Motorcycle Repair: Honda SL125 engine whine, engine whine, honda sl125

Question
Hi Wayne,
I have a 1972 Honda SL125 I have restored except the engine. I did not attempt any restoration on the engine as it ran, cranked, idled, accelerated fine. The only problem is the engine has a very noticeable whine upon acceleration. You don't hear this at idle or during deceleration, only upon acceleration. I am hesitatnt to continue riding the bike in case I may be doing serious damage. I restored the bike to ride, so I would like to continue doing so. Thanks for any help, Robert

Answer
Robert,

Followup:
it is starting to sound like it might
be in the transmission, since it
doesn't whine with the clutch pulled in.
As soon as you release the clutch
the power goes to the mainshaft
and on to the various transmission bearings
and gears etc. Then out the layshaft
to the front sprocket.



-can you isolate where the noise is coming from?
I can't help much since I can't listen to it.
-Could it be a dry speedometer cable or is it
definitely in the engine unit?
-If it is only during acceleration, it sounds
like something whining under the load, possibly a
gear or bearing?
-Does it do it in all the gears?
-Does pulling the clutch change the sound?

I have quite a bit of experience with these
engines but don't recall anything specific
that would cause a whining noise.
Are the sprockets okay and aligned?

-let me know if you can isolate the area
it's coming from. Is it possible to use
a stethascope or sounding rod if you blocked the bike up
securely and tried to listen for the whining noise?