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

Hello there,

I've been lucky enough to purchase a cheap Scott Bonnar 590.
I was planning to respray the entire chassis while the engine is at the local mower shop getting looked at. But...
I can't get the drive roller off the life of me. I'm pretty frustrated so far. I really wanted a project to get me away from the computer - surprise surprise I'm in front of it again If I break it will probably never run again so any help would be greatly appreciated.




Thanks everyone, Paul.

There is no repair manual for that mower on this site - only illustrated parts lists.

It would be nice if someone who has actually performed this operation would tell us how it was done, preferably with pictures. I seem to remember having this conversation with about 3 people who needed answers, and nobody who had experience with this operation has so far offered any solutions.

I have the same machine I also need to remove the drive roller as I currently have no drivee at all....

Joe, one possible cause of that would be a broken plastic gear. I just said that to cheer you up.

When you start the sorting-out project, would you mind taking some pics for us, so we finally get an archive on this process?

Hi guys, just to give you a heads up, there is a metal replacement for the roller gear available which solves this breakage problem.

Thanks Deejay.

I've seen that part, if I could get this apart I probably fork out for it. I'm now taking a different approach and trying to slide the two large roller halfs sideways away from the gear to get a look inside. Done one side (out of picture side) but the other doesn't want to budge yet.

My step dad's an ex-mechanical draftsman, I'm going to get him to take a look this afternoon.

When I find out the solution I'll make sure to post it into the forums.

Good news, that pulley can just be levered off!

My old man took one look and 30 seconds it was off - He could have at least made it look hard!!

Basically it was levered out with a couple of flat head screw drivers on either side of the bearing. He just rocked the little bugger out from the outside of the chassis. Must have been all the WD 40 I've been spraying around the place that loosened it... yep, that's what it was.

Don't forget to remove the screw inside the unit that holds it on. I had already removed it but assumed it was some sort of tension adjustment. It actually holds it all in place.

PM me for more hi res pics if need be. I've inserted a few that show everything important. This should help Joe - let me know how you go. Very happy to be back on track.


The screw that locks it place. This has to be removed first.



Close up reveals the little channel a screw locks into

That is excellent Paul, this thread will now solve the problem for others who need to dismantle SB590s. Could you add another (fairly close-up) picture of the little grub screw that holds it all together, and some instructions for removing the roller after you take off the side bearing/pulley? Well done.

Hi Paul, I definitely agree with grumpy mate, well done!
Can't wait to see the pics when it is all apart; I want a gander at this plastic ring gear that causes probs.

Fantastic, will soak mine in RP7 and get into it, hope it works with mine
I always wondered what that little allen screw did.

Yeah, got my pulley removed now as well, put the machine on it's side and let heaps of RP7 soak through then lever like Pauly80 said.
First glance at the plastic ring/roller gear and it looks okay, will now have to try and work out how to dismantle the clutch to see why it's slipping.
Will upload photos when I have them

Glad it worked Kempe, I PM'ed you with some more pics but it sounds like you're now set.

It looks like I can't do anything more until I get a bearing puller or something simular this week end so I'm posting what I have so far. I've kept the pictures to a smaller size to stop this thread from exploding.

I'm no expert and doing this as a hobby. You'll probably find a better way however the pictures should help you with your project.


Close up of the grub screw holding the assembly in place. Remove or loosen it. This is inside the chassis.




Getting the pulley off ( A dramatic re enactment )It was necessary to jiggle the wheels/rollers as it started to slip out.




Before removing the bolts holding the roller assembly I used two hammers to take the weight.
This made undoing the bolts on each side much easier and meant I didn't have to take the weight when it let go. Undo about 5 bolts holding the assembly in place. 3 On this side and 2 on the other




Close up of the pulley side. I used a 19mm socket on the end with the roller in a vice to remove the nut.




Had to gently persuade the cover off.




The notorious plastic gear.





The other end has a bearing and circlip holding the roller in place (loosened off in this picture)



I'm going to get some advice about removing the bearings. I just went down to repco and they priced a bearing puller at around $100. Bit pricey, might try to rig up something with a steering wheel puller.

That's it until I get the proper tools - probably this week end.

Good luck, Paul.

---

I managed to get the thing apart but couldn't undo the centre nut on the roller as 19mm didnt fit for me, but the plastic gear looked in okay condition.
Made a new clutch out of 3mm gasket cork and refitted everything and was expecting it to work.
The new clutch bit in okay but still didnt have drive, will try again tomorrow.
Think I will have to dismantle the end to get a closer look at the plastic gear
If you want to dismantle the clutch just hold the spline end in a vice and make a special tool that enters the holes in the other side and unscrew it, it's a left hand thread so unscrew in a clockwork direction

Thanks Paul, that clears up several questions (including the mysterious thread on the end of the roller's axle, visible in the illustrated parts list).

You shouldn't have to buy a $100 puller just for this little job. If you can manage to support the roller with its axle vertical by sliding heavy plates underneath the bearing housing, you can tap on the axle with a punch to ease it out. It all depends on what odd bits of ironmongery you have laying about. Failing that, I think a local mechanic would do it for $50 to $80 per hour, and it should only take ten minutes.

Here's the clutch assembly dismantled with the new cork drive plate I made as the old one was badly glazed

What kind of adhesive are you going to use to attach the cork to the clutch member, Paul? I've seen a picture of one in the archive that seemed to have come unglued, and squeezed out radially.

I still have drive problems with mine.
When dismantled, the clutch lining was badly glazed and I identified that as the reason the clutch was slipping.
Made a new one out of 3mm gasket cork that looked very similar to what was already there, I noticed that Grumpy alludes to it being glued to the clutch plate, my old one wasnt and neither is the new one I fitted.
Fired the machine up and everything seemed good.
Lifted the rear end to watch the rollers and when drive was engaged and the hand lever depressed the rollers turned with no sign of the clutch slipping.
Lowered the machine to the ground and the rollers no longer turn with the weight of the machine on them, so I must be losing power transfer somewhere, although there is no visible sign of the clutch slipping.
My thoughts now are that the clutch is slipping under load because it's not glued to the clutch plate, anyone any thoughts or knowledge as to whether it is normal for them to be glued??
Do the replacements have glue already on them??

Hi Kempe, you've caught us on the hop, so to speak, because the Scotty 590 was the last of the breed, and I have had no personal experience repairing them.....However, the cutter and roller clutches of the Model 45 have cork linings and both are glued in place. I suspect yours would have to as well.

From what I have read the glue to use is a good quality contact cement such as Bostik Gel or Bear Contact following the directions carefully. The reason your machine may have stopped driving initially, was most probably caused by the cork lining coming unstuck
Please let us know how you get on.

PS. as an aside, that plastic ring gear in your pic is notorious for breaking; with age they get brittle. Have you thought about replacing it with a metal one, whilst you have the machine apart?

Mine is a Diplomat 430 I think but is almost identical to the SB 590.
I can see a crack in the ring gear but dont think it is causing my drive problem and will need to look at the online shop to see if you sell ring gear for a Diplomat.
I will glue the cork lining tomorrow and if I have a drive will take the plunge and get a metal ring gear if available, it only takes me 10 minutes to dismantle now that approx 40 years of being together is broken

Hmmm, still no drive.
Glued the clutch lining to the plate assembly and it made no difference.
The clutch catches and the pulley and plate rotate and with the rear rollers lifted off the ground the rear rollers drive.
As soon as the weight is on the ground the power is lost to the rollers and nothing happens, and the pulley and plate are still locked through the clutch. (no clutch spin)
Will pick up a new drive belt on Monday, but am clutching at straws now!!

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.

Hi grumpy, Pauly80 and Kempe, well at long last it seems we have got an great archive for removing the rear roller and ring gear of the SB 430 and 590 Diplomat.
I think Pauly's old man needs a mention also, as he helped immensely with the pulley removal.
It would be great if we can have some detailed pics of the new replacement steel ring gear....grumpy is right in his assumption, it is purpose built to fix the original prob with the cheap nylon gear...I honestly don't know what Scott Bonnar were thinking when they designed that piece of #*%$ .....oops! I guess I'm not being very "Diplomatic"

I think they were caught out, Deejay. Calculation would tell them that the ring gear didn't have to transmit much torque, and nylon gears are very quiet as well as not needing lubrication. The problem is, sooner or later someone will find a way to put a much higher load on that gear than anyone expected - either trying to climb a kerb, or during a service operation. If you have a weak gear, the normal approach is to ensure the drivetrain can't transmit enough torque to harm it, and I'm not sure they did that. Nevertheless I'm a bit sympathetic to Scott Bonnar, in this situation. However I do think they should have published a manual telling people how to dismantle that mechanism, and made the manual widely available. The combination of not enough information, and a fairly vulnerable gear, was bound to end badly in a lot of cases.

Here's the metal ring gear for archive purposes.
Fitted it today and everything works great and cut the lawns already.
Great to have the old SB back again as it nearly went to landfill and replaced with a cheaper rotary which would have been a shame for a Santa Anna Lawn.

Interesting design. They made the hub, web and gear a single item so it is easy to fit and service. However they chose to fabricate it from sheet, except for the hub. The hub is welded to the web, but the ring gear itself is fabricated from multiple layers of sheet, pop riveted together. They may have pop riveted the sheets after stamping them into circles of the right diameter, then cut the gear teeth, then bolted the fabricated ring gear to the web. However I notice that the gear teeth are triangular, not involute, in shape so I doubt they were cut: more likely they were stamped with the teeth included. This enabled them to use cheap stampings for the gear. The downside is that the stampings will be mild steel, so the gear is fairly sure to be dead soft. Also, the triangular teeth of the ring gear will not mesh properly with the involute teeth of the mating pinion, and because the pinion has so few teeth, it may lose the argument. On the positive side, the ring gear itself will still be a whole lot stronger and tougher than the nylon was. The hub should be fine, since it is now welded to the steel web.

With stamped teeth, this gear should have been quite cheap to make. Someone is probably making a huge profit on them.

Hi, I've just joined this site and have found this particular topic o be of great use as I've inherited a 590 and it has lost drive when engaging the clutch. I'm not mechanically minded or skilled so I've put the machine into a shop to try and get a quote to get it fixed.
Can anyone tell me how much the metal ring gear costs and where it is available from?
I live in country WA

I paid $132 plus delivery from Turf Machinery Services

Gezza, depending on whether you have examined the belt drive and clutches on your mower, you may have a much simpler and less expensive problem than kempe had. Most times, loss of drive is just a belt adjustment or perhaps clutch relining issue.

Thanks. I'll check with the repair shop and advise.

I have been to the shop and inspected the part and it is the same problem. The plastic has cracked in two places and the replacement has now been ordered.Thanks for this forum and the experts available to help.

Thanks for letting us know, Gezza - it gives us another useful case for the archive. I'll close this thread.