PDA

View Full Version : Small crankshaft and connecting rod



davidwdyer
08-06-2011, 07:49 PM
I am making a small crankshaft with a connecting rod for a small, as yet unannounced machine.

I already made a crankshaft out of stainless and the rod out of steel. The results were not good. The crank galled and stalled.

Remembering the trouble some have had with stainless bolts in steel, I think the stainless may have been a bad idea.

Anyway, I am now going to remake the crankshaft with steel and change the throw some too.

The question is: can I get by without bearings? I'm sure there are a lot of guys here who have done small engines of various types who might have some ideas.

This setup will not run for very long times. I have put a grease zerk on the rod where it connects to the shaft so I can grease it frequently. I'm hoping I can get by without a bearing, but... what thoughts are out there?

JoeCB
08-06-2011, 08:31 PM
I vote for a steel crank and either a Bronze or Aluminum rod. many small engines use a plain aluminum rod running on a steel crank. I made an aluminum conn rod for a small 2 cycle outboard some time ago and its run several hours now with no problem. Suggest a hard strong Al alloy like 2017 which has high copper content.
Joe B

Forestgnome
08-07-2011, 11:33 AM
Whether or not you can get by without a bearing depends entirely upon your application. Not enough info. And that would be a "bearing insert", since without an insert you're still using a bearing (bearing surface). There are steel bearings, aluminum bearings, cast iron bearings, all depend on the application.