CT110 with manual transmission

Discussion in 'CT90, CT110, ST70, ST90 Discussion' started by fatcaaat, May 14, 2019 at 9:57 AM.

  1. fatcaaat

    fatcaaat Well-Known Member

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    This is a conversion that I've always wanted to do...and I finally have completed it. This is a 1986 CT110 that I grafted a honda CL90 manual clutch onto. It's fairly straight forward, but does require a few perm mods to CT110 and the CL90 parts.

    1. Get yourself a CL90, S90, or SL90 engine. For my purposes I used an S90. There is an important difference between the drive plates...you need one with the larger spline cutout. Different years had different splines. One will directly fit the CT90 and the other the CT110.
    2. On the clutch pack, I rebuilt mine using a honda Trailbikes manual clutch rebuild kit for a CT70 as the plates and fibers interchanged with the drive plate. So now I have a 3-plate system instead of a two plate system. For the springs, I used atc110 springs in it since that's what was laying around. I might like some stiffer springs but these will do for now.
    3. I had to chop the shift shaft end off so that it works correctly inside the engine. This is permanent to the CT110 engine. I plan on purchasing a CT110 replacement should I ever want to go back. I assume the CT90 will directly interchange but the atcs will not as they are longer. The CL90 shaft is too short.
    4. I had to mill the kickstart shaft through hole in the clutch cover. Based on my measurements, i used a 5/8" endmill and came right down through the center. It was a perfect fit.
    5. For the seal, you will need a 26mm OD and 16mm ID seal for it. Easy enough to find. If you want to use a CT110 seal going forward, you will need to mill the seal pocket in the clutch cover out to 28mm OD. I elected not to do this as the sea was easy enough to find.

    Works exactly like it should. Now the CT110 is a full manual transmission with hi-low range. I elected to do this as it will actually improve driving all around IMO. On the street, naturally, the manual is preferred. On the trail, if you are in the low RPM that requires a lot of grunt, the semi will just slip as you cannot get the rpm's up. with the manual, I control the slip and should have an easier time with low speed steep climbs.
     

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  3. kirrbby

    kirrbby Well-Known Member

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    Thanks for posting fatcaaat.
    So the finished product is the ct110 engine? You'll be running it in your CT110?

    You used the clutch and clutch cover from the S90. You used the shift shaft from the CT110, and cut it to work with the S90 cover. But you'd recommend trying a CT90 shift shaft first. Is that all correct? Did you use any other parts from the S90 engine?


    Last I knew, the 110 engines were difficult to build any bigger than 110cc. Are you planning any other mods? Or 110 does the job.
     
  4. racerx

    racerx Administrator
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    I haven't checked lately but, dratv used to offer a bore-up kit and a hotter cam. That's about all the performance stuff I've seen for these engines, since the late `90s. If you want to go fast, this engine family is not the hot ticket. OTOH, if you want bulletproof durability, or just a bit more grunt from a CT90/110...
     
  5. fatcaaat

    fatcaaat Well-Known Member

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    Kirby, you need everything on the clutch side from an S90, CL90, or SL90, but the internal splined drive plate that goes in the clutch basket is different on different years. One has a narrow spline which works on CT90 and one has wider spline for CT110. I don't know the years. For the shift shaft, you have to cut the original CT110 shaft down to remove the end that the auto uses to depress the basket. You have to make it look like the manual shaft from a CT70. I suppose you could use a CT90 shift shaft interchangeably..at least I think so. No other parts from the S90 engine were used.

    The picture I posted is the final product...it is a CT110 engine original to the bike with a manual clutch on it. As for go-fast goodies, Racerx is correct...there's nothing out there I am aware of that you can do to these. Even the postie community in Austrailia do not have a good answer for upgrades that do not require major surgery. I suppose you could just bore the heck out of the cylinder and add a big piston and have webcamshafts grind you a cam and then port, carb, exhaust. That's not what I was going for with my build though. It runs 45mph all day long as is. I will say that both my previous CT110's I used a PZ19 chinese carb on and it gave enough boost just from that to regear the rear 3 teeth smaller. Stock carb is only 15 or 16mm and those 3mm do make a difference.
     
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  6. fatcaaat

    fatcaaat Well-Known Member

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    I gave the bike a good ride today...just under an hour as I commuted errands over lunch plus a nice 15 mile loop around 45mph sustained on some back roads. This is my impression of the conversion.

    1. The pull is soft and there is no adjustment on the cable or as part of the mechanism. All i can do is adjust at the lever the slack. You could have a ton of free play as the clutch releases very close and fast to the top. I can fix this with some custom machining of parts, most likely thicker oil bushing that goes in the end of the basket.
    2. The clutch is soft. With the stock atc110 springs in there, the clutch does slip on kicking but does not slip when riding. I believe I can get improved clutch feel and fix the kicking slipping with the simple addition of some stiffer springs.
    3. It's really smooth operating. The best part is there is no lurching or clunking on shifting gear to gear as you can slip the clutch smoothly to make good transitions. No matter how much you try and dial in the auto on a CT110, it's never super smooth.
    4. Gear changes might be easier. I don't know if this is true or not but now I notice this because i'm looking for it. The ability to get into and out of gear seems easier. And shifting down rapidly from 4-1 with the clutch is much easier. It is noticably lighter on the foot when shifting as you no longer using your foot to depress the clutch.
    5. You can still lug it. I knew that the ct110 engine could be lugged but it also relied on the one-way clutch when things got too slow. I was surprised just how slow you can get this going before it will stall. I bet 600rpms. I believe that the auto clutch engages around 1400-1500 so that is definitely a different feeling.

    I"m not quite satisfied yet. I think with new springs and a different lever up top, i'll be good enough and maybe I'd consider messing with the adjustability of the throw at the clutch cover in the future.
     
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