OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers SB-MORRISON - need a rare part!!!

Hi all,
This is my first post and comes at a last resort...sorry!!
I have had sitting in shed for at least a decade an old Scott Bonnar Cylinder Mower, i have no idea of its history. Found roadside collection after someone tried to flog it for $300....written on side for sale $300!!!! After coaxing life back into the motor and bearings and so on I find that the plastic insert in the rear roller is worn down. It is used to drive the roller from the gear in the casing which is belt driven,
Only info i can find about the machine is a sticker. Morrison New Zealand No 64510. cutter is 16" and catcher and frame except handle bars are painted red.
I hope someone can help me here
Cheers
Peter

I think our reel mower guys will need pictures of that mower to be able to identify it, sorlawn. The reference to a plastic gear driving the rear roller sounds like an SB Diplomat (model 430 or 590) but that doesn't lead me to a Morrison sticker.

If you have a Diplomat with a broken or slipping roller drive gear, that is a characteristic fault in those machines, and unfortunately the plastic gear is no longer available.

Grumpy, I think you may be right about availability of the part. I will try and work out how to up load a photo later, tried now but no luck. I wonder if anyone has tried to modify this somehow to make the gears work again, but failing that i will use it for an excercise machine AKA push mower!!!

We need to know whether it actually is a Diplomat before we can discuss it, sorlawn. Scott Bonnar provided an aluminium replacement as a service part for a time, then a mower repairer sold fairly awful steel "gears" (they didn't really qualify as gears, but they did drive the roller) for years, until just months ago. I don't know of any remaining new ones available. However if you search "diplomat" in our archives, you'll find several threads giving details.

Hello Sorlawn and Global Mod Grumpy,

As Grumpy says, we need that picture.
This is, however, sounding more like a Masport-Morrison, branded as a
Scott-Bonnar. This may be the simplified design with a single clutch in the
belt case. More importantly, it has reduction gearing with plastic gearing in the
roller (I think).

I'm hoping it is - in that this opens the way to the possibility that there
may be some interchangability between the Masport and Diplomat transmissions:-
[the clutching is different but the reduction gearing may be the same].

So, we'll just have to wait for that photograph.

All very interesting.
---------------------------------
JACK.

Jack,
the cutter and rear roller is driven by one belt, and does have reduction gearing with plastic in the rear roller and metal drive gear.
another feature I have omitted is the front roller is 3 segmented wooden rollers (in good condition)
I will try again uploading a photo in the meantime is some one could tell me how!!!!!!!

Hello sorlawn and GM Grumpy,

Yep, that's the one.
So it has a metal pinion that works on a reduction plastic ring gear.
Grumpy might be able to tell us how similar it is to the Diplomats (that now have the same issue).

BACKGROUND
Masport took over Morrison in 1986.
In fact their current line-up of Olympic reel mowers owe their existence to Morrison.

Yours is a modified form of that - it was a cheaper version that removed the main clutch
and triple chain transmission and plate clutch and used a transmission that engaged the
reel and roller as one.

I think the first thing to do is this (assuming no one comes forth with a solution):-
Contact Masport Australia at http://www.masport.com.au/contact/general
Upload a photo and query a parts list and parts availability.




Relevant Posts:-
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=35924&page=1
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=12548

Hope this helps.
------------------------------
JACK.

The Morrison uses a plastic internal ring gear on a pressed steel mounting. That mounting bolts onto something not shown in the picture, but which is probably a steel web-plate and hub. The only problem it is likely to give is if some foreign body, or or perhaps a rather large overload, destroys the plastic ring gear. The Scott Bonnar Diplomat used a far less serviceable design. Here is a picture of the ring gear, from another thread:


As you can see, the SB version made the internal ring gear, its drive web, and part of its hub in a single nylon moulding, which was moulded onto a steel inner hub. Drive was transmitted between outer (plastic) hub and inner (steel) hub by knurling on the outside of the steel hub. The problem was that the outer hub was not nearly thick enough radially, and the result was radial cracks in the plastic as it strove to transmit the driving torque, which the knurling on the steel inner hub converted into a bursting load on the plastic outer hub. The hub in the picture had developed quite a number of radial cracks in the outer hub, one of which had propagated to the web, and right across the web and ring gear. Loss of drive occurred when the various cracks in the outer hub cumulatively enabled it to expand enough under load, for the outer hub to slip around the inner hub without rotating it. I haven't heard of a Diplomat plastic gear having lost drive due to a failure of the ring gear part: it is always the failure of the outer hub allowing it to spin around the inner hub, or the long cracks across the web which eventually form, propagating circumferentially and leaving the web in two separate pieces, with the hub isolated from the ring gear. I'm not sure the latter case has ever actually happened, however: some people break the web while struggling to remove the gear and its hub from the axle, and in some cases may think that fracture was already present.

Thanks GM Grumpy,

That has helped all of us in understanding the issues.
I think you have convinced me of the superiority of the Morrison design.

The SB Diplomat, as you know, was an Australian Design Award winner.
The basis for that award would have been safety (enclosed reel) and
manoeuvrability (rear catcher). The quality of design and manufacture
of transmission components seems to have been overlooked in the criteria.

In any case, I hope sorlawn makes an inquiry to Masport, and that
we receive notification of the outcome.

Grumpy, is there a set life to these plastics before they break down,
become brittle and fail (as compared to steel and alloys)?

Cheers
-----------------------
JACK.

Thanks guys, been busy today, you know its a sunday off...not!!
Cyber Jack has indeed posted the identical picture of the mower and will fire off an email to masport as suggested. will keep you in the loop........
Many thanks
Peter... Sorlawn...

hi all this is my reply from Masport..
Hi Peter

Unfortunately this machine is 20+ years old and there are no parts for Scott Bonner anymore.

Kind regards

Sueanne Griffiths

so back to square one, help!!!
I am wondering as a last resort to weld a little more onto the ends of the metal gears, say 2mm and see if this will then engage the plastic gears? As I say last resort.....

Hi Peter,

thanks for posting the reply for all to see.
As you now know, folks with SB Diplomats face the same problem.
It's a real shame that so many otherwise serviceable machines could be
forced into retirement because of the failure of one critical part.

I'm not sure of the response from members will be. Probably ... sorry.

From my understanding, the glimmer of hope will be in the increasing sophistication
of 3D printing technologies. In the photo below, the original worn part is on the
left, the 3D printer replacement part on the right.



Moreover, I have read about liquid metal printing HERE.

Just a few more years and a whole new industry may emerge in the replacement
parts industry for one-off parts at a realistic cost.

I guess there is also a warning in this story - for folks buying these machines
from auction sites. They could acquire what turns out to be 'horticultural boat anchors'.

Hope this lends some comfort.
----------------------------------------
JACK.

Hi Cyberjack, sorry I missed your post on the failure of SB Diplomat plastic gears.

Gears are usually made from thermoplastic, most often nylon, and they do age in the presence of moisture, ozone, photochemical smog, and various other noxious conditions. The modest temperatures likely in the Diplomat drum drive gear should produce very little effect. Hence I suspect the problem here is a combination of the design of the gear, and given the date of manufacture, the likely absence of reinforcing fibres in the plastic. You will notice that the broken Diplomat gear shown above, has not changed colour noticeably: it is still a rather pristine white, which suggests the material may be in good condition.

My guess is that if the design had provided either a greater radial thickness of plastic around the hub, or the fibre reinforcement normally used in plastic gears for the past 20 years, there would not have been a problem. Note that I am not certain fibre reinforcement was not used, I am merely speculating that this might have been the case, given the date of manufacture.

I may be missing something, but I don't see why SB could not have had the gear mould remachined as soon as the problem became known. It looks as if all that would have been required is a very simple lathe or milling/boring operation on the mould. Instead they provided what must have been very expensive aluminium gears as a service fix. Mind you, the Diplomat may not have been a sales success, so long-term solutions may not have been a priority.

It would certainly be very interesting to get a really close look at a NOS aluminium Diplomat gear, and work out the manufacturing process/es that was used for them.

I think Deejay has some knowledge of the use of aluminium gears, Gadge, and IIRC he said they became unavailable years ago. Given that the fairly awful aftermarket steel gear became unavailable last year, and we've had several people desperate for a gear of any kind since, there probably isn't much chance of them all having missed an NOS aluminium one out there somewhere. There will be used aluminium ones still in service though.

Yep, I realise that they are as common as rocking horse dung, even in-use examples!

But it would still be interesting to see just how they were made. I.e. single or multi-piece; gear teeth cast or machined; and so forth. The nylon gears were of course injection moulded - no mystery there.

Hi to Gadge and grumpy,
For archival purposes, here are some pics of the after-market gear manufactures by the now defunct Turf Machinery Services....



Note: This ring gear is NO longer available.