[Shop-talk] Mower blade orientaaion relative to piston

[old dirtbeard]

Hi Bob,

I believe you, of course, but I have never heard this before.  I have a
Craftsman 21" walk behind and I usually sharpen the blade and do
maintenance this month, so I think I will see if the engine will fire with
the blade removed for sharpening.

For this to make sense to me, there would need to be some sensor on the
blade, or they are using iron mass of the blade as part of the inductance
field to signal the position for coil firing. The aluminum sump of the
motor protrudes through the steel deck of the mower, so I suppose it is
possible. There is quite an air gap between the blade and the sump of the
engine, however.

You have me very curious and I will let you know if the mower will fire
without the blade attached (if it does, I will not let it run as it is hard
to predict what would happen without that flywheel attached to the
crankshaft).

best,

doug

On Tue, May 18, 2021 at 5:35 PM Bob Spidell <bspidell at comcast.net> wrote:

> Possibly of some interest: I had a Craftsman walk-behind that quit running
> suddenly. I tore the engine down, didn't find anything, then finally took
> it to a repair shop. They told me the blade had a crack in it that caused
> the problem; supposedly the blade is part of a timing loop that fires the
> spark. Sort of makes sense if you think of the blade as a flywheel with a
> position sensor on it.
>
> Bob
>
> On 5/18/2021 2:55 PM, Brian and Wendy Warrick wrote:
>
> I run Snapper walk behind mowers and have never gave it a thought. I can't
> see why it would matter. If it did, they would have designed the adapter
> differently.
>
> Brian
> Nampa, ID
>
> ------------------------------
> *From:* Shop-talk <shop-talk-bounces at autox.team.net>
> <shop-talk-bounces at autox.team.net> on behalf of Karl Vacek
> <stearman809 at gmail.com> <stearman809 at gmail.com>
> *Sent:* Tuesday, May 18, 2021 3:52 PM
> *To:* 'shop-talk at autox.team.net' <Shop-talk at autox.team.net>
> <Shop-talk at autox.team.net>
> *Subject:* [Shop-talk] Mower blade orientaaion relative to piston
>
>
> Last time I sharpened my 21” walk-behind mower blade I thought of
> something that’s never occurred to me, after using the same brand of mower
> for 25 years..
>
>
>
> On a Snapper, the blade can actually go on any way onto the square adapter
> keyed to the crankshaft.  The mounting point is square, no pins, no longer
> side, nothing.
>
>
>
> One way would be aligned with the cylinder at TDC/BDC, and the other way
> would be across.  It’s been off many times and there’s no way to tell how
> it was mounted originally.  The manual is silent on this.
>
>
>
> Power stroke shouldn’t matter, but maybe some dynamic issue one way or the
> other?
>
>
>
> Thanks!
> Karl
>
>
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