Why is my blade hitting the blade guard

a bent crank shaft or a damaged blade. have the blade balanced. should be good. unless you have hit something and damaged the crankshaft.

remove the power cord from the socket in the wall first
if there is a small hole in the blade , place a phillips screw driver in that hole and turn until the driver is locked against the depth guard
use the correct size spanner /socket and undo the spindle nut holding the blade on
if there is no hole ,then place the screw driver in the teeth of the blade to lock it

the motor will spin so that the teeth cut against the direction of cut ( up into the guard or up through the depth guard ( blades normally have a arrow for rotation direction)
tighten the spindle nut and if no hole in the blade use a hammer and hit the spanner with a hard rap

Link,
Usually you will have to remove the blade guard to get access to that. There is usually a rubber stop with a screw going through it that you will have to remove, and a spiral spring clip on the inside of the hub of the blade guard that will also have to be removed and then you should be able to lift the blade guard off the saw. The spring will hook around the blade guard and the other end will hook to the saw housing. Hope this helps!

Never heard of this brand of saw. A Google search indicates that MacAllister only makes big earth moving equipment. Otherwise, most saws have an appropriate washer and retaining clip that holds the guard on. And you'll need the original spring to return the guard to the closed position every time you use it. Then there are two shaped washers that fit on the armature that have a 5/8" shoulder to fit a normal saw blade. Finally there is the nut that holds everything on. Hope you didn't lose all these parts. If you did, go to eReplacementparts.com and and enter your make and model. If they don't have what you need you might be plum out of luck. But a new saw.

Remove power or battery. If the guard is removable, take it off. Use a pair of pliers to grab the end and hit the release lever. If the blade is too short, advance the motor by moving the blades with a screw driver until the reciprocation advances the blade to you. If it's shorter than that, check for screws holding the case.

Theres a nut on the guard you need to loosen. Guard will then open enough to change blade. if you want to remove it completely theres a phillips srew you also need to remove.

loosen the guard screw, UNPLUG tool first, move the guard out of the way, there is a spindle lockon the backside of the gearcase push it and slowly turn the blade until it engages and then remove the bolt, it is a left hand thread. DO NOT disassemble the guard, just loosen bolt and move out away from blade also you need to have the head in the raised position.

Removing the Blade
1. Unplug the saw.
2. Raise the arm to the upper position and raise the lower guard as far as possible.
3. Loosen, but do not remove guard bracket screw until the bracket can be raised far
enough to access the blade screw. Lower guard will remain raised due to the position
of the guard bracket screw.
4. Depress the spindle lock button (Fig. 3) while carefully rotating the saw blade by hand
until the lock engages
5. Keeping the button depressed, use the other hand and
the wrench provided to loosen the blade screw. (Turn
clockwise, left-hand threads.)
6. Remove the blade screw, outer blade clamp, and
blade. The inner blade clamp may be left on the
spindle.
Installing a Blade
1. Unplug the saw.
2. With the arm raised, the lower guard held open and the
guard bracket, place the blade on the spindle against
the inner blade clamp with the teeth at the bottom of
the blade pointing toward the back of the saw.
3. Assemble the outer blade clamp onto the spindle.
4. Install the blade screw and, engaging the spindle lock,
tighten the screw firmly with wrench provided. (Turn
counterclockwise, left-hand threads.)
5. Return the guard bracket to its original position and
firmly tighten the guard bracket screw to hold bracket
in place.
WARNING:
• The guard bracket must be returned
to its original position and the
screw tightened before activating
the saw.
• Failure to do so may allow the guard
to contact the spinning saw blade
resulting in damage to the saw and
severe personal injury
you can download a manual at: http://www.dewalt.com/tools/machinery-miter-saws-dw713.aspx

OK first raise the cutting head. Loosen the screw that holds the guard in place and move out of the way. Find the spindle lock on the right hand side of the gearcase and turn blade by hand (UNPLUG SAW FIRST) until it locks. With the wrench supplied with saw put it on the blade bolt and turn it clockwise to loosen, it has left hand threads, remove outer flange and blade. Let me know it you need any more help

Stop using speedo guards and get yourself an oster 76 and all the blades.