Sparx rotor and stator don't align?

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Jun 14, 2007
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Sooooo... I just installed a new 3-phase Sparx alternator. Unlike the stocker, in which, when installed, the front of the rotor and that of the stator are pretty much aligned, the Sparx rotor is more "recessed," such that the front edge of the rotor is maybe 1/4" back from the front edge of the stator - so even though the rotor is wider than the stator, there is 1/4" or so of "unswept" stator at the front.

Doesn't seem right, but so far as I can tell everything is installed properly - all shims and spacers in original places.

Anybody been through this, who can offer some advice?

Thanks - Brian
Install a thick distance piece (spacer) behind the rotor. don't go too thick or the retaining nut will not have enough purchase on the crankshaft.
Thanks guys. I did a little checking around on the 'Net, and have seen a bunch of photos of the alternator installed - the "recess" appears to be the way it is intended to be. Looks odd, and I would think that it means it generates less electricity than it could, but I guess I won't worry about it.

Appreciate your replies. Thanks - B
I'd have to dust off my old notes from Navy B.E.& E. school, but I think the better the interface between stator and rotor, the stronger the alternator's output.
Strangely enough, I responded to the same question regarding alternator rotor and stator misalignment on another website only yesterday from a T140 Bonneville owner who had noticed the rotor misaligned inwards by around 1/4".

The rotor position on my T140 being exactly the same, somebody else said the same thing, (although none of these were Sparx units as far as I know?) so I don't think that loss of output if any, is going to be that critical especially with a three phase alternator, but if you are in any doubt then I suggest you contact Sparx and get their opinion?
Thanks guys. Would have to agree that some of the area of the stator being "unswept" by the rotor would presumably lower the power generated, but I guess - and hopefully - the thing still cranks off more than enough. It's just a Commando with EI and a halogen headlight, not a BMW with heated....everything!.... so I hope to be good to go.

Thanks for your help. The help I get here - and how quickly it comes - never fail to amaze me. I am grateful. - Brian
My understanding would lean toward thinking that the output at lower RPM may not be as high as it COULD be if you have full interface.
I would be interested to know if the Sparx three-phase stud set was supposed to be used with your kit Brian? And whether it moves the stator position relative to the rotor?
I am sure that the stud kit does exactly that.

The one norton I saw a Sparx 3-phase installed on, the alignment was done with a thick spacer. The primary cover cleared with no issues.
I haven't seen any vendors (other than Sparx itself), including CNW where I bought mine, mentioning the stud kit - although it certainly makes sense. I'll ask Matt Rambow and revert with an answer. Brian
I don't think a stud kit could do other than offer a tad more latteral movement to get the correct shimming of rotor to stator. The stator itself rests against the alloy bosses cast into the inner cover, which the studs screw into. I do observe however that most British bikes I have worked on seem to have the rotor recessed more than would seem optimum to a layman.
Good point Dave. The stator CAN'T go back further, regardless of the studs used. A spacer, as grandpaul suggests, would do the trick, but I've not heard of that before - certainly, there's no mention of it in the instructions that came with the Sparx kit.

I'll see what Matt Rambow says and then let you guys know, but I'm betting he says that the "recess" is normal.

Thanks as always - Brian
My parts book indicates that there are two different shims available for spacing the rotor out further. These are 'rotor shim .010" pt#060665' and rotor shim .036" pt#060664' The quantity is listed as 'AR' which is 'as required'. I suppose the limiting factor is the amount of thread that the rotor fixing nut engages with the crankshaft - as pointed out by Grandpaul. It is recessed so there is a fair amount of leeway. I ordered up a selection of these shims and always end up using some of the thicker ones to get what I feel is a more satisfactory interface. I can find no indication in any of my Norton technical information what the optimum alignment should be.
Interesting, Dave. I imagine to make an appreciable difference, though, I'd need a bunch of those 0.036" shims though. My rotor is recessed about a quarter of an inch. I'm hoping Matt tells me things are fine the way they are. Appreciate the info in any event. Cheers - Brian
Only one (per stud) came off my bike, and the OEM rotor lined up with the stator. - Brian
BrianK said:
Only one (per stud) came off my bike, and the OEM rotor lined up with the stator. - Brian

Yes, three in total = one on each stud, sorry if I did not explain that clearly.
Quite right Les, I was looking at a bare inner case and missing the obvious. One can always machine a little off these three spacers tp recess the stator a bit, although at a certain point I seem to remember that there are clearance issues.
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