+- Austinsevenfriends (https://www.austinsevenfriends.co.uk/forum)
+-- Forum: Austin Seven Friends Forum (https://www.austinsevenfriends.co.uk/forum/forumdisplay.php?fid=1)
+--- Forum: Forum chat... (https://www.austinsevenfriends.co.uk/forum/forumdisplay.php?fid=14)
+--- Thread: fantastic but not cheap (/showthread.php?tid=2195)
RE: fantastic but not cheap - Bob Culver - 31-01-2019
Hi Alan, (but worded for others)
I guess it is questionable whether crank wobbling in flywheel or vice versa is the factor!
Unless especially requested and some precision mandrel provided, the crank and flywheel usually balanced together, in which case any dynamic balance within flywheel not likely to be corrected at source.
A colleague recently broke irreplaceable 2 bearing crank in a 4 cyl jowett 10, not long after supposed crack test! With hindsight, excess flywheel runout was suspected...
RE: fantastic but not cheap - Zetomagneto - 01-02-2019
(31-01-2019, 11:58 PM)Bob Culver Wrote: Hi Alan, (but worded for others)
I guess it is questionable whether crank wobbling in flywheel or vice versa is the factor!
Unless especially requested and some precision mandrel provided, the crank and flywheel usually balanced together, in which case any dynamic balance within flywheel not likely to be corrected at source.
A colleague recently broke irreplaceable 2 bearing crank in a 4 cyl jowett 10, not long after supposed crack test! With hindsight, excess flywheel runout was suspected...
Crank is normally zero balanced on its own, then add flywheel, then add clutch so each item is in effect individually balanced, thats how one well known vintage race engineer local to me does it.
RE: fantastic but not cheap - Alan - 01-02-2019
Yes that’s how mine are done. But a lot of people assume the crank is in balance as it comes - they rarely are. Then they static balance the flywheel assembly. That isn’t enough. You have to eliminate the couple imbalance because I think it’s that that causes cranks to break.
RE: fantastic but not cheap - Chris KC - 01-02-2019
Normal practice these days to balance crankshaft and flywheel individually so any flywheel can go on any crank. The precision mandrel is a problem which might be overcome by first balancing the crank then once again with flywheel fitted (but strict instructions not to touch the crank).
RE: fantastic but not cheap - Zetomagneto - 01-02-2019
(01-02-2019, 01:46 PM)Chris KC Wrote: Normal practice these days to balance crankshaft and flywheel individually so any flywheel can go on any crank. The precision mandrel is a problem which might be overcome by first balancing the crank then once again with flywheel fitted (but strict instructions not to touch the crank).
Thanks Alan and Chris, that's always been my understanding of how it should be done.
RE: fantastic but not cheap - Ruairidh Dunford - 01-02-2019
Have any of you dynamically balanced a crank and flywheel separately and then put them together? The results may surprise you, as they did me.
RE: fantastic but not cheap - AustinWood - 01-02-2019
How the crank taper fits the flywheel will have a big effect. Might not be perfectly square of perfectly central.
RE: fantastic but not cheap - Nick Turley - 02-02-2019
(01-02-2019, 09:45 PM)Ruairidh Dunford Wrote: Have any of you dynamically balanced a crank and flywheel separately and then put them together? The results may surprise you, as they did me.
I have and it convinced me that they need to be done as a unit.
RE: fantastic but not cheap - Ruairidh Dunford - 02-02-2019
Precisely my experience Nick - I suspect for the very reasons AustinWood suggests.
RE: fantastic but not cheap - Chris KC - 02-02-2019
That's interesting. I'm not even going to try & guess why, dynamic balance is a complex thing.
The 'modern' way is doubtless based on the relatively fine tolerances / consistency of modern (and new) components, and the imperative to minimise cost of production and maintenance; might not work so well when applying to 1930's parts or copies thereof.