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.

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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!!