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Discussion Starter #1
I saw an xt200 today and the motor looked very similar to the tw200 motor. How long has the motor in the tw been around?
 

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The TW motor does have a lot in common with the XT motor. They introduced the XT200 back in 1980 and i suspect that this engine design goes back a lot longer than that. I think i read somewhere that the family it is derived from was originally built in the 60's. Regardless its been around for a while and the TW200 flavor since 1987 and its been relatively unchanged in that time. Changes being ignition, cam chain tensioner and carb changes in 2001.
 

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I had a 1982 Yamaha SR 185cc Exciter street bike years ago, which I believe is essentially the same engine with slightly smaller displacement. I am not sure when this engine design was born but I think it goes back for years.

Others more knowledgeable can shed more light on this, but I have a hunch that the engine family (SR185, SR250 and right up to the SR500) are all born of essentially the same basic design. It morphed into the TW200 and XT engine models, and possibly others.

If you compare the SR185 Exciter engine to the TW200 and XT engines they look almost identical and I believe used the same manual cam chain adjustment systems (and what not else) before the change to an automatic etc.

In terms of reliability, I was interested to learn that Craig Vetter of Windjammer fairing fame (google it) worked with the SR185 engine in fuel economy trials and was able to squeeze well over 200 mpg out of his machine fitted with his special streamliner full body fairing.

Popular culture has it that the SR185 motorcycle and it's larger displacement siblings which were mostly intended as basic transportation motorcycles, and cousins, are bullet proof, running a long time without requiring much attention at all. This, as we know, is no different than our beloved TW 200 and the XT family. All very similar design.

Paddy
 

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Is the motor in the Bw200 the same as the Tw?
Many parts are shared but there are some differences. Here are the ones that I am aware of:

-Some BW's are kickstart only, some are both kick and electric start.
-BW's have a compression release feature on the head that is actuated via a cable tied in with the kickstarter.
-BW's used a carb with a single throttle cable instead of the two on the TW.
-While I can't confirm this, I read somewhere that the BW's have a 4-plate clutch instead the 5-plates on the TW. If this is the the case, BW's would likely have different clutch baskets, actuating rod, and possible a different right side engine cover.
-And of course, since the BW uses a jackshaft instead of an extended output shaft on the TW, the left side engine cover, sprocket cover and output shaft are different.

I hope this helps,

Brian
 

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Discussion Starter #7
Very interesting answers here. I hadnt even thought that the basic design of the engine could have bred many different engines. I also didnt even think about the crazy bigwheels jackshaft system.
 

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Not a fool proof metric, but the oil filter fits similar displacement bikes clear back to '81, that being the SR185 Exciter.
 
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Great write up somewhere on this. Certainly started as 125 almost remember something about adapting a 2 stroke case but me mind quite murky.
 
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