Can anyone tell me why the crank big end regrind specifies a 0.090 radius and is labelled "Important." I have always wondered
- Thread starter DennisMo
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Is this something particular to these cranks or is this a common practice in crank regrinding?
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Specified to eliminate/reduce stress riser that would propagate a crack. Its important to mention to the re grinder as its specific to these cranks and their grinding wheel will need a custom dressing to put the radius on. It eats into the life of the wheel so some will not be keen to do the full radius.
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This importance of this has come up a number of times in the past.
Has anybody taken a Norton engine to a machine shop and been told they won't or can't grind it as requested?
Or even worse got the engine back with no radius as requested?
Has anybody taken a Norton engine to a machine shop and been told they won't or can't grind it as requested?
Or even worse got the engine back with no radius as requested?
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- May 31, 2012
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Couldnt agree more. A local shop had my crank for over a month before returning it, telling me they cant do it. Mile High turned it around in 2 weeks and did it right.
acotrel
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There was a crank grinder in North Melbourne which was run by two drunks. When we went there, we always went to the pub next door to find them. If we requested a certain dimension for a journal it was always returned dead on size with the radius perfect. The obvious conclusion is you need to be drunk to do a crank grinding job properly.
acadian
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Since you're in Canada a safe bet is Canadian Chrome & Crankshaft in Markham, they have much experience with norton cranks and are able to produce the proper radius: https://www.canadianchrome.com/
Fast Eddie
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AFAIK all cranks have a radius there? The ‘problem’ is that many (all?) modern car cranks have an undercut radius, so the big end can be ground with a flat faced wheel without disturbing the radius at all.
The issue arises when you take an older radiused crank to a re-grind shop that’s only used to such modern cranks, and the operator either doesn’t notice or (more likely) doesn’t care, and they grind it with a flat faced wheel and grind away the radius leaving a sharp corner.
That sharp corner makes for a VERY weak crank.
The issue arises when you take an older radiused crank to a re-grind shop that’s only used to such modern cranks, and the operator either doesn’t notice or (more likely) doesn’t care, and they grind it with a flat faced wheel and grind away the radius leaving a sharp corner.
That sharp corner makes for a VERY weak crank.
Sudden changes in geometry are stress risers; it's particularly dangerous in components subjected to cyclic loads, which causes material fatigue.
- Knut
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- Jan 23, 2010
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A typical place for cranks to break. We have had that once in our "family racer" even though the radius was correct. Richard Negus told me the crank they had in his 24 hours in Spa at over 100pmh average was ex-expermental with ROLLED, not ground, radii. After that crank had had it in a later race they never again got that reliability in their race cranks.
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- Aug 13, 2008
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I believe John retired and they are no longer in business. I used them a number of times and they did excellent work. The first time I walked in John said , "A Norton crank. It will need a .090" radius".
