[tireshark]

My riding lawnmower just broke while i was mowing leaves. I've rebuilt lawnmower engines before, and I'm fairly certain the piston rod broke, but i couldn't remember what the symptoms of a sheared flywheel are. Would a sheared flywheel key cause the engine not to rotate when you spin it by hand? It will move an inch or so and then stop like it's hitting something.


Like i said, i'm fairly certain something broke inside the engine and that it cant rotate because it is hitting the part... but wanted to check anyway to see if a flywheel key might do anything like this.



It shut down about 45 seconds after i hit a big stick or something with my blades, and i know that is what can shear a flywheel key... but it might have just been coincidence that it stopped shortly after hitting something... or that jolt might have caused the internal parts to fail.

 

[de-nagorg]

If the flywheel key is sheared, I would be looking into why it sheared.

As you think there are very few ways to shear them, unless the engine actually locked up, I cannot think of any other way.

So plan on a major rebuild of that engine.


ED

 

[SeniorSitizen]

First, make sure the stick or a portion of it isn't lodged preventing rotation.

Riding mowers are more forgiving than push powers when hitting foreign objects because of the belt driven blade(s) but still the spark plug needs to be pulled and observe if the piston moves when it rotates that inch. Try rotating it backwards from the point where it stops.

 

[Colbyt]

No insult intended, I would also make sure it is "not in gear".

 

[BigJim]

If it had sheared the fly wheel pin, it would not have continued to run as long as it did. It could have cracked your crank and finished breaking a little later.

 

[tireshark]

Thanks guys, it's probably a broken rod... was just hoping it might be the key, but after reading your replies and reading up on keys, i can see that it wouldn't really cause this condition.

stinks because i actually tore down and rebuilt this engine last winter due to a broken connecting rod. really disappointed that it only lasted one season... but i guess that's the risk you take with a rebuild. I used a new piston and connecting rod, but i reused the old journal which had just a tiny tiny nick in it... so now i wonder if that might have contributed to this failure. I'm going to tear it down just because im curious as to what broke, but i doubt i will rebuild it... probably will buy a new motor off ebay to put in it.

I debated buying a new motor last time, because i probably spent close to what it would a new engine would cost to rebuild this one... but i did learn a ton by doing so, so it wasn't a complete loss. Before i rebuilt it i couldn't have identified the carburetor, but when i was done, i was familiar with pretty much the entire engine and electrical system.

Thanks again.

 

[de-nagorg]

Quoted from the above


i reused the old journal which had just a tiny tiny nick in it... so now i wonder if that might have contributed to this failure.


YES ABSOLUTELY, if not, it was a bad idea.


ED

 

[tireshark]

Yeah, i knew it was a risk to reuse it, but i cleaned and buffed it really good and was hoping it would squeak by since it was such a small imperfection. Also i honed out the cylinder with one of those drill honers, but it certainly wasn't 100% perfect either. Guess i now know why a lot of people were recommending to trash it instead of rebuild, haha.

Still, even though i only got 1 season out of it, i learned a tremendous amount by rebuilding it. Since then i've used that knowledge to troubleshoot and fix several different small engines that i would have previously had to send to a repair man.

Ebay has some scratch and dent 10.5HP B&S's with 2 year manufacture warranties for $340... i imagine i will probably do something like that.

 

[de-nagorg]

It's good that you learned some things from this experience, and saved money on those other engines.

Life is a journey of amassing knowledge, keep on learning as it keeps you out of trouble.

When you take it apart to see exactly what is broken, I would be interested to know also.



ED