CG transmissions, and a potential 6-speed swap.
 

Hi guys, I've managed to get my hands on not one, but two Honda NX125s. They aren't the model sold in the US, but rather European models. I'll write up/show some of the more interesting features in another thread.

This model is an electric start, 6-speed, OHC motor, and it appears that it has XR200 transmission ratios. It doesn't come with a kickstart, but I think that there is a way around that, I might be able to mix and match some parts to add one, I'll let you know how that works out.

Part of the reason I'm asking about this is one of the NX125 motors will be disassembled, as it's consuming oil, and I'm going to drop a big bore kit into the motor, assuming that things measure out (as, referring to my post about 11 vs 12 bolt clutch covers, we know that normally, excepting the newer CRF motors, as far as I can tell from a Honda perspective, the 11 bolt motors all had a smaller case spigot), or I'll be putting a stock bore cylinder/piston if things don't measure out favorably.

One of the things that some people on here have expressed interest in is potentially adding a 6-speed to their Hawk/other CG replica powered models. Some people think that potentially an XR200 transmission will swap in, but from extensive research that I've done online, this probably won't work unless CG cases were wider than the standard Honda 5-speed cases; for example, you can't put an XR200 6-speed into an XL200R, an ATC200X, or a CB125, etc.

Additionally, there are some people in the XR200 racing community that will change to a 5-speed transmission because the XR200 transmission has historically proved to be a weak point for racers/people with built up motors. When they switch, they have to change the cases, too, because the 5-speed won't fit in the 6-speed cases, and vice versa.

That brings us back to the motor in question. Apparently the XL125S, which has a 12-bolt clutch cover, and a couple of other Euro-market Honda 125s have a narrower 6-speed that I've heard would fit, and the NX motor does have a 6-speed, along with an 11-bolt clutch cover.

How can you help me in this? I need some measurements of spacing, diameter, etc. If anybody has a CG transmission that they can make measurements of, it would be extremely helpful. Additionally, the spacing between the primary shaft and crankshaft (mm would be preferable, center to center) and the primary gear ratio would be helpful.

The dimensions that I'm looking for on the transmission are the following:

Total countershaft length:

Distance between cutout for countershaft sprocket retainer and end of countershaft:

Countershaft diameter at both bearing surfaces:

Mainshaft length:

Amount of mainshaft protrusion from the clutch side (with clutch removed):

Mainshaft diameter at both bearing surfaces:

Length of assembled gear stack on both countershaft and mainshaft:

Shift drum diameter and length:

Shift drum bearing surface diameters:

If I get all these specs from the collective, I'll provide the same measurements for everyone. Unfortunately, I don't have a CG replica here to compare, so I figure I could ask the collective here. Unfortunately, due to licensing restrictions here, there are almost no 200cc/"250" CG motors on the market, excepting the occasional ATV.

I think that this is something that I'll need the help of the collective on, as the IN Honda info has conflicting information that doesn't seem to reflect reality. Anyway, thanks in advance, and feel free to ask any questions!

Can't wait to see how this turns out. Is the 6th gear a 2nd overdrive?

I had an NX125! one of those that I regret selling. I dont feel mine had a six speed though :hmm: Perfect height, could go 65, easy to get unstuck in trails because it was so light.

Yep, high .7 ratio.

Did you have the drum front brake? Mine's the JD12, which means it has a disc front end :clap:

I kind of want to do something about the triple trees, it feels like they're 10lbs each.

Great! I'm watching for the results. I have the 6 speed in mind for another project that might be coming up. ;)

I probably won't get to do actual fitment, my CG is in the States, and I'm in Europe. That's why I'm asking for measurements. Also, if anyone knows of a source for Chinese ohc clone crankshafts, I might be interested...

I'll be following this thread with interest! I know I have the parts around to measure, but it'll be a matter of finding them. I have an intact CG150 laying around, but it may or may not be the same as the 200/223 transmission. Indeed, the 200 and 223 have a dissimilar frame of architecture in terms of cylinder stud spacing.

Look to the Honda Fat Cat for inspiration. They were equipped with electric and kick, and they used a centrifugal clutch. Quite an oddity.

What is the fork diameter? What is the center to center spacing of the existing trees?

I bought a CB250 single cylinder OHC crank on Taobao.

Weld -- I'm looking for an FML crank, I don't think that the FMM cranks work in the smaller architecture. They're 35mm forks, not sure on center spacing, I can check and let you know, I'll send you a PM. I think that the Fatcat motor was more similar to the centrifugal clutch ATC motors, I'm not sure it'll get me anywhere.

I only found a CG 6spd with 1 2 N 3 4 5 6
6th takes the place of kicker so no kick start

I think if Honda managed to do it with standard CB 5 speed cases (cf. XL125 S and R), so can I, barring differences between CB and CG cases besides some of the obvious stuff.

That being said, those motors, and the 5 speed cases they fit in, are all 12 bolt clutch cover motors, barring the NX125. That's why I'm on a fact finding mission.

I think mine had dual drum brakes. I'll have to find a pic.

Quick update (if anyone's interested :) ). I checked this out last summer... The 6th gear was added by removing the kickstart idler gear. The lengths were fine, but the diameter of the bearings were different, to make it all work, one would have to make some bushings to work with the case bearings, or else find some different diameter bearings. I'm also not sure if the US market NX transmission is the same, so think of this as a possible project if one must have a 6 speed, and is okay with getting rid of the kicker. You'd also have to make a plug for the kickstarter shaft.