Four cylinder A7

[Greybeard]

Coil ignition Austin Seven, (A7) engine fitted to a BSA frame.
My 1929 Austin 7 had the same engine. The distributor is mounted on the end of the dynamo. On this bike the starting handle 'nose' has been cut off and capped. The pulley for the fan belt has been removed. I assume an electric fan has been added behind the rad. The engines didn't have a water pump, relying on thermal circulation. I'd like to see the flywheel end of the bike to see how the primary was connected.

[duTch]

 Interesting, but metinks not an A7 frame based on the tranny- must be from a single, and it mounted behind the frame downtube

 Based on the engine, I guess it can be called an A7

[Greybeard]

 Interesting, but metinks not an A7 frame based on the tranny- must be from a single, and it mounted behind the frame downtube

No, I think it's a B series frame. A7 came from the Austin 7 engine.

[ironhead]

I recon that's an M series frame. Bottom frame tubes go through to the bottom of the front down tube.

[Triton Thrasher]

Looks like a Triumph gearbox.  Don’t think its got any cooling fan.


Good enough for Brough, anyway:

[Greybeard]

I've seen one of the Brough Austin Seven jobs at the National Motorcycle Museum. Note the twin rear wheels.

[Butch (cb)]

So is that just a twin main bearing engine in those?

[Greybeard]

So is that just a twin main bearing engine in those?

Mine was. After about 1931 they went to three bearings.

[Butch (cb)]

Mine was. After about 1931 they went to three bearings.

Keeps the block very short, but I don't know how much tune you can put through them. My Nimbus is like that, and I've seen one being prepped for the salt flats.

https://www.autoevolution.com/news/odin-s-fury-the-nimbus-to-tackle-the-bonneville-salt-flats-video-97610.html

[Greybeard]

Mine was. After about 1931 they went to three bearings.

Keeps the block very short, but I don't know how much tune you can put through them. My Nimbus is like that, and I've seen one being prepped for the salt flats.

https://www.autoevolution.com/news/odin-s-fury-the-nimbus-to-tackle-the-bonneville-salt-flats-video-97610.html

Tuned Austin Seven racers achieved 100mph at Brookland with a two bearing crank. It was said that at high revs the middle two pistons would hit the cylinder head because of crankshaft whip. The big-end diameter on early engines, mine included was 1 1/8".

[Greybeard]

https://www.autoevolution.com/news/odin-s-fury-the-nimbus-to-tackle-the-bonneville-salt-flats-video-97610.html

The Nimbus crankshaft looks just like an Austin Seven one.