OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Engines Boundy BMS Engine - What's Inside?

This is the early BMS Boundy engine with 46mm bore, found on Lawn Cub and Pathfinder mowers. I am rebuilding this engine at the moment so I thought that while it was apart some pictures of the internal crankshaft magneto would be of interest.

3 large bearings support the crank which is good because it is quite heavy, you can clearly see the magnets and pole pieces fitted into the cases.

Biggest drawback in the design is that the case seals can only be replaced from the inside. Incidentally I have done my homework and rings and piston are the same as JAP Model 80 also being 46mm.

Hi Paul
This is an important post for many reasons ...

Many thanks for the great images ... it's hard to find Boundy
engine images taken from the inside!

I was shocked to see the crankshaft - in that the magnets seem so
crudely placed and ill-formed! I wonder if this had anything to do
with evidence of de-laminating of the crankshaft on early engines?

Your commentary is priceless for the Boundy record.
I mean, the internally placed oil seals and - most of all - your connecting
the JAP design to Boundy. That is a first!!!

I will add this ...
We now have clear evidence that Victa, Pope and now Boundy took inspiration
from UK and Euro engine makers for their own AUS designs!

Brilliant!
--------------------------------
Jack

Hi Jack,

Your observation about the magnets it exactly what I first thought and then I remembered the age of the engine, must have been a big ask to design this one and have it all stay together.

On the topic of the pistons the Repco parts catalogue carries the same part numbers for both JAP and Boundy piston & ring sets.

Hello CyberJack,
I guess they figured the consumer would be non the wiser and it worked just as well as if it fitted straight and even. It does give a bad impression on their manufacturing processes at the time though.

Hi Mowerfreak

The first paragraph of this memoir suggests it was a money issue:

https://www.outdoorking-forum.com.au/forum/u...tshire-boundy-the-bob-davies-memoir.html

Cheers
Jack

Hi Jack,

Yes your right, anything is only as good as the money that you can throw towards development. Good reference to the final model fitted with the Briggs engine.

Hi Paul and Mowerfreak

I think the Bob Davies story at least gave a glimpse of an 'underdog'
company - and its owner - that took on the big end of town.

I do feel it was new capital - from Wiltshire - that gave us a very good
engine in the BMS 10 in the late 1950s.

Boundy advertising proclaimed they had 1,000 new owners a week in late 1958.
[Of course, Victa had 10 times that!].

I'm not convinced the Boundy engine offered any real advantage at all.
In fact, it would be easy to argue that a heavier crankshaft would mean
poorer governor response - on rotary lawnmower engines often subjected to
irregular spike loading.

But that misses the point: Boundy dared to be different. That's what I like.
And at such an exciting time in rotary mower development!

Thanks again Paul for showings us the inner workings of an early John Boundy engine.
I might also add, that your images are of first rank in composition. The gallery images
tell a great story. My favourites: Images 1, 2, and 5. Calendar material for tragics like me

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

Hi CyberJack. I ended up reading the entire article. A good insight into what they had to battle. They were more like workers than business owners.
I liked the condenser incident in particular!

Damn, I wish I had said that!

G'day Mowerfreak,
Well said - because it reveals my same assessment of the times.
John Boundy had a go!

The 1950s was the 'Golden Era' in AUS rotary lawnmower development.
It was a decade when battlers could have a go.

By the 1960s it was BIG companies that dictated the market.
There was no room for small lawnmower makers!

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

Hi CyberJack and Mowerfreak,

The later and larger Lawn Patrol was equipped with the BMS Series 10 engine which has a 52mm bore. As Jack has previously mentioned the bugs were sorted out by this time. Below is a short video of my Lawn Patrol running for the first time in a very long time. The shroud and starter are not fitted at this time.

Hi paul_c,
sporty!

Great sound eh!

A very throaty sound
The first Lawn Patrol I have heard and seen running.

Paul, I just realised the significance of this.
The first Lawn Patrols were fitted with a JAP 80 engine -
so Boundy had an easy template for bits on his own engine.
Sorry for not catching-on to your point.

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

Hello ODK members,

A little update on the engine rebuild, it all back together. Replacement piston and rings, bearings and seals.

First run is in the video below, after that I adjusted the timing and fitted another plug. Started with the good old CJ8 but changed it to the correct L14. Now it runs a lot smoother and will idle nice and low.

Not impressed with the carb on these, I have quite a few mowers fitted with them and they just won�t prime. I have been right through them and they refuse to put out the extra fuel for starting.

Hi Paul and members
A nice one for the record. Many thanks

I suspect the old-style 'ticklers' on carbies merely were vacuum
release devices - so that tank head pressure could do its job.
The prime objective was to fill the carby bowl, not ensure a
fuel charge for quicker starting.

That was left to good carby design and general condition
of the engine that does the 'sucking' of the fuel.

That's my amateur understanding, anyway

Some carbies prime better than others,
and I have heard comments that support what you say about that carby.

It is interesting that in 1964 Victa re-produced comments about this:-
https://www.outdoorking-forum.com.au/forum/u...a-news-cuttings-june-1964.html#Post95680

I think modern primer bulbs do a better job - they do prime
rather than fill a fuel bowl.

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

Good Afternoon ODK Members,

I have been restoring a Boundy Lawn Scout and as always I pulled down the engine to have a look at condition etc. Now this one I have had running but only after removing the air cleaner and muffler, I figured the seals were probably hard and the rings a little worn.



I found the crankshaft was cracked right through, I would say that the magnet had worked its way out a little and was picked up by the the inside of the crankcase.



I have a spare crank which is lucky, pays to have a look inside. The base is ready to go once I get the engine sorted. Bearings and seals are from the local bearing shop and rings for this model are the same as JAP Model 80.





👍😀

Great looking mower, lucky you had a crank, doubt whether they would be common.

Hi All

Yes,this Lawn Scout is coming along well, I was just reading the purpose of the tickler further up the page and
thought a few extra details were missing in the operation of how the tickler works like a choke for a richer mixture
,my understanding was the fuel tickler does ensure a richer fuel charge for quicker starting by increasing the fuel
height in the fuel bowl above the normal needle valve cut off point. The higher the fuel level is in the fuel bowl
the richer the mixture will be and this will help with cold starting. In essence the tickler enriches the fuel charge
for cold starting in a different way to using a choke butterfly valve,the tickler like the butterfly valve changes the
air fuel ratio.

https://www.mopedarmy.com/forums/read.php?6,1796075,1796087
Cheers
Max.

Hi Max,

Yes you are right, the primer rod literally just floods the carb and allows fuel to flow up through the main discharge puddling in the carb throat. Pretty rich mixture.

All the best
Paul