I broke off the threaded stud on front end of the camshaft on my R90/6. Is there a way to fix this short of replacing the entire camshaft?

In short, YES. And it will save you a ton of money. But, and here's the warning, you have to proceed slowly and methodically. I'm going to step-by-step OUTLINE the method:

1)Remove front wheel, fender and anything else hanging in front of the motor.

2) Put bike on table or lift where it can be accessed easily. This ain't a "laying in the driveway" job.

3) File the broken cam nose smooth and flat. DON'T remove the D-shaped boss!

4) Centerpunch the exact center of the cam tip carefully with a nice sharp punch (automatic type, not hammer type)

5) Drill the cam tip to a depth of 7/8", in a series of small size increments, up to 11/64" (For tap drill sizes see: http://www.spiralock.com/docs/rec-drill-sizes.pdf ) Remove the drill and clean out the chips several times. Use tapping oil for drilling and tapping.

6) Tap the perfectly-straight hole to 5x0.8 mm thread, to a depth of 3/4" Clean out chips often. Use cutting oil.

7) Clean the hole. Reassemble everything and secure the advance unit using a 5x15mm bolt with a flat and wave washer. Use blue low-strength Loctite on the clean, dry bolt threads. When snugging the bolt, hold the advance unit counter-clockwise against the D-shaped flat to remove any slop and prevent shifting.

8) Call your friends over, show them the professional job you did. Be sure to reinstall the front wheel before riding...

Tom Cutter

(Originally posted to the Airheads list)