Dynamic Balancing

Yes, but if you drill the crank cheeks as a substitute 'dynamic balance',
then this could well alter the static balance factor.

And, isn't there an account on the NOC Forum that AMC static balanced the cranks
on the assumption that the crank cheeks supplied were all the same ??

Triton Thrasher said:

Jseng's quoted BenG idea is a subsitute for dynamic balancing.

Static balancing to a factor is likely to be done by drilling the flywheel.

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Rohan said:

I'd have thought that balancing Norton crank cheeks without the flywheel being involved
could well end up with a different balance factor ?

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Presumably folks have done this, and compared the results, or dynamic balancing wouldn't get such good press.
(And the V8 engine folks especially, but their cranks are a tad longer)

You also see all sorts of schemes for easily being able to alter balance factors,
for assembled engines (Commandos) - heavier or lighter plugs to bolt into the flywheel for example.
The factory must have done something like this for various new models, or they would have had to build
a whole fleet of engines with various factors to test out...

Fast Eddie said:

The way to do it would be to rebuild an engine and have the crank statically balanced to the required / correct balance factor. Then ride it somewhat to see what it's like. Then strip it again and have the crank dynamically balanced without changing the balance factor and evaluate the difference.

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"Yes, but if you drill the crank cheeks as a substitute 'dynamic balance',
then this could well alter the static balance factor."
more than likely. But If you are balancing the crank without the flywheel then I see it as a 2 step proceedure.
Dynamic balance first (without the flywheel) then static balance (with flywheel) to your desired balance factor.
Or am I missing something?

Rohan said:

Yes, but if you drill the crank cheeks as a substitute 'dynamic balance',
then this could well alter the static balance factor.

Click to expand...

Yes.

1. It might not matter much.

2. You might correct it when the flywheel is in place.

3. The first thing that was said about it by jesng was "poor man's." You may well find faults in it, compared to dynamic balancing on a £30,000 installation.

And, isn't there an account on the NOC Forum that AMC static balanced the cranks
on the assumption that the crank cheeks supplied were all the same ??

Click to expand...

AMC were capable of worse bullshit than that.

Rohan said:

Now, Mr Gilbert Smith was the MD at Nortons for some years.
At some point - post AMC ? - he was gone.
Not the same one ?

The story goes that Enfield's big twins had some terrible vibration problems,
and they resorted to dynamically balancing the cranks to finally resolve these problems.
Alone amongst British motorcycle manufacturers, it was said.
They were supposed to be smooth, but not perfect...
You CANNOT ever perfectly balance a reciprocating system with an out-of-balance flywheel, of course.
And still have to decide on what balance factor to go with.

I'd have thought that balancing Norton crank cheeks without the flywheel being involved
could well end up with a different balance factor ?
Especially if more than a little material was involved ?

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this shows how the Enfield guys did it.

That is one sturdy looking little one piece crankshaft. The mainshafts appear to be almost as big in diameter as the conrod journals.
There appears to be barely enough of a land for the mainbearing and seal before the mainshaft goes into the spline, but it must work.

Unfortunately the cases on the Royal Enfield were paper thin, perhaps that is where the reputation for fragility came from.
There again, I'm referring to some empty Constellation cases that I had a good look at. Things may have been beefed up for the Interceptor.

Glen

worntorn said:

That is one sturdy looking little one piece crankshaft. The mainshafts appear to be almost as big in diameter as the conrod journals.
There appears to be barely enough of a land for the mainbearing and seal before the mainshaft goes into the spline, but it must work.

Unfortunately the cases on the Royal Enfield were paper thin, perhaps that is where the reputation for fragility came from.
There again, I'm referring to some empty Constellation cases that I had a good look at. Things may have been beefed up for the Interceptor.

Glen

Click to expand...

looks pretty stout to me

https://www.auctiva.com/hostedimages/sh ... 0&format=0

heres some more Royal Enfield Interceptor photos

Those Interceptor cases are beefed up considerably from the Constellation.
Sure like the look of that crank.

Glen

I think people still managed to break Interceptor cranks.

Fast Eddie said:

Fantastic video! Cool for my kids to watch too as a lesson in physics!

Not wanting to be too dull about it, but that showed something that would be way out of 'static balance'.

I personally finding it interesting to hear the different views on static balancing vs dynamic balancing. Mr Maney is adamant that his cranks do not need dynamic balancing, instead proper / careful static balancing is all that's required.

What say our forum experts about this...?

Click to expand...

And Steve balanced my 80.4 crank very well as far as I am concerned, using a balance factor I am now told is too high!

In the '70s I had a MKIII crank balanced by Owen Greenwood, who was the guy who started balancing race cranks in the '60s, yep, it was done statically, and he offered to re-do it if there was any vibration at any point in the rev range I used, yep, you guessed, I never had to go back.

That doesn't mean I wouldn't consider dynamic balancing and would suggest that anyone in the UK who thinks they might benefit from it go to see Bassetdown Engineering. Personally I think longer 4 cylinder cranks might benefit most.

If a crank is well machined and each side is symmetrical (balance wise) then it should already have good dynamic balance. Cast cranks like stock Nortons are not as accurate.

If you remove the flywheel and twist the cheeks into 180 deg crank configuration then yes - you must balance the cheeks to achieve dynamic balance 1st and then bolt everything back together and cut/drill the flywheel to achieve the desired static balance.

You can send out your crank to have it dynamically balanced on an expensive machine. But I don't like to send things out unless I have to. "Experts" can still make mistakes. One balancer insisted on having all the parts on hand and then ground some metal off the top of the rod where it was thin - making it weak and ruining it. Another job came back after being dynamically balanced on an expensive machine - when I checked it I found that the vertical static balance was a little off - the counterweight did not hang exactly vertical when set up on edges to check the alignment. It needed some correction. This can happen because balancing machines use a tall stack of gram washers that are bolted to the journals and if that stack is not perfectly symmetrical (if the bolts & assembly are skewed out of center line with the journal), then the weight can be a little offset and throw off the alignment.

Balancing the cheeks "poor man's dynamic balance" is a way of balancing the ends of the crank and thats what dynamic balancing is all about - keeping the ends from wobbling. Like I said - I haven't tried it yet but it makes sense. Of course its better to dynamic balance - but there are diminishing returns. Dynamic balance is a left/right refinement and probably won't make as big a difference as good static balance. Once you get down to a few grams from perfect or a balance factor a couple percent high or low - you probably won't feel the diff. Presently my crank is only static balanced and its smooth enough that I never think about it even in a solid frame. But my pistons only weigh 170 grams each bare so there isn't much shaking going on.

SteveA said:

Fast Eddie said:

Fantastic video! Cool for my kids to watch too as a lesson in physics!

Not wanting to be too dull about it, but that showed something that would be way out of 'static balance'.

I personally finding it interesting to hear the different views on static balancing vs dynamic balancing. Mr Maney is adamant that his cranks do not need dynamic balancing, instead proper / careful static balancing is all that's required.

What say our forum experts about this...?

Click to expand...

And Steve balanced my 80.4 crank very well as far as I am concerned, using a balance factor I am now told is too high!

In the '70s I had a MKIII crank balanced by Owen Greenwood, who was the guy who started balancing race cranks in the '60s, yep, it was done statically, and he offered to re-do it if there was any vibration at any point in the rev range I used, yep, you guessed, I never had to go back.

That doesn't mean I wouldn't consider dynamic balancing and would suggest that anyone in the UK who thinks they might benefit from it go to see Bassetdown Engineering. Personally I think longer 4 cylinder cranks might benefit most.

Click to expand...

My Maney crank has been statically balanced by Maney using JS info and specs to match the JS rods & pistons and thats how I'll be running it me thinks.

jseng1 said:

...there are diminishing returns. Dynamic balance is a left/right refinement and probably won't make as big a difference as good static balance. Once you get down to a few grams from perfect or a balance factor a couple percent high or low - you probably won't feel the diff.

Click to expand...

Well put.

If you were to cut off one of the cheeks and weld it onto the remaining cheek on the opposite end of the crank, you could still statically balance it. Dynamic balancing, on the other hand, would (or, should) show you how far off things would be. For most of us (general road work) with a stock form crank, statically balancing it to the correct balance factor (whatever that may be) will take care of anything we could ever feel in the bars.

Nathan

Fast Eddie said:

SteveA said:

And Steve balanced my 80.4 crank very well as far as I am concerned, using a balance factor I am now told is too high!

Click to expand...

My Maney crank has been statically balanced by Maney using JS info and specs to match the JS rods & pistons and thats how I'll be running it me thinks.

Click to expand...

Yes I provided Steve with the specs for the JSM rods and pistons, but after discussion the balance factor we agreed was high 70s, not as Jim now uses high 60s.

But I am perfectly happy with the results, it just doesn't seem to align with current views.

Owen Greenwood used 80% as a baseline!

SteveA said:

Fast Eddie said:

SteveA said:

And Steve balanced my 80.4 crank very well as far as I am concerned, using a balance factor I am now told is too high!

Click to expand...

My Maney crank has been statically balanced by Maney using JS info and specs to match the JS rods & pistons and thats how I'll be running it me thinks.

Click to expand...

Yes I provided Steve with the specs for the JSM rods and pistons, but after discussion the balance factor we agreed was high 70s, not as Jim now uses high 60s.

But I am perfectly happy with the results, it just doesn't seem to align with current views.

Owen Greenwood used 80% as a baseline!

Click to expand...

I had a Norton crank (in a Triumph motor) balanced at 80% (dynamically, by Basset Down) and it was great.

65% 70?% or 80% balance factor.

First you should specify wet or dry. A wet balance factor of 65% equals a dry balance factor of 72% with a stock Nort crank.

And can't just rely on the numbers. There is a problem. If you weigh each end of the rod and get (for example) 100 grams on the small end and 300 grams on the big end - you have one set of numbers to use to find a balance factor. Now if you take the same rod and switch the rod cap to a heavier cap that makes the big end weigh 400 grams (instead of 300) then it will make the small end of the rod appear to weigh less because when you weigh the small end you suspend the big end in the center of the journal and the heavier cap will counterbalance the small end - making the small end appear to weigh lighter when the mass of the small end has not changed. Imagine an extreme case where the cap and bolts extend way out from the journal center and is so heavy that it completely counterbalances the small end and makes the small end appear to weigh 0 grams on professional balancer - its Bullshit. This throws off your balance factor specs. You need a different way of weighing rods depending on how heavy the rod caps are. So its all goofed up and no one that I know of has the solution - they all crunch numbers but don't take the rod cap weight into account.

You need different balance factors for each kind of rod. Alum rods with steel caps will need a different BF than all steel or all alum rods etc. Every brand will be different.

The only way I found to get the BF right is here (a crude technique that needs refinement - but it pointed me in the right direction). You will have a different BF for each setup.

balance-factor-scratch-test-tool-t15134.html?hilit=BALANCE%20FACTOR%20SCRATCH%20TEST%20TOOL

jseng1 said:

65% 70?% or 80% balance factor.

So its all goofed up and no one that I know of has the solution - they all crunch numbers but don't take the rod cap weight into account.

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Doesn't really matter how goofed up it might be Jim, in both cases, Steve Maney and Owen Greenwood, I was/am happy with the results!

If it works - thats the bottom line and all that really matters. Its a headache if you delve too far into it. But generally speaking - 80% and above (wet) is too much and less than 50% (wet) is too little. Small wonder that 65% (in the middle) works well.