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re: "... they are using iron mass of the blade as part of the inductance
field to signal the position for coil firing ..."
That was my guess, based on what they told me; the motor was otherwise
in good shape (how I managed to get it back together still amazes me).
IIRC, it was a Tecumseh 5HP engine. The name of the shop was 'Knife
Stalkers.'
I'm looking into possibly rebuilding a couple chainsaw motors, the coil
and 'points,' or whatever solid state switch they are using, are very
simplistic. There may be a magnet in the crank gear to trigger the
spark. I use Pertronix in several cars and, except for one they have a
cap on the distributor cam with magnets to fire the electronic switch.
Surprising to me, the one on my 4-cyl Austin-Healey doesn't use the cap,
apparently the lobes on the distributor cam are sufficient to fire the
Hall Effect sensor.
bs
On 5/18/2021 7:38 PM, old dirtbeard wrote:
> 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@comcast.net
>
> 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@autox.team.net>
>> *Sent:* Tuesday, May 18, 2021 3:52 PM
>> *To:* 'shop-talk@autox.team.net
>> *Subject:* [Shop-talk] Mower blade orientaaion relative to piston
>>
>> Last time I sharpened my 21â?? walk-behind mower blade I thought of
>> something thatâ??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. Itâ??s been off many times and thereâ??s
>> no way to tell how it was mounted originally. The manual is
>> silent on this.
>>
>> Power stroke shouldnâ??t matter, but maybe some dynamic issue one
>> way or the other?
>>
>> Thanks!
>> Karl
>>
>>
>
> _______________________________________________
>
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re: "... they are using iron mass of the blade as part of the
inductance field to signal the position for coil firing ..."<br>
<br>
That was my guess, based on what they told me; the motor was
otherwise in good shape (how I managed to get it back together still
amazes me). IIRC, it was a Tecumseh 5HP engine. The name of the shop
was 'Knife Stalkers.'<br>
<br>
I'm looking into possibly rebuilding a couple chainsaw motors, the
coil and 'points,' or whatever solid state switch they are using,
are very simplistic. There may be a magnet in the crank gear to
trigger the spark. I use Pertronix in several cars and, except for
one they have a cap on the distributor cam with magnets to fire the
electronic switch. Surprising to me, the one on my 4-cyl
Austin-Healey doesn't use the cap, apparently the lobes on the
distributor cam are sufficient to fire the Hall Effect sensor.<br>
<br>
bs<br>
<br>
<div class="moz-cite-prefix">On 5/18/2021 7:38 PM, old dirtbeard
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAG1pxgaBSqYewhJsaMJPPRkp6xBJ5YNUE5vSLVO4RCGhrSgFUQ@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Hi Bob,
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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).</div>
<div><br>
</div>
<div>best,</div>
<div><br>
</div>
<div>doug </div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, May 18, 2021 at 5:35
PM Bob Spidell <<a href="mailto:bspidell@comcast.net";
moz-do-not-send="true">bspidell@comcast.net</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div> 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.<br>
<br>
Bob<br>
<br>
<div>On 5/18/2021 2:55 PM, Brian and Wendy Warrick wrote:<br>
</div>
<blockquote type="cite">
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
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.</div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<br>
</div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Brian</div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Nampa, ID</div>
<div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<br>
</div>
<hr style="display:inline-block;width:98%">
<div id="gmail-m_-6852136761353026904divRplyFwdMsg"
dir="ltr"><font style="font-size:11pt" face="Calibri,
sans-serif" color="#000000"><b>From:</b> Shop-talk <a
href="mailto:shop-talk-bounces@autox.team.net";
target="_blank"
moz-do-not-send="true"><shop-talk-bounces@autox.team.net></a>
on behalf of Karl Vacek <a
href="mailto:stearman809@gmail.com";
target="_blank"
moz-do-not-send="true"><stearman809@gmail.com></a><br>
<b>Sent:</b> Tuesday, May 18, 2021 3:52 PM<br>
<b>To:</b> '<a
href="mailto:shop-talk@autox.team.net";
target="_blank"
moz-do-not-send="true">shop-talk@autox.team.net</a>'
<a href="mailto:Shop-talk@autox.team.net";
target="_blank"
moz-do-not-send="true"><Shop-talk@autox.team.net></a><br>
<b>Subject:</b> [Shop-talk] Mower blade orientaaion
relative to piston</font>
<div>Â </div>
</div>
<div lang="EN-US">
<div>
<p style="margin:0in 0in
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">
Last time I sharpened my 21â?? walk-behind mower
blade I thought of something thatâ??s never occurred
to me, after using the same brand of mower for 25
years..</p>
<p style="margin:0in 0in
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">
 </p>
<p style="margin:0in 0in
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">
On a Snapper, the blade can actually go on any way
onto the square adapter keyed to the crankshaft.Â
The mounting point is square, no pins, no longer
side, nothing.</p>
<p style="margin:0in 0in
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">
 </p>
<p style="margin:0in 0in
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">
One way would be aligned with the cylinder at
TDC/BDC, and the other way would be across. Itâ??s
been off many times and thereâ??s no way to tell how
it was mounted originally. The manual is silent
on this.</p>
<p style="margin:0in 0in
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">
 </p>
<p style="margin:0in 0in
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">
Power stroke shouldnâ??t matter, but maybe some
dynamic issue one way or the other?</p>
<p style="margin:0in 0in
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">
 </p>
<p style="margin:0in 0in
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">
Thanks!<br>
Karl</p>
</div>
</div>
</div>
<br>
</blockquote>
<br>
</div>
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