Motorcycle Repair: strange bits in oil, should I worry?, honda ct90, drip oil

Question
I have a 1970 Honda CT90 that has only about 4500 miles and I have it running perfectly.  Curiously when I change the oil there are a pinch of black bits in the bottom of the oil drain pan.  They look and feel like sand and are not attracted to a magnet.
The engine does not use or drip oil?

Is this a sign on impending catastrophic failure and the engine should be torn down.  Or should I just change the oil often as its not really worth the cost of rebuilding.
Thanks, Kirby

Answer
Kirby, about the only source of "black bits" inside the motor would be shown here:

http://www.cmsnl.com/honda-ct90-trail-90-k0-us_model619/partslist/E++04.html
The camchain tensioner/guide rollers and tensioner rubber tip.

Although you have low miles on the engine, the parts are now 39 years old and have been subjected to heat/cold cycles, plus being bathed in hot/cold oil for many years.

Change the oil about every couple hundred miles or less and watch for further indications of debris like this. The rollers started out being a hard rubber, but have now progressed into the hardened plastic stage, where they start to chip off a little at a time. They are not known for catastrophic failures, but will gradually create noise from the contact with the chain and as increasing roughness affects the interface between the chain and rollers.

Keep the oil changed and just ride it..

Bill Silver