What lubricant is used to lubricate the gear box on the gc720r roybi tiller attachment

If the gearbox has oil/fluid and the level is correct, I would dismantle the shifter, clean and lubricate it with dry lube. Using oil based sprays, WD etc, will cause a dust/grime build up and make it jam up again.

engine 4 stroke --15w-30 engine oil ( around 300 mls )
in the gear box --gear oil
quantities =--to the full level of the fill plugs or dip sticks
check owners operating manual

normal engine oil in the engine sump
gear oil 80 oep in the gear box

check for a filler plug and top up accordingly

type gear box trouble you having.have you replace gear box lubricant or check lubricant level.

the worm gear that is inside the unit may need to lubricated,, remove the bottom case and lubricate gears and shaft with a teflon or silicone based lube. also on my sailboat when this happened I found that I needed to re-calibrate the unit - take the boat out into a very calm and open water and ' spin the boat ' in CAL mode ( this will re-orientate the internal compass ).
have fun on the water and have a great night,

c...

Hole in the top side casting ... remove the plug. 90 or 110 weight gear oil available at yor auto parts store or other fine retailer who sells lubricants.

Doesn't use a lubricant its hermetically sealed. But if you need just get some standard gear oil at pep boys or Hydraulic jack oil will do in a pinch. But that is a dry box to my knowledge.

Your worm shaft or tine shaft and gear assembly are probably shot. Welcome to the club. Long live American manufacturing.

The gear box can be removed, reset and resealed using gasket magic. It is not a quick fix and during this process I also replaced the tine shaft seals as I had lubricant leaking from the gear-box to the tine shaft. When you are tilling you should avoid rocky areas. It iseems sudden tension due to bouncing is what knocks the chain loose.

DO NOT remove the belt pulley from the top of the gear box. It is unecessary. You must remove the entire assembly from the rear of the machine. It is set in place by 6 bolts and come off as a whole unit. Once it is removed then undo the three bolts and spacers that hold the case in place. Remove the case from the frame by sliding it out the open end. You will have to remove all of the bolts around the outside of the case; a cordless drill really comes in handy here. Lay the case on its side, as you remove the bolts you may experience lubricant dripping from the centers of the removed bolt holes, or at the center holes where the case connected to the frame. This is not a problem as you will need to replace the 90 weight lubricant after you have resealed the case anyway. Once you have removed all of the bolts, using a flathead screwdriver and a mallet or hammer. break the seal around the outside of the case. You may have to go around a few times, but eventually it will pull apart revealing the sprockets, bound chain and remaining lubricant. Since it is open this is an ideal time to check for wear on sprockets and remove any large debris from the case. reset the chain so that the tine shaft moves freely and the corresponding sprockets spin as you move the tine shaft. Using a gasket sealant (Gasket Magic**) put a thick bead of sealant in the center of flat outside edge where the two sides of the case come together. Add a little extra around bolt holes. Replace the two covers snugly together and begin finger-tightening the bolts back into the crank case. Once you have completed this task, go back over the bolts and tighten with a hand wrench. Once the case is back together allow 45m to an hour for the sealant to completly harden before introducing lubricant to the system. Then reattach the case to the rear assembly and then put your tiller back together.

This occurrence seams to be an issue with these machines, however the problem is avoidable as it is persistant use in rocky or hard ground areas which causes causes the system to jump and bind. If you happen upon a hard patch of earth or rocky area, go slow, do not force the tiller and remove any large debris when possible before tilling.