OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Four Stroke Lawn Mower Frames Scott Bonnar Viking

Hello all I have a Scott Bonner Viking 4 stroke frame with no motor on it.
My question is what replacement motor can I put on it.

I have heard that most newer engines have a different crankshaft length and are therefore unsuitable ( It had a b&s 3.5 on it originally with a snapped bolt in the bottom of crankshaft Which for the age of the motor was terminal).Will a decent second hand motor of the same vintage. do the job providing it has the right boss on it?
Thankyou
Shaun

Hello Hermosil

There is some design 'flexibity, particularly with vert crank engines.

Manufacturers would typically offer a couple of different specs.
These would involve short or long crank lengths and a couple of
different crank widths.

The Viking was SB's high arch design (Model 520 or 720).
The bottom line is that any engine, boss or blade holder should place
the blade tips about equal height with the bottom of the base skirt.

I have seen Scott Bonnars with spacers to adjust the height - and these
came from the factory.

Below is a 520 and a 720 base.
Note how the first has spacers; the second seems to have a spacer plate.
That is promising in that either a short or long crank is possible.

I might add, in many cases, different cranks were not a hindrance.
Offering different engines for the same base was not restricted by
a specific crank. This enabled mower makers to best utilize
their inventory - they could use, say, a 3hp engine with a
No 1 crank; and a 4hp engine with a No 2 crank- on the same base!




So, the idea is to match and engine with a recognised boss
and blade holder. If the shaft is too long it will require spaces.

If the blades are way below the base, the machine will not catch
efficiently and will be unsafe. If way above the skirt, you will not
be able to cut short grass.



Hope this helps.
------------------------------
Jack

Thanks for that reply mine looks like second one the 720. I don't want to spend a lot of money on it But I will keep my options open and see whether a suitable motor turns up.

Hello Hermosil
yes, my records show the Viking was, in fact, a 720 base (the second one).
Yes, the name 'Viking' is a good clue too

I failed to mention that boss and blade holder design will also impact.
Some blade holders are 'dished' more to compensate for crank lengths.

I guessed economy of price was paramount in this case.
I think this was the best way to explain things - the principles involved.
The caution - for all members - is not to produce an unsafe machine,
where the blades extend below the skirt.

I hope you sort it out.
----------------------------
Jack

Hi Jack, I finally picked up my first of 4 Scott Bonnar rotary mowers. I've looked up a bit of Scott Bonnar history here and in the section about 72 and 52 high arch rotaries, it shows known models and their numbers.

The one I have acquired is missing 1 number, the 6 at the end I believe.
Mine is Model number: 72001
Mower number: 7200501

It's an identical match for Model 720016 advertisement, I found on ODK. It's a green 4 HP Viking with a Kirby 2-stroke engine and a glossy black catcher.

If you could possibly point me towards some more info on ODK, it would be greatly appreciated!!! I'll continue to post my mowers as I slowly pick up all of the stuff I've organised during lockdown, and we're talking a lot of mowers, catchers, collectables and rare parts.

I'll post a couple of pictures including the advertisement, a screen shot of the Scotty rotary models on ODK, the model and mower numbers and the mower and catcher.

Hi Sean
The History Record you looked at is the best I could
work out on the 720's and 520's.

https://www.outdoorking-forum.com.au/forum/u...odel-72-52-high-arch-rotaries-c1971.html

You have already seen that.

I agree that yours is most probably a 720016.

Sorry I have no other information at this time.

Cheers
----------------------
Jack