Hi a friend contacted me, he has an M20 engine with the number stamped PU M20 694 can someone tell me what year it is?
Cheers Barry

email (option): deadhorsesdontgetbackup@hotmail.co.uk

PU Engine Number was used on Howard Clifford rotovators fitted with M20 engines, I still have a pair of cases stamped with this number in my workshop..

Thanks for that Dave, I didn't know that they supplied engines for anything else. Would you have any idea of when it would have been supplied?

email (option): deadhorsesdontgetbackup@hotmail.co.uk

Here's the beast...



BSA supplied modified M20 engines for a few industrial applications...Another was for a machine to move railway trucks in marshalling yards...It was called the 'mechanical horse' I believe in reference to the time when horses did that work..

I have most of one Clifford engine and about half of another. Many had the cylinders robbed off them as they were covered by the cooling cowlings and suffered very little corrosion as a result...

Interestingly, as they were fan cooled and the air was drawn across the engine the fins ran the opposite way to those of the motorcycle version...
The head is alloy and those were introduced for 1951 on M20 motorcycles so I guess the rotavator was mid 50s to mid 60s approximately. It shouldn't be too hard to tie that down more with a Google search...Ian

email (option): ian@wright52.plus.com

Thanks for the picture Ian, I've tried a Google search but drew a blank with only youtube results coming up, this maybe because I live in NZ and this limits the search. Cheers Barry

email (option): deadhorsesdontgetbackup@hotmail.co.uk

Barry, there is nothing to stop you logging in to Google UK and searching from there. I'm abroad and do it all the time to reduce the number of US responses to English-language searches.

Also layed on their backs and used in Hargan saws here in Australia.

To say the least that looks leathal

Is that saw from the country with compulsory bicycle helmets ?

Isn't that crazy !! :scream:

Yes they were lethal.
The blade came off and ran down the operator.
I had a flattie whose father was literally cut in 1/2 by one.
Being a young country we had not cut down all of our old growth forests as Europe & the UK had so we had some very big and tough trees down here.

Immediatly after the end of WW II the biggest national project was the building of the common gauge railway line Adelaide to Brisbane
That is over 2000 miles worth of railway sleepers just for starters.

The Hargan Swing saw was invented in 1946 by Don Hargan, using surplus BSA M20 engines.
The blade rotated on the long axis so you could cut at any angle from vertical to horizontal and use it to plunge cut or as a drop saw. Thus the same saw could fell a tree, limb the tree and rough mill the trunk, where it dropped into fence posts, railway sleepers, truss beams etc. It used a single operator for milling and 2 operators for felling as the operator had to pull against the saw as the blade spun away from the operator.
However the blade nut had a bad habit of coming undone then the blade running away. Blades were up to 6' diameter
In the years 1945 to 1951 around 600 of them were made, they were very popular , particularly if you were a farmer who had to build 50 miles of fence in order to maintain ownership your selection or had to cut down all of the trees in order to keep your farm ( Aussie pollies were all Poms after all so they all knew that "rain follows the plough" ) .
In 1948 the Mobilco swing saw hit the market and the Mobilco blade spun the opposite way so it self tightened in use and did not pop off at 60 mph.
Thus Hargans literally got left in the forest or fields as soon as the landholder could afford a Mobilco that also used M20 engines on the early model before they switched to BSA model GPL stationary engine.
Thus there are a lot of old Hargans lying around the place where as the Mobilco's ended up in the machinery shed then being pulled down & repurposed when the owner got a chain saw where as the Hargans tended to be left where they were being used when the the new Mobilco arrived.
Mobilco sold 3000 of these units before chainsaws became available and are very rare.

You see a lot of ex-Hargon saw M20 engines around and the give away is a 6" long decompressor which was the only way for the operator to stop the saw in an emergency ( not easy to do ).
The vintage crowd love them because they usually have a horse shoe magneto fitted replacing the mag-dyno

email (option): bsansw1@tpg.com.au

Here's a typical Hargan saw engine on ebay AU. Notice the oil return fitting and pipe fitted to the case near the mag pinion (bottom of the engine) and returning to the scavenge side of the oil pump via the sump plate. As Trevor states, we see these everywhere down here, I'm surprised there were only 600 built and not 10X that amount as they pop up so often

https://www.ebay.com.au/itm/BSA-M20-Engine/232664906943?hash=item362be8bcbf:g:45EAAOSwjIVag5g5

And from the same seller. Note the hole for the oil return fitting.

https://www.ebay.com.au/itm/BSA-M20-Bottom-End/232646921943?hash=item362ad64ed7:g:oggAAOSwRUhY-WI9
Note the hole for the oil return fitting.