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<div> <font size="3">I would find it mildly surprising if they were triggering off of the blade but any motor I've worked on is at least 20 years old. On those motors (a couple Briggs and Scrapiron and a Tecumseh) had the magneto in the flywheel on the opposite end. They will run without the blade attached. Triggering off the blade means that motor is a special-purpose model for that application. The economies of scale favor a more generic design.</font><br>
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<div style="clear:both"><font size="4">Dave </font><br>
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<div style="font-family:arial,helvetica;font-size:10pt;color:black"><font size="2">-----Original Message-----<br>
From: old dirtbeard <dirtbeard@gmail.com><br>
To: Bob Spidell <bspidell@comcast.net><br>
Cc: shop-talk@autox.team.net<br>
Sent: Tue, May 18, 2021 9:38 pm<br>
Subject: Re: [Shop-talk] Mower blade orientaaion relative to piston<br>
<br>
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<div dir="ltr">Hi Bob,
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<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>
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<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>
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<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>
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<div>best,</div>
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<div>doug </div>
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<div class="yiv5420248293gmail_attr" dir="ltr">On Tue, May 18, 2021 at 5:35 PM Bob Spidell <<a rel="nofollow noopener noreferrer" shape="rect" ymailto="mailto:bspidell@comcast.net" target="_blank" href="mailto:bspidell@comcast.net">bspidell@comcast.net</a>> wrote:<br clear="none"></div>
<blockquote class="yiv5420248293gmail_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 clear="none">
<br clear="none">
Bob<br clear="none">
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<div>On 5/18/2021 2:55 PM, Brian and Wendy
Warrick wrote:<br clear="none">
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<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>
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<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>
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<div dir="ltr" id="yiv5420248293gmail-m_-6852136761353026904divRplyFwdMsg"><font style="font-size:11pt;" face="Calibri, sans-serif" color="#000000"><b>From:</b>
Shop-talk <a rel="nofollow noopener noreferrer" shape="rect" ymailto="mailto:shop-talk-bounces@autox.team.net" target="_blank" href="mailto:shop-talk-bounces@autox.team.net"><shop-talk-bounces@autox.team.net></a> on behalf
of Karl Vacek <a rel="nofollow noopener noreferrer" shape="rect" ymailto="mailto:stearman809@gmail.com" target="_blank" href="mailto:stearman809@gmail.com"><stearman809@gmail.com></a><br clear="none">
<b>Sent:</b> Tuesday, May 18, 2021 3:52 PM<br clear="none">
<b>To:</b> '<a rel="nofollow noopener noreferrer" shape="rect" ymailto="mailto:shop-talk@autox.team.net" target="_blank" href="mailto:shop-talk@autox.team.net">shop-talk@autox.team.net</a>'
<a rel="nofollow noopener noreferrer" shape="rect" ymailto="mailto:Shop-talk@autox.team.net" target="_blank" href="mailto:Shop-talk@autox.team.net"><Shop-talk@autox.team.net></a><br clear="none">
<b>Subject:</b> [Shop-talk] Mower blade orientaaion relative
to piston</font>
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<div lang="EN-US">
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<div style="margin:0in 0in 0.0001pt;font-size:11pt;font-family:Calibri, sans-serif;">
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..</div>
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<div 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. The mounting
point is square, no pins, no longer side, nothing.</div>
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<div 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. It’s been off many times
and there’s no way to tell how it was mounted originally.
The manual is silent on this.</div>
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Power stroke shouldn’t matter, but maybe some dynamic
issue one way or the other?</div>
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Thanks!<br clear="none">
Karl</div>
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