Some CB(small) technical modification questions

Keiff Hardcore

Keiff Hardcore

Loves anything that burns oil
hi, im pretty new here but ive read through several builds and there is one thing that has been bugging me. almost everyone's bike (in grey scale) looks identical, and i dont see many modifications done to the heart and soul of a bike, the drive train. this brings me to my questions.
all questions relate to the CB175/200/250

-has anyone attempted a dry clutch conversion?

-Has anyone attempted a chain to belt conversion?

-has anyone used the CB360 6 speed crank case on the CB175/200/250?

all these questions stem from the idea of getting the most efficiency out if these little motors.
 
Keiff, I want to say: no, no, and no. But could be very wrong. Have you looked at this post yet?

http://www.dotheton.com/forum/index.php?topic=12552.0

The first post has all the small builds organized, and at the bottom are some links to different sites pertaining to the 160/175/200 cc Honda's. There's probably more, but I haven't looked for years......
 
i dug through all of those and didnt find any that went much further than a engine rebuild.

although from my own research a KZ440 from the late 80's was belt driven, and if i can get a spoked hub i can work it in.

dry clutch isnt a good option as the cost and effort wouldnt net much results.

all i realy need to know now is if the crank case to a CB360 is the same as a 250...
 
anyone know if the CB/CL250 motor shares the same cylinder size with the 360? the shop manuals include cb360 and cb250's in the same manual...
 
Why not just use a 360? Most people want bigger cylinders. How much performance are you gonna gain by decreasing displacement? Sounds like you want to revolt, but in order to do that you're gonna need some ideas. Everyone's bikes look the same because they are building mostly Cafe's here (it's a cafe' site). If it looks too different, it would be called something else. Belt drive sounds fun, but the gains wouldn't be worth the work. If you enjoy working on tedious expensive projects and don't care that the effort is fairly fruitless, then belt drive is for you.
 
The 250 models that are in the 360 manuals are more or less detuned 360s. They share a lot of the same parts. There are plenty of discussions around either on DDT or honda twins if you search for them.

They do NOT cross over to the earlier 350/250 detunes and they do NOT work with any other bike that I know of for that matter, just the 360 line.

The 175/200s are completely different engines.

The six speed really doesn't due much for performance, it just splits the shifts up ONE more time. Honestly for a bike that made that little of power its really over kill. I spend alot of time shifting in and out of gears compared to my 450. It does do good job of keeping the rpms in the range that the engine does make power but its a pain in town.

I would reason that a belt would suck more power but then I've never even understood the reason to change to an o-ring or x-ring chain. Chain lube is cheap, the chains are cheap, the sprockets are cheap. Keep them adjusted and lubed and they will out live the tires 2 or 3 times.

I've never seen a dry clutch conversion for any of the smaller twins, but I bet they do exist, I can get one for my 450 if I had the $$$$$$$$$$ for it.
 
frogman said:
The 250 models that are in the 360 manuals are more or less detuned 360s. They share a lot of the same parts. There are plenty of discussions around either on DDT or honda twins if you search for them.

They do NOT cross over to the earlier 350/250 detunes and they do NOT work with any other bike that I know of for that matter, just the 360 line.

The 175/200s are completely different engines.

The six speed really doesn't due much for performance, it just splits the shifts up ONE more time. Honestly for a bike that made that little of power its really over kill. I spend alot of time shifting in and out of gears compared to my 450. It does do good job of keeping the rpms in the range that the engine does make power but its a pain in town.

I would reason that a belt would suck more power but then I've never even understood the reason to change to an o-ring or x-ring chain. Chain lube is cheap, the chains are cheap, the sprockets are cheap. Keep them adjusted and lubed and they will out live the tires 2 or 3 times.

I've never seen a dry clutch conversion for any of the smaller twins, but I bet they do exist, I can get one for my 450 if I had the $$$$$$$$$$ for it.
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thanks for the information, the reason to do the 6 speed swap is so that highway RPM's can be lowered. by adding that additional gear, i can change the rear sprocket to lower 60mph RPM' so that highway riding is more enjoyable.
the belt conversion would give you "free" HP by reducing rotating mass, just like using lightweight wheels and such.
 
Part of the reason why both my 360 (6speed) and my 450 (5speed) both got the FRONT sprocket changed to ONE extra tooth was get me to 70-75 without wearing things out as fast. Both end up final drive ratio about the same. Same rear wheel same tooth count.

Funny thing now is I'm thinking about putting them BOTH back to stock. The 360 is my town bike and that long of legs makes it a pain to ride sometimes. The 450 will easily handle 80 MPH plus all day long now, which is fun for sure but the bike WANTS to run that RPM so it runs better at 80 instead of 70.
 
frogman said:
Part of the reason why both my 360 (6speed) and my 450 (5speed) both got the FRONT sprocket changed to ONE extra tooth was get me to 70-75 without wearing things out as fast. Both end up final drive ratio about the same. Same rear wheel same tooth count.

Funny thing now is I'm thinking about putting them BOTH back to stock. The 360 is my town bike and that long of legs makes it a pain to ride sometimes. The 450 will easily handle 80 MPH plus all day long now, which is fun for sure but the bike WANTS to run that RPM so it runs better at 80 instead of 70.
Click to expand...
so the 360 doesnt really like to stay in low rpms doe to power bog or is it just because it feels like it want to rev faster?
 
360s don't make much for power before 4k and not much after 8k so you have to play a lot with that area. It goes fine off the line but I find I have to keep it up over 4k just to cruise around town, any less and lugs the heck out of the engine. I have non stock mufflers that are louder than stock so it just annoying I guess to rev it that high in town.

It is as properly tuned as I can get it most days, its my current main ride although that will change once I get my 450 painted.
 
Keiff Hardcore said:
thanks for the information, the reason to do the 6 speed swap is so that highway RPM's can be lowered. by adding that additional gear, i can change the rear sprocket to lower 60mph RPM' so that highway riding is more enjoyable.
the belt conversion would give you "free" HP by reducing rotating mass, just like using lightweight wheels and such.
Click to expand...

The 6 speed is only a small amount more of overdrive. The CB350 5th gear is 0.900 to 1, the CB360 is 0.86 to one. First gear is the same ratio. So the six speed just is a little closer through the gears.

So top gear and first are close to the same, so you end up just shifting more on the 360.

I found the CB350 had a nice range of gears, appropriate to the engine characteristics. The six speed 360 isn;t as "neat" and requires a little more rowing, without any real benefit except I can say "6" rather than "5". If top gear is too busy for you, just change the sprocket ratios as Frogman suggested.

I liked the CB350 Transmission/engine/Ratio's a little better than my 360. the 350 just seemed to be "right"


For the record, the CB250/360 are the same engine, except for Bore. Stroke, compression ratio, transmission, all the same.

The earlier CB350/250 are similar. the bore was the only change. So pistons were different, but not cranks, or stroke, or any other part.

No detuning. In fact, the CB250 seemed to be a little better in tune then the 360. 1/3 less displacement, but only 1/4 less HP.

More to do with internal friction versus bore diameter, than anything else.

Oh, the badges are different on the 250, as the number are different... 8)
 
Only small-cc hop-up conversions i did where on my GF's cb200 twin. Hydraulic clutch, external oil feed to cam & needle bearing on cam. Topic is here;

http://www.dotheton.com/forum/index.php?topic=32298.0

i personally do not see the logic of overboring those small engines. Just fit a bigger engine, takes about the same amount of labour.
 
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