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Lawn Mower Issue: Pull Cord-Engine Cough-Pull Cord yanks back violently


aglue's Avatar
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09-04-08, 07:16 PM   #1  
Lawn Mower Issue: Pull Cord-Engine Cough-Pull Cord yanks back violently

Hey all,

First time forum poster so I hope I communicate this correctly:

I have an issue with a small Craftsman "single" pull gas lawn mower. The unit is a few years old and has been sitting in storage for a long while.

After ensuring a new air filter is installed, oil and gas levels are correct, I have this problem:

1. Pull the start cord...nothing.
2. Pull the start cord over and over... nothing
3. Pull the start cord and suddenly a quick puff of white smoke from the exhaust and,
4. The start cord retracts/"catches" violently, and gets ripped out of my hand. Engine doesn't start.

It almost feels as if the engine "catches" but then the start cord is still engaged. The last time I tried this the handle ripped out of my hand, wound itself around the lawn mower push bracket and smacked my arm, broke skin! Ow!...

I figured that was the last straw and that I would seek out some wise folk who might help me out.

Is there anything a do it yourself type can do? What could cause such dramatic lawn mower behavior?

Thanks for your time!

 
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cheese's Avatar
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09-04-08, 10:18 PM   #2  
There are two things that would cause this. One is if the blade is not on it, or loose. The other is if the flywheel key is sheared.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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09-05-08, 02:45 AM   #3  
Posted By: aglue 1. Pull the start cord...nothing.
2. Pull the start cord over and over... nothing
3. Pull the start cord and suddenly a quick puff of white smoke from the exhaust and,
4. The start cord retracts/"catches" violently, and gets ripped out of my hand. Engine doesn't start.
The reason behind the diagnosis behind what cheese has said is

1) The blade acts as a flywheel too, without it when the engine fires at the low starting speed there is not enough energy stored to carry the machine around to the next revolution and it snaps back through the recoil start.

2) If the flywheel key is sheared (which can be done by a sudden stoppage) it throws the timing of the ignition off, and potentially be firing the fuel-air mixture in the cylinder signifigantly before the piston is near top dead center which just causes that energy to force the engine backwards, which if the recoil start is still engaged (IE mid-pull) it will snap back quickly.


Hope this helps.

 
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09-05-08, 10:23 PM   #4  
Lawn Mower

ah....thanks guys. Yeah I was in the process of replacing the blade and it's not installed yet. Wow, never thought about the physics of not having that on.

I'll reinstall and give it whirl and report back.

Cheers!
-Aglue

 
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09-14-08, 04:29 PM   #5  
No es bueno: sheared key?

So I reinstalled the new blade and pulled the cord and sure enough the think yanked out of my hand. I'm thinking the flywheel key is definitely sheared.

So, what's the fix? Is there one? Or, are we talking about a new lawn mower here all together?

Incidentally, the reason I replaced the blade was that the old one was severely damaged by the previous operator... evidence of "sudden stoppage".

Thanks guys!
-ag

 
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09-14-08, 05:17 PM   #6  
Yes it looks like it may be time for a new one

LOL a new flywheel key that is...

You need to remove the blower housing around your engine, then (depending on the brand and model of engine) there will be a retaining nut or starter clutch holding down the flywheel. Unscrew whatever is holding down the flywheel and then the flywheel will need to be pulled from the shaft, the the key can be replaced!

Brand, model and spec/type nos from the engine would be helpful in providing more detailed information on flywheel key replacement.

Best of Luck...

 
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09-14-08, 09:34 PM   #7  
You might check to be sure the crankshaft isn't bent before doing the flywheel key, but if it's the key itself it is not a bad job to do.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

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09-15-08, 09:24 AM   #8  
More info on the sheared flywheel key mower

Awesome, ok so here's more info then...

The unit is a Craftsman Eager-1 4.5HP mower, model 917.382781
Below is a link to the parts available from Sears. I don't see anything specific for the freewheel key but I do see a replace engine on there (for $249 or something). At that price point it's almost worth just replacing the whole thing..but, that wouldn't be very DIYish right?... What do you guys suggest?

http://************/5nlcz2

I wonder what a repair service like this at a small engine repair shop would run me?

Thanks guys,
-AG

 
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09-15-08, 11:18 AM   #9  
611004 FLYWHEEL KEY shows to be the part number for the flywheel key on your engine, based on the model number you posted.

I don't know what the charges run in your area, but if I came out for a service call and this is what your engine needed it would run around $60.00 parts labor and trip charge. If you took it in to a shop it would be a little less.

 
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09-15-08, 11:20 AM   #10  
Got it... thanks for the help. I didn't realize this forum strips out URL's too... that makes sense I suppose.


$60 or so isn't so bad...

Posted By: 30yearTech 611004 FLYWHEEL KEY shows to be the part number for the flywheel key on your engine, based on the model number you posted.

I don't know what the charges run in your area, but if I came out for a service call and this is what your engine needed it would run around $60.00 parts labor and trip charge. If you took it in to a shop it would be a little less.

 
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09-15-08, 12:00 PM   #11  
Aglue I think the URL may not have shown, just because you haven't been here very long, maybe, not sure?

I do know if its a very long url, it may truncate some of the characters.


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04-16-12, 02:12 PM   #12  
Power Mower Flywheel key

Wow! I just experienced exactly what is described in this thread. Pull cord was ripped from my right hand and slashed across my left hand which was holding the stop/safety handle. Blood everywhere. Blood and big bruise but appears to be healing OK.

Called a local small engine repair shop for an estimate using information from this thread (flywheel key). Shop tech appeared to know exactly what was the problem and mentioned possible bent shaft. Gave me a basic estimate and their shop procedure. (Nice to be able to speak to tech with a degree of intelligence gleaned from this site.)

I'll report back with cost when mower is repaired.

Thanks.

MJ

 
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04-16-12, 07:18 PM   #13  
Glad the thread was useful to you! Hopefully the crank isn't bent.


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God bless!

 
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06-14-12, 05:45 AM   #14  
Painful indeed

I was very happy to read this thread. I've been troubleshooting my Murray (3.5 B&S motor) all week.

My pull cord also snapped back but caught me in the chest drawing blood and knocking the wind out of me...beat up by a lawnmower lol

Anyways, I have noticed that mine will only snap back violently if I have pressed the priming bulb. Otherwise this doesn't happen. Is this indicative of one particular issue?

Thanks

 
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06-14-12, 09:22 AM   #15  
The reason it doesn't snap back is there isn't any fuel in the combustion chamber to be ignited, when you press the primer fuel is made present for the combustion chamber, as ignition starts the timing is off and the combustion forces the pistion back down creating the violent jerk. Have a good one. Geo

 
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