I recently put on a slightly larger tire on the rear of my 1974 ty250 and noticed the tire rubbing on the chain gard.  After looking closely it appeared the rear sprocket was out board of the engine sprocket ( not aligned). Also the tire is not centered with the forks.  I have two ty 250s the other is the same so I don't think it is damaged.  I built a couple bushings to move the rear wheel to the right now it is aligned with the engine sprocket and centered in the forks.  I haven't had a chance to give it a good test ride as it has not stopped snowing the last three months.  So I'm curious if any have noticed this?

 

 

Was the original sprocket dished ?

what size is the tyre, I thought they only did 1 size 4.00x18

its the only 1 you can use in the uk if your riding in trials

 

The sprocket is dished about 3 mm which I am sure is stock, I checked both bikes one is stock and the other is aftermarket.  THe new tire is 400x18 although it is wider than the stock by about 6mm which is not unusual, different manufactures build them slightly different size.  I did put a 4.50x18 on one bike, that required rebuilding the rear swing arm.  Any one check their old ty 250 for sprocket alignment and is your tire centered in the swing arm? I'm in the U.S. And live in a remote area, not many trials bikes to check.  Which brings up another subject  you guys in the UK have so many trials bikes,wish I could figure out how to get them shipped for cheap.  

What do you mean tyre centered in the swingarm? Centered between the axle tabs? Centered between the pivot tube ends? Tyre edges same distance from the swingarm arms at the front end?

I'll measure some TY250s if you tell me what you are measuring. Please also confirm that you have the first type swingarm with the simple flattish plate gusseting rather than the later type with the formed, curved gusseting between pivot tube and arms

I just of thought of some things I have found with TY250s that might be relevant

Someone had respoked the rear wheel and it was offset relative to the hub. TY twinshock rims should be centered on the hub spoke flanges

Another one had a swingarm that had both swingarm arms bent slightly sideways

 

The sprocket is dished about 3 mm which I am sure is stock, I checked both bikes one is stock and the other is aftermarket.  THe new tire is 400x18 although it is wider than the stock by about 6mm which is not unusual, different manufactures build them slightly different size.  I did put a 4.50x18 on one bike, that required rebuilding the rear swing arm.  Any one check their old ty 250 for sprocket alignment and is your tire centered in the swing arm? I'm in the U.S. And live in a remote area, not many trials bikes to check.  Which brings up another subject  you guys in the UK have so many trials bikes,wish I could figure out how to get them shipped for cheap.  

 

 

Thanks for the ideas. I'll do some measuring and get back . 

I did some measuring.  The tire is about 8MM to the left in reference to the center of the swing arm.  THe swing arm has the flat metal gussets.  THe hub is centered in the rim. I removed the skid plate and took a picture from under the bike and added a picture.  You can see the engine case seam which is the center and I added a center mark on the frame.  The swing arm is visible if you look close and can see the tire is not in the center.  Both my bikes are the came so I don't think they could both be bent the same.  Just curious if this how they are built how May that effect how it handles.

The sprocket is dished about 3 mm which I am sure is stock, I checked both bikes one is stock and the other is aftermarket.  THe new tire is 400x18 although it is wider than the stock by about 6mm which is not unusual, different manufactures build them slightly different size.  I did put a 4.50x18 on one bike, that required rebuilding the rear swing arm.  Any one check their old ty 250 for sprocket alignment and is your tire centered in the swing arm? I'm in the U.S. And live in a remote area, not many trials bikes to check.  Which brings up another subject  you guys in the UK have so many trials bikes,wish I could figure out how to get them shipped for cheap.  

 

 

Thanks for the ideas. I'll do some measuring and get back . 

Sorry for the seemingly stupid question but is the hollow side of the dish in the sprocket facing outwards?

With the axle in the position as shown in the photo where the front edge of the tyre is too far towards the left side arm, is the side of the rear wheel parallel with the front wheel? (use a straight board and allow for the difference in widths of the front and rear tyres)

jbird,

You mentioned on another thread you live close to me.

I have 2-74's and a 76-250 your welcome to look at. On the 74's, one has a Michelin and the other has a Dunlop. The 76 has a Dunlop.

Cheers

We really need a picture of the rear wheel from both sides. Just from logic it looks like the spacers are in the wrong side as the long one should be on the brake side.

Tony

I lined up a straight board on the sides and I think I have a bent swing arm. The spacers are on correct and all else checks good, rear axle aligned, sprockets. Thanks for all the helpful information.  I have another swing arm and will change it.  This is a bike I just purchased and all I done was install a new tire so I don't know the history. I will get back will on the forum if that doesn't fix it.   GOOD DAY.   Jbird 

Well I changed the swing arm and now it is aligned  odd thing when comparing both swings arms it was hard to see any problem.  Thanks for all the help.