Concrete Saw: Blade Won't Spin

A bearing is a device that allows a shaft to rotate inside a stationary housing, while reducing friction and handling stress. Due to constant stress on a bearing, they tend to wear out and can seize.
To check your concrete saw, start by removing both belt covers. Depending on your model, one could be the recoil. Relax the tension on the belt by turning the tension nut counter clockwise until it stops. Remove the belt by walking it off both pulleys. With the belt now off, try spinning the blade with your hand. If it does not move, or is very tight, then the bearing (or bearings) has seized and will need to be replaced.
First, disconnect the water line and separate the saw in half. Remove the nut holding the pulley in place. For this step, an impact wrench works best. However, if you do not have one handy, you can also remove the nut by holding the pulley in place with channel locks. On the other side, take off the arbor by inserting a screwdriver in the backside. This allows you to hold the blade steady as the arbor is being removed. Take out the blade flanges and spacers and then remove the blade cover. Remove the cutting device assembly, which will be different on all models. Clear any snap rings, bolts or screws in order to do so.
At this point, you can either replace this whole unit, which houses the bearings, or push the bearings out. When pushing the bearings out, be careful to ensure you do not damage the housing. Install the new bearings evenly into the housing.
Once completed, you can begin reassembling the unit. Reinstall the blade cover, inner flange, spacer, blade, outer flange/spacer and the arbor and tighten. Next, reinstall the pulley tight. Reassemble the two halves of the saw back together. Connect the water line. Reinstall the belt by walking it on both pulleys and then reapply the tension by turning the tension cut clockwise until it stops. Lastly, put the belt cover/recoil back on.

The belt in your concrete saw transfers power from the motor to the blade. It rides along two pulleys that are attached to the motor and blade assembly. If you notice the blade is not turning, check the belt. Start by removing both side covers – depending on your model, one cover may be the recoil. If the belt is broken, it needs to be replaced. From here, release the tension on the belt by turning the nut counter clockwise until it stops. You may not have to do this if the belt has snapped. For a broken belt, you will not be able to put the new belt on if the tension nut is not loosened. Remove the old belt and install the new one by walking it on the pulleys. Turn the tension nut clockwise until it stops. Lastly, reinstall the belt cover/recoil.

The electrical motor supplies power to the unit. If the blade does not spin and the motor hums when you pull the trigger, you could have either a bad armature or dust build up inside the motor. Concrete saws produce a lot of dust, which is a major killer in electrical motors as it can overheat and short out. The armature has a commutator, located on its shaft, which is what the brushes ride on. The commutator acts as a switch for the electromagnet; constantly flipping the flow of electrons at the exact moment, causing the armature to rotate.
Start by taking off the end cap for the motor and remove the carbon brushes with a screwdriver and set aside. To access the motor, remove the screws to take the cover off and separate the covers. Once you have reached the armature, pull it out. Clean it thoroughly of dust, including inside of the motor housing.
To check for a bad armature, you can perform the 180-degree test. Take the detached armature and stand it up on a bench. With an ohmmeter, attach the two ends to each side of the commutator to measure the resistance of the windings. As you move it around the commutator, the reading number is not important. You are looking for a consistence reading, indicating all the windings are good. If it varies, radically reading a zero, or open circuit, then the armature is bad.
Another test you can do is by attaching the ohmmeter on each bar adjacent to each other on the commutator and look for a consistent reading. If the ohm reads zero, or open circuit, that is indicates a bad armature.
You can also do a bar to ground test. This is done by placing one end of the ohmmeter to the top of the armature’s shaft and the other to the commutator. If the armature is bad, install a new one. Once replaced, replaced, reinstall the covers, brushes and the end cap of the motor.

The pulleys are what the belt, or belts, ride on to transmit power from the engine to the saw blade. If a pulley has seized up, it can force the belt to ride on top of it, causing the belt to burn up. To check the drive pulley, or saw pulley, start by removing the starter, or belt cover, on the engine side of your saw. Then, take off the belt cover located on the blade side. Release the tension by turning the belt tension nut counter clockwise until it stops. Take the belt off the blade pulley by turning the blade with your hand, and then walk it off the clutch pulley by turning the clutch drum.
Try spinning both pulleys – they should spin free. If they do not, you will need to replace the bad pulley. Your first step is to remove the nut holding the pulley in place. For this step, it is best to use an impact wrench but you can also try to lock the pulley in place while using a wrench, or you could use a pulley remover (this method will vary on each model). Take out the old pulley and clean the shaft. Install your new pulley and secure it down tight. Next, reinstall the belt by walking it back on the pulley, and then reapply the tension by turning the nut clockwise until it stops. Put the belt cover back on the blade side as well as the cover, or starter, on the engine side.

Brushes provide the electrical current to the armature by riding on the commutator. If these brushes become damaged in any way, it can impact their ability to provide the electrical current and cause the motor to not rotate, stopping the blade from rotating. Start by removing the motor end cap and locate the brush caps. Using a screwdriver, take off the brush caps and remove the brush from the motor. The brushes may be worn down completely. If the brushes are damaged from overheating, you may need to use a small screwdriver and pliers to pull out and break what is left of the carbon brush. Next, clean out the inside and insert the new brushes by aligning the wings on the end of the brush with the holder. Hold the brush in place and reinstall the cap. Do not over-tighten the cap, as it can break easily.

If the clutch drum is worn, the clutch shoes will have troubles locking in place on the drum, allowing rotational movement. See “clutch replacement” as you always want to replace the clutch drum with the clutch so both parts break in and wear together. Replacing one without the other can later cause problems and a second clutch repair job.

The clutch transmits the power from the engine to the drive shaft, using centrifugal force. As the engine speeds up, the clutch rotates faster, locking the clutch shoes in place against the clutch drum and transmits the power. If the blade will not rotate when you throttle up, the engine clutch is not locking in place. Usually, before this happens, there will be a burning smell coming from the clutch and it will start to slip before it actually fails.
The following procedure is going to vary on all models, as they are different, but it will be a similar process. To prevent an accidental start up, remove the spark plug wire and the spark plug. Depending on your model, take off the starter, or clutch cover, and then the belt cover. Release the tension on the belt by turning the tension nut counter clockwise until it stops. Walk the belt off the clutch pulley by turning the clutch drum. Now, rotate the flywheel to get the piston to the bottom, dead center. Stick a small screwdriver down the spark plug hole to feel for the piston at the bottom. To ensure the piston remains in the down position, insert a cord, or rope, in the spark plug hole. Remove any clips on the crankshaft in the front of the clutch. Using a clutch removal tool, take out the old clutch. Some clutches have an arrow on them, indicating the direction of removal (normally it is clockwise). Remove the old clutch and pull out the clutch drum. Clean the crankshaft and install the new clutch drum, ring spacers and then the shoes part – ensuring it is put in correctly. It should say “top” on the side facing outwards.
Now, using the clutch removal tool, tighten the new clutch into position. Remove the cord, or rope, from the cylinder. Reinstall the belt by walking it on the pulley and reapply the tension by turning the tension nut clockwise until it stops. Lastly, reinstall the belt cover and the starter or clutch cover.