CB360 Big Bore Engine Build - questions

[mattfeet]

1.) The GS850 pistons are lighter than the CB360 pistons by 11%. 8.33oz vs. 9.44oz for the CB360 pistons. This is including pistons rings and clips. Will this difference in weight be enough to throw the crank out of whack?

2.) If the difference is significant enough, what measures need to be taken to get the GS850 pistons closer to stock weight?

-Matt

 

[mattfeet]

GS on left - CB on right

 

[speedwobble]

I will add to this, being that this is my piston set up there in the pic...

Cutting the crank counter weights, or adding metal for balancing, is typical in automotive machining.. From what I know of that, this difference in weight is a BIG No-No in engine balancing.. The question is then, do the same rules apply here? (I would assume so) but then, others seem to have gotten away with not addressing this issue when building a 360 motor with these pistons. So what's the scoop gents? Is there some magic about motorcycle motors that I don't know about?!

TIA

 

[rockcitycafe]

never rebalanced the crank in mine, no problems in that department...

 

[mattfeet]

Nice. So just drop them in, measure, and go? New gaskets obviously but no other machine work besides overbore?

 

[crazypj]

Yep, thats all
I've never re-balanced a crank, lighter pistons give the rods an easier time
The stock 360 isn't as smooth as it could be, personally I think lighter pistons cut vibration not add to it

 

[timberwolffxdl]

reviving an old topic to ask a followup question... can someone tell me the part number on which to search for stock bore GS850 pistons?

Also...if I have to buy a set of 4, anyone want to split with me?

 

[crazypj]

You'll have to look for NOS, Suzuki discontinued them years ago.
I had to buy a complete cylinder and piston set from eBay, liners were too rusty to use but pistons more or less OK (you bore to piston size so slight wear doesn't matter)
I think the only alternative to used or getting lucky with NOS is to go aftermarket but that will be expensive

 

[timberwolffxdl]

You'll have to look for NOS, Suzuki discontinued them years ago.
I had to buy a complete cylinder and piston set from eBay, liners were too rusty to use but pistons more or less OK (you bore to piston size so slight wear doesn't matter)
I think the only alternative to used or getting lucky with NOS is to go aftermarket but that will be expensive

I've got the pistons and couple sets of 360 cylinders. Even got the copper gaskets ordered from Lani. I see rings on eBay, but want to make sure I'm getting the right one.

 

[focusinprogress]

aren't GS500 twin pistons another option for big bore in a cb360?

 

[crazypj]

Not really, you need to be able to do your own machining to go 8mm oversize compared to a straight bore job 2mm oversize with 850 pistons

 

[crazypj]

I've got the pistons and couple sets of 360 cylinders. Even got the copper gaskets ordered from Lani. I see rings on eBay, but want to make sure I'm getting the right one.

All the GS850's use same rings (or at least they are all compatible)
If you have a piston ring filer you could use oversize and file to fit for correct ring end gap