I have a new to me TY250A twin shock and the rear sprocket lightly rubs on the swing arm.  Do they normally have very little clearance?  The bike appears unmolested and with low hours.  The axle hardware/ spacers match what is shown on the part list.  The rear sprocket is steel, looks original and is marked PORTCO YA-311-53.  The sprocket runs reasonable true and is not bent.  My attempt to check sprocket alignment with a home improvement type laser suggests that the rear sprocket is about 1.5 mm farther out than the front sprocket.  Is there something else to consider before installing a 1.5 mm spacer or taking 1.5 mm off of the mounting surface of the sprocket?  Purely by eye, the sprocket looks 1/4" out from the front sprocket. 

 

 

Edited April 24, 20242 yr by mcman56
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No of course it shouldn't rub on the swingarm. Here are a few possible reasons for why yours is rubbing.

The axle may not be square to the centreline of the bike.

The swingarm arms may be bent to the side.

The sprocket may have too much dish.

You may have the wrong length spacer on the brake drum side although it looks right to me in the photo.

The sprocket looks like an aftermarket one I ordered in at a local shop 25 years ago and did not accept because it had too much dish.

Were the original sprockets aluminium?  This one is magnetic and all references I see to the brand on line are all old so it could be a 25 year old aftermarket sprocket.  Is the OEM offset listed somewhere?

 

Everything looks straight as far as I can tell with a tape measure, eyeball and the bike together.  One odd thing is that the paint is rubbed off the swingarm where it touches but I would expect to see it more torn up from the chain.  If I mis align the snail axle adjusters by one step, I get about 2 mm clearance.   

 

 

On 4/25/2024 at 9:26 AM, mcman56 said:

Were the original sprockets aluminium?  This one is magnetic and all references I see to the brand on line are all old so it could be a 25 year old aftermarket sprocket.  Is the OEM offset listed somewhere?

 

Everything looks straight as far as I can tell with a tape measure, eyeball and the bike together.  One odd thing is that the paint is rubbed off the swingarm where it touches but I would expect to see it more torn up from the chain.  If I mis align the snail axle adjusters by one step, I get about 2 mm clearance.   

 

 

Yes original is aluminium. I'll measure the offset on an original sprocket

On 4/25/2024 at 9:26 AM, mcman56 said:

Were the original sprockets aluminium?  This one is magnetic and all references I see to the brand on line are all old so it could be a 25 year old aftermarket sprocket.  Is the OEM offset listed somewhere?

 

Everything looks straight as far as I can tell with a tape measure, eyeball and the bike together.  One odd thing is that the paint is rubbed off the swingarm where it touches but I would expect to see it more torn up from the chain.  If I mis align the snail axle adjusters by one step, I get about 2 mm clearance.   

 

 

The standard offset is 4.8mm

Thanks for that.  I did find that manufacturers list an XT225 sprocket as having the same offset as a TY250 sprocket and happened to have one from an XT.  The sprocket that came on the TY has about 5 mm too much offset.  I did some measuring and my numbers are slightly different from yours but also found that different manufacturers (on Amazon) list minor differences in sprocket thickness.  That seems odd.

 

6 hours ago, mcman56 said:

Thanks for that.  I did find that manufacturers list an XT225 sprocket as having the same offset as a TY250 sprocket and happened to have one from an XT.  The sprocket that came on the TY has about 5 mm too much offset.  I did some measuring and my numbers are slightly different from yours but also found that different manufacturers (on Amazon) list minor differences in sprocket thickness.  That seems odd.

 

If you had an OEM sprocket to measure, why did you not just compare it with the one causing the issue on the bike?

 

I did not realize that XT225 = Ty250 offset until I found it on line.  I only had the XT225 sprocket.