TW200 and TW225 engines will fit.
Got an 2002 Yamaha TW125 standard with the square headlight.
I love it and got slightly attached to it so can't bring myself to sell it to get a faster bike. So I want to strip it and make it a custom and fit a bigger engine to it.
Do any of you know any engine that fit well into them? I can do frame mods but obviously dont want to do to many
TW225 engine is a bolt-in. TT-R225 and XT225 engines are not. Better be sure which 225 you are talking about.
They are bolt in if you swap transmission...TW225 engines are ONLY available in Japan (JDM), unless it was somehow imported grey
to Europe. So unless you are in Japan, you won't find a tw225 engine...xt and ttr 225 engines may also be tough to find in Europe. I know xt225's were imported grey market to the UK though.
For some reason I have the idea that a Serow 225 is the euro version of the XT.
It is not necessary to swap the entire transmission. The TW countershaft can be ground down to accept the XT or TT-R 6-speed. You will also need to use the TW case cover with the outer support bearing for the countershaft. I don't know for sure whether or not the XT and TT-R cases are capable of oiling the countershaft support bearing. Those with whom I've spoken who actually have big displacement and/or 6-speed TWs are built on the TW200 or TW225 cases with the XT/TT-R parts. I'm sure the builders would have used the XT/TT-R cases had such a conversion been easier.
Why wouldn't they? there are some differences in crankcase ventilation, but I don't think oil flow, The TW just uses a slightly lower profile case side output bearing and seal to fit around the larger shaft diameter...Not sure if a xt clutch cover would fit the TW brake pedal either. In either case (6 speed mod or 225 bore up or xt225 engine) you need to split cases to install a TW output shaft....Only one he wouldn't have to split is a tw200 engine, or went to japan for a tw225 engine. The only reason to really bore out the TW cases is if you want your stock engine numbers.
I guess what I'm trying to say is, you can't use the xt/serow/ttr cases without using the xt/serow/ttr clutch cover. If you mix and match by using a TW clutch cover then you will run into crankcase ventilation problems (although this can be overcome by an experienced builder). So It's best to stick with 5 speed TW transmission + six disk clutch + xt clutch cover.
200 cases(to 225cc upgrade)
Or alternately, switch an XT crank+balancer assembly into a bored out TW200 bottom cases then use the 5 disk clutch.
The easiest route by far is just to install a tw200 motor in place of the tw125 motor. But..... TW200 motors only came to certain countries, and since the OP said he had a TW125, then he is not from one of those countries, hence the above mix and match solutions. Below is 125 cases mix recipe
You'll need a 225cc entire top end, a case bore to 78mm, entire 225 crank assembly, 225 balancer, bearings, flywheel, and a 200cc 5 disk clutch would be highly recommended, you can use the TW125 transmission. It is also possible to use the 200cc top end/crank, but it is the same expense and hassle as the 225 stuff, so why bother.
There is a difference in the 225 cases in the left balancer bearing area that allows a larger bearing, and some ventilation differences. It may be easier to use a 200cc balancer in 200/125 cases because of this, Yamaha used the 200 balancer in "early dirt only" 225 trikes, so it is perfectly OK, but there may be slightly more vibes on the street.