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I recently got the blade stuck in a tree stump, the grass was kind of tall and I didn't see it. The engine stopped when it got stuck and I had to pull the blade out of the tree stump. After pulling it out the blade was loose and as I pulled the starter to start the engine the blade fell off after 2-3 pulls. Now every time I put the blade back on I tighten it as much as I can, its pretty tight. But when I try to start the engine, 2 - 3 pulls of the string and the blade falls off again.

I don't know what to do, I keep putting the blade back on but it falls off and the engine doesn't start because of that (I think its a safety feature).

Do you think there's something causing the blade to come loose really easily even after I tighten it on?

what type of mower is it ..Is the crank shaft bent that happens sometimes when you hit something ...I would look closely where the blade mounts some have little pins that shear off once you hit something That hold the blade center ..When you tighten the blade you have to come on to it pretty good ..I lock the blade with a peace of 4x4 ..I put block against the housing of the mower and use it to hold the blade while i tighten it down (just be-careful please and i would by a new blade and lock for it just to be safe ...

I'm assuming you are talking about a push mower and it's the MTD Yardman your profile refers too:


Sounds to me like you may have sheared the key stock. It's meant to shear when you hit something to prevent serious damage. If the key is broke you won't be able to tighten the blade properly. It's either that or when the blade fell off you lost some parts, might want to go back to the stump with a magnet and see what you can excavate.
I have an MTD and I've broke mine several times. I keep spares around so I can get it fixed quickly.
If yours is like mine the blade bolts to a cast iron piece that attaches to the crankshaft. The key slides into a groove between these 2 parts.
Disassemble the blade assembly to the crank and see if this is not the case. Be sure and remove the plug wire and remember if you turn the mower over it going to leak gas and oil if you don't drain it. This is a good time to change the oil since you're going to be under there anyway.
If the key is sheared you should be able to get one from any briggs dealer or online but your done until you have a new one. Might want to get a few (thier cheap) in case that stump jumps out in front of your mower again:biggrin:

If the crank is not bent also check the aluminum key on top of the engine... they will shear completely, or only partially causing, no start or timing being way off... Abrupt stops like you describe is exactly what shears the soft key in the flywheel... :smile:KennyV

KennyV said:

If the crank is not bent also check the aluminum key on top of the engine... they will shear completely, or only partially causing, no start or timing being way off... Abrupt stops like you describe is exactly what shears the soft key in the flywheel... :smile:KennyV

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Yes i do agree there lol T.C s are good for that ...:thumbsup:

stanley said:

I recently got the blade stuck in a tree stump, the grass was kind of tall and I didn't see it. The engine stopped when it got stuck and I had to pull the blade out of the tree stump. After pulling it out the blade was loose and as I pulled the starter to start the engine the blade fell off after 2-3 pulls. Now every time I put the blade back on I tighten it as much as I can, its pretty tight. But when I try to start the engine, 2 - 3 pulls of the string and the blade falls off again.

I don't know what to do, I keep putting the blade back on but it falls off and the engine doesn't start because of that (I think its a safety feature).

Do you think there's something causing the blade to come loose really easily even after I tighten it on?

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The blade of what, an axe? Sorry to be sarcastic, but why don't you tell us what kind of mower you have? I sounds like the blade is spinning on the blade adapter, which could mean that the adapter is damaged. When you say the blade is pretty tight, what do you mean. The bolt should be VERY tight, with no chance that the blade can slip against the adapter. An impact wrench is a great idea,

Yes, most push mowers require the blade to be attached in order to start as the blade functions as a flywheel for the motor. Some high-end mowers allow the mower to run without the blade.

I was going to say there maybe a problem with the key, if it has sheared then there is nothing to prevent the blade from falling off, it shouldn't be too expensive to fix.

My first question was "What brand and model is your machine?" It sounds like a very simple and inexpensive repair job. Once you know the part that has been damaged, you can probably do the the work yourself.

I think the fixture (or housing) that holds the blade in place has become cracked or broken. In all liklihood, you'll have to take the mower to a professional shop to have it evaluated and fixed.

stanley said:

I recently got the blade stuck in a tree stump, the grass was kind of tall and I didn't see it. The engine stopped when it got stuck and I had to pull the blade out of the tree stump. After pulling it out the blade was loose and as I pulled the starter to start the engine the blade fell off after 2-3 pulls. Now every time I put the blade back on I tighten it as much as I can, its pretty tight. But when I try to start the engine, 2 - 3 pulls of the string and the blade falls off again.

I don't know what to do, I keep putting the blade back on but it falls off and the engine doesn't start because of that (I think its a safety feature).

Do you think there's something causing the blade to come loose really easily even after I tighten it on?

Click to expand...

Similar issue. Craftsman m230 with a Briggs and Stratton motor. Turns out it was the recoil starter. There is a plastic piece that prevents the fly wheel from reversing and it blew up. 20 dollar fix for the assembly.