Right Angle Cranks

One of the more unique aspects of the traditional 2-cylinder, double-acting steam car engine is the crossplane, two pin crank. The world is full of two pin cranks having pins at 180 degrees ... and a smattering of cranks with both pins on the same side... but right angles was sort of unique. That was before the advent of the 2-cylinder engine with a 270 degree crank.




Of course, these engines have a center bearing rather than a sprocket, and they also have outboard main bearings. This is definitely a stronger setup, and runs much more true than a built-up crank. (based on industry standards, they are probably within 6 microns of design spec).

Hi Ken,
So what is better for a double acting 2-cyclinder steam engine? Keep in mind a standard Stanley engine set up with 2-bearings, cantilever and inside the crank throws along with center gear direct drive on the rear axle.

A Doble was 180 Degrees...right.

Thanks,
Rick

Hi Rick,

I once ran across a lengthy article on crankshaft design that went into calculating stresses on the crank's various components -- part of it breaks down into simple leverage calculations. It didn't take very long to find out just how much stress you get with an overhung crank. When you have a crankpin supported on both sides, the load is split among two bearings. Besides that, the crank arms are now under a compression load, which they can easily resist. With a single bearing, the connecting rod is outside of the bearing and it applies a twisting force to the crank arm -- which more readily produces fatigue. It also tries to twist the crankpin itself. Think how much a diving board bounces up and down and then think about how much more steady it would be if supported on both ends. Of course, these twisting forces are also applied to the crank bearings. This is why even small, single-cylinder modern engines have bearings on either side of the crankpin rather than using an overhung crank -- even though that would be a bit easier to make.

This probably didn't matter as much on a Stanley engine because the open framework construction already invited a certain amount of twisting and flexing, but a number of the more advanced steamers avoided such construction either by adopting something more like ICE design or by replacing the open framework with solid, unitary castings.

Honestly, I rather like the design that Abner Doble's father and brother were using for the small truck project. They placed a double acting V-2 engine right behind the cab and extended a driveshaft to the rear axle. This gave them a simple and cheap crank with just one throw ... but having bearings on each end made it more rugged. The layout gave them exactly the same kind of torque distribution as you could get with a Stanley -- 1 impulse every 90 degrees. The primary unbalance for each cylinder combines into a rotary force that can be cancelled by crank counterweights leaving just a secondary side to side shake that is partially cancelled by about 30 percent.

As I recollect, the cranks on the 2 cylinder Doble-Detroit and the Series F engines were set at 90 degree angles. The Series is a cross compound and therefore a bit weird.

A lot of Stanley engines when needing rebuilding and the crank pins have been Magnafluxed show cracks under the pins. This could be caused in the forging of the crank web and pin in the same press or the years of use, but is your rebuilding a Stanley engine have the pin and web Magnafluxed.

Rolly

hi.i think that traditional 2-cylinder, double-acting steam car engine is the crossplane, two pin crank is the best..get info on google rrbbilaspur



Edited 1 time(s). Last edit at 12/23/2021 03:13AM by theone1211.

You know Theone,
I have recently been working on rebuilding my own 10 HP Stanley Engine. Further I've been evaluating it and really just understanding the design.

The attached picture shows the crank with crank throws along with the eccentrics. Note that the way the keyway is located, one crank throw will fit on at either end.

From a practical engineering stand point, the Stanley design is pretty good and relatively easy to work with. The design blends the use of eccentrics and crank throws.

Cheers,
Rick

Don't discount the stiffening of the crankpin which is added by the inner race of the ballrace which must significantly reduce the effect of the pin "overhang" off the crank web as the race is tightly clamped on the pin. The pin itself does look thin for the forces involved but the ballrace must help. I'd still go for new cranks if rebuilding an engine.

Mike

All files from this thread

File Name	File Size		Posted by	Date
270 degree crank.png	167.2 KB	open | download	frustrated	10/21/2021	Read message
Crank Throw Angle.jpg	483 KB	open | download	Rick.H	12/20/2021	Read message
Eccentric Angle.jpg	515.9 KB	open | download	Rick.H	12/20/2021	Read message