Just ordered an engine to jam in my ct90!

poncho167

New Member
Well I hipe this doesn't turn out to be a bad idea. I chose the ts125 because it seems to be a good size and should cruise a5 highway speeds really nice. I also really love 2 stroke engines and they tend to pack a bigger punch in a smaller package. The ts125 I have has a 6 spd transmission and I really like the sound of that. I also like having unique stiff and this I think would take the cake.
Yes, build the subframe first, then motor and subframe as a unit onto your bike. But also think about long term what you're going to end up with, what it'll look like, what it'll cost in terms of time and money and will it all be worth it. In the meantime, I almost literally threw this bike together, cost me next to nothing, and though it's not done yet, it runs, is very fast and rides surprisingly well. I Should have it all wired up in a couple of days. And if I can sell it for $900, I'll be happy.
What engine did you end up using to make it very fast?
 

Old Guy Too Many Bikes

Well-Known Member
3/4" is smaller than most bicycle frames, but it would work if the walls were thick enough. It's a lot of work though. I've re-purposed many bicycle frames in the past and bending them for me is tough, as is the notching and welding them to look pretty. I've had better luck with steel plate and box beam cut and welded at different angles.
 

Gordy

Active Member
I plan to order some thick walled stuff and use a tubing bender. I also bought a tubing notcher. I don't expect to build any of the motor mount for a while. I want to get the bike a rolling chassis and fully painted first. Then I will make the engine cradle. After that I will fully rebuild the engine and get it running and riding, and after all that wiring. Like I mentioned before, tgis is a long term project so I don't mind spending alot of time and money to get it exactly what I want.
 

Old Guy Too Many Bikes

Well-Known Member
What engine did you end up using to make it very fast?
When I had the 140 in my CL90, it always ran real well, and the riding position is kinda sporty. It also had real tall gearing 18/32. On the C105, the riding position is more up right, and the gearing is much shorter 17/35 with smaller wheels, so that bike really leaps when you get on it.
 

Old Guy Too Many Bikes

Well-Known Member
I plan to order some thick walled stuff and use a tubing bender. I also bought a tubing notcher. I don't expect to build any of the motor mount for a while. I want to get the bike a rolling chassis and fully painted first. Then I will make the engine cradle. After that I will fully rebuild the engine and get it running and riding, and after all that wiring. Like I mentioned before, tgis is a long term project so I don't mind spending alot of time and money to get it exactly what I want.
Tubing benders and notchers are cool, wish list stuff for me. As for your build, I would do almost the opposite. I would get the engine running first, then the chassis, and the last thing I would do is paint. I've never had the patience for long term projects. When I restore a car, I get it running first, I don't mind it sitting on blocks as long as I can start it up, or driving a rolling wreck, then work on the individual items. That way I won't lose interest or get discouraged.
 

Gordy

Active Member
Tubing benders and notchers are cool, wish list stuff for me. As for your build, I would do almost the opposite. I would get the engine running first, then the chassis, and the last thing I would do is paint. I've never had the patience for long term projects. When I restore a car, I get it running first, I don't mind it sitting on blocks as long as I can start it up, or driving a rolling wreck, then work on the individual items. That way I won't lose interest or get discouraged.
My reasoning for getting the bike painted and looking good before the engine is so I don't loose my patience and say "screw it, I'll just cut the frame." I really don't want to do that and if I decide not to use the 2 stroke I can order a 140 and bolt it right up in.
 

Old Guy Too Many Bikes

Well-Known Member
The "right" way to do it, (which I have tried and have never been able to do) is to build whatever it is so that it functions perfectly and get all the bugs worked out, and then take it completely apart and clean, polish and paint every part and then meticulously put it back together. I wish I had that kind of patience.
 

Gordy

Active Member
The "right" way to do it, (which I have tried and have never been able to do) is to build whatever it is so that it functions perfectly and get all the bugs worked out, and then take it completely apart and clean, polish and paint every part and then meticulously put it back together. I wish I had that kind of patience.
My plan is to get the chassis to that pont, then the engine to that point with the cradle, then get the 2 to work in unison. I know it's not the way most perfer, but I decided to go this way and it will take alot to change my mind.
 

Gordy

Active Member
Here's an Idea. I could solve 2 problems in 1 go. I could build a subframe and swingarm. The swing arm can bolt into the subframe. The only problem I can see is it could screw up handling. I may Just build 2 versions of said subframe. 1 that goes with the original swing arm and just cradles the engine, and one with a swing arm. Sure it's tons of work, but I'd be willing to do it.
 

Old Guy Too Many Bikes

Well-Known Member
Although rear suspension travel is a factor, handling is most affected by the rake and trail of the front end. Also, it is absolutely vital when fabricating an engine cradle and swingarm, that the drive sprocket aligns with the centerline of the swingarm, otherwise, chain tension will vary as the suspension moves. The sprockets also need to be in line on the horizontal axis. I think it would be best not to mess with the original bike's geometry and let the original frame be your starting point. You mentioned earlier about a disc brake conversion and here's another idea I still may try. The front drum brake on the CM250 is massive compared with the one on my CL90. Since they both have 36 spokes, it would not be too difficult to lace the 250's hub onto my CL90 front rim.
 

Gordy

Active Member
Although rear suspension travel is a factor, handling is most affected by the rake and trail of the front end. Also, it is absolutely vital when fabricating an engine cradle and swingarm, that the drive sprocket aligns with the centerline of the swingarm, otherwise, chain tension will vary as the suspension moves. The sprockets also need to be in line on the horizontal axis. I think it would be best not to mess with the original bike's geometry and let the original frame be your starting point. You mentioned earlier about a disc brake conversion and here's another idea I still may try. The front drum brake on the CM250 is massive compared with the one on my CL90. Since they both have 36 spokes, it would not be too difficult to lace the 250's hub onto my CL90 front rim.
I like the Idea of a cb125 fork. The rear may end up being drum, but I don't use the rear brake that much when riding. It all depends on what I decided when the time comes, I'm currently just researching options and seeing what you guys think. As far as the chain goes I am going to try my best, but sometimes it is not an option to have perfect tension. If this is the case I will design and make a chain slider like alot of dirt bikes have.
 

Old Guy Too Many Bikes

Well-Known Member
As I said before, visualize what you want it to be, have a goal, make a plan, figure the budget in terms of time and money. Make it a fun project, not a chore that becomes a money pit. Keep it simple whenever possible. About 2o years ago, I fell in love with Velomobiles, streamlined, lightweight, human powered vehicles. very popular in the Netherlands. I wanted one so bad, so I decided to build one. I bought a recumbent trike, and I handbuilt a streamlined aluminum body for it. It was so cool, it even made the cover of a magazine. But then reality set in. It was faster than a roadbike on level ground, but horribly slow going up hills. And it was too damn fast going downhill, I was going through brake pads like sh*t through a goose. And I almost got hit by cars more times than I could count since it was so low. And I was always getting pulled over by the cops. It was too wide to stay out of traffic, and too narrow to take corners fast. And it took up more room than my Harley in the garage. I finally ended up selling it for less than half of what I had in it, and was glad to see it go.
 

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Gordy

Active Member
Alright guys, it's been a while since I have had time to even look at my bike, but today I had a bit of time. I made some decisions today.

I do want to use the ts125 engine I have, and after a thorough examination, my engine is in alot better shape than I thought. It does have rust on the crank and cylinder walls, but that's about it. The transmission is in great shape and the bottom end (aside from needing new bearings) is in great shape. Hopefully a quick hone can take care of the jug, and some steel wool and wd40 can take care of the crank. Another descuon I made is I will build a subframe to hang the engine from the original ct90 mounting points to keep my modifications reversible. I took the bike off the workbench to see where the engine might line up, and with the engine centered the output should line up with the rear sprocket. I hope to get this thing a rolling chassis in the spring and get working on making this engine work with the bike.
 

Gordy

Active Member
I want to put discs on the front and rear, but the issue with the rear is I can't get a 17" rear wheel. I was considering doing an 18". Would an 18" rear and 17" front make it handle poorly?
 

Old Guy Too Many Bikes

Well-Known Member
I would make a scale drawing of your CT90 frame and your TS125 engine, maybe even full size. Then you can design your subframe out of paper or cardboard first. Last time I had a project where I had to fabricate a frame with a bunch of angles and bends, I drew it on my garage floor with a sharpie. Then I bent and welded the pieces together to match the drawing. I would get the motor done and running on the bench. It'll clear a big hurdle and give you incentive to move on. You probably can't go with a wider rear rim. A wider rim means a wider tire, and then you have to worry about the chain hitting the tire. To fix that you'd have to move the sprocket out. Then that may create a problem with the swingarm needing to be wider and might mess up the geometry with the front sprocket. Going with a front disc and rear drum rear should work well, the front brake does most of the stopping anyway. The main thing is to not get discouraged or lose interest in the project, even if you only work on it one hour a week. But the main thing is to have fun and take pride in your work.
 

Gordy

Active Member
I would make a scale drawing of your CT90 frame and your TS125 engine, maybe even full size. Then you can design your subframe out of paper or cardboard first. Last time I had a project where I had to fabricate a frame with a bunch of angles and bends, I drew it on my garage floor with a sharpie. Then I bent and welded the pieces together to match the drawing. I would get the motor done and running on the bench. It'll clear a big hurdle and give you incentive to move on. You probably can't go with a wider rear rim. A wider rim means a wider tire, and then you have to worry about the chain hitting the tire. To fix that you'd have to move the sprocket out. Then that may create a problem with the swingarm needing to be wider and might mess up the geometry with the front sprocket. Going with a front disc and rear drum rear should work well, the front brake does most of the stopping anyway. The main thing is to not get discouraged or lose interest in the project, even if you only work on it one hour a week. But the main thing is to have fun and take pride in your work.
I have a plan to do a rough 3d model and go from there. I have a few projects I bounce between to keep from getting too impatient and frustrated. I plan to get the bike rolling first so I have room to tear the engine down as I am working out of a 10 x 20 shed half full of garden tools, gas cans, chainsaws, and such. I take a huge amount of pride in my work, I'm not the type to booger weld something together and call it good enough. Thanks for the help and encouragement!
 
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