# Does a snowblower engine shear key ever shear?



## JLawrence08648 (Jan 15, 2017)

I was at someone's house to look at his non-start engine, Zongshen, on his Craftsman snowblower. I was there in October to fix his Honda riding mower, for the 3rd? 4th? time. All the times it was bad gas, water or old gas. Then in October I had to remove the carburetor and put it in my ultrasonic cleaner. After emptying and removing his old gas off the premises, I discovered he had 12 gallons of old gas. So in the past, after removing the old gas and having him buy new gas, instead unknowingly to me, he reached in to the vault and used another gas can of old gas! While I was there in October, I drained the old gas from his snowblower, fresh gas, then started it. It was surging. I put Seafoam in the tank and asked him to start it several times a week to try to have the Seafoam to clean the carb. He never did. I wanted to return to check in the progress but I never did, until this week when he called he couldn't start it. It did work on the storm a month ago. I drained the tank/carb, a lot of water in the gas. After putting fresh gas in, my gas! I couldn't start it. Taking the carb cover off, and spraying ether, even putting gasoline in the spark plug, it would not start. It wanted to, really tried, pleaded, but never did, popping out puffs of white smoke from the exhaust. It sounds like the engine flywheel shear key is sheared, the timing is just a hair off. He claimed he never hit anything. Doesn't have enough knowledge about shaft shear pins. Does a snowblower flywheel shear key ever go? Engine kickback maybe? Does it use a Honda? I was going to check it, if needed have the local shop match it up. Thoughts?


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## Oneacer (Jan 3, 2011)

I would surmise it is possible.

I have replaced bent lawnmower keys, but never a snowblower.


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## 140278 (Aug 27, 2020)

no it has a steel key of the half moon style in the crank zongshen is the company MTD has make the powermore engines for them

old thread Chinese Engines even scot made note of it on Jan 20, 2013


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## drmerdp (Feb 9, 2014)

I’ve heard anecdotal mentions of flywheel keys sheering but never witnessed one.


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## JLawrence08648 (Jan 15, 2017)

So I'm wasting my time to pull the flywheel off? Steel key?

Where do I go next, pull the carburetor and clean it in my ultrasonic cleaner?


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## Fat City (Feb 11, 2017)

If water in Gas caused engine to sputter, the erratic firing could shear, even a steel key . Customer Gas is always an issue . I give people a clean, empty, milk jug and a bargain store funnel . I tell them to pour some gas in jug, let it stand, hold jug up to light, and verify fuel is clean .


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## badbmwbrad (Jul 30, 2019)

A couple years ago, I fixed an old Ariens 10,000 series snowblower whose engine would not start. It was powered by a 7 HP Tecumseh Snow King engine. Its engine would not start because the flywheel key was sheared.


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## 3vanman (Nov 21, 2017)

Fat City said:


> If water in Gas caused engine to sputter, the erratic firing could shear, even a steel key . Customer Gas is always an issue . I give people a clean, empty, milk jug and a bargain store funnel . I tell them to pour some gas in jug, let it stand, hold jug up to light, and verify fuel is clean .


While the odds are slim, I am have seen backfires and such cause many things.
Anything is "possible", and while not probable, the amount of time required to check the key and keyway is one of the obvious steps in any small engine diagnostic. 
btw, just checked my MTD trouble shooting flow chart for spark engines (61, 65, 70 and 75 series) and it goes check for spark, then check for correct spark plug, check fly wheel and key for damage or sheered key.


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## Nordford (Feb 6, 2021)

My 1984 JD826 with a Tecumseh HM80 sheared the flywheel key. When I got it, it would start and idle fine but die under load. Cleaned carb, replaced carb, new plug, checked valves, etc. pulled the flywheel to inspect the points, etc and there it was. Sheared flywheel key.


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## 3vanman (Nov 21, 2017)

captchas said:


> no it has a steel key of the half moon style in the crank zongshen is the company MTD has make the powermore engines for them
> 
> old thread Chinese Engines even scot made note of it on Jan 20, 2013


Not to offend anyone, or start a disagreement, I agree with the comment that the crank is made by zonshen, I can find no support for the comment "no it has a steel key of the half moon style", and further I find it strange that MTD lists a flywheel key for snow blower engines. 
Of course I could be mistaken, won't be the first time.


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## Clutch Cargo (Dec 27, 2015)

A "half moon" style key is called a Woodruff key, so named for the milling cutter used to make the keyway in the shaft to accommodate it. 

I have never experienced such a failure in a flywheel, but I have seen failures of pump element keys (and keyways) and input couplings due to torsional vibrations. In some instances, particularly failures of old-style "damper plates" in inboard marine gasoline engines, this was indeed caused by bad fuel, a misfiring plug, or bad wire. Therefore, if this person did run his engine with bad fuel (and its associated rough running and misfires) for many hours IMHO it is entirely possible for the key to shear off.


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## Shovel (Mar 26, 2019)

If they flywheel nut wasn't properly torqued it can sheer the key without hitting anything.
Common?..Not really ..I have seen it twice on outboard engines.I was in one of the boats when it quit..Once on a saw .
It would be worth checking...if that nut isn't tight it beats the key to death...especially the jerking around that happens when we shut off an engine. 
But first I would try a new plug.
While you have the plug out ...twirl the engine several times...may be water in the cylinder. 
Next put a little oil and gas down the hole and twirl it some more...oil will help seal the rings back up.
Put the new plug in and see what happens..if no luck then check that key.

Sent from my SM-A115U1 using Tapatalk


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## JLawrence08648 (Jan 15, 2017)

I've changed the spark plug, checked the spark, left the plug out to clear the cylinder, let the machine sit,

SO - What do I do next?

I've decided

I'm going to check the flywheel key, I need to in order to eliminate it. If it's moved, I stop and replace it unless I have to remove the gas tank to get to the flywheel then I'll remove the carb because in order to remove the carb on this machine, I have to remove the fuel tank because of the carb linkage unless I can double nut the studs and remove them, possibly other things to remove, who knows what to remove to remove the flywheel. Remember, the machine was surging in the fall. I have no choice but to remove the carb if I have to remove the gas tank and can't get the studs out. It may have gotten worse.

Fortunately next week will be 45°, I'll do it then, with his already given permission as this week it's 27°. He has a long driveway and parking area but 3 grown young construction sons that can shovel as we may get 3"-5" this Thursday.


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## 140278 (Aug 27, 2020)

3vanman said:


> Not to offend anyone, or start a disagreement, I agree with the comment that the crank is made by zonshen, I can find no support for the comment "no it has a steel key of the half moon style", and further I find it strange that MTD lists a flywheel key for snow blower engines.
> Of course I could be mistaken, won't be the first time.


 no disagreement
to be sure i looked at a photo in the MTD shop manual for it before posting ,steel half moon key they even showed it's proper alignment to slide the flywheel back on easy
now if it was a old tech engine yes check it as many have the soft alloy shear away key


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## 3vanman (Nov 21, 2017)

JLawrence08648 said:


> I've changed the spark plug, checked the spark, left the plug out to clear the cylinder, let the machine sit,
> 
> SO - What do I do next?
> 
> ...


I found this video on line, don't know how much help it might be, but may give you some guidance.


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## 140278 (Aug 27, 2020)

THANK YOU
right at 5,15 he points out the steel key.
it's tiny anything can happen anything is possible yet on a snow blower rare,


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## tabora (Mar 1, 2017)

drmerdp said:


> I’ve heard anecdotal mentions of flywheel keys sheering but never witnessed one.


FWIW, here is a photo of a partially sheared flywheel key, a fully sheared one, and interestingly an intentional offset "partial" that is meant to adjust timing (from the good olde days)...

Partially Sheared Key









Fully Sheared Key









Offset Key


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## JLawrence08648 (Jan 15, 2017)

The bottom is steel?


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## tabora (Mar 1, 2017)

JLawrence08648 said:


> The bottom is steel?


Not 100% sure of your question, but all the engine shaft keys I've ever dealt with have been steel or rarely, titanium.


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## JLawrence08648 (Jan 15, 2017)

I've got it running.

I was not sure of the issue, I initially figured it was either, bad gas which it was, carb dirty which it was, flywheel key which it wasn't, or bad spark plug which I'm not sure but it may have been.

I changed the gas, it wouldn't start on ether, almost back firing, popping, so I figure it may have been the flywheel key.

Last year the carburetor was surging so since I couldn't get it running, I figure I'd have to clean the carb in my ultrasonic cleaner. On this Zongshen engine, to remove the carb I can't remove it easiIy because of the studs so I had to remove the coverings, the gas tank but I can't remove the gas tank unless I remove the muffler, then some other bolts, if I had to do this, I'm now almost to the flywheel to check the key, the key was not sheared, it was steel, not aluminum. I took the carb home, cleaned it and came back. The owner had 2 spark plugs, LG, and a AC Delco R42XLS. I installed a NGK BPR6ES. I put the carb on, muffler, the NGK plug, started right up. Was it the carb or spark plug? I'd guess it was the spark plug but I was so focused on the dirty carb surging or shear key. I was not thinking about the spark plug plus I didn't have a NGK spark plug in my tool box, now I do, with a Tec Champion, and I had a hard time believing that 2 spark plugs would be bad enough not to make it start. Maybe. The snowblower is running fine, owner is happy, so am I. And he's now has an adjusted snowblower.

By the way, the flywheel key on this Zongshen engine is steel.


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## paulm12 (May 22, 2015)

Interesting. Glad you got it running, but yeah, would have been nice to figure out which was the culprit.


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## 3vanman (Nov 21, 2017)

Just watched this new Donyboy73 vid and thought of this problem. Hidden Carburetor Fuel Filter Screen On Small Engines! Must see! - YouTube


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## RIT333 (Feb 6, 2014)

Don't is great. My chain saw carbs have that screen, but I didn't realize that some snowblower carbs have them also.


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