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Flywheel Runout
#1
I have read somewhere about the recommended maximum runout for the flywheel. I thought this was in Woodrow, but cannot now find it.

Measured mine this morning at .015", which I'm pretty sure is too much. Recommended fix is to lap it on the high side to straighten things up.

Can anyone tell me what the tolerance is supposed to be please?

Many thanks,
Colin
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#2
Hi Colin

I think 15 thou is at the upper end of OK.  Others will probably correct me.  Be careful, trying to correct run out by enthusiastic lapping of the taper will bring the flywheel too close to the engine and cause all manner of problems. I had this problem with my special.  In the end I left the runout at about 15 thou (even though the taper was not perfect) and used Loctite 660 on the taper.

Howard
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#3
Page A2-46. I also find it hard to find things in Woodrow. You see something then can never find it again. It says runout should not exceed 0.004" but then says many engines are over that. It then says if over 0.015" it should be reduced with a lower figure being desirable.

One thing to note that surprised me is some flywheels have a relieved taper where the middle section is lower than the ends. At first I thought something was wrong but that's normal for later flywheels apparently. Don't try to lap that away!

Simon
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#4
Relieved flywheel taper eh?... You learn something new every day!
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#5
(05-02-2019, 10:29 PM)jansens Wrote: Page A2-46. I also find it hard to find things in Woodrow. You see something then can never find it again. It says runout should not exceed 0.004" but then says many engines are over that. It then says if over 0.015" it should be reduced with a lower figure being desirable.

One thing to note that surprised me is some flywheels have a relieved taper where the middle section is lower than the ends. At first I thought something was wrong but that's normal for later flywheels apparently. Don't try to lap that away!

Simon

And now you've pointed that out I see it's at A1-39 as well! If I become immobile in my dotage I might attempt the creation of an index. 

So .015" is acceptable but the ideal is .004".
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#6
(05-02-2019, 10:42 PM)Colin Wilks Wrote:
(05-02-2019, 10:29 PM)jansens Wrote: Page A2-46. I also find it hard to find things in Woodrow. You see something then can never find it again. It says runout should not exceed 0.004" but then says many engines are over that. It then says if over 0.015" it should be reduced with a lower figure being desirable.

One thing to note that surprised me is some flywheels have a relieved taper where the middle section is lower than the ends. At first I thought something was wrong but that's normal for later flywheels apparently. Don't try to lap that away!

Simon

And now you've pointed that out I see it's at A1-39 as well! If I become immobile in my dotage I might attempt the creation of an index. 

So .015" is acceptable but the ideal is .004".


Amen to that Colin - Woodrow contains some good stuff but the next edition(?) would benefit greatly from page numbers and an index.
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#7
I wouldn't run an engine with a flywheel runout of 0.015". I would remachine it to less than 0.002" maximum and then get the unit balanced.
  This is what happens when things are swapped around. Measuring original crank/flywheel units they have clocked up to around 0.002" total runout. That is basically 0.001" out of true position .
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#8
On cars and elsewhere very many tapers are relieved in the middle. It increases the pressure at the ends where loosening begins. Ford 10 axles which are prone to loosening are remedied by relieving.

Runout tolerance depends on the rpm. Effect is 4X increased at 7,000 rpm cf 3,500. .015 is certainly a lot. Perhaps if it is orientated to compress the inside radii at rear journal at revs it might benefit! Assuming the crank runs true, tapers can be adjusted by careful scraping.

Dynamic balancing of the flywheel alone is dubious unless runs on mandrel exactly as on flywheel. If balanced on crankshaft the shaft ideally needs to be balnced separately first, and correction limited to the flywheel. All a lot of expense. Being a thin plane, just static balance of flywheel assembly is often worthwhile for those with patience.
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#9
(05-02-2019, 08:12 PM)Colin Wilks Wrote: I have read somewhere about the recommended maximum runout for the flywheel. I thought this was in Woodrow, but cannot now find it.

Measured mine this morning at .015", which I'm pretty sure is too much. Recommended fix is to lap it on the high side to straighten things up.

Can anyone tell me what the tolerance is supposed to be please?

Many thanks,
Colin
Runout at the flywheel ideally should be no more than 4 thou in my view.
It is easy to sort using the recommended method.
Because you are fitting a new crank your flywheel needs lapping anyway.
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#10
As Nick indicates I'm taking my new crank and the flywheel into Park Engineering at Malton for them to balance the two together. The run out measured is on my existing installation, but I was wanting to give Park a sensible target to aim for, which sounds like <= .004", but I shall quote Robert Foreman's .002" and see what they say. As is obvious, I am not an engineer so don't know what it is reasonable to expect.

Thanks all.
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