OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Removing drive roller from SB 590

The belt drive SB that I recall seemed to have two clutches, one for everything and one specifically for the rear roller. The everything clutch consisted of tightening the belt with a hand lever.


Does your belt have an automatic tensioner, or a belt clutch? As I recall you have to route the belt to the rear of the tensioner, or it can't work.

Incidentally, this is the picture that shows what happens if you don't glue the clutch facing material to the disk.

It has a park and drive position, the photo is the drive position, I'm not convinced the belt is in bad enough condition to be the problem.
Very frustrating because it is just so simple.
Engage drive
Press handle grip to activate cable clutch.
Pulley moves outwards and engages the outer clutch plate (the one with the 2 holes)
That then drives the pinion gear which is engaged with the ring gear.
Rear roller should turn.

You should be able to see where it is slipping, since the slip rate is so high. You can see the engine pulley turn, and you can see whether the reel and roller pulleys turn. Either the belt is slipping or the roller clutch is. If the belt is slipping, with full movement rearward on the lever clutch, you need a new belt.

From the picture, it looks as if the belt may be bottoming in the engine pulley. If it is bottoming you should be able to see that the bottom of the pulley is shiny, and probably the bottom of the belt too. Worn belts bottom in pulleys, and they can't drive that way, they have to wedge in the V of the pulley.

You can also see in the picture that with the clutch lever all the way back, the tensioning spring is not stretched, so there is just about no tension on the belt. That can only happen if the belt is worn or stretched.

Fitted a new drive belt and still got no drive, double checked the clutch and it is not slipping.
Have taken the drum partially apart to look at the ring gear and it is cracked (see photo)
Anyone know how to remove the ring gear, there is no where to lever?
Did notice that if I held the opposite end of the centre shaft with vice grips I could rotate the ring gear in both directions by hand, so I think this is where the "slip" is coming from.
Can't see how the ring gear wouldn't slip tho as there doesn't appear to be a key way or splines to stop it from turning.
Looked at the part list and the replacement ring gear on TMS but it is unclear.
So does anyone know how to remove the ring gear without breaking it further, and does it have splines or key way of some sort to make it turn the centre shaft.
Currently got it soaking in RP7 to help removal.
One last question the bearings are not the best, can you go to any bearing shop for replacements??

Kempe, could it be sprag gear?
If it's not slipping, and it's not tension it's all that I can think of that's left. Mind you, the difference between the 430 and 590 in the drive area is pretty immense and my knowledge is limited to a subscription to the manuals area and only about 3 weeks of owning a Scotty.

On the bearings - I was passing a bearing place and they supplied me with new bearings straight away. Cost me about $13. They just needed the code from the side of the original bearings. Just as well, I had to take one off with a angle grinder. From the advice on this thread I was on my way back from my mechanic (who couldn't remove it either).

Hi Kempe,

Sorry just had a proper read of your post, previous reply I was racing through it while cooking dinner.

I've pulled mine apart, I'll take some photo's of all the parts and but I'm pressed for time at the moment.

Paul.

What does the other end of the drum-half look like? From what you said it sounds as if the outside of the ring gear is loose in the drum-half. If this is so, and it is not falling off the axle already, it is presumably tight on the axle shaft. It has a couple of ratchet boxes on that axle, which may be bolted to webs on the drum halves. That would explain why the ring gear is loose in the drum-half: its job is to drive the axle shaft, not the drum-half.

In the crummy picture in the parts list, it looks as if there is a web in the center of the ring gear, so the collar in the center of it has to come out toward your camera, not by pushing it down through the ring gear.
That suggests that if you try to push the axle shaft down through the ring gear, it will be difficult to support the far side of the ring gear well enough to keep from cracking it. In fact you may end up with a set of fractures of it, very similar to the set it currently has. In other words, maybe somebody hammered on the end of the axle in an attempt to remove it, without taking steps to support the ring gear from the other side. That probably isn't the way to go.

What prevents the axle shaft from moving upward in the picture (toward the camera, taking the collar in the center of the ring gear with it)? There are a couple of ratchet boxes on the axle shaft, driven by Woodruff keys, but it may slide through those by sliding the keys along keyways. So, can you support the inside of the ring gear by resting it on a ring slightly larger than the collar on the shaft, then push on the far end of the axle shaft?

Hi Kempe, I have spoken to a Scott Bonnar repair expert this morning about removal of the nylon ring gear. This is his advice:

Once the plastic ring gear has cracked it is cactus and cannot be repaired or re-used. A steel drum ring gear for Models 430 and 590 Diplomat Scott Bonnar cylinder mower rear roller replacing the nylon and alloy ring gears, should be purchased. The cost is $132.

To remove the stubborn existing gear, you carefully break it by any method you choose....drilling holes and breaking it in segments would suffice...just remove as much of the nylon as possible. The centre portion is on a key-way and his advice is to use heat, (oxy works fine) and pull it towards the camera in your pic.

Re: the bearings, after removal, just take them to any bearing supply company or perhaps purchase from the firm that will supply the replacement ring gear...they have them in stock.
Please let us know how you get on.

Cheers, I'm planning to replace the ring gear, apparently the centre boss is keyed to the shaft.
When I get this drive working will be continuing to renovate this machine but will stop short of painting it.
New soleplate, front roller end caps, new bearings throughout, clutch cable and cutter blade regrind all on the agenda.
But firstly need to restore the drive.

PS Have now got the ring gear off but not the boss, and have new ring gear on order.
What I think was happening to make me lose drive was the ring gear was slipping on the boss, which was why with the rollers lifted she would drive but when the weight was on the rollers the ring gear slipped on the boss.

New ring gear should be here by next week so have till then to remove the boss, which according to TMS might not be easy.
Okay, off to get the blow torch and try some heat to expand it.

Kempe, now that the ring gear is off there should be a gap behind the boss, and it might be wide enough for the jaws of a puller. If you put plenty of penetrant on the joint between the boss and the shaft, and leave it at least overnight, before you try the puller, it may come off fairly easily.

It is odd that the end of your axle shaft shows hacksaw marks, since the axle was lathe-turned. There may have been foul play somewhere along the line.

Hi Grumpy and Kempe, well spotted grumpy, I looked at the end of the shaft yesterday and thought the same....methinks foul play!
I also agree with you on a good soaking with penetrant, according to the advice I have received, it should slide off revealing the keyway.
Kempe, could you please take some pics of the roller-half when you get the boss off, for archival purposes it will come in handy for future reference....Thanks mate. Plus the fact we would all like to see what's behind the ring gear....he he...

Have removed the boss.
I did as advised on here and soaked it overnight in RP7.
Then I screwed the end nut on (to protect the thread) and held the the axle vertically and hammered down on the concrete.
The weight of the half roller acted like a hammer and contacted the boss squarely and slowly removed it.
Will post pics later tonight of it all disassembled

Well done Kempe, you just invented a poor-man's slide hammer puller. Hope you didn't break any important concrete. I'll look forward to the pictures - as mentioned earlier, we badly need an archive on that SB roller drive.

Thanks Kempe, looking forward to seeing the pics...well done mate!

Pauly80 deserves all the credit as he is the one who posted how to remove the pulleys.
When the ring gear arrives I will lay everything out flat and post a pic of the assembly and where all the washers, circlips and spacers go.
Let me know if you want any other angles photographed, as it wont be getting assembled till next week when postie delivers the new ring gear.

Axle shaft showing the key and pawl holder



Axle shaft with pawls in place (there's another 3 pawls on opposite side to drive the other roller



Outside view of left roller with ring gear removed, those 3 holes look a bit dodgy and are badly drilled


Inside view of left roller


Inside view of right roller


Outside view of right roller


Moderator edit: Sorry folks, these pictures were all from an outside picture service, and we didn't notice that until most of them had timed out. I am localising the surviving ones now, but we've lost a lot of them.

I just grabbed the camera to take some pictures but Kempe's done an excellent job of that already. Now I got some spare time to start removing some rust wohoo!

Mine looks exactly the same. No difference I can tell between the 430 and 590 including the three dodgy drilled holes. I'm guessing they rolled out of the factory like that.

Do you guys think a silicon lubricant would be best where the 3 pawls sit? I'm guessing anything greasy could clag up. It probably doesn't need anything but I would like to make sure everything is at its absolute best before putting together.

Those three dodgy holes look as if they are cored rather than drilled - that is, they were on the pattern used to make the iron casting, so they are cast, not machined. I'd need to see a closeup of the surface finish to be sure of this.

It looks as if the four pop rivets inside each roller-half are holding the ratchet wheel that those pawls engage. That is, the finely machined ratchet wheel is on a separate part which is riveted on to the cast roller-half.

Can we see a more detailed pic of each end of the axle shaft? I can see the left hand end, where the collar slides on over the key, fairly well but can't see detail on the right hand end. I'd also like to see detail of the collar itself, so we can see how the ring gear drives it. I'm guessing there is something like a spline on the inside of the ring gear and the outside of the collar. A key would be sufficient for a metal gear, but not a plastic one, and the design was intended to use a plastic gear. If my guess is right, you may find you get a replacement collar with your steel ring gear, so a simple key can be used, instead of having to broach an internal spline in the steel gear.

I notice both roller halves have pressed in bronze bushes at each end - I take it these are a close fit on the axle shaft. They will need lubrication.

You could use a dry lubricant on both the pawls and the bushes. In the old days we used stuff called Dri Slide, which was a suspension of graphite powder or molybdenum disulphide powder in a very thin volatile hydrocarbon. You dripped the Dri Slide over the joint line, and the liquid carried the powder onto the bearing surfaces, then evaporated leaving the dry powder behind. That sounds like the right technology, but you might try asking a mower dealer's service technician - sometimes they know a special trick, sometimes they don't. If they propose using anything that leaves a film behind, I'd keep looking. You might also try asking a counter-jockey at a Repco outlet - so far I've found them quite knowledgeable, and they have a good range of fairly exotic products.

So, the little pinion on the pulley-clutch shaft meshes with the ring gear, which is splined to the collar, which is keyed to the axle shaft. The axle shaft rotates with the ring gear, and turns the double pawl-block in the center of the axle. The pawls engage the ratchet wheels riveted to the two roller halves. That gives a positive forward drive, but either roller half can over-run the drive in the forward direction only.

Your right Grumpy it is cast iron

Close up of left side axle shaft


Close up of right side axle shaft


Close up of boss with part of ring gear, there is no key way securing it just a tight fit with the criss cross pattern to grip.
One little crack with age and it will start to spin.
The boss is one inch and a quarter high

No evidence of being splined or keyed, looks like a tight fit held by the roughness of the criss cross pattern.
It's the weakness in the system as I see it.
Will look again tomorrow in daylight as it does seem strange

Kempe, that is a knurled pattern on the boss (i.e lathe-turned criss-cross pattern), and I think the nylon gear was molded over the knurling. It isn't nearly as bad as if the gear had just been pressed over the boss, but it isn't all that strong. Obviously you won't be able to re-use that hub with a steel gear. Most likely the steel gear includes the bush, all on one piece, with a keyway in its bore. It should work properly this time.