OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Diplomat 590, belt setup

Hi guys
I have recently purchased a diplomat 590, while still looking for a sb45.

I'm having trouble working out the belt setup, can anyone help with how it should look? Any pics would be great

I'm able to dig out my 590 and take a pic but it won't be until tomorrow afternoon. It was pretty simple from memory

Here is a picture of the belt drive, from another thread:

Good one grumpy, I knew there was a pic that I'd seen but couldn't remember in which thread it was...

Barry, a warm welcome to the forum, It's great to have another Scott Bonnar owner on board, I am sure that you will find some info on the 590 and the Scotty 45 in the Parts and Manuals area. Subscription to that area is required, but the manuals will come in handy in future.

Thanks guys, should it be a stretch to get the belt on? I have a brand new a38 belt.

The belt should be easy to put on, and according to the marked up parts list in the manuals section, A38 is the correct size. Remember to move the clutch lever on the top of the belt housing forward (Park position), to relax the spring that pulls the belt tensioner back into the belt. Then you can loop the belt around the pulleys, and slip it behind the tensioner, pulling the tensioner forward slightly if necessary.

thanks grumpy. I think my model is slighly different to above, in that I dont see a manual clutchlever.

I'll have a play this arvo

Can you post a couple of pictures, Barry? It sounds strange, so it's worth documenting and figuring out.

does the photo above help ?
the top photo of the one posted shows a pull type level which im assuming puts it in park or drive. Mine doesnt have this, and wondering if its strange that the whole process is linked by just the clutch from the handlebar ???

Well, I got the belt on, and cranked over, but slipping a fair bit (has new steel drum gear)..noticed now the reel is stuck, so in the process of pulling the whole thing apart

Barry, the handlebar clutch normally only operates the drum clutch, controlling forward movement. The park/drive lever stops everything (reel and drum), by relaxing the tension on the belt that drives everything. I've never seen one like yours. We can see if anyone else has seen one like that, but the mechanism looks home-made. I'm wondering if it is not the previous "tenant's improvements" which have left you with something not very usable. Deejay, have you seen anything like this belt drive?

If the reel is stuck either it is adjusted too close to the bedknife, or the reel bearings have seized. You might check the adjustment before pulling the reel out.

Hi Grumpy, no,I have never seen that belt set up before , then again, I have never clamped my eyes on a Model 590 before...the pic you posted may be a Model 430 Diplomat, which, one would presume be the same as a 590....but, there may be differences between the two....
I cannot see the holes drilled for the handle...I think this may be a different set-up entirely....
I will make some inquiries early tomorrow as it is a bit late now....

above pic shows the front sticker which is slightly different to the ones ive seen in various posts.

The first problem I seem to see at the moment, is that there appears to be, in effect, no automatic belt tensioner. The belt is tensioned manually with the screw and nut. To fit a new belt you'd need to slacken the manual tensioner all the way, then fit the belt, and adjust up the screw and nut again. Then you'd have to keep watch on the belt tension, adusting it as necessary. This is the system that cars used back when they had V belts driving their accessories, before serpentine belts with automatic tensioners were adopted. It can work, it's just an extra maintenance item.

The second problem I believe I see at the moment, is there does not seem to be any way to stop the reel when the engine is running. I would regard that as dangerous. There may be a clutch in the engine output shaft, but if so it is concealed by the safety cover in the picture above.

Can we please have a pic without the cover....It seemes that this is an entirely different set-up to the Model 430 Diplomat,

Hmm so on these there is a second lever to drive it? I think mine is missing the drive one, perhaps the ring gear in mine isn't dead.... I will save that for another thread. Once you get this sorted can you put up a couple of pics of where each lever directly connects to?

Joe, as I understand it, the belt drive SBs have a handlebar lever that operates through a Bowden cable to engage the clutch that is built into the drum drive pulley. The 430s at least, also have a "Park-Drive" lever that tensions the drive belt. The lever sticks out from the top of the drive cover. So for the 430, you start the engine in Park, shift to Drive when you want to start the reel rotating, then squeeze the handlebar lever when you want forward drive of the drum. Of course for close manoeuvreing and backing up, you just push it with the handlebars without engaging the drum clutch.

If some of the mowers don't have a "Park-Drive" lever, it seems like they must have a lever operated clutch in the engine output shaft, like the chain drive SBs, or there would be no way to run the engine without running the reel. I don't know about you, but I'm not going to tune up a mower with the reel running.

Hi to All,
we're really flying blind here...I just downloaded the parts list for the 590....it's a different machine from the 430....without seeing the machine, I can't figure out how it works...there doesn't appear to be a cutter clutch...

My recollection is that at least some of the belt drive models have a rear catcher. Depending on the geometry, that could call for a shroud over the reel, reaching to the back of the mower. If the reel is shrouded sufficiently, there wouldn't be a safey concern over the reel running all the time. (The blades run all the time on a rotary mower, and it isn't all that unsafe so long as you keep all four wheels flat on the ground and keep your feet away from it.)

thanks for your help guys. I might have a play and take some more pics on the weekend..

Yesterday I picked up a SB45 17inch from evilbay, and gave it a run.... runs a little rough, but cuts well. Aim is to slowly restore.....

Hi Barry, I think you will find the Model 45 easier to work on, I have had one for years and the good thing is all parts are still available.... they were the most popular model that Scott Bonnar made...so much so, that after Rover took over SB, they kept it in production badge engineered as the Rover 45.
There are manuals and parts list in the Manuals area on this forum.
Can you please post some pics of your new machine?

Hi there, sorry for the poor quality of the photo but is my belt / clutch setup. It has the handlebar clutch setup which when at rest (deactivated) the drive and cutter drum is disengaged.

According the engine production (99% sure its original) date it is circa 1980 model.

Hi fritzymark, and a warm welcome to the forum. Its great to have another Scott Bonnar owner on board. We all like to learn new things and tinker here.
Thanks for posting the photo of your 590...its easy to see how yours works because of the Bowden cable and the tang welded to the chassis frame to support and adjust it....if you compare that with the pic on page one of the topic...the belt set up is the same except there is no tang on which to support the cable....its got me tossed how it can drive.
Once again, fritzymark,

It could work just as well if the crank pulled by the Bowden cable in fritzymark's machine is actually a bell crank in the original machine, with the operating lever on the opposite side of the side plate.

Hi Grumpy, that's just the thing....the Model 590 doesn't have a lever on the opposite side.....how does it engage the drive?

Deejay, I was wondering if it had the Bowden cable termination on the other side, rather than the long hand lever that the 430 has. In other words, a bell crank, but a short one.

not a comment or any help but i to have a diplomat thats model 430 a runner i was wondering do the chain drive models have a constant speed mine tends to bolt its hard to keep an average speed with the clutch lever is this due to riding the clutch or the belt heating up with the lever all the way out it tends to make me run behind not literally of course know what i mean a slight jog obviously it should have a steady walk not a run is this why there not that popular also the catcher has a tendancy to fall of the engine however a briggs 3 hp runs like a swiss clock even after yrs of dormancy it also says on the instruction manual its an edge trimmer any one used it as an edge trimmer it definately looks dangerous no covers maybe never happened the part no for the trimmer is434394

Hi impala, and a warm welcome to the forum. It's great to have another Scott Bonnar owner on board.
In order for us to answer correctly...we need you to post some pics of the machine from different angles and especially the troublesome areas...
Once again, impala, to the OutdoorKing forum.

A bit late to reply but I couldn't help myself, I just mowed my lawn today with my SB430 and it is hard to drive slow which is a proper pain in buttocks when your in a small area. A new belt and low rpm would be good I think. My belt slips making it slow to take off when the revs are up.
As for the catcher falling off there's a spring clip that seems a little weak and my catcher has fallen off a couple times because of it. A stronger spring should solve that.