When I turn on grinder, the motor hums but wheels don't turn. I tried to adjust the wheel nuts and finally got the wheels to turn but the motor will stop with just a slight amount of pressure to the wheels. What should I do

there is a nut and bolt that holds the little shelf below the grinding wheel. Loosen it and adjust the shelf or rest to within approximate ly1/8 inch of wheel for safety.

Unplug the grinder. Remove the guard on the side you want to change. Grasp the wheel with one hand while you turn the nut with a wrench. Remove the nut and arbor washer from the arbor shaft, pull the wheel from the shaft and replace it with a new wheel - DO NOT remove the paper label! Put the arbor washer and nut back on, spin the nut down snug, grasp the new wheel with one hand while you tighten the nut with a wrench. DO NOT overtighten the nut.

It may help to grasp the SECOND wheel (which should still be tight) with one hand while you tighten the nut on the new wheel. It may also help to loosen & tighten & adjust the new wheel several times until it runs as straight as possible before you really tighten it.

After tightening down the nut, dress the wheel with a wheel dresser to get it to run as balanced as possible and give you a smooth round wheel so your workpieces don't bounce against the wheel and so it cuts freely. Repeat as necessary to keep the wheel cutting freely, and to keep the grinding surface flat.

A bench grinder has left handed threads on one shaft and right handed on the other,so that the grinding stones don't unscrew the nut as you grind something.I haven't ever gotten around to getting a bench grinder,but on my father's, I used to just hand tighten the nut,then grab the grinding wheel with my hand while tightening the nut with a wrench.(You don't have to make it real tight,as the wheel pushing against the nut will keep it tight)

there is usually a spindle lock on the gearcase somewhere that you need to depress while turning the spanner wrench. If this fails what I have done to remove a "stubborn" wheel is use a punch UNPLUG TOOL FIRST and hit against one of the holes counterclockwise to loosen the nut.

Hi there, with out seeing it I`d say your brushes are gone and ceasing. I hope this solves your problem.

Hi Chip , have you tried !!carefully!! turning the grinding wheels whilst the grinder is powered up and humming and does this start the machine , if it does your motor start capacitor ( a cylinder/tube with 2 wires or connectors on it ) will be deffective or the leads might have became detached from it , a replacement capacitor is quite cheap but you must replace it with the exact one ( a motor start/run capacitor of the correct Mfd or uF rating typically 30 uF/Mfd and at the correct voltage 110/220V )
if this dosent fix your problem most likely your motor start windings in the motor field coils are burnt out and the grinder is uneconomical to repair .
hope this helps .

on a grinder the nut that holds the wheel on has left handed threads.....that means it has to be turned in the opposite direction than conventional nuts do..there should be a button on the casing to hold in..this keeps the grinding wheel from turning wheel being removed....remember to unplug first..thanks and have a great day

There is an adjustment you can make to the top guide wheel to make the blade stay on track. There is a screw with a lock nut just beneath the main bearing for the top wheel that is used to "tilt" that wheel to allow the blade to stay where it is suppose to. This needs adjustment periodically due to normal wear in the bearings or maybe due to a blade which is made a little different than the last one that was on there. Loosen the lock nut, then turn the adjusting screw to tilt the wheel in the direction needed to keep the blade on. Not much adjustment is usually needed. After turning the screw, jog the motor on briefly (with the blade on) and check how it runs. Keep adjusting until you get it running true. Lock the nut and you should be good.
Good Luck. Be Careful while jogging the motor to check the runout, as you will need to do this with the guards out of place.

Just put a wrench on the nut on the opposite side to hold the spindle. They will both tighten at the same time. Tighten them "snug". The threads are made so the nuts will self tighten or should I say will not come loose due to the way the wheels turn and pressure from use is applied.

There is a nut that you release from the middle of the grinder wheel, (grinder blade)
This nut is flat and has four holes in it.

You will see you are providing a spanner wrench to remove this nut. The wrenches' actual name is Lock Nut Wrench. It has a U shaped end with two pins sticking out. On on each side of the U shape.

The pins are inserted into the holes in the flat lock nut, located in the middle of the grinding wheel. The wrench is laid flat against the grinding wheel, with the two pins of the wrench going into any two holes of the nut.

At the top of the Makita grinder you will see a Black button. The button is pushed down to keep the grinding wheel from spinning. Holds the grinding wheel in place, as you turn the lock nut loose. When you release the button, a spring inside pushes the button back up out of the way.

As you view the Makita grinder, Release Button towards the Back, grinding wheel towards you, the nut is turned to the LEFT, to loosen. It is a Left threaded nut.

The grinding wheel spins to the Right. Using a left threaded nut insures that the nut will stay tight, due to the direction the grinding wheel spins.