Crankshaft and bearing alloy

[Cyruscosmo]

Hey all got a quick question for ya. In making crankshafts and parts what alloy should I use? I would like something I can machine and then temper on my own. Also what alloy of bronze should I use for a large dia bearing? Like an eccentric bearing?

[fredrosse]

ASTM 932 Bronze, SAE 660 Bearing Bronze - 20,000 PSI yield stress, Difficult to machine

ASTM 936 Bronze, SAE 64 Bearing Bronze - 21,000 PSI yield stress, Easier to machine

ASTM 954 Bronze, - 32,000 PSI yield stress, Corrosion Resisting, Most reliable, but not as easy to machine

SAE 841 Bearing Bronze - 11,000 PSI yield stress, Sintered Bronze - oil filled, holds oil, "self lubricating" Easy to machine

For bearing pressures above 1000 PSI (force x bearing projected area), solid bronze materials recommended, with lubrication supplied. For light duty bearings, the sintered material gives good service with less attention to lubrication.

[fredrosse]

Building a crank:

Ordinary low carbon steel can work well, and can be case hardened (surface treatment) after machining, then bearing surfaces must be ground for final surface finish.

Alloy 1045, higher carbon, hardenable, low cost

Alloys 4130, 4140, stronger/harder materials, can be heat treated for hardening. 4130 is weldable.

I have made cranks with ordinary commercial "Drill Rod Steel" it can be hardened as tool steel, but is usually hard enough for engine journals without heat treatment. Drill rod journals with heavy press fits to crank cheeks. Machines well and has a surface finish that is directly usable as a bearing journal without any grinding.

One other option you may find useful, use a crank from a gasoline or diesel engine, these are plenty heavy duty for steam engine service, are available with crank journals from less than one inch diameter to well above 40 inches diameter. One, two, three, 4 (etc.) cylinders with just about all conceivable crank angles available. Usually can be had for a small fraction of the cost to build your own crank, if your engine can be adapted to the ready-made junkyard cranks.

[Oilking]

From the Baldwin-Lima-Hamilton manual for the Liberty Ship engine, " The bearing metals for crankpin bearings and eccentric straps, main bearings, and crosshead slipper, are a high-grade babbitt equivalent to Parsons No. 2 bearing metal. All bronze boxes on the engine are made of 88-12-2 bronze."

As I understand i,t #2 babbitt is the most commonly used grade of babbitt bearing metal. The bronze is 88% copper, 10% tin, & 2% zinc, H. Kramer lists it at the top of their product list as conforming to S.A.E 905.

Just a bit of history on what was done on the big ones.

Keep having fun

Dave

[Oilking]

The bronze in the text should have been 88-10-2, not 88-12-2 Which would make 102%!
Dave

[Cyruscosmo]

Hey Fred

Thank ya for the info. I had thought of using a crankshaft out of some existing engine but there were none I could find at the moment. I am using a crank out of a 13 hp honda engine for a small test rig.

I have been experimenting with the waste oil burner and have had good controllable results. Am using it as a shop heater at the moment. Next step is to build a full size one with fire brick/refractory cement of some kind. My aim is a removable fire box that can use either solid or liquid fuel with a minimum of change over fuss.

Scott

[Cyruscosmo]

Hey Oilking

Thank ya for the information. I have watched a few you tube videos on pouring babbit bearings. Very interesting stuff. But for the crank I am leaning towards ball bearings and for the slides I... well there will be no slides if all goes well. I am working towards the pistons being the only thing that slide in the engine.

Scott

[DetroiTug]

Quote: "working towards the pistons being the only thing that slide in the engine"

Not sure what you're planning to do exactly, but I tried that principle many years ago. I used an old 2" x 3" brass pneumatic cylinder with a eye on the end. Made a gantry type frame in which the cylinder hung from the top and could pivot back and forth. Then a light built up crankshaft mounted on the bottom, no crosshead, just a straight shot from crank throw to piston, seemed simple enough.

The issue was balance, anything over 100 RPM the engine shook violently as the cylinder and rod mass worked back and forth. Ran it once and pondered a fix for it, never came up with anything.

Also, I now realize the packing and bearing on the piston rod wouldn't have lasted long countering the inertia on each oscillation.

Whatever you're doing, good luck with it, just posting this to save some possible disappointment.

-Ron

[Cyruscosmo]

Hey DetroiTug

Thank ya for the reply. No I had my fun playing with oscillating air driven gizmos years ago. The silly things rattled so much they did not need legs to walk off the bench. The thought of scaling them up and applying steam would be fun to watch but I am not going there.

Actually I am working more towards Barts direction of roller slides... sorta.

Scott

[DetroiTug]

Actually I am working more towards Barts direction of roller slides... sorta.

Good call, some steam car engines like the Mason C used roller ball slides with great success. Two concave straight races.

-Ron