TY 250b flywheel

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GSX 1300R
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Bike: 1975 Yamaha TY 250 B
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TY 250b flywheel

Postby GSX 1300R » Mon Apr 29, 2019 9:59 pm

Hi all Can somebody please advise the effects of fitting a ty250 C flywheel which is noticeably heavier to a standard ty250b I expect more low down power but will there be any problems thank you



David Lahey
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Re: TY 250b flywheel

Postby David Lahey » Tue Apr 30, 2019 5:47 pm

A standard B model flywheel is the same thing as a standard C model flywheel. The only different TY250 twinshock flywheel is on the A model and on it, the cup is the same as the BCD models, but the A model has a smaller outer steel band
Using the heavy BCD models flywheel makes the motor quite slow to respond. It is a common mod to either use an A model flywheel or to lighten the BCD flywheel to make them nicer to ride. Of course if you are making it into a 320cc motor, the heavier flywheel would be a benefit


relax, nothing is under control

GSX 1300R
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Bike: 1975 Yamaha TY 250 B
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Re: TY 250b flywheel

Postby GSX 1300R » Wed May 01, 2019 11:20 pm

Thanks for your response David My original B model flywheel is definately heavier than the C model flywheel that I have I have owned this B model TY since late 70s When I bought it it looked like a original untouched bike When I replaced the crank seals a few years ago the primary side had the A model seal with the extra O ring under the primary cog Also the bike came with what I believe is a different looking A model petrol cock My question is have you come across a B model with A model parts from the factory before cheers



GSX 1300R
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Bike: 1975 Yamaha TY 250 B
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Re: TY 250b flywheel

Postby GSX 1300R » Wed May 01, 2019 11:22 pm

PS I'm thinking the bike came with a A model flywheel also



David Lahey
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Re: TY 250b flywheel

Postby David Lahey » Thu May 02, 2019 9:16 am

Yes a friend has a TY250 that is a combination of A and B model and seems to have come new like that.
There are two different A model cylinders and both are different to the B model cylinder and the C/D/E models cylinder.
A tell-take difference in the motors is that the A model motor has a splined drive for the gear on the crankshaft and the later ones have a drive key.
It was and still is common practice to swap flywheels.
At the time of the release of the A model, Yamaha got quite a bit of blowback about the "too fast" motor and the bulbous engine casings on the A model. They introduced the heavier flywheel and flatter engine casings on the run as quickly as they could, which is not normal practice for Japanese manufacturers, hence one reason we sometimes see things on TY250s that are not cut and dried.
One outcome of the haste are the parts books they produced. There is an A model parts book and an A/B model parts book and a C model parts book. The A/B model parts book is good at showing the things they changed. Also I suspect that some countries didn't actually get what we call the B model, and some countries did get it but they called it something else, but I can't remember the word they used.


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David Lahey
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Re: TY 250b flywheel

Postby David Lahey » Thu May 02, 2019 9:18 am

As for the petrol tap they leak pretty soon and are interchangeable between TY models so having the wrong model tap doesn't mean much. I use KT250 fuel taps on most of my Yamahas


relax, nothing is under control

GSX 1300R
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Bike: 1975 Yamaha TY 250 B
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Re: TY 250b flywheel

Postby GSX 1300R » Thu May 02, 2019 11:11 am

Yes my B model has a splined primary drive cog Another different part was the sump gaurd Mine was a smaller pressed steel one with holes in it which bent in easily I fitted the aluminium tray type one years ago I was looking at a photo of the Japanese J model which had a similar sump gaurd I still have original petrol cock fitted Have replaced rubber seal twice in 40 years Last time I fitted extra wave washer which works well no leaks cheers



David Lahey
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Re: TY 250b flywheel

Postby David Lahey » Thu May 02, 2019 11:39 am

About the fuel taps, I don't know how many times I replaced the rubber seal thing in my TY175B tap since I got the bike in 1976 but it would be around 10. The main problem was that when I went to buy new ones from the Yamaha shop, they were old stock and so the rubber thing was fairly cactus even before they went in. The price for the rubber thingy had risen to about $15 each by the 2000s when I finally gave up and bought the last remaining few genuine KT250 fuel taps in Australia from my local Kawasaki shop. Since then replica KT250 taps have become available (for about $25 I think) and I've bought a few of those too.
I've would prefer to have my bikes look more standard so would be interested in knowing if you can get newly-made rubber things for them


relax, nothing is under control

tat ty
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Re: TY 250b flywheel

Postby tat ty » Thu May 02, 2019 9:34 pm

David.

An EBay seller called "VINTAGEBULLS" in the US produces replica rubber parts for bikes. They actually make the peacock rubber thingies for Bultaco petcocks. May be worth an email.

Alastair.




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