Super cub rod knock sound? Other possible causes? Auto clutch?

jas67

jas67

Member
I recently picked up an early super cub, C102, with the 49cc pushrod motor.

After attending to the leaky petcock, changing the oil, and putting in a new battery, the motor is running.

Here's the "BUT" -- it has what sounds like a rod knock under load. The sound seems to be coming from the crank case, maybe even the right side (clutch)?

I recall seeing a comment in a post on another forum (of course, I can't find it now) that described a noise coming from an auto clutch that sounded like a rod bearing problem.

Thoughts?

I can also make the noise happen running the bike in gear up on on the center stand and then stopping the wheel with the rear brake; then noise happens a little as the brake loads the wheel down and stops it.

Short of tearing down the motor, what else can I do to diagnose this?
 
jas67

jas67

Member
bc17a said:
I'd start with a valve adjust. Also, how bad was the oil?
Click to expand...

I doubt that the valves being out would cause this, but, I do need to check them anyway.
Ignition timing, however, can cause a knock. I did check that, and it is(was) spot on.

The oil that came out was dark, but, not sludgy, and didn't have any visible particulates in it.

DFull said:
loose clutch basket - they sound terrible. Check first.
Click to expand...

I'll check that next.
 
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