200x Piston in a YTM 200????

[KingNothing]

So I have my buddies 84 200x tore down here for rebuild. Also at the same time I am rebuilding my 86 Yamaha BW200. I started looking at the difference in the heads and cylinders. The Yamaha cylinder looks to have slightly larger valves and an all around beefier set up. However they only offer a 10.25:1 piston. The 200x piston is available in a 12:1. The distance from top of the piston to center of the wrist pin checked out to be the same or damn close... The piston is pretty much identical except for the wrist pin being slightly smaller in the honda.

The guy who owns the 200x just happens to be a machinsiet and said he'd make me a bushing if I wanted. Looks like its a pretty easy swap....

the factory 200x is 65mm bore, but there is a 67mm piston available. Which happens to be the stock size of the YTM cylinder

Looks like there is plenty to work with as far as porting the yamaha head.

The BW200 shares alot of parts with the TW200.... There are cam and exhaust upgrades available

Has anyone ever done this???


I have never seen a yamaha 200 come even close to a honda as far as performance.




plan b.... 86 yz250 motor still not out of the question...... 4 strokes are a pain...

[Yamaha_Rules69]

I would stick with the parts the motor came with. I dont think putting a yamaha piston in the honda cylinder will make any sense at all. There are plenty of things you can do to the 200x motor, like stroker cranks, cams, pistons, basically anything you would want. Powroll.com is your best friend if you own a 200x or XR 200. You would gain huge power if you have the money and know how to do the right things. Good Luck.

[KingNothing]

sorry i didnt specify.... i would put the honda piston in the yamaha..... After checking it... there is about 1 mm difference in the wrist pins... probably just take the piston and machine it for the larger pin.


probably beating a dead horse.... but it would be nice to actually get some power out of it. (BW200)

[Nick_R_23]

I think the 2 biggest things you will need to watch for are:

1. Will the 200x piston skirt clear the crank?

2. Are the valves in the Yamaha head in a different position (further in, further out, more to the left or right) then the Honda head? This might create issues with the piston's recesses for the valves not providing the right clearance, ESPECIALLY if you are trying to use a high compression piston.

It would be interesting to see if you could get it to work though!

-Nick :TrikesOwn

[AutoXer]

10.25:1 should be enough compression to make power.

[lndy650]

like nick r 23 said watch the valves and skirt. as you said the yami has bigger valves so they might hit the 12:1. also i have bored some pistons like that but make sure your machinist can recut the circlip grooves