Lawnmower blade retaining nut - clockwise or anti?

Forums › Home Workshop DIY › Lawnmower blade retaining nut - clockwise or anti?

geekIT

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#247723 19-Feb-2019 09:50

Standing and looking down on my new Masport 4-stroke mower, the blade rotates clockwise when I pull the start cord.

Which way should the blade retaining nut be threaded? Right or left-hand thread?

Logic tells me it should be a regular right-hand thread (which should undo anti-clockwise) but it's not budging in that direction.

I don't want to get tough with it if I'm trying the wrong way. It's not a big nut and could easily be damaged.

BTW: I'm not familiar with petrol-powered machines. My last mower (which endured 15 years of hard use and total neglect) was an electric Black and Decker. The blade retaining nut (plastic, like just about every other part of the mower) was regularly threaded.

EDIT: Can I lay the machine on its side to work on the blade without draining the oil and petrol?

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#2183453 19-Feb-2019 09:58

Generally counter clockwise if you're looking at the nut.

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RunningMan

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#2183458 19-Feb-2019 10:03

Just clean any gunk off the remaining threads and see which way they go.

tdgeek

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#2183459 19-Feb-2019 10:07

Can be confusing if you are looking down at the mower, or looking at the bade or nut on a tilted mower. To untighten, move the spanner or ratchet in the same direction as the blades cutting edge, i.e.that the blade and spanner are rotating the same way

Gordy7

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#2183467 19-Feb-2019 10:13

Likely the thread direction will be so that the nut is tightened when the shaft is driving the blades.. so undo in the opposite direction.

Plenty of CRC on the thread and under the nut.... for some time so that it penetrates the thread.

Use an impact nut driver when you are 100% confident which way to undo the nut.

Gordy

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Bung

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#2183523 19-Feb-2019 11:20

All of my B&S powered mowers use a BOLT to hold the blade and blade holder to the crankshaft. It fits a 9/16 AF spanner and is normal RH thread. It can be difficult to start as there is usually 20 - 30mm thread engagement. There may be other smaller bolts holding the blade disc to the blade holder.

Always disconnect the spark plug before moving the blade!!!

Most of this is in the manual. The bolt thread direction isn't mentioned but that is usual for normal bolts. I would expect LH threads as in weedwacker blade holders etc to be mentioned.

geekIT

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#2183691 19-Feb-2019 15:06

Thanks, guys, Gordy7 and Bung especially.

Yeah, I should have said BOLT, not NUT. My bad.

Seems the consensus is the BOLT will be a conventional right hand thread. So I'll go with that.

But, and this is purely for sake of argument, it strikes me as counter-intuitive that the bolt wouldn't be left-hand thread for a blade rotating in the direction that mine does.

Follow me through this:

Viewed from above, with the mower on the ground ready to mow, and me standing beside it, the blade rotates in a clockwise direction. Obviously I can't see the blade but I've checked this.

So, it stands to reason that, if I were to tip the mower upside-down, like an inverted tortoise with its legs waving in the air, I see the blade rotating in the opposite direction, i.e., anti-clockwise.

But that's also the direction that undoes a right-hand thread bolt. So why would this direction of blade rotation tighten the bolt?

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tdgeek

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#2183693 19-Feb-2019 15:11

geekIT:

Thanks, guys, Gordy7 and Bung especially.

Yeah, I should have said BOLT, not NUT. My bad.

Seems the consensus is the BOLT will be a conventional right hand thread. So I'll go with that.

But, and this is purely for sake of argument, it strikes me as counter-intuitive that the bolt wouldn't be left-hand thread for a blade rotating in the direction that mine does.

Follow me through this:

Viewed from above, with the mower on the ground ready to mow, and me standing beside it, the blade rotates in a clockwise direction. Obviously I can't see the blade but I've checked this.

So, it stands to reason that, if I were to tip the mower upside-down, like an inverted tortoise with its legs waving in the air, I see the blade rotating in the opposite direction, i.e., anti-clockwise.

But that's also the direction that undoes a right-hand thread bolt. So why would this direction of blade rotation tighten the bolt?

Thats why I referred to the cutting side of the blade, when you look at it that way, clockwise anti clockwise is not relevant. You can see what direction the blade moves. Opposite to that to tighten. Loosening is same rotation as the cutting edge, the rotation.

Bung

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#2183771 19-Feb-2019 16:03

geekIT:

Viewed from above, with the mower on the ground ready to mow, and me standing beside it, the blade rotates in a clockwise direction. Obviously I can't see the blade but I've checked this.

From above with everything rotating clockwise just think of the end of the crank as a nut rotating in a normal doing up direction.

If you have another nut and bolt pair either side of the bolt they don't self tighten so they probably should have a self locking nut or spring washer at least.

geekIT

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#2183857 19-Feb-2019 18:21

tdgeek: What you just said must make sense to you otherwise you wouldn't have said it. Unfortunately, your 'explanation' hasn't answered my question.

Bung: Sorry mate - that doesn't make much more sense than 'tdgeek's' offering.

Is there no-one out there with a grounding in physics?

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tdgeek

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#2183872 19-Feb-2019 19:06

geekIT:
tdgeek: What you just said must make sense to you otherwise you wouldn't have said it. Unfortunately, your 'explanation' hasn't answered my question.

Bung: Sorry mate - that doesn't make much more sense than 'tdgeek's' offering.

Is there no-one out there with a grounding in physics?

Ok. One liner. The way the blade turns, to undo the bolt turn the bolt the same way. To tighten , turn the bolt opposite to the way the blade turns ( otherwise ithe blade may grip the bolt and undo the bolt

Two liner :-)

coffeebaron

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#2183879 19-Feb-2019 19:15

Ok, think of it this way: if you hold the nut still whilst the blade is rotating, is it going to tighten or loosen?

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geekIT

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#2183888 19-Feb-2019 19:27

coffeebaron, you nailed it. Makes perfect sense 😋.

'Those who can make you believe absurdities can make you commit atrocities.' Voltaire

'A patriot must always be ready to defend his country against his government.' Edward Abbey

Bung

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#2183910 19-Feb-2019 19:51

geekIT
Bung: Sorry mate - that doesn't make much more sense than 'tdgeek's' offering.

Is there no-one out there with a grounding in physics?

Physics, that explains it, you are overcomplicating it.

Next time I'll try to draw a picture 😀

tdgeek

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#2183915 19-Feb-2019 19:58

Bung:
geekIT

Bung: Sorry mate - that doesn't make much more sense than 'tdgeek's' offering.

Is there no-one out there with a grounding in physics?

Physics, that explains it, you are overcomplicating it.

Next time I'll try to draw a picture 😀

I was looking for an Einstein type blackboard of calculations... :-)

Fred99

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#2184044 20-Feb-2019 06:09

There are probably instructions in the manual or on a printed label as to what side should be down when you flip it on its side. That would probably be with the dipstick/oil filler side down.

Pull the spark plug lead off. Although the mower shouldn't start accidentally with the throttle in "off" position if you turn the blade, just imagine the mess if it did. You might bump the lever etc while turning it on its side.

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