MM875 Blade Install

billy3p

Member
Joined
Dec 9, 2014
Threads
9
Messages
29
I have a Black and Decker "Lawn Hog" electric mower model MM875 which I am working to change the blade on. Several months back with some perseverance and a lot of PB Blaster I was able to get the retaining nut to finally break free and remove the old and what looks like original blade. I have ordered a replacement blade but with a new and wet weather system scheduled to arrive Wednesday night I would like to re-install the old blade and pick up as many leaves as I can before the rain arrives. I am reversing the order in which I removed the old blade which is the hard plastic blade dampener,the blade,the square metal spacer and finally the retaining nut. The shaft spins when I try to tighten the nut even when I hold the blade static.

Any advice is appreciated.

Thanks to all.

P.S. I posted this in the small engine repair forum before I found out there was a forum specifically for Black and Decker
 

Pumper54

Well-Known Member
Joined
Jun 19, 2014
Threads
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Messages
819
I answered your other post before I found this one. Here is what I said over there:
From the Black and Decker website, not really sure what the difference between the mowers are but I included all 3 type instructions. Seems that you have not aligned the flats in the blade hole with the flats on the shaft.
Type 1 mower
1. RELEASE SWITCH LEVER TO TURN MOWER OFF, WAIT FOR THE BLADE TO
STOP, AND UNPLUG MOWER!
2. Use a piece of 2x4 wood (about 2 feet long) to keep blade from turning while
removing blade nut.
3. Wear gloves. Position wood and remove nut as shown in Figure 9.
4. Remove lower blade spacer, lower insulator washer and blade. (Figure 10)
5. When replacing sharpened or new blade on shoulder of fan, make sure the
GRASS SIDE identification on the blade is facing the ground. Place lower
insulator washer over shoulder of the fan. Now place lower blade spacer and
the blade nut on the shaft.
NOTE: Align flats of shaft with flats in lower insulator washer and lower the blade
space. Position wood to keep shaft from turning (Figure 11) and then
securely tighten blade nut.

Type 2 mower:
REMOVING AND INSTALLING BLADE (FIGURE 9,10,11)
1. RELEASE SWITCH LEVER TO TURN MOWER OFF, WAIT FOR
THE BLADE TO STOP, AND UNPLUG MOWER. THEN TURN
THE MOWER OVER FOR ACCESS TO THE BLADE.
2. Use a piece of 2x4 wood (about 2 feet long) to keep blade from
turning while removing flange nut.
3. Wear gloves and proper eye protection. Be careful of sharp edges of
blade. Position wood and remove flange nut as shown in
Figure 9.
4. Remove square metal blade spacer, square plastic blade insulator,
and blade (Figure 10). Examine blade insulator for damage and
replace if necessary.
5. When replacing sharpened or new blade on shoulder of fan, make
sure the GRASS SIDE on the blade will be facing the ground when
the mower is returned to its normal upright position. After installing
blade, place blade insulator on blade such that the raised lips on
one side engage the edges of the blade. Then install the blade
spacer so that it sits inside the raised lips on the other side of the
blade insulator. Be sure to align the flats in the hole of the blade
spacer with the flats of the shaft, rotating the blade and blade
insulator together as necessary. Position piece of wood to keep
blade from turning (Figure 11). Install flange nut with the flange
against the blade spacer and securely tighten.

Type 3 mower:
REMOVING AND INSTALLING BLADE (FIGURE 9,10,11)
1. RELEASE SWITCH LEVER TO TURN MOWER OFF, WAIT FOR
THE BLADE TO STOP, AND UNPLUG MOWER. THEN TURN
THE MOWER OVER FOR ACCESS TO THE BLADE.
2. Use a piece of 2x4 wood (about 2 feet long) to keep blade from
turning while removing flange nut.
3. Wear gloves and proper eye protection. Be careful of sharp edges of
blade. Position wood and remove flange nut as shown in
Figure 9.
4. Remove square metal blade spacer, square plastic blade insulator,
and blade (Figure 10). Examine blade insulator for damage and
replace if necessary.
5. When replacing sharpened or new blade on shoulder of fan, make
sure the GRASS SIDE on the blade will be facing the ground when
the mower is returned to its normal upright position. After installing
blade, place blade insulator on blade such that the raised lips on
one side engage the edges of the blade. Then install the blade
spacer so that it sits inside the raised lips on the other side of the
blade insulator. Be sure to align the flats in the hole of the blade
spacer with the flats of the shaft, rotating the blade and blade
insulator together as necessary. Position piece of wood to keep
blade from turning (Figure 11). Install flange nut with the flange
against the blade spacer and securely tighten.

Hope this helps
Tom
 

billy3p

Member
Joined
Dec 9, 2014
Threads
9
Messages
29
I answered your other post before I found this one. Here is what I said over there:
From the Black and Decker website, not really sure what the difference between the mowers are but I included all 3 type instructions. Seems that you have not aligned the flats in the blade hole with the flats on the shaft.
Type 1 mower
1. RELEASE SWITCH LEVER TO TURN MOWER OFF, WAIT FOR THE BLADE TO
STOP, AND UNPLUG MOWER!
2. Use a piece of 2x4 wood (about 2 feet long) to keep blade from turning while
removing blade nut.
3. Wear gloves. Position wood and remove nut as shown in Figure 9.
4. Remove lower blade spacer, lower insulator washer and blade. (Figure 10)
5. When replacing sharpened or new blade on shoulder of fan, make sure the
GRASS SIDE identification on the blade is facing the ground. Place lower
insulator washer over shoulder of the fan. Now place lower blade spacer and
the blade nut on the shaft.
NOTE: Align flats of shaft with flats in lower insulator washer and lower the blade
space. Position wood to keep shaft from turning (Figure 11) and then
securely tighten blade nut.

Type 2 mower:
REMOVING AND INSTALLING BLADE (FIGURE 9,10,11)
1. RELEASE SWITCH LEVER TO TURN MOWER OFF, WAIT FOR
THE BLADE TO STOP, AND UNPLUG MOWER. THEN TURN
THE MOWER OVER FOR ACCESS TO THE BLADE.
2. Use a piece of 2x4 wood (about 2 feet long) to keep blade from
turning while removing flange nut.
3. Wear gloves and proper eye protection. Be careful of sharp edges of
blade. Position wood and remove flange nut as shown in
Figure 9.
4. Remove square metal blade spacer, square plastic blade insulator,
and blade (Figure 10). Examine blade insulator for damage and
replace if necessary.
5. When replacing sharpened or new blade on shoulder of fan, make
sure the GRASS SIDE on the blade will be facing the ground when
the mower is returned to its normal upright position. After installing
blade, place blade insulator on blade such that the raised lips on
one side engage the edges of the blade. Then install the blade
spacer so that it sits inside the raised lips on the other side of the
blade insulator. Be sure to align the flats in the hole of the blade
spacer with the flats of the shaft, rotating the blade and blade
insulator together as necessary. Position piece of wood to keep
blade from turning (Figure 11). Install flange nut with the flange
against the blade spacer and securely tighten.

Type 3 mower:
REMOVING AND INSTALLING BLADE (FIGURE 9,10,11)
1. RELEASE SWITCH LEVER TO TURN MOWER OFF, WAIT FOR
THE BLADE TO STOP, AND UNPLUG MOWER. THEN TURN
THE MOWER OVER FOR ACCESS TO THE BLADE.
2. Use a piece of 2x4 wood (about 2 feet long) to keep blade from
turning while removing flange nut.
3. Wear gloves and proper eye protection. Be careful of sharp edges of
blade. Position wood and remove flange nut as shown in
Figure 9.
4. Remove square metal blade spacer, square plastic blade insulator,
and blade (Figure 10). Examine blade insulator for damage and
replace if necessary.
5. When replacing sharpened or new blade on shoulder of fan, make
sure the GRASS SIDE on the blade will be facing the ground when
the mower is returned to its normal upright position. After installing
blade, place blade insulator on blade such that the raised lips on
one side engage the edges of the blade. Then install the blade
spacer so that it sits inside the raised lips on the other side of the
blade insulator. Be sure to align the flats in the hole of the blade
spacer with the flats of the shaft, rotating the blade and blade
insulator together as necessary. Position piece of wood to keep
blade from turning (Figure 11). Install flange nut with the flange
against the blade spacer and securely tighten.

Hope this helps
Tom

Thanks Tom,
I believe my mistake is in trying to reuse a damaged blade insulator and not making certain the blade was seated on the shoulders of the motor shaft. If I am ever successful in removing the flange nut from the motor shaft again I will certainly pay close attention to the details.Somehow I have to foul the shaft so I can remove the nut.

William
 

Pumper54

Well-Known Member
Joined
Jun 19, 2014
Threads
19
Messages
819
William,
Anyway to get a open end wrench on the flats of the shaft to hold it while you remove the flange nut? If that doesn't work you might have to grab the shaft with a set of locking pliers to hold it as you remove the nut. In any case once you get the nut off look for burrs or rough spots on the threads and shaft. The shaft can be cleaned up with very fine emery paper and you can chase the threads with the proper die. Good luck and let us know how it goes.
Tom
 

billy3p

Member
Joined
Dec 9, 2014
Threads
9
Messages
29
Still struggling to loosen the flange nut so I can re-remove the old blade and start over now that I have a replacement blade. There is no space anywhere on the shaft to get either a open end wrench or channel locks to hold it so I can loosen the nut. I have removed the motor housing(needed cleaning as it turns out) and have attached a picture showing what i assume is a sensor of some type that will shutdown the motor to prevent it burning up in the event there is a blade malfunction of any sort. This might be my only place to hold the shaft using channel locks. However, I wanted to get thoughts before doing so as I DO NOT WANT TO DAMAGE ANYTHING BY DOING SO.

Should anyone viewing be in Sacramento or any other location and would speak by phone feel free to send me a message with details on how I can contact you.

Thanks so much
 

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