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Rock Always Wins in Lawnmower Battle

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tekochip
User Rank
Platinum
Playing Horseshoes
tekochip   2/27/2013 8:49:40 AM
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On one occasion a wayward horseshoe found my lawnmower.  I replaced the blade and the blade mount because the shear pins had done their job.  I had trouble finding the right blade, though, because when I replaced the blade with the 22" proudly displayed on the mower deck, I could hear the slight "chirp" of the blade kissing the shield.  No matter, I put in a 21" blade and I was on my way.  As the years wore on, so did the mower, every so often a blade mount would crack, and at one point I had to replace the handle because it had sheared off from vibration.  About 7 years later I was replacing another cracked mount, and as I rotated the blade around I found that the crankshaft was horribly bent.
 
Now it all made sense, the smaller blade, cracked mounts, and the handle breaking from vibration.  I wished I had known about straightening the shaft with a pipe, rather than just taking the mower to the curb.


richnass
User Rank
Blogger
Great fix
richnass   2/27/2013 11:58:57 AM
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Ray, that's a great solution. I suspect the lawnmower makers might be interested. On the downside, it makes their product a little more expensive, and also stops them from selling new mowers to people who own rock gardens.

Ann R. Thryft
User Rank
Blogger
The fixit mentality
Ann R. Thryft   2/27/2013 2:55:07 PM
I, too, live in a rural (although non-farming) community where fixing tools and machines is common--or used to be. Glad to say I don't have a lawn to bother with. But we do like to repair our stuff, or take it to the local fixit guy. There's something really satisfying about not throwing things away, and especially so about fixing something yourself.

econobiker
User Rank
Iron
Now lawnmowers have a flywheel shaft key that breaks away
econobiker   2/27/2013 5:12:23 PM
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when the blade hits a solid ground object.  But most owners either don't know about the the breakaway key or do not have the mechanical ability/ tool to fix the mower, so the mower gets quickly thrown out when the flyway key is broken and the mower will not run or runs badly after hitting an object.

Nothing in the average owner's manual about this either... (Sarcasically) It must be much too dangerous to even ~inform~ the mower user about the flywheel shaft key even to write "This is what could have happened but take mower to service shop because the shop will have special tools to fix it."

"Buy a new mower!" is what the mower manufacturers want.

I, however, have benefited from this by getting the supposed dead mower for free, removing the flywheel, installing a new key, and,  bingo!, an almost new mower with low hours on it! 

[And customizing the mower by replacing the standard aluminum mower flywheel with a heavier cast steel one from a brush cutter mower (from the same type engine) provided a lot more root cutting fun prior to the flywheel key breaking away...]

Charles Murray
User Rank
Blogger
Re: Great fix
Charles Murray   2/27/2013 7:38:45 PM
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I agree: The pipe method is a great solution. I have to admit, my son hit a rock a few years ago and I could never get the crankshaft quite right (close, but not satisfactory). I eventually ended up tossing the mower and getting a new one.

Tim
User Rank
Platinum
Broken shaft
Tim   2/27/2013 7:47:44 PM
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As a kid, I mowed a rock which bent the shaft and the blade on our mower. Attempting to replace the shaft was my first experience with 4 stroke engines. While I never did get the mower working correctly, I did learn about the inner workings of the engine which kickstarted my engineering desire to see how things work.

Elizabeth M
User Rank
Blogger
Re: Great fix
Elizabeth M   2/28/2013 4:25:14 AM
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I love it when the simplest fix can overcome a design flaw in a product. Still, you think there would be some kind of safeguard against this sort of thing! I don't have a lawn that needs mowing, so I don't use a lawnmower. Have modern mowers been adapted so they don't succumb to something as simple and common as a rock?

Davinci87
User Rank
Iron
Before you straighten that crank...
Davinci87   2/28/2013 9:44:08 AM
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Straightening a bent crankshaft with a pipe may sound like a good idea, but keep in mind that the crankshaft is cast iron, not steel. CI is much less forgiving about being bent and bent back. Having a compromised crankshaft spinning a 21" steel blade at 3,600 rpm only 6" from my ankles is not particularly appealing to me. Especially on a mower with an aluminum or plastic mower deck. 

OLD_CURMUDGEON
User Rank
Platinum
MORE on Small engine repair
OLD_CURMUDGEON   2/28/2013 10:32:00 AM
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Small mower crankshhafts can or cannot be formed using cast iron.  Some may be nodular iron, and some, steel.  I have been down this road with small engines for decades.  One of the problems in a vertical shaft engine with a bent crank is removing the (aluminum) base plate from the shaft, even one with only a slight bend.  Forcing the baseplate over the radius puts enormous pressure onto the bearing.  In many small engines, these are not pressed-in roller bearings, but more commonly are simply pressed-in or cast-in aluminum bushing-types.  They almost solely depend on the total immersion of lubricating oil for any expectation of life.

The BEST way to straighten a bent crank is to jig it in a lathe, determine the amount of runout, and then heat it sufficiently to anneal it and then "work" the bend out.  Using pipes or other brute force methods is chancey at best.

Changing a flywheel for an iron replacement is also a dangerous endeavor, since it drastically changes the rotational inertia of the system.  Replacing flywheel keys is far safer.  I DO agree that it would have been a good design to include a breakaway key @ the blade end of a typical garden lawnmower.  Years ago we had a large tractor-style mower.  The mowing deck was approx 48" wide with three staggered, belt-driven blades off the main PTO.  However, each blade also included a hub mechanism which included an easy-to-replace key in the event that a blade hit an immovable object.  Even small tree stumps CAN bend a shaft, so it's NOT only large stones or rocks or bricks, etc.

Decades ago, small engine manufacturers DID carry replacement parts.  Today, however, I doubt whether you can purchase any replacement items for a BRIGGS & STRATTON or HONDA small engine.  IF you move up the ladder to engines included on industrial equipment, then the picture changes.

Does anyone remember CLINTON, POWER PRODUCTS, REO, KOHLER, WISCONSIN?  They all made small engines. and are mostly all part of history today.

Tshooter
User Rank
Iron
Peak a youngster's interest
Tshooter   2/28/2013 10:34:17 AM
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As a kid we had a small engine on a yard vac with not much spark plug hole thread left in the AL cylinder head. We'd screw in the spark plug and start the engine to launch the spark plug like a bullet. Take cover!

The mower I have today is 30 yrs. old with the too-thin tubular steel push-handle attachment to the deck being the weak point. After the first couple of years I  had no choice but to weld smashed 3/4" iron pipe in parallel to the tubular steel handle and down to the deck's anchor points. No problems since.

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