I agree, bearing could be a problem but the op
didn't indicate the age. Still most likely cause
is hitting something. I've never seen anything
that could come loose from the fly wheel and it is
usually protected. The only thing that usually
happens is shearing the key, but that messes up
the spark timing.

John Lawrence wrote:
The off balance doesn't have to be from the bottom. If you hit anything you
could have a bent crank inside, out of sight. The lower crank bearing may be
worn and centrifical forces from high RPMs could cause the crank to whip.
Something may be loose or whatever on the flywheel. There are some flywheels
that have weights added for balance. This is especially critical on 2 stroke
engines because of the high RPMs.
"George E. Cawthon" wrote in message
news
bill wrote:
I have an annoying vibration in a Lawnboy mower that that can be felt in
the handle.

I have 2 lawnboy mowers. The older one (D engine) runs perfectly smooth.
The newer one (F engine) has the vibration. If I run either mower
without a blade, the vibration is slight and equal. Neither mower seems
to have any runout when I look at the shaft while it is running bladeless
or as I pull the starter and look at the shaft (not running). If I put
the same blade, flange, washer and nut on each, the D mower runs
perfectly smooth and the F mower vibrates.

So, it is not the blade, flange, washer or nut. It doesn't have any
obvious shaft runout and the blade runs even on both sides as it is
turned (one side is not higher or lower than the other). It doesn't
vibrate any more than the good one when the blade is off. What could it
be?

Please take the spam-bustin 7 out of my address if responding, so my
e-mail address is actually calbert "at sign" and then mchsi.com

Thanks,

Bill


If switching all the blade parts down to the shaft doesn't stop the
vibration, then the problem is the motor. Probably a bent shaft even if
you can't see any runout.