OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Reel-Type Mowers scott bonnar 45 rebuild

Hi all, we have just been given a Scott Bonnar model 45 and it is running well but is bit smoky and could do with some maintainence.
We are going to rebuild it to a working mower and not a show mower starting with the engine and going on from there, we will post pics of our progress as we go and if anyone could give us any tips it would be greatly appreciated.
Here is what we started with.



p.s. love the forum and enjoyed looking at the gentleman's post who rebuilt his h4-4a.

Hi Mr Jones, welcome to Outdoorking.

Since you are starting your tidy-up process with the engine, I suggest that you continue to use Mr Bonnar's excellent thread on reconditioning his Kirby Lauson as a reference, and keep us posted through this thread. We will be happy to help at any time, and you can just report progress if you don't have questions. It will be useful to develop another thread featuring both a Kirby Lauson, and an SB45.

Incidentally, your reel looks as if there has been welding done on the blade mounting points. Have the blades been replaced in the reel?

Hi Mr Jones, and a warm welcome to the forum. Its great to have another Scott Bonnar Model 45 owner on board.
Thanks for posting the pics, yours is an early twin rail engine deck, still with the early SB logo on the handle cover. It will look a treat when restored, mate.

Hi Grumpy and Deejay,
The reel has had one section of blade replaced but looks well done with the right profile. Will have it ground later in the project.Currently stripping externals from engine and finding 30 years of accumulated dirt build up under everything.Down to the flywheel now and would like to know if thread is standard or reverse.The vanes are razor sharp which makes it hard to hold

Got the flywheel off,has a std thread.Would like an opinion on whether the bore and piston would take a light hone and a new set of rings. Have the motor fully stripped down now waiting on seals. Is it hard to remove and replace the smaller of the two oil seals?

Hi Mr Jones, grumpy is our forum Briggs guru and he hasn't been on line lately....he may be on holidays. Please be patient, I am sure he will pop in from time to time, and give you the correct advice

sorry dejay but it is not a b&s its a kirby

Ummm, wow, I have never seen cooling fins blocked to that extreme for a long time, Owing to that is probably why the rings fried...

That bore and piston does not look happy, however I have used worse, a light hone on the bore with a new set of rings at worst would lower the oil consumption but it may never run at its peak again with that sort of damage without a rebore, new piston and rings and otherwise a full reco.

Bearing in mind a new engine of suitable size whether it be honda, briggs, etc can be had for a few hundred dollars or more depending on what breed you decide to go with...

Motor had sufficient power and ran really well prior to pull down but was a little smokey. The piston did clean up well with some kero and a paint brush so assume damage was light. The new briggs 2100 series looks a nice motor and can be bought for around $300 but that would spoil the fun of the rebuild and its keeping my son and I busy. If it does not work out its no big loss. Need to make a valve spring depressor next and work on that while we wait for oil seals. While I remember the rings I have received have an oil ring, a square section ring and a ring with a 45 degree angle cut on one side only. Does anybody know which order this ring would fit???? Can forward photo if required.

ok. Managed to get motor back together with a couple off issues. Found out to late that the smaller oil shaft needs to be fitted on start of assembly when fitting the crank. Also managed to bend the limiter connecting rod but managed to straighten this up and save it. Motor appears to be oil tight but runs rich. looking at the carb I thought I would find a rubber seal in the needle hole but appears to be metal on metal. Can anyone confirm this is correct? Will post a few picks and hope a few experts will look over our handy work.

GOOD SAVE THERE
SHOULD LOOK NICE ALL PAINTED UP YEAH

HAVE ONE THAT WAS AS FILTHY AS YOUR
I SPENT SEVEN OR EIGHT HOURS ALONE JUST CLEANING OUT THE CARBY
ALL WORTH IT IN THE END LOOKS CARED FOR NOW

Hi Red, and its great to see you back at OutdoorKing.
As a moderator, I would like to point out just one thing mate, please don't use all capital letters in your posts, as it appears that you are shouting. Capital letters in a post are used for emphasis. This, apparently, is part of forum etiquette.

Hi Mr.Jones, I notice that you have been popping into the forum lately, how is your rebuild going? Some more pics of your machine would be nice. Did you get all the engine probs sorted?

Hi Deejay,
Sorry for delay but body parts are currently at the blasters. Engine is back together and running fine but still a little rich which I believe is a result of the needle/carb issues. Will post more pics on return of parts. Appreciate the follow up.

No worries Mr. Jones, looking forward to seeing the pics....Glad to see that you've got the engine running...Good work mate!

I'm used to the carburetors on Kirby-Lauson engines having a mixture screw. With those, all you need to do is rotate the mixture screw clockwise until they aren't rich any more. I'm sure you'd have done that if yours had such a screw, so I'll summarise the problem and possible solution as if there were no mixture screw on your carburetor.

The carburetor needle-and-seat can contribute to rich running if there is leakage between the two, and the float is unable to shut off the supply of fuel to the float bowl. You can test whether this is happening very easily, just by leaving the fuel turned on for a couple of minutes when the engine is not running. If the float bowl floods and petrol drips onto the ground when you do that test, you need to check for leaky needle/seat, or sticking float pivot mechanism, or a leaky float (which no longer floats properly due to having fuel inside it). Conversely if the carburetor does not flood when you do that test, you need to look for another source of rich mixture. The obvious candidates would be choke not opening fully, obstructed air cleaner, float level set too high, main jet not seated (or fibre washer omitted from under head of flat-seating jet) so fuel can by-pass it, or oversized main jet. Oversized main jets are not all that unusual - sometimes previous tenants have drilled them out because it seemed like a good idea at the time.

Thanks Grumpy,
Will inspect carb on the weekend for you described faults.Air filter is new so can pass on that one.Have attached pic of carb so you could highlight mixture screw please.

I have circled in red, the only mixture adjustment you appear to have (unless there is one on the other side of the carburetor). I'm pretty sure it is just idle mixture though, because it is located at the throttle butterfly rather than at the venturi. You could check whether it has any effect, both at idle and at full speed, to verify this. If it is just idle mixture and your rich-running problem is at full speed, you need to look at Plan B, in my previous post.

You have said it is running rich, and we haven't discussed what makes you think so. Can you describe the symptoms please? For example, if it is blowing sooty black smoke, it is running very rich. If it is blowing a short black puff on start-up it may be nothing at all, or a governor issue. If it is blowing bluish white or blue smoke, that is oil and might have some very simple cause -in particular, on a Tecumseh engine, you might have put the crankcase ventilation valve in upside-down, which happens a lot on those engines. (The little drain hole in the valve housing has to go at the bottom, or oil will pass through the breather into the engine.)

Smoke appears to be sooty as you can see from the exhaust. Added screen to protect new air filter from the direct blast of dirt and hot gases. Appears to be a basic design floor? Have not had chance to run motor recently as have stripped rest of mower but should give it a go and inspect your suggestions. Think it will be needle related. Any way parts now back from blasters.

If you haven't done so already, I suggest that you try running the engine with the new air filter removed, in case it is the filter that is causing the rich mixture problem. Also, check once again that the choke is fully open when it is smoking.

I can assure you that the black smoke is not caused by a design fault. I dislike those old Kirby-Lausons, but they were not ludicrously bad: there is no way they blew black smoke when running unloaded. My criticism of them is that they are not as nice as a Briggs or Honda, but they are very reliable and extremely durable. You have a serious carburetor malfunction, and it will damage the engine if you run it that way.