An Australian BSA "Otter".


Gary Edwards has come up with this Superb BSA "Otter", using the information from this site he says...

Well, if by having this website open helps to create a machine like the one below, I must be doing something worthwhile...




Photo Courtesy Gary Edwards.


Gary Edwards BSA “OTTER”


Hi Charlie, a friend wants me to build a trials sidecar to fit on a BSA B40, would you be able to help with some dimensions, maybe a sketch.

Charlie;> I will do Gary.



I built an "Otter" with inspiration from your site.


BSA B25 motor BSA C15 head, Montesa forks and wheels.

Realy happy with result...


Regards Gary Edwards. From Oz...



Gary Edwards From Australia, has built a Superb BSA “Otter” from scratch with inspiration, he says from the BSA “Otter” site.


Well if we have helped him achieve the build of the bike below, I am as proud as Gary must be in his construction, of this brilliant motorcycle.


Montesa front forks and front wheel are fitted like the OTF "Otter" bike of ours, and also he has used a Montesa hub for the rear.


The motor is a BSA B25 unit with shaved down barrel, and a BSA C15 cylinder head grafted on.

The alloy fuel tank follows the modern lines for "Classic trials bikes" today.


Even the alloy bash-plate is has neat a job as I have seen for some time, and shows the effort put into the build...


The frame is built to the Classic Foster “Otter” design.

And is a first class engineering example.

We will put Gary’s Story of the build and some more photos of the machine on when they arrive.

So keep your fingers crossed it is soon.



Here is Gary's Story of the build.

Hi Charlie,
I had been looking to build a trials bike for a while when I found your Otter site.

With lots of photos to study and the frame building page, I started by drawing the frame full size on a board to check dimensions and fit of engine and wheels.

A drawing helped setting up in the jig.

The frame is built from 4130 chrome-moly tubing, more because it is available in a good variety of sizes, and the supplier is not too far away, the price is good and makes a light strong frame.
Frame assembly was straight forward, an easy frame to build with mostly straight tubes.

Welding was with nickel bronze.
My intension was to fit a BSA B40 engine, and I was able to get a dummy unit from a friend Stewart Young to fit to the frame.

Stewart is a local guru on unit singles, and was able to supply parts and advice when it came to engine time...

Engine plates were made and every thing bolted up nice.
Unable to source a B40 in time, I decided to use a B25 I had.

Stewart suggested using a C15 head for better angle for the carby which worked well.

A B25 barrel was cut down to match C15 head. A smear of silicone, the only place I used it, around pushrod tunnel has proved oil tight.

An 18 tooth engine sprocket to lower gearing, Electicworxs ignition completed the engine mods.
I was able to source Montesa wheels and forks on the bike builders friend, eBay.

How did we manage before it.
Next was making the airbox and muffler from photos I had seen, both turned out nicely.
Guards are glass-fibre copies of alloy ones, cheaper to replace when I break them...
The fuel tank was another problem, the high cost a new tank prompted me to have a go myself, what could go wrong.

Now this is where Youtube excels, after watching hours of metal shaping and tank building, I was ready to tackle my own.

And I am quite pleased with the result, it's not perfect by any means, but it holds fuel and I think suits the bike.
Am I happy with my BSA Otter, hell yeah.

A fun bike to ride,steers nice and so light.

It's not for competing but I enjoy playing around in the bush on it .



Thank's Gary for sending the photos .

And I might add, that they would have been on this site a lot earlier had Mr. A Mackintosh put them into the right file.

I suppose he was having his lunch munching on a rosy Apple...


Photo Courtesy Gary Edwards.


BSA B25 Engined "Otter"...



All Photos Courtesy Gary Edwards.


The swinging arm box is also a lot like the one on the BSA Otter SQ frame if you look.

The only difference is, that Gary has welded his footrest-directly onto the end plates...




What a Good idea to fit a C15 cylinder head to the B25 engine, this overcomes the problem with the Induction tract being in the wrong place on a B25 Cylinder-head for a "Otter" frame layout.

I must remember that, the only thing you do have to take care of doing this conversion, is to get a good seal between the cylinder head and barrel where the push-rod tunnel is, and drill a new drain hole for the rocker sump...



I must say that the tank shape suits a BSA Otter very well...



I See Gary used the same method for the front engine mounting plates on the front down tube, as the "SQ  BSA Otter" of ours...

With the two through bolts giving every chance to get the engine in the right position, and room for adjustment, with spacers if necessary...


Nice one...

Also you can see that Gary too fitted a remote Oil filter in-front of the seat tube.

A must I feel, for a B25 motor.

Also a nice BSA type air filter unit has been constructed.

Another nice little touch is running the Oil filler breather pipe down into the sump-plate, that doubles up as a catch tank like on a Race bike.




Photo Courtesy Gary Edwards...


What a superb BSA Otter Build. We hope you enjoy riding your super machine for many years Gary ...

More photos to follow.


And an Update.