OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Scott Bonnar 20" - to re-engine or not

Hi All
Love the forums and the fantastic access to the members knowledge of these great machines.
I have a 17" model serial #11961 and engine 81332 0677-01 7806220 which worked OK but haven't used it for a few years. However now I can't get any spark out of it and the carbie leaks fuel (see photo)
I have seen a new 3.5hp B&S on ebay for $269 delivered link here -- EBy B&S motor . Wondering if this is a better option than trying to get the engine running again, seeing as our local reapir place charge $120 minimum
Any advice would be very much appreciated

Thanks

Hi Jim,

Welcome to the forum! No spark and your fuel leak will most likely be easy to rectify if you'd like to have a go at fixing it yourself. With the expertise of the members here to guide you, it'll definitely save you a lot of money and give you the satisfaction of fixing it yourself. Personally I wouldn't pay the $120 for the repair shop. Deejay is the Scott Bonnar expert so I'll leave it up to him to advise you on your engine options. I guess it depends if you want originality or functionality.

I don't know if it's just the photos but your machine looks wider than a 17", it looks more like a 20" with the 8 blade reel - but I may be wrong. As an early solid deck version it's more desirable than the later twin rail types. Going from your Briggs code the engine was manufactured in 78 and not likely to be original on a solid deck model 45. Hopefully someone else can clarify this for you.

and

Hi Rolla
Thanks for the tip, I measured the blade and it is 508 wide so your right it is a 20". Oh to gain 3 inches so easily elsewhere in my life

How old would it be ?

It's hard to say mate, I have a solid deck SB45 here made in 1969 and I have a twin rail from 1974, so I assume the changeover to twin rails was early 70's. Yours is obviously from before that changeover so maybe late 60's or early 70's as a rough guess. Deejay can hopefully narrow it down for you.

Hi Jim, welcome to Outdoorking.

There seems to be a digit missing from the Code (last of three blocks of numbers) you posted for your Briggs and Stratton engine. This is the part that gives us the engine's date of manufacture. Since I don't know which one was dropped, I won't try to interpret the ones you posted. Here is the Illustrated Parts List for your engine:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6ltuCVJ1DajI.pdf

The low-cost Briggs engines sold nowadays are made in China to traditional Briggs side-valve designs. The company's Chongqing plant seems to have been improving its quality (from a rather low base), and the engines may now be of reasonable quality, though they may not yet have reached the standard of the original engines made in the US quite a few years ago. Hence, depending on how worn it is, your old engine may be at least as good as a new side-valve Briggs - all of which are now made in Chongqing.

You have reported two faults in your engine: no spark, and petrol dripping from the underside of the carburetor.

Your engine will have been made prior to 1982, and hence will have breaker point ignition. From what you said I gather it was working when you took the machine out of service a few years ago, so the problem is probably not due to a failed electrical component. It is more likely to be a corrosion issue, or an incorrect control setting. We can talk about a test program aimed at identifying the fault if you wish.

The carburetor is called a small two piece Flo-Jet:


I do not recall the feature the fuel is dripping from, but it looks like a Welch plug blocking a hole in the casting which was used to support a sand core when the casting was made. It is normal to have a small amount of liquid petrol in the carburetor in that location, but it should not drip out unless there is a sealing problem around the Welch plug. However if the fuel is coming out in quantity rather than as a rather slow drip, it would indicate that the carburetor is flooding due to a float bowl problem. If you left it for years with fuel in it, there will be quite a bit of gum throughout the carburetor, and it will need to be dismantled and cleaned. If the fuel you left in it happened to contain ethanol, the damage might go beyond some gum to be cleaned out.

Essentially, the problems you have reported are probably quite minor, and you may wish to consider working through them with us, and fixing them yourself. Please let us know what you decide to do.

Hi Jim, and a warm welcome to the forum. It's great to have another Scott Bonnar on board.
My thanks to Rolla also who has given you excellent advice and is spot on...

Your machine is an early 20" machine with an 8 blade reel (that was standard fitment) and the 3 segment rear roller and solid engine deck.
It also has the brass SB ID plate riveted to the deck, which again points to an early machine. My best guess would be 1969.
This machine may have had a Kirby Lauson (Tecumseh) engine fitted originally and has been retrofitted with the Briggs at a later stage.

With grumpy's help, (our resident Briggs guru), you may be able to get the Briggs running sweetly and as Rolla has said, have the satisfaction of doing it yourself!

I would like to see some more pics with the chain case cover removed, and some close-ups of the sprockets where they are not covered by the chains...particularly the small top sprocket on the primary chain...We can then assess their condition.
It looks like the cylinder reel and consequently the bottom blade (bedknife) could do with a spin-grind and the reel bearings replaced also at that time.
We can help with advice there also.
Once again Jim, to Outdoorking.

Thanks guys, my late father would ahve loved to have this sort of access to information when he was rstoring his 1949 Triumph 2000.

I'm in Lindfield so would be interested in a nearby regrind place.

Thanks again everyone

Photo's pf the chain sprockets

Thanks Jim for posting the pics....the top sprocket is worn (as I thought it might be) and will need to be replaced as the tips are 'pointy' and the primary chain will also be worn and stretched. These parts are available.
I will send you a private message (PM) re: an engineer to do your regrind. Just look for a flashing envelope next to "My Stuff" in the toolbar above.

Just checked the engine number and it is engine 81332 0677-01 78062203

Hi Jim, that confirms that your engine was manufactured on the 22nd June 1978. I think, that also confirms that the original engine was replaced at some stage well after this date....allowing for delivery time for this new engine.

That makes me think that it would be easier to re engine the mower as it doesn't have the original engine anyway. A lot of developments in 35 years of engine design.

Spend the effort and money on getting the reel and bedknife bought back to new and remove 4 bolts, reconnect the drive shaft and have reliability.

There are better engines than a side-valve Briggs readily available, but not for $269 new. Just moving forward to the 1980s the OHV Hondas were introduced, and are probably still the best new engines available. Relatively recently Briggs introduced its own OHV engines, some of which seem promising. Even the OHV Kohlers may be worth a look. Something in the 120 to 140 cc range should be appropriate for a fairly heavy 20" mower. I think you will be less than enthralled by the prices though. Fitting a new side valve Briggs, on the other hand, does not update your technology except for providing you with electronic ignition and emissions controls.

The ebay ad is for the OHV Briggs. But i agree with you grumpy, the Honda seems the way to go, even if it is a few more $$

Sorry, I hadn't noticed that was the 550 model. I haven't had any dealings with any of the small OHV Briggs models yet, but at least one of them seems to be quite well-regarded. I'm also looking forward to some field reports on the DOV (Direct Overhead Valve) models - I give them marks for innovation, at least, but I can't guess yet how that plastic cam will stand up with what looks like more than an inch of cam lift, due to having about five to one adverse mechanical advantage from the cam to the valve. (That probably doesn't make sense until you look at the design: the cam is in the crankcase, with a bell-crank to operate the valve, so there is an extraordinarily long arm from the cam to the pivot, and the usual short arm from the pivot to the valve stem.)

I personally think the Honda GX120 is the pick of the bunch of potential re-power engines for an SB45. It should have just enough power for a 20".

Thanks guys

I wonder if the GC160 is an option as it is only $365 and it is an Honda

Honda GC160

The Honda GX120 is a popular choice for the SB45 and is perfect for a 20" machine....
Take a peek at the specs....Click HERE

With the knowledge that, brand new, the Scott Bonnar 20" machines were approx $1800.00 each....spending a few extra dollars on this engine would be well worth the effort and the machine, well maintained, will give you hours of mowing pleasure, and last a lifetime.
PS. Here are the specs for the GC160 engine....Click HERE

Jim, the GX Hondas are pushrod overhead valve, while the GC Hondas are overhead cam. The GX engines are rated as "commercial", while the GC engines are rated as "residential". Essentially, the GXs are intended to be highly reliable for a long time, and easy to overhaul. The GCs are intended to run just about as sweetly as the GXs, but tend to be a bit less reliable and are a pain in the backside to overhaul. The pushrod engines have detachable cylinder heads, while the OHC engines have integral cylinder heads and the overhead camshaft is driven by a rubber belt.

There is also a sort of halfway-house: the GS is sometimes advertised as "semi-commercial", despite having an overhead camshaft. As an extra layer of confusion, after introducing the GX22 and GX32 pushrod 4 stroke brushcutter engines, Honda broke its own rules by replacing them with overhead cam engines but calling them GX25 and GX35. I suspect their marketing department did that, rather than their engineering department.

In home service on a reel mower, the GC160 might give satisfactory service. It should run beautifully like other Hondas, but it might jump its camshaft timing, which is easy to fix but rather annoying if you don't recognise the symptoms immediately. Repairers would probably charge quite a bit to retime it, even though it would only take a few minutes if they knew what they were doing. If it ever needs overhaul (which seems relatively unlikely in residential use) you would curse it roundly. Its carburetor is also a bit harder to clean than a GX one, due to a "cost saving" in relation to the idle jet. Bear in mind that the GC160 is 160 cc and 5.5 advertised hp, compared with the GX120's 120 cc and 4 advertised hp.

Is there such a thing !

Reel and baseplate are out ready for a regrind

Yes Jim, you will find using your Model 45 and seeing the result of a manicured lawn that it is actually a pleasure.
Good to see that you removed the reel and soleplate successfully mate.

It was easy - I watched a video of the master do it. He made it look like it levitated out of the mower by using his mind. Also it was built using proper design and engineering.

Attached is the B&S product service information for the 550 series I received from the place selling them. Apparently it is dimensionally a straight swap for the old engine. I have the PDF if you want it for the library