# How often does this happen?



## gsnod (Sep 2, 2013)

Just wondering how often (if ever) a snow blower engine might shear a flywheel key? Reason why I'm asking is a neighbor brought over his B&S engined snowblower, and it runs poorly. So, I rebuilt the carb, using my standard system -- soak overnight in cleaning solution, and then ran it through my ultrasonic cleaner. Put a new carb kit in it. 

Put a new plug in it, whuch seemed to help. I'm thinking I need to also run the older? gas out of it....don't know how long it's been in there. 

Anyway, before I pull the flywheel and check for a sheared key, I'm going to let it run for a while to try and burn the gas out of there. If I still have some backfiring, etc, then I'll pull the shroud and check the key.

Sound like a reasonable plan to the experts?


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## Normex (Feb 21, 2014)

Although some members here are much more expert than I, you definitively have the correct course of action, it is a definite question when the engine timing is off, backfiring being one of them that the shear key might be the culprit.

Good Luck and keep us in the loop


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## Grunt (Nov 11, 2013)

It is quite possible the key is sheared, although it is very rare on a snow blower unless the flywheel was removed at some point and not torqued back to spec. A sheared key would first show symptoms of ripping the recoil out of your hand when starting because of the ignition timing change. If the engine is back firing, my guess would be valves that need adjusting or a valve that is sticking open slightly. Is the engine an overhead valve or flat head?


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## Spectrum (Jan 6, 2013)

Shearing that key is highly unlikely unless somone had been in there an under torqued the clutch. 

Draining the fuel system should have been job one ahead of rebuilding the carburetor. I'd siphon it out and get fresh fuel in there ASAP.

Still running poorly could be a lot of things including carburetor adjustment, ignition breakdown especially if you have points in there or diminished valve clearance.

Pete


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## gsnod (Sep 2, 2013)

OK -- I have no pull back on the rope pull, so I'm inclined to think the timing is not an issue. It runs although still not smoothly. This is a carb than has no adjustment, nor throttle, so it always runs at full throttle. Since I have engine tempo up and down (I can see the linkage moving the throttle), I figure I've either still got some grime in the carb, and/or an air leak. 

So, I'm gonna repull the carb and do another good cleaning via soaking and ultrasounic cleaner.


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## greatwhitebuffalo (Feb 11, 2014)

gsnod said:


> Just wondering how often (if ever) a snow blower engine might shear a flywheel key? Reason why I'm asking is a neighbor brought over his B&S engined snowblower, and it runs poorly. So, I rebuilt the carb, using my standard system -- soak overnight in cleaning solution, and then ran it through my ultrasonic cleaner. Put a new carb kit in it.
> 
> Put a new plug in it, whuch seemed to help. I'm thinking I need to also run the older? gas out of it....don't know how long it's been in there.
> 
> ...


 the shear key is soft aluminum and they do break, I had a 5HP Briggs from a Gilson/Senator tiller, and the key was broken. usually a machine that encounters a lot of resistance in normal use, like a tiller, will break a key once in a while. I filed a new key from a hardened piece of engine piston, that material is a little tougher and not as easy to break. the engine is still running to this day on a go cart


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## 94EG8 (Feb 13, 2014)

Out of at least 200 machines I can't say I ever remember seeing it happen. It's very common on lawn mowers, but almost unheard of with snowblowers.

As far as the carb goes you'll normally need to stick something through the passages to really clean them (torch tip cleaners or wire from a wire brush depending on the size of the passage)


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## greatwhitebuffalo (Feb 11, 2014)

yes it happens on a mower when the user hits a rock.

now they make the mowers with a breakaway mower nut/washer/flange holder, so it breaks there instead, and the user can buy a new one for $6 and reassemble it and go, the motor will still run.

I got 2 mowers identical, one has the breakaway nut/flange, one did not. both hit rocks and were put out by neighbors with "free" signs. I fixed the one with the breakaway flange, for $6. the other one was older, and it BROKE THE CONNECTING ROD in the engine. it was junk. I scrapped everything but a few engine parts.


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## gsnod (Sep 2, 2013)

Sorry guys -- I've been traveling. Ended up pulling the shroud and the key was fine. Fully drained the old gas, and found some water bubbles in there. Put in fresh gas, along with some B-12 and fired it up. Seems to be working well now!


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## micah68kj (Oct 8, 2011)

gsnod said:


> Sorry guys -- I've been traveling. Ended up pulling the shroud and the key was fine. Fully drained the old gas, and found some water bubbles in there. Put in fresh gas, along with some B-12 and fired it up. Seems to be working well now!


I never posted a response on this thread because I was just stumped. But, I was inclined to believe the key wasn't the problem. I'm just dang happy you figured out what actually was the problem.


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## db9938 (Nov 17, 2013)

this is all good knowledge to bank into the memory base.


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## SteelyTim (Nov 14, 2014)

I've only run into a sheared key on one snowblower in the hundreds I worked on. It was on a Toro 724 with a Tecumseh engine. After fooling with the carb forever, I just couldn't get it to run right, it almost seemed like the engine was out of time, and sure enough it was. Key sheared off and the flywheel moved just slightly. 

In that case as I remember, the starter drive stuck onto the flywheel, and the guy just ran it anyway. After a little bit the starter seized up solid and that sheared the key.


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