Would a brass crankshaft work on a model engine?

[Igor_toko]

Hello,

I know that the ideal choice for crankshaft is steel but I have a watchmaker Emco Unimat 3 lathe and it's difficult to machine large steel components.

I am working on a small boxer 4 engine and have already made some components (engine block, cylinder sleeves, pistons, etc.) And now trying to make a crankshaft.

I am thinking of building it from one piece of brass, do you think it will hold? I intent to run the engine slow and with no load, just as a model engine.

I saw a video on YouTube where one guy makes it from aluminium for a single piston engine and it seemed to run.

My main concerns are:

1. Will it be rigid enough?
2. Will it wear down on the contact areas?

 

[gbritnell]

It doesn't have to be a one piece crank. Just make the webs and silver solder the shafts into them. Plenty of fabricated cranks have been made.

 

[Charles Lamont]

Brass would be probably strong enough, but would most likely not wear well, and it would be difficult to get a satisfactory fixing for things like the flywheel or timing gear.

 

[GreenTwin]

I think bronze wears a lot better than brass.

I look at tensile strength on various metals.

There are some bronzes that are quite strong, and bronze can flex a bit without cracking, unlike gray cast iron.

.

 

[xander janssen]

Brass crank webs with drill rod shafts works great. Advantage is that you only have to sawcut the drill rod, no turning needed.

 

[Apprentice707]

I used to machine solid cranks (and had failures) so I now make fabricated crankshafts in a similar manner to Mr Janssen. I have never used brass or bronze for the webs but I think that bronze would be best.

Regards

B

 

[Steamchick]

I agree with Xander... brass webs are probably OK on a low stressed engine, but would use steel shafts and silver solder the whole thing before cutting the main shaft for the gap for the con-rod. I experienced a copper crank on a 1.5cc diesel (made by the original model maker) - that last about 5 seconds when the engine fired! (not mine!). The big-end was bent by the forces when the engine fired. Just an engine I was given and needed finishing. Since then I fabricated a steel crank which stood up to the stresses without problems.
A brass crank on a small steam engine may be OK just for occaisional low-speed use not developing power...
K2

 

[a41capt]

Brass crank webs with drill rod shafts works great. Advantage is that you only have to sawcut the drill rod, no turning needed.

View attachment 147652View attachment 147653
View attachment 147654

I wish I’d have thought about this before I turned the crank for my Pioneer engine! Non-compression and relatively low impulse on ignition/powerstroke would’ve suited brass or bronze counterweights perfectly!

Well, another tidbit to store away until another project comes along!

John W

 

[Ken I]

See link :-
silver soldering Gerry's beam engine crankshaft
Similar to Xander but I Silver Soldered the pins in place - left the big end pin long (with centres) so I could machine it after soldering - which left it looking ugly (as expected) but it all cleans up (as allowed for).

Regards, Ken I

 

[xander janssen]

Some extra info, I did soft solder the webs to the two pins (big end and crank shaft). Then drilled and pressed pins through the soldered assembly. Finally cut the excess material (2x from big end pin and the crank shaft in between the webs).

 

[Igor_toko]

Thanks everyone for your input.

I am making the webs out of brass and will make the shaft out of steel and will solder it with silver. That should make the process much easier. Thank you again for the ideas