How to undo nut on main crankshaft is it definitely LH thread?

There is a left handed thread and a right handed thread on the arbors.

Removal
Right Hand Side (RH)
Wrap a piece of rubber or leather around the threads on the LH side of the arbor & hold with pliers, while turning the RH nut CCW.

Left Hand Side (LH)
Wrap a piece of rubber or leather around the threads on the RH side of the arbor & hold with pliers, while turning the LH nut CW.

Installation
Note: Hand tighten the nut, then 1/4 turn.
Right Hand Side (RH)
Wrap a piece of rubber or leather around the threads on the LH side of the arbor & hold with pliers, while turning the RH nut CW.

Left Hand Side (LH)
Wrap a piece of rubber or leather around the threads on the RH side of the arbor & hold with pliers, while turning the LH nut CWW.

For grinding stones:

• ring test the stone
• discard the stone if it has been dropped
• be sure the paper washers are installed on the wheel

GRINDER SAFETY 101 (graphic injury video so be warned)

http://www.garagejournal.com/forum/showthread.php?t=263083

There is a left handed thread and a right handed thread on the arbors.

Removal
Right Hand Side (RH)
Wrap a piece of rubber or leather around the threads on the LH side of the arbor & hold with pliers, while turning the RH nut CCW.

Left Hand Side (LH)
Wrap a piece of rubber or leather around the threads on the RH side of the arbor & hold with pliers, while turning the LH nut CW.

Installation
Note: Hand tighten the nut, then 1/4 turn.
Right Hand Side (RH)
Wrap a piece of rubber or leather around the threads on the LH side of the arbor & hold with pliers, while turning the RH nut CW.

Left Hand Side (LH)
Wrap a piece of rubber or leather around the threads on the RH side of the arbor & hold with pliers, while turning the LH nut CWW.

For grinding stones:

• ring test the stone
• discard the stone if it has been dropped
• be sure the paper washers are installed on the wheel

GRINDER SAFETY 101 (graphic injury video so be warned)
http://www.garagejournal.com/forum/showthread.php?t=263083

You are not saying which bolt/bolts you want to undo but if it is the main centre bolt it will be a LH thread which means that instead of turning anti-clockwise to undo you have to turn it clockwise. It is designed that way so that it will not undo in normal operation.

Clamp the shaft behind one wheel with 'Channelock' or 'Visegrip' pliers, then tighten both nuts. Check the new wheels for 'off-center' running by spinning them with your hand. They may fit the shaft tight enough that there is no centering adjustment--use a 'wheel dresser' (either a stone type or a multi-wheel type) to true up the wheel so that there is no radial wobble. Hope this helps!

If you put a wrench on the nut on the other end of the shaft, you have a 50/50 chance that the nut you want loose will come loose. If the wrong one comes loose, you can remove that nut completely (and the wheel) then take the nut with you to the store to buy another one. Then put two nuts back on and tighten them together as a jamb nut. Then try again. If the wrong nut still turns, you have to tighten the pair of nuts together tighter. good luck

Hi edward, looks like you posted the same question twice. I already answered the other one. good luck.

Remember if you are trying to change the left side it is a reverse thread nut. You would turn it clockwise to loosen. IF it is very tight, put a wrench on both sides. IF the right side comes loose, remove brush/grinding wheel, and re-install nut, with an extra nut locked to the first one, the put a wrench on both sides again.

On a bench grinder the wheels turn towards you. This means the grinding wheel on the right side, has a right and nut, and the left side has a left handed nut. If you're trying to remove the left side turn the nut counter-clockwise

Hi they are normal nuts so will undo anticlockwise, but to undo this nut/bolt your going to need to lock the flywheel you can do this by either removing the starter motor and jamming a big screw driver in the teeth of the fly wheel so that it lock on the casing of the gearbox or you can undo an inspection panel on the gearbox to give you access to the fly wheel and then jam it that way other than doing this you would need air tools to undo this nut without jamming the fly wheel

assuming you removed the nut already, it may pop off by tapping shaft with aluminum drift and hammer. if not , you will need to use a puller, and after tightening it on, hit the puller shaftwith hammer.