i looked at them, but with the overbore to 62mm going on, thought I'd show them off since they were out.


L8r

Cb673 wrote:Yes I am a machinist. Trained in '98/'99 been in the trade ever since. Lots of repair shops, manual machines, and vtl lathes. I'm CNC functional.... more a fat finger at the console programmer than a mastercam user.
(mastercam writes the program for you once you draw the part in 3-d in mastercam)


I first got the idea of modifying pistons when I saw what NOS piston sets cost, and I found 1 overbore set that sold on ebay for over $600.
I was told there is no way to getting a 650 overbore for a fair price on a few honda cb forums.
At the time my 650s motor was starting to smoke(slightly stuck ring or two)

So I ended with the first useable set I could get rings cheap for.
A 76?77?... the first year of the cb750 hondamatic.
It has a higher dome than any other cb750.
Thats the first piston pot I made. 61mm. Shortly after, piston pot for stock 59.8mm pistons.

Turned only a little off of them in the manual lathe, I think it was the skirt mainly.
I basically copied a cb650 skirt length, deck height.

That first set, I set a manual mill up, and angled the head and positioned the valve pockets by mimicking where they were on a stock set.
And now I had 2 piston lots, 59.8mm and 61mm.

The piston pot is basically a thick walled aluminum sleeve with a custom bolt that goes through the wrist pin bore to hold the piston while machining it in a lathe.
In a mill it was a challenge to be able to get both valve pockets in the exact position in 3 axis, without 2 setups.
But I came up with a fixture I could set a hardened steel pin to center a cnc z,y,x on, and run 2 programs, one for the intake, one for the exhaust valve pockets.

had to use a manual mill to make the aluminum fixture, but I now have a fixture that fits a common good quality vice in most machine shops.


Been a while since i looked at them, but with the overbore to 62mm going on, thought I'd show them off since they were out.


L8r

Very well explained ..