Putting a CT90 Engine into a ST90 frame?

[murrayeliminator]

I was thinking about putting a CT90 engine in my ST90 for the hi/Low range gearing, are the motor mounts the same? and is there any other things i would need to Modifiy?..

 

[Backinthedays]

I am only going off memory and at this stage in life that is not to reliable for me, but I do seem to remember that the CT90 only had two mounting holes and the ST90 has three and one them on the CT90 is a larger 10mm vs an 8mm. I could be wrong though, but I would double check before doing anything drastic.

 

[b52bombardier1]

The bolt holes are not the same. The engine guard is also different as is the center stand and foot pegs. But the stock ST90 transmission ratios are my only minor complaint about the bike so I understand your desire to change things.

Rick

 

[murrayeliminator]

The bolt holes are not the same. The engine guard is also different as is the center stand and foot pegs. But the stock ST90 transmission ratios are my only minor complaint about the bike so I understand your desire to change things.

Rick

Ok Thanks. I'm not sure i want to modify the frame to fit, so I guess it will stay with the Orig engine.

 

[murrayeliminator]

Well after getting the motor running and putting a new chain on it (*it didn't come with one*) it looks like the Tranny is bad..I have no Neutral and getting it in to any other gear besides 3rd is hard so maybe a ct engine is my best bet at this point. Question, these are 3 down shift pattern correct?.with neutral all the way up? just want to be sure i'm trying to get neutral correct.

 

[murrayeliminator]

Bought a complete ct90 engine local yesterday. have the old engine out and it looks like the ct engine will go in with some light mods. will update as i figure this out!.. I also would like to put the CT70 handlebars & triple tree on this.. anyone try this before?

 

[WonderMuscle]

Keep us posted Murray. Take some picture if you can. I have been looking for a CT90 engine to swap out on my ST90 but haven't found any deals that I would go for.

For someone with a bit of fabrication experience I don't think the swap is a show stopper.

 

[murrayeliminator]

Here is the first few pics. as you can see i have the bottom bolt in and you can see where the motor mounts are different.



I had to gring the swing arm just a very small bit. And removed a small amount from the engine case..
http://i967.photobucket.com/albums/ae154/murray-eliminator/misc/st90engswap004.jpg

here is what it looks like so far.


Also the foot pegs/ kick stand bolted right up to the CT motor!
Will post more later..

 

[WonderMuscle]

Lookin' good. A simple triangular bracket incorporating the front frame mounting hole, the engine hole and another fastener to the frame would do the trick for the other mounting location.

 

[69ST]

Simple bracketry may be the best way to go but, I have to wonder if the ST90 cases aren't the same as CT90/110 - aside from the motor mounts. In other words, maybe someone here knows if it's possible to stuff CT90/110 internals into ST90 cases. That could be the best of all possible worlds.

 

[murrayeliminator]

I took the simple approch and drilled a new mount in the frame..

 

[WonderMuscle]

Simple bracketry may be the best way to go but, I have to wonder if the ST90 cases aren't the same as CT90/110 - aside from the motor mounts. In other words, maybe someone here knows if it's possible to stuff CT90/110 internals into ST90 cases. That could be the best of all possible worlds.

The cases are nearly identical except the countershaft seal is larger on the CT90 cases. There was someone who documented a rebuild with modified ST90 engine cases anc CT90 internals. I'll try to find the link and post it.

 

[murrayeliminator]

Well got everything back together and running. Very happy with the results! much better gearing now. Now i will put together a list of parts and tear it back down for a repaint..

 

[69ST]

Suggest taking a good look at the internal bracing around the original upper motor mount and the new one you just created with a drill. You may need to weld-in another layer of sheetmetal to get the same strength & tie-into the original welded reinforcing cradle. Should be a simple mod, at this point, if needed.

 

[WonderMuscle]

Another option if you are comfortable with of bit of machining...... ST90 Page 1

 

[Asp1978]

Hi all and happy new year
Any luck with this project?
Im thinking of doing the same
Anyone can upload the photos because there is nothing on the links.
Thank you