Planet Minis

dfred15

I have an old honda s90 that my brother picked up from someone for like 35 dollars a couple years ago with another bike. It isn't worth fixing because the guy who had it before him let it just sit in a hedgerow outside for years and years in New York. We basically got it for parts. I am building my 92 ct70 motor though and wondered if the 4 speed transmission out of this bike would work in my motor? I did a search on this bike and specs say that it had a top speed of 62 mph. Does anyone know what the gear ratios would be on this bike and if it would just drop into my motor? Any help would be greatly appreciated thanks.

mexicanyella

No. The early 90 motors (the ones that say 89cc on the jug, not 86cc) are physically larger than the 50/70 motors, even though their configuration is similar. Not much interchanges. Surely at least some of that motor is usable, to someone. I bet you could make more than $35 selling it, or parting it, on ebay/craigslist, and use the money to help pay for a 50/70-style four-speed gear set. A lot of people talk about the four-speed cluster you can buy from AHP minis...

Just so you know, that engine's related to what came in ATC90s and 110s, ST90s, CL90s, SL90s, some C90s, CT90s and 110s and the ATC125M. It's got the ignition driven off the end of the cam and in a little cover on the head. Some had dual-range splitter gears on the output shaft. The later 90s, found in TRXs and some C90s and many Chinese clones, are basically 50/70 motors with a 70's bore, but longer stroke (49.5mm instead of 41.4mm) and slightly longer cylinder casting, camchain and cylinder studs to accomodate that stroke. These are the 86cc ones. Other clone motors marked 107cc are the same deal but up the bore to 52.4mm along with the 49.5mm stroke, and are called 110s. Different bore/stroke combo than the old-style ignition-on-the-head 110s.

Even with the four gears, your CT likely wouldn't have enough shove to pull 62 mph in stock form. But reading between the lines in that last paragraph, one might be tempted to think about stripping some Chinese 90 or 110 someone also left in a hedgerow, taking the crank, rod, top end...and putting it in a late-model 12V Honda CT70, which uses the same tapered crank end to mount the ignition...I was tempted to do this to my hardtail Z50 earlier this year but changed my mind because I decided I didn't want to rewire it for 12V CDI ignition, and my points ignition wouldn't fit on the 110 crank. But you wouldn't be faced with that problem on your CT.

An S90 would be a cool bike to have, though.

dfred15

actually my daytona big valve head 119 kit just came in the mail today so the motor will be far from stock. I am just trying to decide whether or not to drop a 4 speed into it. It will be a street legal bike. How much top end speed would I be losing by sticking with the stock 3 speed in the bike? Has anyone ran one with the stock 3 speed and seen what the difference was?

mexicanyella

I'm riding a stock 50 these days, but either way with that much displacement you can probably gear for plenty of top end speed either way. The issue will be how many ratios you have to get you up there. If you're geared to go 55/60 mph with a three speed, you'll need a lot of torque so you won't have to downshift all the time when you encounter hills, and that gap between 2nd and 3rd is a pretty big one. I've never ridden a 119 kit, or even an 88 kit, but on otherwise identical old 6V CT70s, a four-speed presents more options when you encounter a hill. I took turns riding a bunch of different CTs earlier this summer and this was immediately apparent. I am frustrated sometimes by the the 3-speed in my Z; it needs more hp or more gears or both.

While you could probably pull taller gears and get away with 3 now that your motor's bigger, if you're already splitting the cases anyway and you've got some money into it, why not throw another couple C-notes in there, and slip in the four-speed? It'll make your bike more...sassy.

dfred15

Yeah, I'm thinking I'm going to want the 4 speed. I was just wondering if I could get away with the 3. Would the old honda 4 speeds hold up to the horsepower of this motor or would they break? Anyone find out the hard way? I know its probably been asked a million times. Thanks for the input on the subject mexicanyella

mexicanyella

I asked about this myself once and was told the CT70H trans would not take a lot of abuse. I've always thought the SL/CL/XL was the same, but I'm not certain.

I have read several times here on this board that the one to get, if you're going with Honda parts, is the TRX70 atv engine, which was four-speed semiauto.

HymieP

I recently had Terry at Firepowerminis.com change my 1993 CT70 motor (3-speed auto) to a TB117 and put in a 4-speed auto from an XL70 and worked great. Since then, I have decided to change the auto out to a 4-speed manual. I'll let you know how it works.