I'm using a set of T120 front forks and front brake on an 1968 Aermacchi "track day bike" build. Since the bike will have clip-on bars I machined off the handlebar mounting attachments on the top triple clamp for a smooth look and machined the fork tube opening to the exact diameter as an original T120 triple clamp (I only have the bottom clamp). Here's my question. The top of the T120 fork tubes are tapered but the Aermacchi top triple clamp holes for the fork tubes are straight. Should the top triple clamp mount below the taper? If so, that leaves the fork tube taper above the top triple clamp and the fork cap is sitting above the top triple clamp.
I have my reasons for wanting to use T120 forks and Aermacchi triple clamps. How does the taper of the fork tubes fit an original T120 top triple clamp?
If anyone can make sense of my question please get back to me! Thanks, Tom T
On a 68, the top clamp or yoke has tapered holes to fit the tapers on the stanchions which gives a tight joint when you do the top nuts up. When fully fitted the stanchion is about 1/16" below the top level of the upper yoke (triple tree clamp) in the original set up.
As Dave says, the original triple has tapered sockets for the stanchions. The resulting taper-to-taper connection gives a solid abutment for the stanchion; and a rigid coupling without having to resort to a clamp, such as many other bikes do.
If you want to use your Aermacchi top triple without mods, you don't have much choice but to have the taper above the triple.
However, if this results in the stanchions being pulled up through the bottom triple any significant amount, keep in mind that the effective fork length will decrease, and that will affect your bike's handling characteristics.
This of course will be less of a problem if the Aermacchi top triple is the "dropped" style, rather than the normal flat style.
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Thanks guys! At least now I know how they fit in the top triple clamp on the T120. I can probably cut 1/4" or so off the taper and still have plenty of threads for the cap nut. I can play with rear shock length to get the bike to have the proper stance. As for how decreasing the length of the fork tube will have on the external main spring and the handling of the bike I'll have to wait and see. The only reason I'm using the Aermacchi triple clamps is simply because they fit. Before I put the fork tubes in the chop box I'll try and snag a T120 top triple clamp (I already have the bottom) and see if my cups and cones will fit the T120 stem and go from there. Thanks again, Tom T
The shorter fork will steepen the steering angle and shorten the trail which is good. The spring preload will be higher, if you shorten the spring it will be stiffer. The taper tubes never sealed very well because there always was a gap between the nut and top of the tube, oil leaked up the threads.