Briggs sheared key

[Alan W.]

Hit a small piece of wood hid in the grass with the push mower and it died. Tried restarting but no go. Sounded like it was trying to kick back. Pulled the flywheel and yep the key had sheared. Didnt have the right size key stock so my son milled one down to size. Briggs forgot to tap the holes for the puller on the flywheel. Back to one pull starting.

 

[ruffdog]

Was the key made of steel or aluminum?

 

[Alan W.]

Was the key made of steel or aluminum?

It was aluminum. The replacement is steel.

 

[stuckmotor]

Last time I removed a flywheel with a puller, the puller had two self tapping screws that went into the holes in the flywheel. I don't believe they were threaded.

I'll leave it to Ruff to explain why the sheared key was aluminum.

 

[Thomas]

They don't make things like the use to.

 

[ruffdog]

Last time I removed a flywheel with a puller, the puller had two self tapping screws that went into the holes in the flywheel. I don't believe they were threaded.

I'll leave it to Ruff to explain why the sheared key was aluminum.

Yes, the aluminum key. When the blade hits something solid and the crankshaft momentarily stops, the flywheel wants to continue spinning. If it had a steel key, it would not shear so all the twisting force goes into the crankshaft. It is easier and cheaper to replace a sheared key than a broken crankshaft.

 

[RandyT]

Yes, the aluminum key. When the blade hits something solid and the crankshaft momentarily stops, the flywheel wants to continue spinning. If it had a steel key, it would not shear so all the twisting force goes into the crankshaft. It is easier and cheaper to replace a sheared key than a broken crankshaft.

Or explain why there are parts of a flywheel embedded into somebodies body parts when it fragments.

 

[RickB]

They don't make things like the use to.

They make some things exactly like they need to. The key sheared, probably saving a bent or broken crankshaft.

 

[Alan W.]

It did crack the flywheel a bit in the keyway. Or the crack couldve been there. Who knows.
Its got a scatter shield on it.

Its weird they put an aluminum key on a light flywheel that lacks a lot of inertia but on the bigger motors with the heavy cast flywheels its steel for the key.

 

[CalG]

With a steel key, the next wood strike will require a new flywheel.\ DTDT and I have the evidence.....

A wise man learns from the mistakes of others.

 

[RandyT]

It did crack the flywheel a bit in the keyway. Or the crack couldve been there. Who knows.
Its got a scatter shield on it. ��

Its weird they put an aluminum key on a light flywheel that lacks a lot of inertia but on the bigger motors with the heavy cast flywheels its steel for the key.

Most briggs engines use an aluminum flywheel key. The Vanguard is about the only exception and some of those are aluminum. And you will think scatter shield up until you see an aluminum flywheel shatter and tear the blower housing completely off of the engine.

 

[RickB]

It did crack the flywheel a bit in the keyway. Or the crack couldve been there. Who knows.
Its got a scatter shield on it.

Its weird they put an aluminum key on a light flywheel that lacks a lot of inertia but on the bigger motors with the heavy cast flywheels its steel for the key.

Do the larger engines with steel keys have a blade bolted to the opposite end of the crankshaft?

 

[Alan W.]

Good point Ill have my son pick up or make another one out of aluminum.

 

[RandyT]

Briggs aluminum flywheel keys are so common at one time you could pick them up at the grocery store. Now any dealer, walmart may have a multipack, as well as Menards, Home Depot, or Lowes.

 

[mark02tj]

It was aluminum. The replacement is steel.

Yes, the aluminum key. When the blade hits something solid and the crankshaft momentarily stops, the flywheel wants to continue spinning. If it had a steel key, it would not shear so all the twisting force goes into the crankshaft. It is easier and cheaper to replace a sheared key than a broken crankshaft.

I worked in a mower shop during high school and college. You do NOT want a steel key in a small engine. It will do a lot of damage if it hits something.

Flywheel keys are cheap. They used to be about a quarter each, but now it looks like they're 3 for $4.99.

Make sure you get the nut on top of the flywheel torqued down tight! If you don't, the key may shear again even without hitting anything. There is a washer on the top of the flywheel. It should be conical so there's a "top" and a "bottom" to the washer. Be sure that you put it on correctly.

 

[Alan W.]

I worked in a mower shop during high school and college. You do NOT want a steel key in a small engine. It will do a lot of damage if it hits something.

Flywheel keys are cheap. They used to be about a quarter each, but now it looks like they're 3 for $4.99.

Make sure you get the nut on top of the flywheel torqued down tight! If you don't, the key may shear again even without hitting anything. There is a washer on the top of the flywheel. It should be conical so there's a "top" and a "bottom" to the washer. Be sure that you put it on correctly.

Apparently in a cost saving move Briggs quit putting the belleville washers on some engines and mine is one of them.

 

[mike48130]

It did crack the flywheel a bit in the keyway. Or the crack couldve been there. Who knows.
Its got a scatter shield on it. ��

Its weird they put an aluminum key on a light flywheel that lacks a lot of inertia but on the bigger motors with the heavy cast flywheels its steel for the key.

Bigger engine = bigger flywheel = more inertia. The bigger engines will shear the steel key. Either go buy an AL key are start saving for a new mower the next time you hit something.

Also, depending on the engine application, they don't expect the engines to get the shock of hitting something like a directly mounted blade on a mower. Most drive systems will absorb some shock.