Adding the CT90 sub transmission to an s90/cl90

TL_MILLER

TL_MILLER

Member
I currently have 3 S90, 2 Ct90, and 1 CL90 motors. I'm in the process of rebuilding 2 S90 motors.
I was looking at all the motors last night and decided that I'm going to try and build a S90 motor with the CT90 dual transmission, and stick it in a CL90 bike. I think it would be fun to have the dual transmission for off-roading.
I'm going to start with a S90 case/head/cylinder. Then add the CT90 gears, shift drum and left case cover (with the HI/LOW). Also want it to be a manual clutch. Not sure if this will work but I'm going to give it a try. I couldn't find any write ups on it. so let the fun begin.
I will document what works and what doesn't.
CL90.jpg
S90.jpg
s90 motor 2.jpg
123.jpg
 
B

b52bombardier1

Well-Known Member
Some machining / mild drilling may be required to allow oil out of the sub trans and back into the center case. At least this was the guidance I got when I thought about doing the same to an ST90 engine. However, I never got around to actually doing it. Its merely something for you to consider and if you get really serious here, I can put you in touch with somebody who knows more about it.

Rick
 
TL_MILLER

TL_MILLER

Member
b52bombardier1 said:
Some machining / mild drilling may be required to allow oil out of the sub trans and back into the center case. At least this was the guidance I got when I thought about doing the same to an ST90 engine. However, I never got around to actually doing it. Its merely something for you to consider and if you get really serious here, I can put you in touch with somebody who knows more about it.

Rick
Click to expand...

Your right. I just got done tearing down the ct90 motor, the s90 motor is missing the oil hole but it’s fixable.
 
TL_MILLER

TL_MILLER

Member
I mixed and matched parts from each motor. It will work if the oil passage was added. The ct90 trans fits in the s90 case. The stator/hi low gear cover also bolts up.
The cover is a little wider than the s90, so the shift linkage from the ct90 would need to be used. Also have to cut off the end of the shift linkage (the piece that goes to the auto clutch.
 
TL_MILLER

TL_MILLER

Member
S90 is missing a bottom mounting screw. Will also have to add the oil return from the sub transmission.
The ct90 cover mounts up to the S90 case minus those 2 issues.
casees12.jpg
casessss.jpg
 
TL_MILLER

TL_MILLER

Member
The CT90 Stator cover is a little wider that the S90 stator cover, so you will have to use the CT90 shift linkage to clear the stator cover. other than that it works.
cases33.jpg
cases22.jpg
 
kirrbby

kirrbby

Well-Known Member
Looking at your pics. It looks like the ct90 has only 2 mounting points...engine to frame. Or is there a 3rd on the cylinder??

Sorry I'm taking you off track. Wondering if the CT90 has the same mounts as a CT70 or Z.

The oil hole looks like it could be tricky to add to the S90 case...do you have a plan? Guess I should just be patient.
 
TL_MILLER

TL_MILLER

Member
kirrbby said:
Looking at your pics. It looks like the ct90 has only 2 mounting points...engine to frame. Or is there a 3rd on the cylinder??

Sorry I'm taking you off track. Wondering if the CT90 has the same mounts as a CT70 or Z.

The oil hole looks like it could be tricky to add to the S90 case...do you have a plan? Guess I should just be patient.
Click to expand...

Yes the CT90 only has the 2 mounting points. I don't think it will fit in a CT70 frame, but I can check when I get home.

I think the oil hole can be easily added. The triangle area has a gasket that covers it, I could weld the bottom part and drill a hole in the case. It seems to be gravity fed once the oil is pumped into the HI/LOW case area.

I also ran into a problem last night, The bigger side cover hits the swingarm, so I need to figure out what I can do.
casesoil.jpg
 
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