OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers It was going to the tip

A neighbour had put this mower out for council rubbish collection.







As you can see, it's a Scott-Bonnar Diplomat with a Briggs 3hp engine.

I've never played with one of these before, so I have a lot to learn.

It appears to have been rather lightly used but hasn't run in several years. Seems to have been out in the weather for a while.

Lower blade & reel are in good shape, aside from a bit of rust from disuse.

Recoil mechanism on the starter is probably rusty as it retracts the cord very slowly.

I've pulled the cylinder head off to get a look at the bore. Looks OK, no scuffs or scoring. The motor doesn't spin very freely, bottom end might be full of water. There's no spark when cranking the motor. I'll be pulling the motor off the mower and having a look inside the crankcase next. The petrol tank was full of water when I brought it in the garage.

Haven't been able to get the left side cover off yet so I don't know if it has a belt or chain drive. Penetrating oil is doing its thing. When the park/drive lever is set to 'drive' and the motor is cranked, the mower moves, so whatever is in there is still working, it seems.

I have a brand new Tecumseh 3.5hp engine in a box in the garage, bought for a minibike that didn't get built. I have reasonably good hopes that I can make the original B&S engine work, though. It doesn't really look too bad so far. I'd like to put the mower back in service with the original engine if possible.

Any advice or information you can offer on this mower is most welcome.

Thanks!

-Brian

First, welcome to the forum Brian. I agree, your Scotty looks to have been either little used or gently used, and should be an enjoyable project leading to a good result. By coming to Outdoorking you have come to the right place to follow your mower interest - there are many enthusiasts here, including some Scott Bonnar afficionados.

As a first step on your Diplomat, try this thread:
https://www.outdoorking-forum.com.au/forum/u...Words=diplomat&Search=true#Post17291
A search on this site for "diplomat" will turn up some other information as well. As you can see, the Diplomat was a belt-drive Scott Bonnar; they also made chain-drive models (with numbers such as 33 and 45 instead of model names), which turn up here more often than the belt drive ones.

You probably will not have much difficulty getting your 3 hp Briggs engine working properly, and of course people on this site will be happy to help. If there is a lot of water in the engine's sump though, you need to remove that properly. If there is plenty of oil as well as water, there may be enough oil film on the bearings and camshaft to have prevented corrosion damage, but you can't tell yet. Of course there will probably be water in the carburetor, if anyone has tried to start it with water in the fuel tank.

The slow retraction of the cord starter may be due to water/corrosion. You will need to remove it and service it. You can find information on its little mysteries with a search of past posts on this site - essentially it may have rust, and it requires careful cleaning and a rather special lubrication process involving one drop of oil in just the right place (the spindle bearing) and no oil whatever elsewhere in the starter. If you work on the engine one step at a time and keep us posted, we can probably help make this a fairly orderly process. The old 3 hp Briggs is a nice engine, and if it isn't damaged you will probably be happy with it.

Hi Grumpy, thanks very much for your informative reply.

I'm no expert on B&S motors but they haven't changed a whole lot since I was taught to work on them in high school in the late 1970s. I would not be surprised if this mower dates to my high school years!

I do plan to take this somewhat slowly- giving myself about 3 weeks to get it cutting grass. Motor off, pull flywheel, split the crankcase, inspect bottom end, renew bearings & gaskets as required, check magneto coil, disassemble & inspect carbie, repair as req'd, get a look at the drive belt & renew as needed, reassemble the lot and have a go.

I do like to use a catcher because I compost my grass clips. If there's a suitable catcher lying in someone's bonepile somewhere that could be had for something less than a fortune, this pensioner would be very happy to hear about it. Will beat getting my socks full of clips and raking them up.

Once again, thanks very much for your help!

The Diplomat used a rear catcher, where the more common (chain drive) SBs had a front catcher. I don't know how rare those catchers are - Deejay will know and can probably suggest how you may find one, or one of the members may have one.

If your B&S is 1982 or later it has Magnetron (breakerless) ignition. If it is pre-1982 it has breaker points. You can find the manufacturing date from the series of numbers stamped on the engine's cooling cowl: the first two digits in the third (last) block of numbers are the last two digits of the year of manufacture (e.g. 76061708 means the engine was made in 1976).

Once the engine is running properly, you will need to have a look at the rest of the machine - in particular the clutches and the cutting system: the reel and knife. I noticed that your reel has not been resharpened much, if at all, so it should last a long, long time with proper care. The bedknife may be rusty, though. If it is severe it is likely to cost you money.

you lucky bastard

Thanks again for that, Grumpy.

I've gotten a better look at the reel & knife blades today; they appear never to have been resharpened. The paint isn't even fully worn off them. The rust is only light, surface corrosion. They don't appear to have been sitting in a puddle or anything. I should be able to take that rust off with a scotch brite (green plastic scrubber for dishes) or at worst, some 0-00 steel wool. Don't want to use emery cloth or sandpaper on it.

Just pulled off the cooling cowl so I could see the date code data. It reads:

MODEL TYPE CODE
80202 0880 01 82022303

From this I guess it is from 1982.

Still haven't been able to break loose the screws holding the drive belt cover on. They're slot-heads and are not budging even though I'm tearing the heck out of the slots. May have to Dremel the heads off and replace them with something else.

Thanks, mate

heh, we'll find out how lucky I am when I split the crankcase. One thing's certain, this machine is mostly suffering from lack of use as opposed to mowing a few bowling pitches a week all its life. It's a bit like finding an old car forgotten in a barn for a few decades.

Your engine was made on 23 February 1982, so it should have a very early Magnetron ignition as far as I know (I don't know the exact date of the changeover).

If the drive belt cover screws are cheese-head you can usually grip the outside of them with vicegrips and undo them that way. If they are roundhead you are out of luck. I'd probably try to undo them with a punch (center punch or cold chisel) on the outermost part, working on opposite sides for successive taps. It usually works, and if it doesn't, you still have to cut the heads off them, which you would have done anyway.

It sounds like you have been extremely lucky to get that mower. I don't recall whether the catcher was the steel-base canvas type - if it was you can probably make one fairly easily, but for such a good mower it would be much better to have an original one, at least for show (you might use a rougher one in practice for everyday mowing - canvas catchers are not very durable).

Thats a good score Brian, you should be able to get that going again.

Hi Brian, great score there, mate. You've got yourself a Model 430 Diplomat belt drive. The original catcher was purpose built made of hard plastic, and finding one may prove difficult.
to the forum Brian, best wishes,

As this thread is over 2 years old, I will now close it.