Lawn Mower Compression & Dislocated Shoulders

[DerbyDad03]

I've got a Toro mower (Model 20016) with a 4 cycle Tecumseh engine that is trying to hurt me.

When I try to start it, the start cable will pull out about half-way, under normal starting tension, and then it feels like the compression of the engine trys to yank it back in. It will violently pull my arm back towards the mower.

When it eventually does start, there are 3 - 4 loud knocks (*not* backfires) and then the mower runs fairly normally. I say "fairly normally" because it no longer runs as smooth and quiet as it used too.

The mower is at least 4 years old. Should I be looking at the fall sales flyers?

[Bob F]

Either the blade is loose, or the flywheel key is sheared, causing the timing to be off.

Bob

[DerbyDad03]

Blade is tight...one of the first things I checked.

[Jeff Wisnia]

Then, as the prvious poster indicated, the blade may have struck something solid, stopping the engine shaft suddendly, and the inertial energy in the flywheel made it want to keep turning so the flywheel key sheared. Now the flywheel is a little "forward" of where it needs to be, causing the spark to occur too soon.

Pull the engine cover and the flywheel and if you find the key fully or partially sheared, replace it. The key itself costs next to nothing.

HTH,

Jeff

[DerbyDad03]

Thanks!

Will I be able to/have to move the flywheel back to where it should be? Will it be obvious how to do that once I pull the cover?

[Meat Plow]

You will have to remove the flywheel to replace the shear key. That is usually accomplished by lifting one side of the flywheel and smacking the shaft with a wooden or plastic mallet. You might need to do this a few times while relocating where you lift the flywheel. The key ensures the proper position of the flywheel so there is no guesswork.

[Bob M.]

It will be obvious. In fact you may be able to tell if the key is partially sheared without even removing the flywheel. just look at the shaft/flywheel contact area. If there's a square aluminum 'key' there and it's still square, it's not the problem. But, most likely you'll have to remove the flywheel to find out for sure.

[Oren]

I don't recall seeing the key being obvious; until I removed the retaining nut from the flywheel.

You can test for movement in the flywheel (FW). Remove the plug wire for safety. With some help, hold the blade steady and rotate the FW to observe for any movement back and forth. It is not totally accurate, but a seriously damaged shear key will be obvious. YMMV.

Small fractures in the key will not be obvious, as well!

About the hammering on the shaft. I use a block of wood to deaden the blow AND I always leave the loosened nut on the shaft. It prevents damaged to the thread.

-- Oren

"I don't have anything against work. I just figure, why deprive somebody who really loves it."

[Oren]

They can be a booger now and then; when placing the FW on. The key might slip a tad. I use a tiny bit a grease to help hold the key in the crank slot - if I ever have to do it again. :)

-- Oren

"Well, it doesn't happen all the time, but when it happens, it happens constantly."

[Meat Plow]

Yup forgot about the old grease trick.

[Steve Barker LT]

It does sound like the timing has advanced. And the only way for that to happen is for the key in the flywheel to shear and the flywheel slip on the crank. I'd check that first.

s

OR you have some really piss poor gas.

[DerbyDad03]

Assuming the FW key is the problem, how bad is it for the mower to run like this? It's September in Upstate NY, so I only have a few more mows before I'd be putting it up for the winter anyway. I'd just as soon wait until the season's over before my first foray into small engine repair.

[Meat Plow]

Your guess would be as good as mine.

[Steve Barker LT]

If the timing is advanced too far, it will burn a hole in the piston or detonate it self to death.

steve

[DerbyDad03]

- If the timing is advanced too far, it will burn a hole in the piston or detonate it self to death.

THEN do I get to buy a new one? ;-)

[Frank Drackman]

You could buy a new one now.

I agree with Steve, you could do some serious damage by running it without fixing it first. My next door neighboor tried to "get a few more mowings" out of a motor that need to be on full choke to run. Totally messed up the valves. He got to buy a new one.

[Don Young]

Gasoline contaminated with kerosene can have the same effect.

Don Young

[Harry K]

Be sure to get the correct key, it will be made of softer metal, not steel. They are designed to shear if the blade hits something solid so that the motor itself is not wrecked by a sudden stop. It probably is not sheared completely, even a slight 'nick' will throw the timing off.

Harry K

Harry K

[Steve Barker LT]

sure. If you've got money to blow and are wasteful. go for it. Hell, put it in the dumpster now and buy a new one. Why wait? No need to make a simple repair when you can have new new new stuff and outshine your neighbor.

s

[Jeff Wisnia]

And it keeps the flywheel from flying off if you're pulling up on it real hard, and whacking you in the forehead. (DAMHIKT)

Jeff