Hi Heige,
trial installations the wheel and see;
While I do not disagree with the principle in Peg's advice, it assumes that the ends of the swinging arm do not move apart when the spindle nut is unscrewed so, when you measure the three alignments (sprockets, wheels and disc/caliper), if you believe your bike has a 'gap' that requires an unlisted spacer, in fact the 'gap' is simply as a result of the ends of the two individual 'arms' of the swinging arm moving apart when the spindle nut is unscrewed.
I suspect it will be difficult to be sure the ends of the swinging arm are not moving apart when the spindle nut is unscrewed
- the distance between the ends
might be the same as a standard T140/TR7 swinging arm but the '79 T140D swinging arm is unique - not the same (part number) as either the arm on other '79 twins or the '80 arm (which appears to the be the same part on all '80 twins).
When I was fitting alloy wheels from a twin into one of my T160's, I knew the rear would require a spacer as the twins' swinging arm is narrower than the triples'. While I had been given a spacer thickness by the wheels' seller, I also double-checked using similar methods to Peg's and a stack of washers. However, I discovered that simply "Fit the Brake caliper to it’s mounting bracket without pads, fit the bracket on the spindle and check carefully that the caliper is running central to the disc" is not enough to be
certain "the caliper is running central to the disc" - believing I had "a spacer width gap" in the T160's case between the the caliper bracket and the wheel, I filled it with washers but also checked by tightening the spindle nut on the spindle and then releasing the caliper mounting bracket's pivot bolts on the swinging arm. The caliper mounting bracket is longer horizontally than just the caliper and, while the caliper had
appeared to be "running central to the disc", releasing the caliper mounting bracket's pivot bolts on the swinging arm showed the bracket wasn't aligned with the swinging arm.
The solution was to remove one or two of the 'spacer washers', this allowed the spindle and nut to squeeze the swinging arm ends slightly closer together (around 1/16-to-3/32 of an inch) and align the caliper
and mounting bracket with
both the disc and the swinging arm. Subsequently, I was able to obtain the correct dimension between the ends of T160 swinging arms, and the knowledge that the ends are not always the 'correct' distance apart when not tightened by the spindle and nut around wheel, caliper mounting bracket, speedo. drive, chain adjusters, etc.
It seems obvious why the whasher was place against the caliper mount, to take up the slack and avoid squeezing the swingarm too much. Maybe I should just find, or make, another proper washer to fit on the right side of the caliper mount.
Your T140D has a different caliper mounting bracket and method of securing it to the swinging arm from a T160. Absent being
sure that the distance between the ends of your bike's swinging arm remains correct even when not tightened by the spindle and nut around wheel, caliper mounting bracket, speedo. drive, chain adjusters, etc., maybe first fill the "gap" with standard washers, tighten spindle and nut then release the "Brake Torque Stay" from the swinging arm and see if the Stay end and arm bracket remain aligned?
I still have a feeling that the washer belongs to the spindle nut (due to its size and the parts figure in post #4).
The standard 83-2266 washer that fits between the spindle nut and the timing-side chain adjuster is only 1 inch OD, smaller than either a standard 5/8" ID washer or the OD of the chain adjuster around the Spindle.
If I was feeling extravagant I might buy a pair of stainless steel chain adjusters, make a stainless steel spacer and then weld it to one of the chain adjusters
Depending on the thickness of any required spacer,
T160 drive-side chain adjuster has a spacer attached ...
I believe the 1980 T140 Swingarm was different to the 79 swingarm.
If the parts books are correct, all '80 twins (including the T140D) used the same swinging arm and caliper mounting; otoh, '79 twins except the T140D still used the underslung caliper (unless the change was made on all twins during '79?); however, '80 swinging arm and overslung caliper mounting are not the same parts as '79 T140D swinging arm and overslung caliper mounting ...
Hope this helps.
Regards,