To fix the problem of a not driving Honda HRU216 Rotary mower you need to check four specific areas in the machine, The Clutch cable, The Drive Wheels, The shafts and the Gearbox itself.
First Check if the Clutch cable is properly adjusted, A lot of people bring their lawn mowers for service complaining that it,s not driving properly or it has a crunching sound before it starts driving which is sometimes just an easy fix.
What you can do is just adjust the Clutch cable just make sure that you have enough tension on the lever to engage the clutch, Bring the adjuster downwards to give the lever more tension that makes the engaging lever on the gearbox close to engagement.
Next is check the Drive wheels, The HRU 216 Buffalo Pro Self Propelled has Ratcheting wheels which engage on the shaft when driving forward and spin free when pulling backward.
Remove the 14mm bolt that locks the wheels in place and checks the Ratchet mechanism make sure that it is working properly, sometimes it sieze a little bit and only needs to be lube, or if the two small cams are not working or one is missing or spring is not working then you must replace it.
A malfunctioning ratchet mechanism is actually rare to happen because these parts are designed to carry the weight of a machine, just spray some lube when you check them.
The Shaft is the quickest check that anyone can do on their Honda lawn mower, The driveshaft is a tube with spines on both ends that connect the output shaft of the engine to the input shaft of the gearbox and should be constantly spinning with the engine.
If the engine is Running but the shaft is not spinning, then check the shaft if it’s been seating properly or if the spines are worn out.
The shaft is being held in place by a circlip, make sure that the circlip is in place otherwise the connector that can go more on one side and might cause the gearbox to no work.
If you are done checking all areas and the lawn mower is still not driving it is now time to focus on the gearbox itself, but first, don’t conclude that you might need to change the gearbox straight away because a defective Gearbox is also very rear to happen especially that its a Honda brand and should be tough enough.
What often happens here is your gearbox is not being held in place properly which makes the gears that connected on the shaft being out of Mesh and that is usually causing a crunching sound.
If the crunching sound didn’t fix by adjusting the cable the check the gearbox, make sure that it’s bolted properly no bolts is missing and make sure that the sliding pin on the gearbox is not moving too much on the guide.
The sliding pin on gearbox is responsible of keeping the gearbox in place even when you lift up or bring down the height of the lawn mower, the slot where the pin slide is the most common to cause the gearbox to have an excessive movement and causing the driving malfunction which creates the crunching sound so it’s better to be fix.
You can remove the bracket where that has the slot where the pin slides and fix it measure the diameter of the pin and make sure that the groove or slot is about the same size as the pin so it will not gonna have to much side play.
To fix it just tap it with a hammer or use a big plier to squeeze and make it tighter and bring the slot size the same as the pin then put it back on the on.
Hopefully has been helpful and if there is anything else that I didn’t answer here please write it on the comment and i’ll put it in.