Different types of crankshaft radius - what's the (dis)advantage?

I was looking at various models of crankshafts and noticed there are 3
different types of implementing a radius. My technical English isn't
very good, so I made an image that clearly shows the 3 different types:

<http://www.tweakers.net/ext/f/46946/full.png>

Number 1 is probably the most used type. It's easy to understand this
will make the crankshaft less prone to cracking.

But what's the deal with number 2 and 3? At first sight both make the
crankshaft even weaker, but it probably has an advantage. Otherwise it
wouldn't be used.

I've seen 2 and 3 both used in in recent as well as in old engines. Both
in performance as well as in normal engines. So it's not some weird
thing, but it's common stuff.

Can anyone explain what advantage and/or disadvantage each of the 3
different radius styles has?

--
mahi

>Subject: Different types of crankshaft radius - what's the (dis)advantage?
>From: mahi lid
>Date: 11/12/04 11:17 GMT Standard Time
>Message-id: >
>
>I was looking at various models of crankshafts and noticed there are 3
>different types of implementing a radius. My technical English isn't
>very good, so I made an image that clearly shows the 3 different types:
>
><http://www.tweakers.net/ext/f/46946/full.png>
>
>Number 1 is probably the most used type. It's easy to understand this
>will make the crankshaft less prone to cracking.

This a conventional radius formed by a radius on the grinding wheel edges when
the journals are ground. Used on cast iron cranks and some steel cranks.


>
>But what's the deal with number 2 and 3? At first sight both make the
>crankshaft even weaker, but it probably has an advantage. Otherwise it
>wouldn't be used.

2 is used on steel cranks. The radius is rolled into the steel with hardened
steel rollers. As well as forming a radius it compresses the metal surface
rather like shot peening which helps reduce stress cracking. This process
obviously can't be used on cast iron cranks.

3 is just a variant of 2 where the forming rollers have undercut the side
flanges to some extent.

Another advantage of 2 and 3 is you can usually regrind the crank journal to at
least the first undersize without losing the original radius or being reliant
on the machinist to have a properly radiused grinding wheel and knowing what
the original factory specified radius was.
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)

"Dave Baker" wrote:

> This a conventional radius formed by a radius on the grinding wheel edges when
> the journals are ground. Used on cast iron cranks and some steel cranks.
> [..]
> on the machinist to have a properly radiused grinding wheel and knowing what
> the original factory specified radius was.

Thanks a lot Dave!

--
mahi