Mystery Engines

[mikehamptonParticipant @mikehampton]

I have a pair of vintage (1930-1950?) UK 15cc 2 stroke model engines that looks like they were used in a boat (they have a flywheel).
I suspect they are home construction made from castings.
I am very keen to identify the make of these; can anyone help?

[bernard towersParticipant @bernardtowers37738]

They look interesting I presume the screwed on plate is the transfer port. I am presently trying to put together a M & M 29 from 1939. I have done some parts but am waiting on the weather to do a casting run for the crankcase. Best of luck with your enquiries.

[Tim StevensParticipant @timstevens64731]

The design with a single transfer port opposite the exhaust is pre-WW2 (except for a home made version which may well be in someone’s catalogue still). Later designs were based on Schnurle ideas (umlout on the U, I think) with two transfer ports, mirrored, ending at 90 degrees from the exhaust, and pointing away from it. Better for power at speed but irregular tickover and low bottom end power.

Another clue is the top of the piston – pre-WW2 has a thick ridge ‘deflector’ across the top of the piston, post WW2  has flat or slightly domed piston.

Cheers, Tim

[MichaelRParticipant @michaelr]

A site that may be of help with your engine query is “ON The Wire” Link https://www.onthewire.co.uk/duffield.htm

Lots of vintage engines for boats and cars of vintage years, you may be able to contact the site.

Michael

[bernard towersParticipant @bernardtowers37738]

Unless its piston port like my M & M then its got a big hole in it!!

[Tim StevensParticipant @timstevens64731]

A piston port can be used with either system, but more common with the earlier design. The port then is shorter, going through the piston on its way to the base of the barrel, and then out through a port opposite the exhaust and slightly lower than it, so as the piston closed off the exhaust, gas already moving up the port would be trapped for next time. On the way, it helped to drop some oil (from the petroil mix) on the little end, and helped cool the inside of the piston.

Clever things, two-strokes.

Cheers, Tim

[bernard towersParticipant @bernardtowers37738]

My M & M has a petal valve on the rear crankcase for induction which occurs as the piston is on a compression stroke, on ignition as the piston is forced downwards it opens the sideport exhaust and loses momentum which is when the piston carrier takes over and opens the piston valve allowing fresh mixture above the piston and as the crank goes from BDC it closes the piston valve and completes the cycle. (Hopefully)

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