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61 Posts
Discussion Starter #1 (Edited)
Hello guys, I'd like to post my motor work. I could not up load all pictures that I took. I put on to my blog if you have interest. Thanks,

Modified point:

XT250 piston
TTR230 crankshaft

Webcam 89 cam with valve spring
KFR Big valve (Exhaust)
WPC treatment
Ported cylinder head
2001~ model ECU and electric wiring etc.

This bike came here with extra used motor. It wasn't running. We picked and put in good parts together and rode for while. But we knew that motor needed rebuilt. One day, bike start leaked motor oil. Now it's time, we decided split motor and rebuild with a little more fun.


Here is some picture and detail about modified.

Bore x Stroke 74.0 x 58.0 mm as XT250.

After re-sleeved

First what we needed was cylinder re-sleeve. XT250 piston is bigger than stock. This work we've ordered and done by LA sleeve. They could put nikasil aluminum sleeve and that will be great combination with aluminum forged piston but we didn't put this time by running purpose and cost.

measure, measure,,

We need bored out crank case hole caused by bigger cylinder sleeve.

Before (stock)


Still crank case needs grind work little bit for cylinder sleeve install.

Grind needed both sides little..

Fit in finally.

Cleaned off crank case and repainted.

Now it's time for assemble TTR230 crankshaft and other all parts.
All bearings, transmission gears are new of course.

Assemble is nothing special, just make sure every piece is set right position.

stock 200cc motor off.

We clean off and repainted swing arm at once. Looks nice!

Let's see TW stock piston and new XT piston.

Left is stock TW, Right is XT250 (forged) piston.
Piston rings are much thinner.

Newer design piston has thinner wall thickness also. And more holes.
Sophisticated design.

TW stock piston with rings 184.7g

XT piston with rings 191.9g

New piston and rings are treated by WPC treatment. (Yamaha stock XT piston has not same color shown as pictures.)

We forgot measure and take picture with piston pin! Pin is also shorter design than TW's. We can expect total lighter weight but again, XT piston is bigger and forged.

Installed piston.

Mount cylinder head and check piston-valve clearance.

Put too much clay. Closest clearance In 1.9mm Ex 2.0mm at least, good enough.

Things don't go smooth usually, cranking by hand feels something not right.
It happen when piston position around bottom dead center.

We found piston skirt has interference with balancer. NG.

We decide to cut off piston skirt this time. (Sorry, don't have pictures.) That work made piston weight 0.3g lighter, well done.

Back to assemble again with custom head gasket.

Cam chain will stretch easily than stock after changed to strong valve spring so, better keep watch tensioner adjustment. You can think of cam chain is like "Drive train" as well. It is very important for this motor.

Time to run!

27% bigger displacement from stock motor pulls so much torque and HP. Gearing is 15-50 now, and you can still release clutch from idle for start.

We can recommend this modified to TW200 or TTR230 user however, better remind always Engine modified has effect and side effect. Good effect is nothing but more torque and power. Side effect is you have to always pay attention to motor health and operation. It is tuning up motor even if build by Yamaha genuine parts. It will be short overhaul cycle than stock for sure. Cam chain stretching is common problem for this motor. And running will not have the same handling feel as 200cc motor, it is bigger bike. Someone like, someone maybe not.

Currently, we made 1000 miles test ride for custom cylinder head (with KFR original big exhaust valve) and 500 miles for whole motor without problem. What surprise thing that runs fine without any carburetor jetting or adjustment. Possible reason are large piston making more vacuum suction and all stock (regulated) intake system. We can think about this motor possible to make more high output. But this bike is for street use mostly. High power performance is not everything for street stage. This motor making 72~73MPG actual gas on city ride. Stock 200cc was made about 74~75MPG. Do you like or not?

Our best recommend is up to 223cc by Yamaha TTR parts. You can tell that is still "TW". This 250 motor is 'not racing horse but not work horse' as stock motor. Better not take serious ride.

Hopefully you enjoyed this example.


11 Posts
very cool, but after riding for a while, was it worth all the work you put in it? i would love to see a youtube vid of this bike vs a stock tw

61 Posts
Discussion Starter #6 (Edited)
sean0 :

Thanks, I feel worth it for myself. Bike is easier and faster. Cruse speed is higher and also easier at 'stop and go' town ride, even my wife sit on back seat.
This bike won't push me try to go faster like MX competition model.

Tiny-Wheel-200 :

Thanks for comment. Yes, it took few month because I have many projects. No matter what weather condition, this TW is my best transportation now.

old mad max :

Thanks for comment. Yes, but not much. It has vibes. Frequency was changed from 196 to 249 cc so, not too bad for myself. We can try TTR balancer. That will be help for less however, heavier balancer also means 'friction' for motor. We have to take our own balance point somewhere. I'm fine with it for now.

B-dub :
Thanks, I'm look forward to shoot video too!

4 Posts
Tumbleweed, just found your blog surfing around the net for TW200 performance options. Nice build! Any ideas how much more horsepower was obtained. Did you think about using a 6 speed out of a TTR or other T model?

61 Posts
Discussion Starter #8
Hi Scotty, thank you for interest. I think you can make lot more horse power if you want. It just what stage do you want to ride or race.

Yes, I thought about six speed. I rode once with 243cc motor before. That was great feeling. But my bike is really fit in my purpose so, this bike stay on five speed for now.
I'd like to build one if I had another chassis and motor. :)
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