Split-single Two-stroke

[Ferrier120]

I purchased this motor a few years back, purely because of it's unusual design, but have no idea who, where or when it was made.
The motor is a superimposed twin cylinder having a bore of 42mm and a stroke of 64.5mm using a common combustion chamber. The pistons are 68mm long and the lower piston is set about 20 to 25 degrees ahead of the upper piston.
Fuel is drawn into the cylinders by both pistons, but there is only one transfer port, which is in the top cylinder. Exhaust exits through a port in the bottom cylinder.
The digits B 38 S No 402 are stamped on the bottom of the crankcase. The number 20 is stamped into a copper core plug. The carburettor is made by Dellorto.
The silencer looks to be home made as the alignment isn't quite right and prevents the exhaust manifold from bolting on correctly.
Someone suggested that it could be a German DKW, but the only split-single design he has seen is where the cylinders are side-by-side, using a 'Y' shaped con-rod working off a single big-end journal.
Any suggestions?

[Charles uk]

Did you find that at Beaulieu? as I looked at a real odd outboard there, much like that 7 or 8 years ago.

[Oyster 49]

Interesting motor. A company called EMC made split single bikes in the late 60s in the UK at Isleworth, the designer was a Austrian chap, who developed DKW technology. Apparently they were very fast at that time. They also imported a 125 cc Puch split single engine.

https://en.wikipedia.org/wiki/EMC_Motorcycles

I wonder if this engine is related to that? An EMC was on show at the recent classic bike show at Bath.

[Charles uk]

The mystery motor appears to be 180 ccs if you can calculate it in the normal manner.

[Ferrier120]

Yes, Charles UK, it was Beaulieu but I think it was only about six years.

[AusOB_Collector]

Maybe a French 'Gutbrod'?... A couple of similarities, but also a few differences.


Picture taken from Doug Penn's website.
Cheers
BP

[Charles uk]

That Gutbrod is a parallel twin not a split single a very major difference.

I can't really see any similarities.

[Charles uk]

Ferrier can you post a picture of your cylinder head, to paint a clearer picture of the logic behind this design.

The picture Oyster posted illustrates a "Garelli type split single quite well, as conceived by Garelli, & followed by TWN, Puch, E.M.C & D.K.W.

But the major offset in the bent big end pin is very different to the designs of the above & doesn't seem to be mentioned in any of the reference books.

Do any of our European members recognise that lower unit & from where, which looks very much like a mass produced item, as do all the other components including the Italian carb & pistons.

[AusAnzani]

Interesting outboard Ferrier.

I searched the net yesterday and came up with a few potentials but nothing that instils 100% confidence. More photos would be helpful eg from front, back, left side, right side, top etc plus any markings.

I would have thought the markings on the piston would give some clues, but 'm not familiar with the.

looking forward to see/know more about this one.

Regards,
Spiro

[Nudge]

I believe the engine has BORGO pistons! (Italian) Borgo piston co.


https://it.wikipedia.org/wiki/Borgo_Pistoni

The Borgo Pistons (publicized in Italy itself also as Borgo Piston Co. was one of the best-known engineering companies) Italian in the field, founded in Turin in ten years ; the company was first merged with Associated Engineering in 1961 (becoming AE Borgo and - in 1969 - Associated Engineering Italy spa [1] ), later bought by a multinational in 1988 , then closed for good in 2006 . He has had different logos; the first, was simply consists of the stylized shape of a piston. Subsequently, the logo, replaced the first O in the word Borgo, was constituted by a piston surrounded by a crown d`alloro. After the acquisition by Associated Engineering, the logo was made up of the AE uppercase and linked together.



Very interesting engine
Any other marking at all? I will keep looking

[Oyster 49]

I'm sure between us all we will come up with something. Can't beat a mystery

[Keith.P]

Well I had a look about, nothing outboard related, maybe some one will find something.
I didn't know the amount of motors that used split twin or twingle configuration, garelli, trojan car, Puch and triumph.
The EMC style crank was used with the spark plug over one cylinder, not in the centre of the two pistons.

[Ferrier120]

Thanks everyone for your input. Here are the rest of the photos I have at present - taken when first purchased, so if any specific area is wanted then I'll have to dig the motor from the back of the shed.

[Ferrier120]

Rest of photos.

[Charles uk]

Weird looking piston, made by the firm that used to manufacture OE pistons for Ferrari, Lamborghini & Ducati!