Engines > Your Own Design

The "2-Bits" V-Twin

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RReid:
Introducing the “2-Bits” 50 degree V-twin engine.

I've been working on the plans for this project in the background all through the Stirling Fan build and even before. It is inspired by; based on; but not a scale model of the engines developed by Glenn H. Curtiss for use in his successful line of early motorcycles. The V-twin was introduced as an option to the “standard” single starting in 1903, and continuing until mid 1913 when the the motorcycle factory assets were offered for sale. Mr. Curtiss was turning his attention completely to aviation, an interest sparked in 1904 when he began to supply V-twins to Captain Thomas Scott Baldwin to power the dirigible he was developing that was soon capable of sustained and controlled flight even before the Wright Bros. first powered flight.







For anyone interested, a good and much more detailed history of these early years may be found here:
https://curtissmotorcycles.com/history/

As I said, my version is not intended as an accurate scale model. It does, however, include the most distinctive features of the Curtiss engines.
> 50 degree V-twin cylinder layout
> Atmospheric intake valve
> Intake-over-Exhaust valve arrangement.
> Exhaust cams mounted low and centered, just above the crank axis. Each valve is driven by pushrods acting through a pair of rockers on a low mounted shaft external to the crankcase.




For those who may not be familiar with the term, "2-bits" is an American colloquialism for a quarter of a dollar, or 25 cents. This engine has two "bits" in the form of cylinders, and is 1/4 of a V8! I plan to install a 25 cent piece on the finished engine in lieu of a builders plate.

Bore and stroke of the engine are 0.75" x 1" (19mm x 25.2mm). This is the same as the Upshur engine I finished recently, and a size that worked out well with my equipment,

RReid:
I commenced cutting metal for the crankcase this morning. My original intention had been to make the main body of the case from a piece of heavy wall brass tubing (3” OD, 0.25” wall), but at around $50 for a two inch piece of material I had second thoughts. The same size piece in aluminum would only be a few bucks and good second option, not least because the Curtiss engine did use an aluminum crankcase.

Then I considered those chunks of ali I brought home from Tx that have been a source of material for a few parts in other projects already. The larger one is 1.5” thick, which is just what I need. That's the “Pac-Man” in the first image below. And I have an almost unused (therefore sharp, hopefully) 2.125” OD x 1.75” deep hole saw. If I can get all the way through with that, then there will just a relatively small amount left to bore.

So I got to work cutting out a blank on the bandsaw. That poor thing must have been thinking “this isn't in my contract”, but it got the job done.






Then I mounted it in the 4-jaw to start turning one end to near size.

propforward:
This looks like a great build! I’ll be following along.

Art K:
Ron,
For our anniversary in Oct. 2018 we visited to the National Motorcycle Museum in Anamosa, Iowa. This was on display. It is a 1906 Curtis.

I personally am partial to the 27 Brough Superior but have no idea how to find enough info to build one, even if I didn't have 3 or so engines on the list to work on first.
Art

Hugh Currin:
Ron:

I've always loved these first gen motorcycle engines. Will be fun to follow along.

I don't understand the valving, but sure it'll become apparent as the build progresses.

Thanks.

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