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Home > Archive > Home Repair forum > May 2006 > Lawnboy Mower Vibration
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Lawnboy Mower Vibration
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| 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
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| m Ransley 2006-05-30, 12:21 am |
| Try a new blade
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| I installed the exact blade, flange, washer and nut that ran perfectly
smooth on my D mower on the F mower and it still vibrated just as much.
I took the exact blade, flange, washer and nut from the F mower and
put it on the D mower and there was no vibration, so it is not the blade.
Thanks,
Bill
m Ransley wrote:
> Try a new blade
>
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| Joseph Meehan 2006-05-30, 9:21 am |
| 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
The blade would make a very small amount of runout very noticeable.
That would be my guess.
--
Joseph Meehan
Dia duit
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| m Ransley 2006-05-30, 10:21 am |
| Look for and compare end shaft side movement, just because the new
mower does not vibrate does not mean it was built as well as the old
unit. A New blade would be the cheap and easy way to confirm a bent
shaft or a loose tolerance on the main shaft bearing , that vibrates
with a poor blade, plus you only have one blade now. I just threw one
away that seemed balanced off the mower, I thought the shaft was bent.
It does not take much to ruin a blade.
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| George E. Cawthon 2006-05-30, 3:21 pm |
| 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.
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| John Lawrence 2006-05-30, 4:21 pm |
| 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" <GeorgeC-Boise@worldnet.att.net> wrote in message
news:oK%eg.114610$Fs1.32592@bgtnsc05-news.ops.worldnet.att.net...
> bill wrote:
> If switching all the blade parts down to the shaft doesn't stop the
> vibration, then the problem is the motor. Probably a bent shaft even if
> you can't see any runout.
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| George E. Cawthon 2006-05-30, 9:22 pm |
| I agree, bearing could be a problem but the op
didn't indicate the age. Still most likely cause
is hitting something. I've never seen anything
that could come loose from the fly wheel and it is
usually protected. The only thing that usually
happens is shearing the key, but that messes up
the spark timing.
John Lawrence wrote:
> The off balance doesn't have to be from the bottom. If you hit anything you
> could have a bent crank inside, out of sight. The lower crank bearing may be
> worn and centrifical forces from high RPMs could cause the crank to whip.
> Something may be loose or whatever on the flywheel. There are some flywheels
> that have weights added for balance. This is especially critical on 2 stroke
> engines because of the high RPMs.
> "George E. Cawthon" <GeorgeC-Boise@worldnet.att.net> wrote in message
> news:oK%eg.114610$Fs1.32592@bgtnsc05-news.ops.worldnet.att.net...
>
>
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| Larry 2006-05-31, 12:21 am |
| The F engine mower that vibrates was just built using mostly unused old
stock parts. The short block including crankcase, piston, rod, etc. is
all new. It was already assembled in the factory box. The flywheel
might be used. I have wondered about the flywheel. Maybe adding mass
to the other end of the shaft might give an unbalanced flywheel
something to react against.
George E. Cawthon wrote:[color=darkred]
> 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:
>
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