New Chain Adjustment

[bengtphorqs]

Today the new chain was installed on the '74 TY250 resto. I went with a 428, same as before, and also changed out sprockets to a 53 rear and 13 front. My concerns are two fold. Having installed new Betor shocks I only have a 2, maybe 3 milimeters clearance between the shock spring and the chain. How much clearance is acceptable?

Secondly, I adjusted the chain to the fifth detent on each adjuster cam, still have lots of adjustment left, however I'm concerned about the chain rubbing across the top of the swing arm. When under power, will the chain tension correct so it doesn't rub on the swingarm? The chain tensioner runs below the swing arm but there is no kind of rubbing block on the top. Any ideas or suggestions?

[tony283]

All of what you mention is normal! For best performance in modern day sections I would advise coming down to a 12T engine sprocket. Do not be tempted to go to 11.

Tony

[feetupfun]

If the chain hits the shockie spring while you are riding and it annoys you, you can fit a washer or two behind the shockie eye to space it out a bit. Remember that the original shockies on that bike had the damper bodies at the bottom so gave more clearance for the chain than modern shockies with the bodies at the top (and spring going all the way to the bottom). I find that even 2-3 mm side clearance is enough to stop it making noise. When I run Falcons on my TY250 twinshocks I find that I do need to pack the shockie across about 3mm to give enough clearance. Some people run with less rear sprocket offset than standard to provide more shockie spring clearance, but this is hard on sprockets due to chain misalignment.

Yes when the bikes were new there was a rubber chain rubbing block that fitted over the swingarm pivot tube end. They are no longer available from Yamaha but may be available from someone making replica rubber parts. You will find when you get aboard the bike, the chain will move away from the swingarm pivot tube and only touch it briefly when the rear wheel unweights on obstacles, hence why hardly anyone bothers about fitting a rubbing block there. The shockies you have may well be longer than the originals which will make the chain tend to rub more than with the original shockies on full droop of the rear suspension.

[bengtphorqs]

Feetupfun, you mention that modern shocks run upside down? I have installed the Betors with the damping resevoir on bottom and springs on top. Should this be reversed?

[b40rt]

Feetupfun, you mention that modern shocks run upside down? I have installed the Betors with the damping resevoir on bottom and springs on top. Should this be reversed?

Have the writing on the shock the right way up !

[bengtphorqs]

Got it, that's the way I had it. By the way, I mispoke earlier. The new front sprocket is a 12 tooth as Tony suggested. Thanks again.

[richty250e]

Here's my solution to chain rub on my expensive powder coated swingarm: make up a small chain guide from sheet alloy lined with carbon fibre or nylon. The guide is secured at the rear by a cap head bolt screwed into a riv nut set into the swing arm chain lube filler hole, it wraps around the swing arm at the front.

[bengtphorqs]

Very clever, Rich! I'm not using the chain lube and that would solve the problem. Mighty pretty I might add. Do you have any pix of the full bike? I didn't go to near that effort and expense and this will be mostlly a means to re-aquainting myself with trials again. I suspect it will probably land sideways quite a few times as I ramp up the learning curve.

[richty250e]

I've chucked a few photos in the TC garage of the whole bike.