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Blade falling off

#1

S

susiep303

I am not sure how to work this forum so bare with me.
I bought a new self propelled craftsman walk behind mower in 2017 for my 5 acres. I have never had a problem with it but this year on my first mowing, it began vibrating and the blade fell off. I put it back, tightened it, same thing. It doesn't have a problem tightening.....and holds securely for several steps before starting to vibrate again. I asked several people and they told me I bent my blade. I replaced the blade and same thing. Does anyone know an easy, cheap fix (for a single female) without having to take it to a shop. I live in a small town with limited services available so they are expensive and I need to know what to look for if I have to take it. Thank you for any answers you can give me.


#2

Scrubcadet10

Scrubcadet10

It's possible your crankshaft got bent, have you hit anything with it?
Or you might try a thread locking liquid, although it would be hard to remove when you replace the blade.I
Most blade bolts are torqued to around 30 foot pounds, that's what I do on my push mowers.


#3

S

susiep303

Scrubcadet10 said:
It's possible your crankshaft got bent, have you hit anything with it?
Or you might try a thread locking liquid, although it would be hard to remove when you replace the blade.I
Most blade bolts are torqued to around 30 foot pounds, that's what I do on my push mowers.
Click to expand...

Is the crankshaft that thing I attach the blade to; if so then it's not bent. I hit some sticks I didn't see under the grass, but they weren't unusually big.
I am really sorry, but I have no idea what 30 foot pounds are. How do I measure that?
I am ignorant....not stupid, just ignorant. I am learning as I go...replacing inside of toilet and a leaking sink pipes are all new to me....


#4

Scrubcadet10

Scrubcadet10

Okay, the crankshaft shouldn't be bent if you havent anything large. And yes the blade bolts onto a adapter on the crankshaft.
You would need to buy a special torque wrench to get 30 foot pounds, and it applies a certain pressure to the bolt and holds it in place. but that shouldn't be necessary to use in this case.

may i ask what you're using to tighten the bolt?
And the bolt should have a washer on it, or with it. is that washer still in place, or not laying in the grass anywhere.

As i stated earlier try to buy or order some Blue Loc-tite.
If you use loc tite, pour a little on the bolt and thread it in and get as tight as you can. and that might help with the bolt backing out.
https://www.amazon.com/Permatex-242...words=loctite&qid=1556131742&s=gateway&sr=8-5

another thing is, some times the blade adapter that blade bolts too will have a star shape to it, or a another shape, that the blade hole fits on, like a puzzle, if they are mis aligned the bolt may seem tight, but wont be.
But usually only riding mowers use the shapes to help hold the blades. I've never seen it on a push mower, yet.
do you have the model number of the mower?


#5

S

susiep303

Scrubcadet10 said:
Okay, the crankshaft shouldn't be bent if you havent anything large. And yes the blade bolts onto a adapter on the crankshaft.
You would need to buy a special torque wrench to get 30 foot pounds, and it applies a certain pressure to the bolt and holds it in place. but that shouldn't be necessary to use in this case.

may i ask what you're using to tighten the bolt?
And the bolt should have a washer on it, or with it. is that washer still in place, or not laying in the grass anywhere.

As i stated earlier try to buy or order some Blue Loc-tite.
If you use loc tite, pour a little on the bolt and thread it in and get as tight as you can. and that might help with the bolt backing out.
https://www.amazon.com/Permatex-242...words=loctite&qid=1556131742&s=gateway&sr=8-5

another thing is, some times the blade adapter that blade bolts too will have a star shape to it, or a another shape, that the blade hole fits on, like a puzzle, if they are mis aligned the bolt may seem tight, but wont be.
But usually only riding mowers use the shapes to help hold the blades. I've never seen it on a push mower, yet.
do you have the model number of the mower?
Click to expand...



I don't have the model number but can get it for you. It's in my mower book at home. The blade adapter has a star shape. Yes there is a washer also. I know that because I had to buy a new washer with the new blade because one side of it was worn almost all the way through. I was very careful taking it apart so I could get it back the right way. Thank you so much for your help. I will try the loc tite


#6

Russ2251

Russ2251

I beg to differ.
No one recommends Loctite on a mower blade.
There must be an underlying problem which the Loctite would simply cover up and very likely won't work at all.
Find the problem and fix it.
A hunk of metal slinging around at ~3600 RPM is nothing to screw around with.


#7

D

Darryl G

Usually those are spring washers and need to go on so that it's cupped upwards toward the blade. And note that you should always disconnect the spark plug when doing any work on the mower, just grab the rubber boots and pull if off and make sure its away from the spark plug.

Are you using a block of wood wedged between the deck and the blade to tighten it? If you're just holding it with your hand you likely aren't getting it tight enough.


#8

tom3

tom3

If that has the star pattern for the blade attachment and it has been damaged that's probably where the issue is. I'd pull the spark plug, (make it easy to turn and safe) rotate the blade on the mower and look for runout, around the edge and high and low at the tips judged by the housing sides.


#9

S

susiep303

susiep303 said:
I don't have the model number but can get it for you. It's in my mower book at home. The blade adapter has a star shape. Yes there is a washer also. I know that because I had to buy a new washer with the new blade because one side of it was worn almost all the way through. I was very careful taking it apart so I could get it back the right way. Thank you so much for your help. I will try the loc tite
Click to expand...


OK...it's a 21 inch craftsman...bought new in 2017....model number 247.377440
Does that help?


#10

S

susiep303

tom3 said:
If that has the star pattern for the blade attachment and it has been damaged that's probably where the issue is. I'd pull the spark plug, (make it easy to turn and safe) rotate the blade on the mower and look for runout, around the edge and high and low at the tips judged by the housing sides.
Click to expand...

Thank you for answering me but I have no idea where the spark plug is or how to remove it. I do not understand "runout, around the edge and high and low at the tips or housing sides". It sounds like I need to find a lawn mower person. But thank you.


#11

S

susiep303

Darryl G said:
Usually those are spring washers and need to go on so that it's cupped upwards toward the blade. And note that you should always disconnect the spark plug when doing any work on the mower, just grab the rubber boots and pull if off and make sure its away from the spark plug.

Are you using a block of wood wedged between the deck and the blade to tighten it? If you're just holding it with your hand you likely aren't getting it tight enough.
Click to expand...

Thank you for answering. I didn't know about the block of wood. I was just using my hand. I will try that.


#12

D

Darryl G

Something like this.

Attachments





#13

D

Darryl G

As far a the spark plug wire, it will look something like this. You really should disconnect it any time you're working on your mower, especially working on the blade.

Attachments





#14

S

susiep303

Darryl G said:
As far a the spark plug wire, it will look something like this. You really should disconnect it any time you're working on your mower, especially working on the blade.
Click to expand...


Oh wow!!!! Thank you so much. The pictures helped immensely! Thank you!


#15

D

Darryl G

susiep303 said:
Oh wow!!!! Thank you so much. The pictures helped immensely! Thank you!
Click to expand...

You're welcome. A picture really is worth 1,000 words. :biggrin:

And as far as how tight to get it. I'd say as tight as you can get it using just your lower arm strength, not straining or putting your body into it.


#16

S

susiep303

Darryl G said:
You're welcome. I picture really is worth 1,000 words. :biggrin:

And as far as how tight to get it. I'd say as tight as you can get it using just your lower arm strength, not straining or putting your body into it.
Click to expand...

Thank you.


#17

J

jp1961

If you blade is straight, you can check for a bent crankshaft by measuring the distance from the blade tip to the bottom of the deck, then rotate the blade 180 degrees and measure again, should be the same.

It doesn't have to be bent much for it to vibrate.


#18

cpurvis

cpurvis

Scrubcadet10 said:
But usually only riding mowers use the shapes to help hold the blades. I've never seen it on a push mower, yet.
do you have the model number of the mower?
Click to expand...

I just replaced the blade and star-shape adapter on an MTD 21" push mower (Walmart cheapie). The adapter was broken and part of it was missing.


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