OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers just bought this

got this baby off ebay, note the custom exhaust. this is my first scott bonnar and first post so i hope it works and i havent stuffed it although its a fair bet i have.
the motor seems to have decent compression despite the dodgy silver paint but the front roller is wobbly and the reel seems stiff to turn, this may be due to some surface rust on the edges and the fact i have no idea what im doing.

Welcome to Outdoorking, biglenny. The exhaust looks as if someone has just welded a piece of tube onto the original Briggs muffler, probably because that side of the muffler had rusted away. It should be replaced with a standard Briggs muffler, of course. It is usual to do a tune-up on the engine when you first buy a mower: change the oil, inspect and gap the spark plug, clean or inspect the air filter, make sure the speed control and kill switch work properly, and see if it starts easily and runs smoothly through the speed range without hunting. I haven't been able to see what kind of carburetor you have there, but it might be an early type with the choke in the air cleaner. Just make sure the choke works properly, including having full movement.

The front roller is a wearing part on those SBs. Yours looks to be the type with the plastic end caps. These need to be replaced when they wear out.

If the reel (rotating blades) is not free to turn, there are two likely explanations. One is that the bearings have deteriorated. The other is that either the bed knife (fixed blade) has been adjusted incorrectely or there is rust on both fixed and moving blades, reducing the clearance. The latter is the more likely cause of the problem. Any rust will need to be cleaned off carefully, without rounding the corners of the blades or removing metal.

Please keep us posted on your progress in getting it properly tidied up. There is quite a bit of craft in adjusting the blades, and people here can help you with that, but there is a lot of information in the Outdoorking archives that you might look at first.

hi your front roller end caps are alloy latter types have plastic end caps regards steve.

believe it or not the muffler is actually intact. the exhaust tip is from what i'm assuming is some sort of pimp my mower gone wrong. the dude i got it from advertised it as complete, only needing a tune up to get it going. LIAR. lucky i'm a nice bloke. it's a project. more photos to come.

The fact that somone wanted to 'Pimp' their mower is something i find both funny, and sad...

Hope she comes up well for you!

We could be charitable and say he just didn't like the smoke and oil droplets getting blasted onto his pants by the original muffler (assuming the old Briggs is about ready for some new rings).

That is a fair point grumpy, And i hope its the case.

Heck, i remember our old mower when I was a kid, an old red rover utility with a black briggs on it, vertical start, i had a go at mowing for the first time at 8 (Under close supervision) but ran for the hills the moment it shot a good lot of flame out the old muffler!

Sounds like it may have been time somebody checked the tappet clearance of that exhaust valve, Ty. That and a lapping job might have prevented a nasty experience.

Kids' first tries at operating engine-driven equipment can be a bit traumatic if things go wrong. I recall my first exposure to driving was a three-wheeled motorcycle (Turner Tri-Van) in the back yard at age 11. Not knowing any better, I rotated the twist-grip throttle the wrong way to slow down. The vehicle finally came to rest with its back wheels jammed against the back wheels of two very valuable antique cars, and the trike's engine still screaming while its front tyre was still skidding on the bricks. At that point I tried moving the throttle in the opposite direction. Aside from a U-shaped back axle on the trike, and a few nightmares for me, no harm was done - but I still remember it quite well. Didn't seem to learn much from it though: I put my younger daughter on a postie bike at the same age and she did the same thing, but figured out the error before she hit anything. Maybe the younger generation are smarter than we were - they certainly claim to be.

after having a jolly good look at the rest of the site i haven't seen any resto's done in a way other than better than factory original. the pimped look may be a new thing, if done in the right way with a lot more thought and care....
hmmm im starting to get a few ideas here, black frame, red engine with some chrome work. custom handlebars and braided fuel lines. sort of the hot rod look while keeping the mechanics standard so it still cuts the grass well..
thoughts???

That sounds like a remedy that would well have helped the old beast, sadly it is long gone now (Hope to find one the same oneday)

As for the generations, cant say i'm much of a fan of Gen Y (my own) as a collective, to happy to throw than fix!

And Lenny, you might just start a new craze there, who knows!

I can't see an argument for saying that pimping your mower isn't legitimate, lenny. Like over-restoration - which is not uncommon among collectors' mowers - it becomes an art form rather than preserving a heritage. We all have different tastes in these things - I prefer antiques to look old, for instance, but some people want them to look new, and others want them to look like a modern interpretation of the same artistic theme.

To put it more bluntly, I can't stand Harley choppers, but I can't stand original Harleys either. I wouldn't like to see a pimped Jaguar D type, but if someone wanted to cut a hole in the bonnet of a 2+2 E type and mount a GMC 6-71 blower on it, I'd say, "That's a car that truly deserved what it got." And that goes double for an XJS.

So, your mower is not rare, so you aren't buying the Mona Lisa and having your wife's face over-painted on it. Nobody is being denied a part of his or her cultural heritage. What you are doing is inventing a new art form that could become popular, and even profitable. Think of it as creative destruction. Schumpeter would be proud.

who?

[quote=grumpy]
To put it more bluntly, I can't stand Harley choppers, but I can't stand original Harleys either. I wouldn't like to see a pimped Jaguar D type, but if someone wanted to cut a hole in the bonnet of a 2+2 E type and mount a GMC 6-71 blower on it, I'd say, "That's a car that truly deserved what it got." And that goes double for an XJS.[quote]

ha ha there used to be a XJ6 getting around here with a monster v8 with 6-71 blower and a 3 barrell bug catcher getting around here, speaking of bugs there also used to be a VW beetle with a frount mounted 308 around here as well. im stuffed if i can work out how he ever got that thing registered but it went like mad.
as far as the bikes go id rather a "71" norton commando but i dont mind some harleys [just the smaller ones im only 75 kilos] i reckon id look out of place on a big bike.

I used to know a woman who really liked riding her flat-four BMW. At one point she rode it from Melbourne to north Queensland. I pointed out to her that if she ever put it down, she couldn't possibly pick it up, but she just said she'd been riding for years and it had never happened, why worry?

So far as the beetle is concerned I seem to have heard of people who turned the back axle around and put a V8 where the back seat had been. That can work fairly well, with enough engineering work. Putting an engine in the front, though, is just dumb. The front suspension doesn't amount to much to start with, and the understeer would be terminal with all that weight on it. The wheelspin would be extensive, but the acceleration wouldn't amount to much due to lack of weight on the back wheels. On top of that you've put the engine where the fuel tank used to be, so the tank would end up in the back seat. It would be a chore to make a good enough firewall and externally-vented compartment to make that safe, and since you are losing the back seat anyway, why not just put the engine there?

Having said all that, we are subverting the Scott Bonnar forum and I think I'd better drop out of this.

Hi biglenny, I would like to give you also a warm welcome to the forum.It's great to have another Scott Bonnar owner on board. Thanks for posting the pics of your machine and look forward to seeing the resto pics as you go along....
Once again,

G'day, took a few more piccies of the old girl and thought i'd post them. I really have no clue as to what i'm doing so if you see something that's had the richard please point it out. There looks to be a fair bit of meat left on the reel but i reckon i'm up for a new bedknife.

engine number is 60102 0302 69051

The two small sprockets are worn out, and the nylon idler looks as if it is now eccentric, which would mean it's a goner as well. You should check your chains for pin and side-plate wear: hold the chain horizontally on its side and see how much it droops. The droop is due to slack in the pin joints, and it increases the pitch of the chain, which ruins the sprockets.

I don't recall a nylon idler on that mower - I think it should be a metal idler. The nylon thing may not have pivoted freely, and may have not been rotating, causing eccentric wear. You should fit the proper chain tensioning idler.

Grumpy, How do you tell that the sprockets are worn, I'm working towards getting a reel mower, so it would be useful to know.

To me, the above sprockets, just look like sprockets, i cant tell any more than that.

Hi Ty, You can tell that the sprockets are worn out when the teeth become "pointy", as in Biglenny's machine...putting on new drive chains would be a waste of time and money because the worn sprockets would ruin the new chains in no time.
For Biglenny....can you please post some photos of the chain-case side of the mower so as we can see the entire chain set-up. Also from the original pics, I can see that you are missing the front roller height adjuster mechanism; the replacement parts are still available.

Ty, expanding on what Deejay said, if you look at the teeth of the small sprockets you will see two anomalies. First, the dip between the teeth has become wider than it should be, and is not the right shape. This allows the stretched chain to sit in the gaps between the teeth of the sprockets. Second, the tips of the sprocket teeth have acquired chamfers, because the next roller arriving at the tooth each time, is in the wrong place due to having more than the correct amount of pitch, and the wear on the base between the two sprocket teeth is allowing the arriving roller to be even more "late" in arriving. Consequently in severe cases like this one, the tip of the tooth experiences excessive pressure as it tries to pull the arriving roller into position. As the roller moves down the tooth it eventually "jumps" into position to allow it to roll down the rest of the way.

Often the wear on the chain is a bit less than this one, and instead of the sprocket teeth developing chamfers on their tips, they just wear severely down below the tips of the teeth. The teeth thus become more and more undercut just below the tips, until the tips fall off. You then have what motorcyclists used to call a "burned out sprocket": the toothless sprocket allows the chain to jump. I can recall as a small child riding on the back of an old Series 2 Square Four Ariel that had the problem: no matter how briskly the rider engaged the clutch, the bike accelerated slowly and smoothly except for a sort of hissing/clattering sound from the sprocket.

My guess would be that this mower had the sprockets burn out, and the owner replaced them without replacing the chains. This resulted in rapid wear, causing the deformed bases between the teeth, and the chamfered teeth.