MTFCA Forum

I determined that my original cast aluminum magnet spools were damaged by my last effort at leveling (that means I was over zealous with my hammer after the last engine rebuild). I am now setting up my magnets on my flywheel and am trying an alternate method.

I do not have a KW magnet setting tool. Erik kindly offered the loan of his tool. That would require about a 60 mile round trip and a second trip to return it. I am going to revert to my original method with a new twist.

I installed all new spools and screws. Next I measure the height of the keepers and enter them on a state of the art spread sheet.
What I do after listing the magnet heights is to determine the limits of variance in height I find acceptable. Having polled a few knowledgeable T mechanics I chose 0.010”. That translates to +/-.005”.

So after checking the spread sheet I identified the target height at .005” below the tallest magnet. The first step is to add shims to all magnets which fall more than .010” less than the highest one.

I obtained some fine imported Bavarian shim stock measuring .004”-.005”. Using a notebook hole punch and a larger gasket punch shims were produced.

I had planned on sanding down some of the higher magnet’s spools but that might leave the ends out of parallel. It soon became apparent that the required precision could be obtained with one to two shims.


The result was arrived at by repeating this process adding and removing shims and re-measuring about three times before planned accuracy was obtained.


The next step will be to verify the job by putting the flywheel back onto the crankshaft and turning it to measure each magnet against the same field coil pad using brass feeler gauges.

This method is easy and non-invasive, no magnets or spools were harmed in the performance of this task!

TH

Do you have a spare starter ring gear?

I found that if you lay this on top of the magnet plates you can check that the ring gear is parallel to the flywheel face with a vernier depth gauge and you can identify the high and low spots very easily.

Nice work Terry

: ^ )

I went through that problem a few years ago.

I measured the height of all the new spools and thought I could just assemble the magnets, as they were all the same.

That did not work so goo!

The magnets were a complete original set with all the same markings and were randomly .018 difference in thickness.

The first time I read or heard of lowering the high magnets by whacking them down with a hammer I hated the idea. I still do. I make my shims out of brass stock I picked up at some auction. I get all the keepers within two or three thou. Within the prescribed range of .025" to .040" I figure .002" or .003" is no big deal.

I went through a similar process on my last two rebuilds. In a chance purchase of some other toolmakers stuff, I found a pair of steel blocks with multiple machined holes with their sizes stamped next to them. In another drawer were numerous hardened steel slugs, which were a precise fit for the various holes except for one missing one. Using brass shimstock, sandwiched between the plates, the slug is driven through to make a neat punched hole, first for the screw and then a larger one to complete the washer. I got lazy in the end and cut the sides out to make C shaped shims which could be slid in place without withdrawing the screw each time.

Because he could, I had my godson put the flywheel on their surfacing grinder, and he took the last .002" variation out once I had finished. It sure made setting the gap to the coilplate much easier.

Allan from down under.

Great "fix"!

Terry's posting highlights the importance of getting the magnet clamp heights all the same. IF you have the ability or access, another method that takes this to the next level is to roughly set the height, then chuck the entire flywheel in a lathe, indicate the rim of the flywheel and face off the magnet clamps. Then I also face the crank mounting flange surface of the flywheel, removing only a few thousandths. This 2nd step keeps the magnet clamp surface dead true to the crank flange, eliminating any source of runout.

Dan, not being able to swing an assembled flywheel in my lathe led me to have the magnet clamps trued up by mounting the flywheel in the machine shop grinder set up for this purpose. The grinding process seems so much more gentle than the interrupted cuts made on a lathe. We proceeded gently, finally stopping just as the last of the keepers was kissed by the wheel. A side benefit of grinding is there is less cleaning up to do when the grinding is finished.

Allan from down under.

Most automotive machine shops have flywheel grinders that would make short work of kissing the top of the magnet clamps but they would not be able to grind the mounting flange because they can't get down into the 4" dia counterbore. The interrupted cut in the lathe is never a problem because the cut is very light and we use a sharp tool with a diamond lapped point and small nose radius to keep the cutting forces to a minimum. An air blast during this makes short work of the tiny chips- must better in fact than trying to clean things up after.

You guys are going about leveling the hard way. As Dan McEachern says and it's the way we do it quick and easy.
Any local machine shop can resurface the magnets as we have .

<<<The official magneto gap is .025" to .040". That's a range of .015". Does a variation of .002" or .003" within that range really have any appreciable effect on magneto output?

Steve, it is possible for some folks to misunderstand your post. You are referring to two different measurements. Gap between magnets and field coil and the totally different magnet height variation.

The allowable gap (.025"-.040" is a range of .005" ) can be expressed as .0325" +/- .0075.

So allowing the magnets to vary .003" means your gap must be held to .037"-.024" to remain in specs. The variation on magneto output varies with the square of the gap so no, a .003" change is negligable . Since the target gap is .030" the variance of .003" in magnet height is 10% of the gap. The square of 10% (.1 X .1 = .01) is 1%. If one magnet was moved .003" it's effect would be on 1/16 of the output since there are 16 magnets. So the output would decrease 1/16% which is 0.0625% truly negligable.

What my original post was concerned with is being able to assemble the flywheel with normal hand tools and not end up with a magnet striking the field coil or going out of specification. Leveling the magnet keepers with a surface grinder or on a lathe is absolutely the fastest and most accurate method. One could just about bolt anything up with no measuring and have a superlative result by grinding or turning. Of course the surface grinder or lathe is not a hand tool and not in every shop. You would also be well advised to dynamically balance the flywheel after surface grinding, and to remove all grinding particles from the magnets afterwards... I'm not sure how to do that (pressure washing?). Not everyone wants to add a shop charge on to the magnet setting procedure.

IMHO, TH

Most flywheel grinding machines do not have magnetic chucks- they use a center bolt and a centering cone to hold the flywheel to the grinder table. Just pointing out that a commonly available service of automotive machines shops is flywheel resurfacing, where as most automotive machines shops probably don't have a lathe large enough to chuck up a flywheel, and if they do, it probably means pulling the gap piece out of a smaller machine, which is a PITA= $$$.

Electromagnetic chucks use DC power. Running AC thru a chuck makes it into a demagnetizer.