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#1963628 - 07/23/10 05:37 PM Can I run a mower without a blade?
Nayov Offline


Registered: 08/01/09
Posts: 768
Loc: ME
I hit a metal protrusion (probably a piece of an old farm implement) with my less than a year old mower(Toro with the 6.75 TQ). The motor stopped instantly and as quickly as a gunshot. Started it up and ran fine but with a vibration. I looked at the blade and it is bent (hopefully that means it absorbed some of the shock). The reason I want to run it without the blade is to see if the crankshaft is bent. Is this advisable? If not, how can I check to see if the crankshaft is bent?

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#1963655 - 07/23/10 06:03 PM Re: Can I run a mower without a blade? [Re: Nayov]
S2500Dog Offline


Registered: 08/15/09
Posts: 524
Loc: Fort Worth, TX USA
Check out this video from Davidsfarm on how to check for crankshaft dmages. http://www.youtube.com/watch?v=P-QINnsFYw0 USA


Edited by S2500Dog (07/23/10 06:03 PM)
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#1963665 - 07/23/10 06:08 PM Re: Can I run a mower without a blade? [Re: Nayov]
doitmyself Offline


Registered: 06/03/02
Posts: 4791
Loc: MI
I can't think of any reason you cannot run a lawn mower engine without a blade. But, there is a better and safer way to check for a bent crank shaft. Even at idle, you may not be able to see a bent crank shaft. I'm surprised you didn't shear a key.

You may need an assistant. First you need to remove the plug wire and make sure that the engine cannot start, one way or another.

Tip the mower on it's side (make sure gas?oil doesn't pour out of the carb, tank,breather, etc.). Have your assistant pull the starter rope slowly while you observe the shaft end for "wobble". A better way to detect a tiny bend is to jury rig a stiff wire (clothes hanger?), ruler, etc. so that it's tip is fixed just a millimeter away from the end of the shaft, on it's side. Then, pull the starter rope again and see if the shaft rubs against the wire at any point while it is rotating.

A dial indicator to check for "run out" is what a shop might use.

Here is another you tube video, but I question his sledge hammer repair method. See minute 2:25 http://www.youtube.com/watch?v=wjSZu2hlmsk

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#1963685 - 07/23/10 06:23 PM Re: Can I run a mower without a blade? [Re: doitmyself]
firefighter Offline


Registered: 09/30/09
Posts: 105
Loc: Pennsylvania
No you cant run a push mower with out a blade. It will vibrate very badly, if you can even get it started. The blade is the balancing mechanisim. A lawn mower shop should be able to straighten the crank if it is bent. My uncle does lawn mower repair in the evenings, and he has a press for just that purpose. Try putting a new blade on or take the plug out and like doitmyself said spin it slowly and look for wobble

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#1963719 - 07/23/10 07:07 PM Re: Can I run a mower without a blade? [Re: Nayov]
mechanicx Offline


Registered: 10/23/09
Posts: 8576
Loc: Ohio
I think you can run a lawnmower without a blade, I've done it before but it probably won't tell you much. It'll probably run smoother but that doesn't tell you if the vibration with the blade on is due to just the bent blade, a bent crank or combination.

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#1963728 - 07/23/10 07:18 PM Re: Can I run a mower without a blade? [Re: mechanicx]
Warstud Online   content


Registered: 09/02/05
Posts: 2913
Loc: MIchigan
I tried to pull start a mower once without a blade and it almost ripped my arm off.

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#1963766 - 07/23/10 08:09 PM Re: Can I run a mower without a blade? [Re: Warstud]
greenaccord02 Offline


Registered: 04/22/07
Posts: 5215
Loc: Houston, Tx, USA
You can't do it: the weight of the blade works as a flywheel in most mower engines since they switched their "real" flywheel from cast iron to aluminum some years ago.

With the blade off, look at the crank from the side. Pull the starter slowly and look for any variance in the angle of the shaft. If you can't see any variance, it's been my experience that there isn't enough variance to matter.

Also, check and replace your keys both for the blade attachment as well as the 'real' flywheel, on either side of the crank. One or both of these may have sheared. Your vibration may be a timing issue caused by a partially sheared flywheel key.
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  3. '99 Camry 1MZ-FE - PP 5W-30 - M1-209

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#1963780 - 07/23/10 08:29 PM Re: Can I run a mower without a blade? [Re: greenaccord02]
doitmyself Offline


Registered: 06/03/02
Posts: 4791
Loc: MI
Well, I guess I have to retract my statement above about running an engine without a blade. My thoughts came from my experience running small engines with just a small sheave (pulley) on them for "clutched" belt applications. The sheave certainly doesn't provide much flywheel effect.

But, what you guys say makes sense.

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#1963802 - 07/23/10 09:05 PM Re: Can I run a mower without a blade? [Re: doitmyself]
moklock Offline


Registered: 01/13/09
Posts: 458
Loc: FL
I have run an old B&S before w/ no blade. It ran rough and when starting kicked back almost like it had a partially sheared flywheel key.

As I understand it a Tecumseh powered mower usually would not run period w/o a blade attached, never tried it though.

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#1963807 - 07/23/10 09:07 PM Re: Can I run a mower without a blade? [Re: doitmyself]
mechanicx Offline


Registered: 10/23/09
Posts: 8576
Loc: Ohio
Well I know you can run a B&S without a blade at least briefly because I've done it before. It actually ran smooth, but it would even if the crank is bent anyway and I am not recommending it. It could be stressful to the flywheel key, but they are not so easy to shear. You can easily tell if the crank is bent without running it. If in doubt whether it's just a bent blade or crank, I'd just take the blade off and lay against a level floor.

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#1963816 - 07/23/10 09:22 PM Re: Can I run a mower without a blade? [Re: mechanicx]
hemitom Online   content


Registered: 03/12/07
Posts: 745
Loc: canada
I tried to start a 5 horse briggs without a blade, kicked back so hard i thought i broke my thumb.
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#1964015 - 07/24/10 02:13 AM Re: Can I run a mower without a blade? [Re: doitmyself]
greenaccord02 Offline


Registered: 04/22/07
Posts: 5215
Loc: Houston, Tx, USA
Originally Posted By: doitmyself
Well, I guess I have to retract my statement above about running an engine without a blade. My thoughts came from my experience running small engines with just a small sheave (pulley) on them for "clutched" belt applications. The sheave certainly doesn't provide much flywheel effect.

But, what you guys say makes sense.


The engines that are made for running stuff with a pulley, like larger small engines, commercial stuff with a clutch, or small edger engines are equipped with a flywheel that can provide them with the right inertia. But for your average 6hp and less push mower engines - I'm not going to say you can't start them without a blade, but you'll have one [censored] of a time doing it.
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  2. '97 Accord F22-B1 - M1 5W-30 - Bosch 3312
  3. '99 Camry 1MZ-FE - PP 5W-30 - M1-209

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#1964213 - 07/24/10 10:03 AM Re: Can I run a mower without a blade? [Re: greenaccord02]
Steve S Offline


Registered: 01/20/03
Posts: 18449
Loc: East of IGO
Yes you can run an engine with out a blade .No problem though as posted it is surprising how much flywheel effect the blade adds and most of the noise is from the blade. I have done it and is foolish to think otherwise.
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#1964258 - 07/24/10 10:51 AM Re: Can I run a mower without a blade? [Re: Steve S]
JTK Online   content


Registered: 08/14/03
Posts: 7378
Loc: Buffalo, NY
The few cheapo gas push mowers I've fiddled with with the blade off would not start with the recoil start. Like hemitom says, the recoil just ripped from my hand. Not to say it's impossible for them to run, just the limited experience I have with this scenario proved to be a no-start. Like greenaccord said, small horizontal and vertical shaft utility engines are a different animal with more of a weighted flywheel.

Joel
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#1964440 - 07/24/10 02:34 PM Re: Can I run a mower without a blade? [Re: JTK]
greenaccord02 Offline


Registered: 04/22/07
Posts: 5215
Loc: Houston, Tx, USA
Next time I sharpen the blade on a mower, I'm going to try and get it to fire up without the blade. If I can do it, I'll post video.
_________________________
  1. '95 Dakota 3.9L - M1 0W-40 - MC FL1A
  2. '97 Accord F22-B1 - M1 5W-30 - Bosch 3312
  3. '99 Camry 1MZ-FE - PP 5W-30 - M1-209

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