OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Reel-Type Mowers Scott Bonnar 45 - Clutch Resto

just joined the forum after acquiring a scott bonnar reel mower,(found it at the scrap metal yard when I was dumping some copper off) brought it home and cleaned it up a bit and she fired up. Anyway, it does need some love, the reel doesn't disengage it just spins when you start it and stops when you turn the engine off. After reading the forum topics and seeing some photos of previous members, I noticed my mower doesn't have the screw in the clutch drum )closest to the engine). would this be the reason the the clutch doesn't engage or disengage. If it isn't, what would be the reason and how do I fix it?. Need help!

Hi Jeremy, welcome to Outdoorking.

Our reel mower guru, Deejay (a died-in-the-wool Scott Bonnar 45 freak) is currently away from home for a family birthday, so he may not answer immediately but can certainly sort this out when he gets a moment to reply. Essentially, if the engine side clutch-half can slide along the crankshaft, the cutter clutch will not disengage, and that sounds like your problem. However SB/Rover used two different methods for holding that clutch half, a captive cotter pin on the earlier units and a pair of grub screws on the last ones made. There can be problems over time, especially with the cotter pin type, so Deejay will want to see pictures of the mower, the clutch, and the crankshaft where it goes into the engine-side of the clutch. If you post these right away, he will be able to help you more quickly when he comes on line.

Had trouble putting up photos of the mower. surely there's an easier way of adding photos to the message, but any way, i believe it is the earlier type models with the captive cotter pin. I noticed on the parts page it doesn't show the part no. for the captive cotter pin. What is the process on ordering this part? I also noticed there is a bit of play on the clutch body around the crank shaft of the engine. Would this be the clutch body has worn as well as the cork inner cone and needs to be replaced? also on the carby the idle spring (I think, its the bigger of the springs) has lost its tension and the engine doesn't maintain constant revs when its going. Can you get a generic spring with the right tension for the engine or do I have to get a scott bonnar genuine part?
sorry about the vagueness and the lack of photos. But do your best.
Thanks
Jeremy D

Sorry, Model no. of the mower is 45058. Don't know if that helps any.

We need the pictures, Jeremy. Just use the fifth icon from the left at the top of the Quick Reply window. Browse to find the picture on your hard drive, press Open on your Windows Explorer window, then Add File From Your PC, wait for it to upload, then All Done.

It sounds as if you have a problem with the engine side clutch half, the captive cotter pin was a barely adequate design solution, and it is not unusual to end up with the bore of the clutch half worn and the cotter pin no longer restraining the clutch from moving toward the engine under spring pressure. The cheap and not very good solution is to put a collar of just the right width on the crankshaft so it bears on the upward step in diameter right near the engine, at one end, and on the engine-side clutch half at the other end, thus keeping the clutch half from sliding along the shaft. If the clutch half is still a good fit on the crankshaft it can work reasonably for a few years, but if the clutch half is loose, you will have to replace it. The good news is that the replacement clutch half uses two grub screws at right angles instead of the captive cotter, and it is likely to be a permanent solution.

Please post the long string of numbers stamped on the cooling air cowl of your engine, if it is a Briggs and Stratton. We'll see if we can find a parts list for it, to identify the correct governor spring. (If you have a very early SB45 with a Kirby Lauson engine, we can probably even solve that problem, but we need pictures.)

The clutch has slid along the crankshaft until it hit the step-up in diameter right at the engine's crankcase cover. The clutch operating lever then doesn't have enough movement to release the clutch. I can't see the cotter: has it fallen out altogether in that picture?

The engine's governor spring is trashed and will have to be replaced.

sounds as if I'm up for a new clutch body half as the cotter pin is missing and by the sounds of it its not worth replacing the pin if its not really a good design. If and when I purchase a new clutch half, what sort of gap if any, should there be between the engine and the clutch body? Also interested in looking into a new engine for the mower. What should I look out for with places selling engines that they say are compatable to scott bonnar mowers. I believe the crankshaft should be 3/4 to fit the clutch body. Is that correct?

Jeremy, I think you need Deejay's involvement to do the set-up and adjustment of your clutch. He posted a thread on it recently though, in the Scott Bonnar reel mowers forum, and that will set you on the right general track:
https://www.outdoorking-forum.com.au/forum/u...p;Words=clutch&Search=true#Post39243

The SB45s are pretty old now, and we are seeing a rash of clutch halves that use the captive cotter design, coming very slightly loose then rattling on the crankshaft enough to wear out and become very loose. Fortunately the clutch halves now available do not use captive cotters - they use two grub screws at 90 degrees to each other, one of them directly above the key. That is a traditional British design that works very well. Can't say I have much respect for the captive cotter system. Hence if you replace the engine-side clutch half with a new one you should have a permanent solution.

Clutch halves are available with both 3/4" and 5/8" bores, to suit the two available crankshaft diameters. However as far as I am aware, just about all modern horizontal-shaft engines in the 2.5-4 hp range usually have 5/8" shafts, though other sizes may be available as factory options. I suggest you should look at various engines, choose one, check the standard shaft diameter it comes with, then order your clutch half. There are standard layouts for mounting bolts and output shaft positions for those engines and most common types will conform to them, so the engines will be a straight bolt-on fit to your SB45, but you need to check anyway. We had a recent thread where someone bought a nice but unfortunately non-standard small Japanese engine, and had to mount it on an adaptor plate. Nearly all the engines fitted to SB45s as replacements are small Briggs or Honda models, which fit straight on - but you have to watch the shaft length and diameter, because they have optional shafts and you might happen to choose an engine that has one.

The simple summary of new engine choices I would offer is that you can buy a classic side valve Briggs (probably of 8 cubic inches displacement), or a modern pushrod OHV Honda (probably a GX120), and either can work very well. The Honda is more elegant and pleasant but costs substantially more. I personally would avoid any Honda model that is GC rather than GX: these are OHC engines rather than pushrod types and are marketed as "residential" where the GX types are "commercial". In other words, there is a large difference in how many hours' trouble-free work they can be expected to do and how practical it would then be to overhaul them.

Hi Jeremy, and a warm welcome to the forum. It's always nice to welcome another Scott Bonnar Model 45 owner on board.
Sorry for the delay in replying, my wife and I were marooned in Queensland and had only limited access to the internet.
Thanks for posting the pics, it makes it mush easier to diagnose any probs your machine may have.
Thanks also to grumpy for his replies; he has put you on the right track....you will need to replace that inner clutch half.
Could you please remove the chain case cover and take some pics of the chains and sprockets....the latter where the chain does not cover the sprocket....we need to see the condition of the sprockets.
Also, can you please take some of the cylinder reel and the bedknife (bottom blade).
Once again Jeremy to OutdoorKing.

Recently bought a new outer clutch housing and inner clutch lining. when put them on the mower and started it up it didn't engage and disengage all the time, only sometimes. I decided to mow the lawns and tinker with it when I finished because the lawns desperately needed it. Half way through mowing the thrust pad melted. Would this be because the clutch fork needed to be backed off or does the clutch set up need to be slid away from the thrust pad a bit. I noticed from other posts the location of the clutch fork when engaged and disengaged that it wasn't too pronounced past vertical that it needed to adjusted.

Thanks
Jeremy.

Hi Jeremy, you will have to get a new thrust pad if you haven't already and re-adjust the clutch.
Please check out this thread HERE and it should explain that there has to be slight clearance between the pad and the clutch cone. Please re-watch the video also.