OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Scott bonnar diplomat 590

Hi guys I'm new to the forum and would like to say a big hello and say what a great site this is .
I have a drama I have just bought my first reel mower a Scott bonnar diplomat 590
It runs perfect but when I go to cut the grass it seems you nearly need to jog behind it
Am I doing something wrong as the handle needs to be pulled in for the blades to spin but this also moves it
Have I made a rookie mistake and bought a horrible type of mower
Cheers kev

Hi Kevin, and a warm welcome to the forum. It's great to have another Scott Bonnar owner on board!

Never having owned a SB 590, I am not aware of its idiosyncrasies, but would presume it is similar to the other Scotties in operation.

The Diplomat 590 differs slightly from the Model 430 Diplomat in that the 590 does not have a separate cutter clutch....so as you have found, when you squeeze the clutch handle, the slack in the drive belt is taken up and the cylinder reel and the drive roller then work in tandem.

The speed of the machine across the ground (as far as I can tell) would be controlled by (a) the throttle setting and (b) the amount you squeeze the clutch handle. The engine does not need to run flat out to achieve a good cut; just as you don't have to squeeze the clutch handle all the way in, to get it moving correctly.
Hoping this helps,

This thread shows the drive mechanism of the SB590:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=22699&page=1

As I understand it the belt drives both the reel, and the clutch pulley for the rear drum. There is no clutch for the belt on the 590 (but there is on the 430).
Here is the SB430 belt drive, showing the separate belt clutch and drum clutch:


Here is a partly dismantled SB590 belt drive:


The SB590 misses out on the whole belt tensioning lever: it has a belt tension adjuster inside the belt box, but no external way to declutch the belt.

On the 590 there is no belt clutch - when the engine runs, the belt runs and therefore the reel runs. However it has the same drum clutch as the 430, so the rear drum only runs when you squeeze the clutch, and the drum speed depends on how hard you squeeze the clutch. So, there are two ways to control the speed of the mower over the ground:
1. Set the engine speed at a level that provides just sufficient power so it does not bog down and threaten to stall when mowing. Generally, moderate engine speed should be sufficient, and excessive engine speed will make it necessary to slip the drum clutch more than necessary.
2. Expect the drum clutch to be slipping to some extent, all the time. It is designed for this, and will take a long, long time to wear out. Point 1 above is included as a sort of refinement: excessive engine speed wears everything out to no purpose, but even if you run the engine really fast, you just slip the roller clutch a bit more to control the drum speed to what is comfortable for you.

Using a variable slip rate on the drum clutch to manage roller speed is a traditional Scott Bonnar approach on their reel mowers whether they had chain or belt drive. The mowers had large drum clutches to ensure the clutches could be slipped for years without any problem developing.

Hi Grumpy, as I said in my above post, but perhaps not as eloquently.
With us both never owning a Diplomat....it is conjecture as to how they actually perform...my post is a "best guess" scenario. It will be up to aldot to tell us if our solution actually works.

Thanks for the helpfull info guys
It must just be a case of finding a happy medium with the revs and the clutch lever
In relation to grumpys post the clutch that is on the drum what is that used for cos if I have mine running the drum and the reel don't spin till the lever is depressed making that the clutch( tension on belt ) is that right
So what is the need for the one on the drum
Sorry if this is confusing

Ps mine has a clutch lever to engage and dis engage the belt ( clutch)

If the clutch lever that operates the belt is the large vertical one shown in my picture above, this would mean you have a 430, not a 590 - the 590 has no lever.

If you have a 430, with the clutch lever that tensions the belt, the lever starts and stops the reel and the drum clutch pulley. The drum clutch is connected or disconnected from that pulley by a lever on the handlebar, connected by a Bowden cable to the left side of the drum. If you do not have that control, the machine is incomplete and needs to be fixed. It is not really practical to operate it with the drum clutch permanently locked because you would have to bend forward to the lever, then the machine would bolt when you engaged the belt clutch. Furthermore you need the speed control the drum clutch gives you.

I suggest you post some pictures of your machine, so we can clarify what you have.

Cheers

heres the pics guys
you get the general idea
thanks for looking at them

This is your belt drive, from your post. It is a normal Scott Bonnar 590 drive.


This is your clutch control cable. I can't tell from the picture what it does at the lower end. It is presumably operated by the squeeze-handle on the handlebar.

Please post some pictures to show some detail of what the lower end of the clutch control does. It could operate a standard SB drum clutch, or it could operate through a bell crank to tension the belt drive. We discussed this question in a previous thread some time ago, without finding out the answer.

By pulling the lever the belt should tighten and drive is then engaged yes?
But the same belt spins the reel so if I tighten it up to spin the reel all the time won't it want to make it drive constantly
There must be a fine line on the adjustment if that's the case
Thanks again for this help

Kevin, if the bottom of the clutch cable is connected to a bell crank, which passes through the side plate of the mower and pulls the drive belt's tensioning idler toward the rear of the mower, it would work as you have said all along, and operate as a clutch on both the reel and the drum. That would mean that the mechanism inside the drum drive pulley does not contain a clutch on this model, unlike the SB45 and SB430. Because it looks just like the usual drum clutch mechanism I've always believed that's what it was, but your description of how it works suggests that it is a bell crank-operated belt clutch. Can you show us some closer pictures of the mechanism please, to clear this up?

also is there a manual for this model on this site
i paid th 15 dollars but cant seem to find it
cheers

Kevin, what I am trying to find out, is whether the clutch cable on the back of the side plate is connected to the belt tensioner on the front of the side plate. Here is the belt tensioner, circled in red:


Here is the operating end of the clutch cable, circled in yellow:


When you move the clutch handle on the handlebar, does the mechanism circled in red move?
Can you post a view of the clutch cable ending circled in yellow, that shows the underside of it where the cable attaches?
Can you post a top view of the side plate, so we can see whether the mechanism circled in red is exactly in line with the mechanism circled in yellow?

The red and yellow bits may be the two halves of something called a bell crank, which means that the two bits would be connected together and both have the same pivot shaft, passing through the side plate of the mower.

Hi Kevin, unfortunately we don't have an Operators/Owners Manual for the Model 590. There are 2 Parts Lists Manuals (One early, One later date).
Can you please try my method and let us know how you get on?

The parts circled are what the clutch cable goes too
And the shaft goes through to the other bit thats circled ( think you called it a crank bell)
Not near my computer at the moment so can't post a pic

Looks like a 590 with the cable removed?!?!?

which means it will either drive itself as soon as the engine fires (if teh belt has been tensioned right up) ot the thing will never drive itself or cut grass.

I'm looking at buying a 590 right now, but have been a bit put off since finding this thread. may continue looking for a model 45.

Fitzy

Hi Fitzy, the SB 590 cylinder reel and rear roller work in tandem...ie. you can't have one without the other.
You squeeze the clutch handle, the bell-crank over-centres; the belt tightens, and away you go, cutting grass and self propelled. You have not got the luxury of a cutter-clutch.

If I were you, I would wait for the Model 45, which is a better all round machine, and all parts are readily available; whereas the 590 is harder to work on; (especially the reel to bedknife adjustment).

I was a bit late getting to this thread, could have helped being a diplomat owner. Mines going very well, just being to dry to use it as much as last year..