Mike balanced my crank, flywheel, and magneto as a single unit. Since then, of course, I've discovered a broken magnet. That meant that I had to separate the flywheel to get at the magnets to replace it.
Rather than just replace one magnet, I thought it would be a good idea to take all of them off to test them for cracks. Of course that means I'll need to rebalance the flywheel, as the magnets vary in weight.
They weigh from 389 to 402 grams.
I marked all the magnets (on the north poles to avoid confusion) with the number of grams over the lightest. So the one that weighs 389 grams gets 0 and the one weighing 402 gets 13.
I really don't want to take the crank out of the engine, which has only a few hundred miles on it, so I'm thinking what I need to do is this: Try to place the magnets around the flywheel with the weights distributed as evenly as I can by the numbers. Put on the hardware (spacers, keepers, screws) to hold them in place, but don't peen the screws. Put the flywheel with magnets on the balancer and rearrange magnets if one side is particularly heavy, getting as close to balance as possible that way and then fine tuning with a little flywheel drilling if necessary.
Does that seem reasonable? Maybe I'm over-thinking this. The flywheel with magnets will weigh almost 23,000 grams, so maybe a variation of 14 grams between the heaviest and lightest magnets isn't enough to matter. Opinions?
It's too bad you already removed the magnets. It would have been good to mark them in order around the flywheel and also mark the point where they were attached to the flywheel. Then you would only need to balance the magnets you replaced. You could look for a good magnet of the correct polarity which weighs close to the one which was removed and grind a little off it to make it the same weight.
Anyway the faster you go the more that balancing will help the engine run smooth. Good luck with your work.
Steve, my son Anthony takes a set of magnets and works on them with a linishing belt so they are all the same weight. Perhaps a bit of overkill considering the mass of the flywheel, keepers and spools, but it can't do any harm.
Just a thought.
Allan from down under.
Did you index the flywheel and crank before you removed it ?
Having them all weigh the same or spreading the light to heavy ones so the static balance should be about right sounds nice but -
That only works out if they are all uniform in weight at both ends and the center of mass for each magnet is equidistant (sp?) from the center of the flywheel. Does all that make sense?
If selecting magnets from a stack, I'd try to pick those closest to the same weight and then bolt em up to the flywheel. Only then would I start to worry about balancing things.
I am working on doing a dynamic balance on my flywheel. The secret is to use a spare tail shaft mounted to the flywheel so that it can be put into balance with more ease. It will work as you show above if your crankshaft is in balance.
It will also work as you show above when the crank is out of balance as long as you index the crank to the flywheel.
Of course as you know the static balance will get you close but doesn't insure it will be in balance when spinning... for that you need to dynamically balance... which is what I'm working on now for my engine.
We always make sure the magnets that are across from each other, weigh the same. Of course this requires you to have lots of magnets laying around, which we do. Once this is done, then we put two tail shafts that are set aside to be used on the static balancer. Then the heavy side is drilled as far out to the edge as possible on the heavy side, until it is balanced.
Without digging into another magneto for more, I have thirty magnets. Out of those I was able to find sixteen within a five gram range and place them around the flywheel with equal weights opposite. It may not take much to balance this thing after all.
George, yes, I did.
It seems to me that unless you know the exact weights and positions of all of your original magnets then it really doesn't matter. Weight variations of the originals played in to the balancing of the assembly.
If you balanced the flywheel with magnets and the crank together, unless you indexed the flywheel to the crank and weighed and indexed the magnets as you removed them, there will be no way short of removing the crank and starting over to get the balance perfect. Whether on a less-then 2,000 RPM engine this will make a difference or not, who can say? I doubt that Ford worried much about this. Without counterweights on the crank, the assembly isn't balanced anyway.
Steve, it sounds like what you're doing is way better than Ford ever did, good luck with the rest of your buildup!
One (admittedly trivial) question - is there any significance to the dimples that are halfway up the legs of the magnets? I have 20 magnets on a board (16 plus 4 spare) set aside for a future flywheel buildup and none of them have the dimples.
I have no idea whether the dimples mean anything. All the magnets in this magneto had them, but I haven't found them on any others. There is quite a variety of details among magnets. I don't know whether they have to do with different times of manufacture or different suppliers. Maybe both. When Martin drew the magneto apparently the magnets he used had a circle around the washer, but I haven't yet found any that are marked like that.
I'm sorry, but I think you have an issue with the balancing if you balance the flywheel alone. Since it was balanced together with the crank, you may risk that some unbalance in the crank got outweighed by a similar unbalance in the flywheel 180 degree off set.
When I balanced my flywheel, I managed to use a regular wheel balance rig. All you have to remember is, that when the machine says you should add 5 grammes somewhere, you should remove 5 grams on the opposite side.
An even though the few grammes are minimal compared to the weight of the flywheel - it matters a lot when it is rotating 1500 - 2000 RPM.
I grind down the heavy magnets until they all weigh the same.
Terry, are there springs on your machine to resist the oscillation?
How do you test a magnet for cracks?
Yes, that was the thought. I have not gone to a dash pot like in your machine. I also have found in my test that they are not needed. Originally I wanted to limit swing as well as dampen it. The construction of the tail stock limits excursions and gravity seems to do what the springs were intended for.
So they may be removed in the final design. I have built a strobe today and will make up the adjustable mount next.
I've been thinking about getting a small digital scale for precision and ease of use in balancing parts. I have a triple beam balance now. Does the magnetism mess with most digital scales?
Travis, rap it against an anvil or other solid object a few times, first one leg and then the other. If there are any cracks, that should get them to show up.
Thanks for your input Tom. I am sure Anthony would be pleased to know he is on the same track as someone with your experience. Every little bit helps, or at least doesn't detract.
Allan from down under.
Its impossible to static balance a crankshaft and flywheel together and have the assembly be in balance when rotating. It is possible to static balance the flywheel and have be in balance because the shape of the flywheel (essentially a rotating disc) allows it to be balanced in a single plane and due to the shape, difficult for an imbalance condition to create a couple which is an unbalance condition with an axial distance between them. Sorry to say it but the crank needs to come out and be dynamically balanced to do it correctly.
Allan, theoretically it shouldn't matter that the magnets all weigh the same. It should be (theoretically) possible to perfectly balance a flywheel with magnets of different weight. But, if all the magnets weigh the same, should you have to replace one some day for some reason, it might make it easier to do so without rebalancing everything.
Terry, I am trying to wrap my head around your design. My gut reaction is that springs might be counter-productive. I think adding springs would just raise the frequency of the imbalance harmonic, which would require faster rotation of the part being balanced.
You might not need a dashpot if the imbalance at harmonic does not exceed the travel of your machine. To make your strobe trigger correctly, it must do it at the point of maximum deflection because that is the only point in which the oscillation is in phase with the spot of imbalance.
If you need to limit the deflection, simple friction might work. The problem with using friction is that friction dampens in a more or less linear fashion where as hydraulic dampening is logarithmic.
Travis - you could use a dye penetrant (spl?) test.
The magnet thickness was a bigger problem for me.
They all looked the same, but varied in thickness between .005 to .0025 from least to most.
My plan to carefully measure a new set of spools and determine they were all exactly the same thickness was flawed!
James, the reason the spools are soft is so you can squash them to level the magnets.
I suppose you could throw the magnets into a surface grinder so they will not require leveling. I bet hand leveling was faster than precision machining back in the day.
I love discussions like this, because the physics involved fascinates me, and a lot of our regular posters are extremely knowledgeable! And very good at explaining things to dummies. Sometimes the dummy is me.
I HATE discussions like this, because in a past life I sometimes needed to moderate discussions between dissenting engineers (RF is a strange universe). I have a tendency to notice minor errors, but can also be very wrong myself (and often am wrong, been proven so).
I don't really like to point out other people's errors, despite many lengthy diatribes to the contrary.
So there. Preface completed.
I have known Dan McE for more than 40 years. I will rarely disagree with anything he says! He knows much of this stuff better than most people EVER will. He certainly knows balancing over-all better than I do. But his opening statement copied and pasted "Its impossible to static balance a crankshaft and flywheel together and have the assembly be in balance when rotating. " is in error. It is possible, but extremely unlikely, for the exact reason he says.
Dan McE, I caught the same comment you did, only after your comment on it. Thank you for your comment and your explanation.
And I hope I did not offend anybody.
Drive carefully, and enjoy, W2
This is a 1913 Flywheel balance as part of the engine rebuild for a customer from New Jersey: it was off significantly that I had to drill two 7/8" holes to get it to balance. machine saw this imbalance as 134 grams per inch of radius on the flywheel so if left untouched, parts would of flown off the car.