OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Reel-Type Mowers Double SB45 restoration

Hi again,

This point is more so for Deejay and Cyberjack than anyone else and shows that both these mowers have the later serial number ID stickers opposed to ID plates.
I know that these stickers were used until the Rover take over in 1980 but it seems they were already in use in 1977 with the 20 inch machine displaying this type, 1978 with an edger I have and 1979 with the 17 inch machine pictured in this thread.

I also notice that the numbers of the mowers are in rough sequence for the two years of the mowers but my edger which is a model 38 has a much lower number than the 1977 mower has so that seems out of sync with continual numbering. We all know that the brass ID plated machines were all over the shop with no particular pattern that's yet to be discovered, as the same was for the Ally plated machines.

Cheers,
BB

Hi BB, Thanks so much for your inputs into this restoration. Initially I will be focussing my attention on the 20" with the aim of selling it on at completion(if i can bring myself to do so).

In regards to the twin rail engine mounts and the cracks, has anyone made any improvements to the rail design as part of the repair process? ie. cross bracing, solid plate between engine mounts? Its more than apparent that the cracks are common and I see this as a good opportunity to prevent history repeating, but keeping in tradition of the original SB style.

I'm also favouring the new engine treatment on the 20", compared to the original B&S engines, I would have to assume that there would be a lot less vibration from the motor itself, and also the cylinder orientation to the rails in the new B&S and Honda engines being at a 45 deg angle would likely change the application of forces through to the rails. Has anyone seen any crack propagation occur after fitment of newer engines?

Hi mikeo,

One thing that the old Briggs and Rattlers were really good at and that was inducing vibration as that's how they are.

Honda's are the perfect upgrade for a 20 inch machine, for any machine I'd say, but one must think about originality or practicality when embarking on a restoration.

I've always said, the 20 inch twin railer was a design failure from day one and the 17 inch from day two. the earlier solid decks if maintained correctly are still the best design by far, but the twin railers do look a tad better though, but that's just my humble opinion.

Now as far as selling the machine is concerned your size lawn must be taken into consideration as the 20 inch is without a doubt the best machine for a largish lawn, but if a 17 is good enough you might be able to fund the 17 out of the proceeds of the 20, that's if you can get those rails repaired at a sensible cost or no cost a all by knowing someone in the trade of welding.

I've always thought of a piece of 5mm steel plate being welded into place between the two rails but hidden by the engine when fitted. To date I haven't seen it done yet and I think someone on this forum was against it when it was brought up once before.

Happy to be corrected on that though.

Cheers,
BB

BB, preventing the cracking while still having the vertical vibration induced by the engine, hinges largely on increasing the stiffness of the rails. There are two main generic ways to do this. You could increase the number and/or depth of the vertical flanges beneath the deck, which is essentially what the single deck machines had. Alternatively, you could box in the existing rails, preferably by welding a second set of identical rails upside down underneath them and welding the flanges of the original and upside-down rails together. Adding a flat deck contributes very little, except in increasing the ability to withstand horizontal vibrations from the engine.

I haven't seen or heard of a twin-rail machine having its rails boxed in (with the captive nuts for the engine mountings on the inside of the boxes, of course) but it seems like the most effective solution, though of course it does change the appearance of the machine.

I had a good look around at some other photos of cracking in SB's and did some thinking. The cracking is caused by lateral forces on the engine bolts being transferred to the captive nuts, as intended in the original design. The twin rail design is a significant improvement over the solid deck as they are allowed to twist and move independently of each other which lessens some of the cyclic vibrations into the complete frame. Stiffening the rails would remove this flexible feature.

The problem lies in the transfer of the lateral force to the rails. The connection between the captive nuts and rails is simply too small and incorrectly designed. All the cracks I have seen propagate from the two welds on each captive nut.

The best solution would be to remove the captive nuts, repair cracks, replace the nuts with a 5-6mm thick plate sized to fit between flanges of rail and 50mm long, drilled and tapped for engine bolt fixing. The 6mm plate needs to be welded in place of the captive nuts on all 4 sides with ~10mm long fillets in the centre of each side(not corners). That should allow the rails to do what they were intended to do.

I'm not yet convinced, aussietrev, but it is food for thought. I agree that the cracks may be propagating from the clamped joint where the engine mounts to the rails, since we often see cracks there which have not extended to the vertical flanges. Hence that feature would be odd if the problem is vertical vibration, since the top web of the beam should be stressed a lot less than the bottom edges of the flanges. However if the problem were horizontal vibration as you suggest, those holes are right on the neutral axis of the beam and therefore should not be stressed much - a little shear stress, but no tensile or compressive component at all.

The whole issue is contained in your first paragraph. If we can get to the bottom of what is causing the stress, the rest is easy.

Your proposed cure has the effect of greatly reinforcing the structure right at the point where the cracks begin, and that is very often an effective solution. I'm never happy though until I have an analysis that begins with a convincing explanation of how the cracks are being caused.

here is a good example of the cracks and nuts. its a leverage problem to be basic about it. the bolt length versus the nut radius isn't going to work.

If the bolts were being levered from side to side, and the joint had some compliance, that could generate cracks at the base of the nuts, where they are welded to the rails, due to local flexing. That seems to be consistent with your picture, mikeo.

I dealt with a possibly similar problem professionally once, very very long ago. In that instance there was a clamped joint where the pin at the top of a car's rear shock absorber passed through a hole in the floor pan. Cracks were developing at the hole in the floor pan and radiating outward. I fixed it by pressing a 2" diameter anulus (a toroidal indentation if you prefer) into the floor pan around the hole. This permitted the necessary deformation under load to occur over a substantial amount of metal some distance from the hole. It worked: no more cracking.

If this situation is similar, adding rigidity to the rails right at the bolted joints, as aussietrev proposes, could potentially cause very high loads on the engine mounts. At present the thin rails may be acting as compliant engine mountings, instead of the more usual (and durable) rubber blocks. I recall a building services engineer (well his job description said he was an engineer anyway) who had a locally-made centrifugal pump that was so badly out of balance that it continually over-stretched and broke its rubber mountings. This guy deleted the rubber mounts and bolted the pump to the structure, which happened to be the reinforced concrete roof of an office. This resulted in a continuous noise level in the office in excess of 90 dBA. By a miracle the bolts were strong enough to transmit the enormous vibration-induced loads they had to carry.

Perhaps a simple and workable solution in this case would be to sandwich 2-3 mm neoprene strips between the engine and the rails, together with similar isolation between the heads of the mounting bolts and the engine's mounting points. The objective would be to absorb the engine's vibration (both vertical and horizontal) in these rubber joints rather than transmit it to the rails and the rest of the mower. There might be an increase in operator comfort as well as structural durability.

Just to throw this in as mikeo has poo pooed the original design of Sid Bowadich,

Why is it that just about all the twin railers have this issue and the solid decks have hardly any, yes I have seen them in the solid decks as well but to no where near the degree as the twin rail design. Honestly just about every twin rail mower I see now has some level of this issue.

To be brutally honest, repair the cracks and use a Honda engine instead of a Kirby or Briggs. That will end it for once and for all as the Honda's are far more balanced than the early jobbies.

i'm not sure who sid bowadich is. has anyone had the rails repaired and run a honda engine on it for at least 20 years to see if it cracks?

the solid decks have a much larger surface area between the deck and underside of motor to generate more "friction" and lessen the lateral forces on the bolts. that would slow the cracking down, but makes sure all the engine vibrations would go into the chassis.

putting a neoprene or rubber block between the motor and rails would only increase the amount of lateral movement on the bolts. putting the larger tapped plates in place of the captive nuts would just mean the rails would twist rather that the captive nut twisting at the welds to the rails.

On the 20" i'm going to need a new deflector plate as the current one is rusted quite badly. Would it be common to get a replacement made up or are there spares floating around for sale?

Also, I've seen some restorations where the sole plate has been blasted and powder coated. Is it ok to remove the bedknife for this to happen? SHould I watch out for anything when removing the bedknife? Should I be searching the forum to answer these questions?

Hi mikeo,

As far as parts are concerned for a 20 inch machine and all other sizes as well there is absolutely no new panel work available.

Also secondhand 20 inch stuff is really rare, but most stuff is common to the 17 inch machine apart from the reel, soleplate, handle bars, grass deflector and chassis along with front and rear roller assemblies. On the earlier 20 inch machines the reel bearing carries are a different size but this is not the case with yours as it's a very late one.

I must admit that it wouldn't be very hard for a sheet metal shop to make up a replacement if you can supply a original as a template.

As far as the sole plate is concerned as you are going to resharpen the reel and bed knife you could remove the bed knife and give it and the sole plate to your machinist to reassemble but and I say this with some warning, why would you even consider powder coating the sole plate as powder coating is Hygroscopic and will allow moisture in between the powder coating and the cast iron. It won't take long for it to become rusty under the cosmetic surface. Many of the later Kermit Green and Red Rovers have been turned into rust buckets as they were Powder coated and not painted at the Rover factory in Brisbane. No powder coating was ever done at the Thebarton factory in Adelaide.

Also as far as removing the sole plate, I would leave it in place for / while the rail repairs are being done as it's part of the structural integrity of the chassis.

Hope I've given you some insight as to what you are asking.

Cheers,
BB

My strong advise would be to paint it using the same Hammertone as the body panels and chassis etc. as that's how it was from the beginning.

was thinking of the powder coat as was done on this build https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=38803&page=1
if that was painted then i stand corrected. not favouring a particular way, just going with what has done before.

Yes that was powder coated as was the reel. As soon as the reels gets machined then that's when the moisture gets in between the metal and the coating from the freshly exposed section. In no time the coating will start to peel and the rest is history I guess.
Paint is far more durable and chemically / mechanically it's a far better bond. Powder coating is done for the sake of ease and also looking shiny on the showroom floor, but that's about it.

Cheers,
BB

is there much of a demand for genuine 20" parts if this example was to be split up? or is that a bad idea?

major parts:
reel
sole plate
rollers
chassis
front roller
drive shafts

mikeo, physically isolating the engine vibrations from the deck requires that the four engine mounting bolts have clearance in the mounting holes in the crankcase. If the bolts touch the crankcase that is described as a "grounded out" engine mounting. If you've ever driven a car in which that has happened, you'll remember the experience.

Hi to grumpy, BB and Mikeo,
This thread is jumping all over the place...the topic is about the restoration of 2 SB 45's.
If you wish to discuss the cracking issue of the rails, maybe a new thread in "Tech Talk" would be the way to go.

For Mikeo, please don't attempt to remove the bedknife blade from the soleplate yourself....the engineer/machinist will do that if it needs to be replaced and has the tools for the job. The soleplate is cast iron and many $$$ to replace....if you can find one....they can crack very easily

Hello mikeo,

I will say that I am here on this forum for the sole purpose of helping people preserve Australia's mowing history and not destroying it in the name of greed. If you choose to go down that path, not will I just be very disappointed but my help on this thread will automatically cease.

This machine you have is very much a superb example of the 20 inch "Last Of The Australians" and repair work to get over the frame issue is very much a walk in the park for an experienced tradesman and from that point on what you have will be easy to work with and you should be able to come up with the same result as the mower depicted in the thread you highlighted.

If you choose not to go ahead please leave the mower complete and re-offer it to someone that will do to the machine what it so rightly deserves as there are many people out there that would jump at the chance and envy the position you are in, especially considering what you paid for each in the first instance.

BB.

I support BB's point. During the long life of any rare or historically important object its continued existence requires goodwill from every single custodian, while its destruction only requires brief ownership by one Philistine. I do not dispute the right of every owner to do what he or she will to their own property, but what would most people think of a rich Texan who bought the Mona Lisa and had it painted over with his wife's face?

That mower is remarkably original, and in that condition, rather rare. Furthermore it is not some unusable antique preserved only because of its quaint crudity, like something you might find in a science museum. It is a machine that had a clever and fine design, which remains relevant and usable 35 years later. Personally I would never collect anything - it is far too passive a hobby to suit me - but I do value good design, as I think do most Outdoorking members.

If you do not want the mower, why not sell it as a complete machine? I am not suggesting you dispose of it for less than its market value, of course - it is easy to establish that on ebay or by some other process if you prefer.

very convincing arguments you guys put forward.

progress so far: Cracks repaired. parts ordered. will get off to sandblasters this week. in going with a new b&s engine for this one and the throttle motor mounted, i decided to weld up the throttle mount holes(plus 2 other retrofitted holes) on the bars for a cleaner look.

going to go a re-chrome on the handle bars and the clutch handle and was thinking of chroming the front roller just for some fancy(or gloss black).

is there a complete fastener list floating around on the forum or have people had success in cleaning up and polishing original bolts? Will have to get some replacement bolts as 2 of the sole plate bolts were cross threaded.