CB360 Pistons in a CB350

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kbaszak

New Member
So I've inherited a couple bikes from my dad (read:they've been sitting in the garage and I want to get them to run so they're not taking up space). For some reason, he has a complete 360 engine that looks pretty much brand new and has .5 over pistons and I was wondering how they'd work in a cb350. I know the wrist pin is bigger (16mm for 360 and 15mm for 350 if I'm not mistaken) but other than that, how would the compression and skirt length and what not work with a 350.
 
I don't think it works.
I looked at it about 7~10 yrs ago, can't remember much about it but it was more trouble than it's worth. (and I do some weird stuff ;D )
360 motor doesn't fit 350 frame without some major cutting and welding either
You would be better off either finding a titled 360 frame or just building 350 motor
 
wrist pin is for sure different, and I think the 350 pistons are taller (longer distance from wrist pin to dome)... pj's right, just find a 350 engine, they're all over the place
 
Sorry, first post was confusing. I just bought a 350 engine but the walls are toast and it needs to be bored out. My dad had a set of some really nice .5 over 360 pistons but I have no other pistons for a 350. One of my dads really good friends is a engine machining instructor at pretty well known automotive school so the engine work would be free.

Sorry for the pretty poorly worded first post, guys.
 
If you can get it done free it may be worth exploring.
Honda XR/ATC200 pistons may be a better option though (can't remember if they are too short or too long but I know they will fit)
 
I've been trying to find some good specs for both motors but haven't really been able to find anything comprehensive enough. If anyone could point me in the right direction that'd be great
 
Give me a few hours until I get to the garage to change out the tranny in my metro and I'll post some pics with all the measurements for a CB350 stock piston. I still have mine as they were not in bad shape, but figured I would bore it out vs honing and new rings to get a slight (very slight) increase in output.
 
Well here's a pic with measurements as best as I could get with the ole digital calipers.
Pistonprofile.jpg
 
the cb350 and cb360 have different wrist pin diameters. unless you've got a pretty good machining setup, probably including surface grinders and a few thousand in associated fixtures, it's not something you can overcome in your garage. cb350 os pistons and rings are on ebay for really cheap
 
I know someone who teaches a machining class at a pretty well known automotive school so machining cost isn't a problem. So it's either cost of wrist pins or cost of pistons. I haven't really looked at which would be cheaper but I can't imagine wrist pins being more expensive than pistons.
 
It looks like it'll bring the compression down alot though.. Looks like the 360 pistons are about 5mm shorter from wristpin to dome
 
so what's your procedure for fitting a piston with a 16mm pin into a con rod with a 15mm hole? because from my comparatively limited machining experience, that sounds like a rather involved job
 
Roc City Cafe said:
so what's your procedure for fitting a piston with a 16mm pin into a con rod with a 15mm hole? because from my comparatively limited machining experience, that sounds like a rather involved job
Click to expand...

It's actually pretty simple to make some sleeves to fit over stock pins.
They must have an internal lip to prevent 'small' pins sliding out and chamfered for circlips.
Hardest part is making everything accurate enough.
I've use same method in several motors
It's much safer than grinding out small end
 
do the sleeves move against the pistons or do the pins move against the sleeves? seems if the sleeves moved against the pins, you'd have to factor in some method for keeping them aligned with the oiling holes
 
What's the danger in putting the rod on bridgeport with a boring bar and boring it out to 16mm? But now that I've noticed the 360 pistons are quite a bit shorter I'm thinking about just selling them and getting 350 pistons. I'm a pretty broke college student so I was trying to save money where I could on this but I think the lack of compression would be pretty significant.
 
First off, you have to completely strip crank to get rod off it. (it's not like an automotive crank/rod)
There is also the (pretty good) chance that the small end will become weak enough to come apart
0.5mm all round doesn't sound much, but, the rods are build to take the stress of normal piston, not a slightly heavier one with less material in small end
 
pretty sure the bearing surface of the small end is hardened then honed to size, not really something you'd do exclusively on a bridgeport
 
That's the reason they are copper plated, stops the hardening solution making the entire rod too hard (molten cyanide salts I believe?)
 
Not sure if I'm too late with this but you can look for oversized KZ400 piston. They have the same wrist pin and are lighter than the Honda units. I've actually seen this done in a 350 vintage racing bike
 
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