Thread: Honda Four Speed Options

I want to build a four speed motor. my current 3 speed is wasted and i'd have to split the cases to fix it, as well as rebuild it so i might as well try and grab a four speed bottom end if i can. I realize that i can grab a chinese four speed motor, but i don't really want to. I want to stay honda with the engine.

I just read in a thread here that the 6v four speeds can't take much more than the stock power output. I also read in a different thread that the later TRX and ATC 4 speeds had better internals and were therefore stronger.

Also, i want to go 12v. As previously mentioned, my stock motor is wasted, so I think one of the cheaper ways of attain my 12v dreams is to grab a cheap crf50 motor off PM and do a full 12v conversion. That's a whole different story that i'll talk about in another thread.

So basically, i've come to the conclusion that i want a four speed and want it to take abuse (I was thinking tb 88 race head or ported 22/25 ct70 head and MAYBE a 108 down the line. I want to be able to beat on it with confidence.) I've seen take-off JDM monkey 4 speed transmissions on PM, but what can they handle? I know a 108 is a little extreme on stock parts, but let's not worry about that right now and concentrate on a 4 speed that'll handle a healthy 88.

So in conclusion, i want a 4 speed that can take some abuse and is cheap. I know takegawa, kitaco and g craft have four and five speeds, but their prices are astronomical. I'd prefer to do it with either a four speed 12v bottom end, or the monkey four speed in 12v cases, but i don't really care.

Making a strong four speed transmission to fit 49cc cases isn't easy. That's why they're relatively expensive. Custom redesigns/engineering, precision machining and quality metallurgy don't come cheap...especially with low-volume production. As for five & six speeds, the narrow gear width required to fit in the same space as a three-speed makes for some very fragile gears. 6v or 12v doesn't make a lot of difference, in terms of strength. 12v cases have needle bearings in place of the older bronze bushings, but they're non-replaceable. The bronze bushings aren't known for failures, replacement 12v cases aren't exactly cheap.There are more aftermarket parts available for the 12v motors because they're current production. The newest 6v motor is old enough to vote.

There are motors up to 124cc running with Takegawa five-speed trannies, but it's just accepted that gear & kickstarter breakage will happen sooner or later (usually sooner). That's racing, parts don't wear out, they break. The guys running 124 taky motors seem to mostly avoid kickstarting. At that level, they're running race cams, high-compression and lightened rotating assemblies, including inner/outer rotor ignitions and for the really high-revvers (above 11K), a secondary-mounted clutch. One of these high-strung setups will set you back as much as a performance V8 crate motor.

If you want to avoid the costs of major aftermarket clutch & trans upgrades, then you'll need to keep the tuning on the conservative side. Revs above 11000 are risky with a stock, primary (crankshaft-mounted) clutch; they can grenade. Big torque and bang-shifting breaks gears. Kickback, such as what one would get from high-compression/big displacement/radically-light rotating mass and no ignition retard snaps kickstart shafts.

88cc won't increase torque enough to cause gear breakage. 110cc is where things get murky. I'd expect gear life to get shorter at this displacement, but by how much is anyone's guess. It will depend on how hard the bike is ridden. If you mainly cruise along in top gear, then it'll probably give you thousands of trouble-free miles. The three-speeds are stronger and they're cheap. If you can live with one less gear, then a 110 (or even 120) should make enough torque to move you along nicely, especially if you run a moderate cam profile. That still gives you the choice of a manual or aftermarket HD semi-automatic clutch, both of which are inexpensive. If you must have big-displacement and a four-speed, the only choices are taking your chances on an OEM tranny or buying quality aftermarket.

Thanks for the info. I read from two different sources that an 88cc with a stock four speed was iffy, but i guess that's the internet for you. I was actually going to ask about the strength of the 3 speeds, i'm glad you answered it. From what i understand the tb manual clutch is robust and can take a 110 easily, so that's the route i'll be going, for now atleast.