Broken Belt on a overeign SLM 1500. Have replacement belt but am unable to get the blade/plastic blade off its shaft. Any suggestions would be appreciated

You've either broke the motors housing moving the motor out of alignment or the impact on the blade has snapped the drive belt by the sudden torque or it's been jerked off by the sudden stop of the blade it's been yanked off the drive pulleys and the nose is the motor running free with no blade resistance you will need to open up and inspect the drive belt assembley system the blade drive shaft pulley access area and the motor access area to either replace the broken belt or refit the belt if it's not been chewed or damaged by the free spinning motor pulley the smoke it was proberbly the belt rubbing against the motors drive pulley or wrapping up around it burning it through friction
Or your broke the motors drive shaft HOUSING allowing the driving motor and pulley to become misaligned dropping drive belt off
The motor funny noise if a banging around sound then is was the still running motor pulley is bouncing around and rubbing against the deck ect. Causing the smoke if this has happened the impact with the stone has caused a kickback effect on the motor twisting it out of its housing breaking it's secure mounts meaning the decks motor is loose the housing has gone, the MOWER extremely dangerous as the motor can at the speed it's running at 3000rpm it will chew thought the rest of the deck in a matter of seconds throwing and ripping itself from the machine sending chunks of broken deck and the motor flying in all DIRECTION possibly causing injuries to any one within range and as the wires rip apart and a possible nasty and even fatal electric shock please for your own safety do not use the lawnmower
Until it's been inspected by qualified personnel
It is highly unsafe and should either be repaired or replaced which ever the cheaper
Advice to check the area your cutting esp when using a high impact resistant plastic deck lawnmower for hidden foreign objects large and small stones as the small ones can be thrown by the blade like a "bullet"! small toys esp metal cars etcetra will make excellent shrapnel and cut the fabric grass box to ribbion it's also you if directly in the debris path Also not good for your lawnmowers blade or deck
Pavement slabs are defiantly known as the silent MOWER DESTROYER YOU can't hear it, as you aproch you can't see it before it's too late, there's a Loud bang the MOWER stops that exact same instant and the MOWER IS NOW KNOWN AS BROKEN "!
Esp on petrol mowers slabs tend to stop the MOWER dead bending the crank shaft the mowers with a slightly bentccrank will jump Round like it's on steroids or vibrate so badly it will shake itself apart as well as leaving a, very odd sensation in your arms
Deposits from animals are just nasty to clean off the deck and wheels so I clear them up too if THERE are any just in case

Check and see if the shear pin has broken. If the pulleys spin but not the blades then the shear pin in the pulley or shaft has broken.

You got a bent spindle shaft,or a timing belt issue,or the wrong blades on the unit !

UNPLUG the saw! IF your saw is a direct drive; either the blade is loose or the center of the blade is broken, Or the motor shaft has broke off. IF your saw is BELT DRIVEN, check the belt tension, or belt condition.

Is it belt driven and the belt is slipping or broken?
Is the shaft nut holding blade on loose?
Reverse threads are used on the nut to hold the blade. Was the wrong nut used and the blade is not tight?
The bearing on the blade shaft could be frozen.
Some of the possibilities I could think of so I hope this helps.

if your self propel belt is broken use pry bar to push idler back and remove belt from pulley then go under deck and weave belt from around shaft and blade.

If you have a large enough work bench it will make this a lot easier to do but it can be accomplished on the ground.
Lay your mower back on its handle bar and brace it with something heavy enough to hold it in place. This will keep your oil from running out into the air filter and/or into the cylinder as opposed to turning it over on its side.
Spray a bit of good penetrating oil around the shaft ABOVE the blade adapter and let it soak for a bit.
Remove the bolt holding the blade to the blade adapter then using a small hammer, gently tap downward on the blade adapter as you pull on it at the same time. Avoid striking it with enough force to break it. They usually slip off with just a little bit of effort.
Now you should be able to remove the plastic belt guard from the shaft and access the belt.
If you can't work it off the shaft pulley, remove it from the transmission pulley first. You will also need to remove the cover from the top side of the mower in order to replace the belt.
You didn't give a model number so I don't know if there are any screws securing the bottom guard but most of them just sit there on top of the blade adapter and slide into a cut-out area of the deck

my suggestion is that watever spare part u replace, get it replaced by the original manufacturer to avoid future problems. take it to the shop you have bought it from, ask them where u can get one. they may help u better with contacting the manufacturer. i know its time consuming! good luck!!

The belts are available part number is SV150. Call ALM Manufacturing 01423 797208 for advice/stockists.

1) Remove the cover on the top of the belt and
remove the belt from the transmission pulley

2) Lean the mower back on its handle and secure it
with whatever you have that will keep it there while
you work on it, any heavy object will do

3) Remove the blade bolt, the blade, the blade
adapter and the plastic belt guard from the bottom
You should now be able to remove the belt

4) While you have the belt off, closely inspect the
pulley on the engine shaft, they sometimes get
grass built up in the groove and this will cause
the belt to run off and also wear prematurely.

Hope this helps you out

Chuck