Lawn Mower Problem

[Jeffy3]

We have a rear bagger mulching push mower. I accidentally ran over a very thick tree route and it literally knocked the blade right off. I was able to put the blade back on and when I manually turn it it freely spins around but when I try to start the mower it won't start, it makes a loud clunking sound and the pull rope sometimes only comes out about half way and abruptly stops. Anyone have any conjecture as to the nature of the repair and whether it would be less costly to just get a new mower for a couple hundred bucks?

[Worn Out Retread]

I would bet that you have broken internal parts and that could be very costly.

[Ulysses]

It seems very likely that you broke the "shear pin" that holds the flywheel to the crankshaft and keeps it in place. You need a puller to remove the flywheel. Don't pound on it with a hammer or you might break it or damage the magnet. Once you get the flywheel off you may find, as someone else pointed out, that it has other damage too. New shear pins are usually available at hardware stores in the lawn mower parts section.

[Limp Arbor]

Wow! You must have one of those nifty press-on blades

[jeff_wisnia]

FUBAR!

Jeff

[Stormin Mormon]

I was thinking flywheel key. But, also, bent crank shaft. I'd try replacing the flywheel key. But if it's still not running, or runs but shakes violently, might be beyond simple repair.

[Hustlin' Hank]

The only way to be sure is to look at it, since I can't, I'll offer a couple suggestions.

After putting the blade back on, tie down the auto stop and remove the spark plug (so it doesn't start) and turn the blade around. Does it wobble? Is the blade bent? Is the crank bent? If everything looks straight and true, then pull the flywheel cover off and spin it aroound to see if it wobbles or the crank wobbles.

If the crank is wobbling, throw it in the trash. If the crank doesn't wobble, remove the blade and the flywheel and turn it to make sure it isn't the crank and the "sounds" you hear aren't coming from the blade or flywheel. If you still hear sounds, you more than likely have serious problems. Trash it.

Hank

[Jeffy3]

Thank you all for your responses. I did leave out one detail but have no idea if it's relevant or would change anyone's opinion. At one point when I was trying to start the mower, I realized I had forgotten to connect the spark plug. When the spark plug isn't attached, the pull rope operates fine. As soon as the spark plug is connected, the pull rope acts up and the clanking sound starts

[Oren]

[Oren]

Sounds like the shear pin, and the timing is off. Pull the plug out to examine if the piston is moving through the four strokes. (have a compression tester?)

The rope will jerk your arm back when the timing is off and the plug is connected.

Does the noise exist when the plug is out and you yank the cord 5 times?

btw, I've never seen a mower blade "knocked" off.

[Charlie Darwin]

I would check the gizmo that stops the engine when you release the handle. See if that's stopping the engine from turning. If so, it's fixable. If not, start shopping.

Oh yeah, I always follow engine repair tips from guys who call key parts gizmos...

[Bob F]

If the blade is tight, this clinches it. The flywheel key is sheared. The timing is way off, causing the engine to missfire, thus the clunk. A loose blade can cause similar symptoms on some engines.

[clare]

Bent crankshaft.

[Steve Barker]

Broken crankshaft or connecting rod. New engine is in order.

[Steve Barker]

shear pin, (which they don't have) won't keep it from turning.

[mm]

He doesn't need a compression tester for a lawn mower that was working well a little while ago.

Since it's a one cylinder engine, you don't need to disable the other cylinders, so just take out the one spark plug and put your thumb over the hole. If you feel pressure pushing your thumb off every so often, you have compression. That is, at least one valve is opening (but probably both) and then they are both closing, and the piston is moving up in the cylinder. If you have any compression, I'm sure you have adequate compression, give that you hit a route, or root. :)

[Steve Barker]

HE SAID the som bitch turns then stops! It's broke! duh!

[Tony Hwang]

Hi, If I were you, I'd write that mower off. Even if it is repaired it may not be the same.

[mm]

If one plans to fix it, it should eventually have compression, duh.

And my post was a general statemnt about the need for a compression tester on a lawnmower that was recently running well.

[Jeffy3]

Heading out to get a new mower 2nite! thanks for everyone's thoughts.