Exmark Metro- Blade change, torque & anti-seize compound

nuttinshowing

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First time poster here, hello all and Happy Holidays.

Picked up a cordless impact wrench, early XMas gift to myself, for future blade change removal and other DIY functions, Milwaukee M18 Mid Torque. Getting older now figured it would make things easier going forward .Plan on installing blade carefully with wrench set on a low setting and verifying with torque wrench set to about 75lbs per spec. To date, always used manual wrench & socket, never checked torque.

Duh! stupid question coming. The spindle nut on my mower is atop the spindle pulley and runs thru the deck to a nut below deck that secures the blade. Torquing the nut above the deck on the spindle is easier and would be the same torque value as the one below deck that secures the blade, right? It is, afterall,is the same bolt with spacers and washers in between so I'm guessing same torque.

Wondering what the consensus is in using anti-seize compound .on blade bolt. Never used it but considering.
Understand that you torque about 25% less if using it.
 

bertsmobile1

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Blade bolts tighten in use so you don't want to put a lubricant on the threads
If you take the nut off at least once a season it will not be a problem.

You are over thinking the whole torque thing unless your mower has tapered rollers.
Most are stepped and the nut is tightening onto the step via the pulley &/or blade.
Usually you do the blade first because you can hold the blade.
Once the blade is on then do the pulley
If there is a step in the shaft then the tension is only at that end
If there isa spacer between the two bearings then the each nut tensions the entire shaft .
 
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nuttinshowing

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OK. Hand tighten, snug up, blade bolt on bottom of deck and secure blade from moving. Tighten nut on top of pulley to torque. Done

BTW bertsmobile, I enjoyed reading an earlier post of yours concerning anti seize compounds. Lot of good info there. Good defense of your position. Great back and forth by you and others supporting they're position on the subject. I believe it all ended with the statement " do what works best for you"
 

bertsmobile1

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I am not familiar with your mower
If the blade hole is round then the blade must be tightened fully first
If the blade hole is shaped to prevent it turning then the nut only needs to be snugged .
I treat them all as if the hole is round which prevents accidential damage to the shaft .
99 % of people do not understand the concept of tensioning a thread and the other 1% are confused .
The thing which makes this most obvious is how vigerously they will argue about an absolute torque number as if 0,5 ft lbs will make a difference .
Every time a fastener is tightened the torque required to produce the desired clamping force will change.
We had a set up in one of the labs with a load cell between 2 plates which could be held down with bolts in different positons & patterns and of different threads & diameters.
One of the lab techs designed it because he was fed up with replacing broken bolts & studs.
The students eyes used to pop when they saw the effect of tightening a bolt to a modest 50 ft lbs as little as 4 times.
 

Born2Mow

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Picked up a cordless impact wrench, early XMas gift to myself....
A good friend would have gotten us all one. 🤪

• The torque setting comes from the stretch of the bolt's shank, so 'Yes' torque either end to achieve the same tightness.
• I use Never-Seeze on lug nuts and blade mounting bolts... fasteners exposed to a lot of water that are only moved once every several years. That's a good idea.
• However, Never-Seeze would be considered a "Lubricant" and thereby reduces maximum torque values. So you might want to consult torque tables that account "bolt tightening with lubricants".
 
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StarTech

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I just go by whatever OEM spec the torque to be. Most 5 point star Husqvarna's is 55-65 ft-lb and most 6 point MTD's is 85-95 ft-lbs. I figure the OEM have done their homework as to what is best torque value is and I don't second guess them.

When these mounting patterns are use just torquing the pulley nut or screw does absolutely nothing in relation the blade end. Now round mounting is different but even those I tighten the blade end first then the pulley end; just out of habit.
 

bertsmobile1

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A good friend would have gotten us all one. 🤪

• The torque setting comes from the stretch of the bolt's shank, so 'Yes' torque either end to achieve the same tightness.
• I use Never-Seeze on lug nuts and blade mounting bolts... fasteners exposed to a lot of water that are only moved once every several years. That's a good idea.
• However, Never-Seeze would be considered a "Lubricant" and thereby reduces maximum torque values. So you might want to consult torque tables that account "bolt tightening with lubricants".

And here in lies the rub
It is deformation of the thread, not stretch of the bolt
If you think you can stretch a steel bolt over 1/16" diameter with hand tools you are deluding yourself .
Stretch gets used all sorts of places where it is plain wrong
Wound Bowden cable does not stretch, it unwinds so it gets longer
Chains do not stretch, the side plate holes wear oval so the chain gets longer
Kevlar reinforced belts do not stretch, they wear thin so go loose on the pulley.
When you tighten a bolt, you add strain energy to the bolt and apply a shear force to the threads
The threads can creep a little before they yield and strip out but the bolt remains the same length .
When mechanics & engineers were taught properly we used to get them to tighten brass bolts to different torques then mount , section & polish them for microscopic examination .
We used brass bolts because brass grains exhibit a distinctive slip pattern when the move called "Twinning" which is easy to identify under the microscope.
Then the students would examine the bolts end to end & side to side to see where the deformation actually happened.
 

bertsmobile1

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SO I went to the web & found a video of the spindle .
At 1min 50 he removes the spindle and you see that the pulley nut claps the pulley against a threaded flange that retains the bearing
So the tension you put on the pulley nut applies a strain between the threads for the pulley nut & the threads of the bearing retainer so it has no effect on the rest of the shaft & is localised to that short section.
Similar story at the bottom
The retaining bolt sandwiches the blade between the larger diameter blade boss and the washer under the bolt so for it there is no tension in the shaft proper only in the threaded length and again it will have no effect on the shaft .
 

StarTech

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Bert that is the ZTR spindle setup and not the Metro spindle setup.

Metro spindles. Item 57 is a eight inch long 5/16-18 screw so it does tighten the whole assemble. Only the inner bearing is preload against item 26 (spacer) which is slipped over item 51 (spindle tube shaft) which clamp the bearings against this spacer with a series of outer spacers and washers. The lower bearing assembly is actually held in with a snap ring (circlip).

With the spindel setup using the eight inch through screw it doesn't matter which end is torqued as you are torquing the whole assembly at the same time. Actually you are torquing both ends at the same time.

1607682743974.png
BTW screws do stretch when they are torque to near their breaking point. The softer the metal the more pronounce it is. I have stretched cylinder head bolts a lot over a thread width before they snapped. Once stretched they are weaken and should be replaced. Edit: It is to note that this will usually happen in the threaded portion as it is the weaker area.
 
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nuttinshowing

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Star Tech for the win! Thanks Bert for your very technical input. Glad I had some help from others to sort things out.

Going forward when I replace the blade I will hand tighten ++ and secure the blade bolt under the deck and fully tighten to torque spec the nut on top of the pulley spindle.
Still undecided about anti-seize, however, I am leaning against using it based on the totality of internet information I have read from engineers, metallurgists and repair techs.

Thanks again.
 
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