MKIII stator/rotor clearance strategies

As I believe has been mentioned, one can skim the rotor to a smaller diameter to get the required clearance -- at a performance cost, however. In my BMW wrenching days we used to have alternator rotors rewound rather than replaced. The motor shop that rewound the rotors would take a skim cut at the end of the job to make sure they were true. After several customers complained the batteries would not stay up after the rewind, I investigated and found that a cut on the rotor reduced the output from 20A spec to as little as 14A depending on how much they cut. We complained. Ultimately, we changed motor shops when they continued with the skim cuts.

Make sure the inner case support stud nut is backed off so you can tighten up the four nuts that hold the stator carrier/inner case to the crankcase (you have renewed the gasket and made sure the faces were clean and flat?) When satisfied that the inner case is sitting bolted up properly you can run the support stud nut up to the rear of the inner case and then fit and tighten the inside nut. I use a dial gauge reading onto the gasket face when tightening this nut up so the case is nipped with no stress on it at all.
The stator can be filed on the outside in the three areas adjacent to the mounting studs, the top righthand area is larger as it is adjacent to the outrigger bearing and the three holes can be opened up to suit. Be careful when doing this as the laminations can pull and splay apart.
Another area that can cause problems is the stator carrier. Some carriers prevent the stator sitting flat especially when a new stator is used. The stator potting compound around the bolt holes is smaller than the original Lucas stators. The answer is to relieve the carrier around the mounting studs with a Dremel.
Photo showing the difference between stator carriers


Photo showing the stator potting smaller than the stator carrier

marshg246 said:

I don't know much about MKIIIs - Is it possible that the inner primary is cocked or in the wrong location? It would seem that his gap is way off and from what you said, there's no good way to move the stator.

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The actual position of the stator relative to the rotor is determined by the outrigger and the outrigger positively locates to the inner primary by four stepped lugs so there seems to have been a small dimensional error in the machining.

I believe the Mk3 inner case is substantially thicker/stiffer than the pre-Mk3 inner case and attempting to increase the gap at the rear using the support stud doesn't seem to work.

I'm trying to imagine what the actual problem is - personally, I don't like getting around symptoms. If you try the stator in the three possible rotations and the problem remains the same, you'll know for sure that it's not the stator. Of course, it must be in the correct rotation for the leads but that doesn't matter as a test. If the stator is OK, then IMHO, you need to look for the actual problem and not start grinding and drilling.

L.A.B. said:

Stator

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Oops, meant stator - my bad

Stephen Hill said:

The solution is fairly obvious, IMHO.
Step 1. Oversize the three locating holes in the stator to allow lateral movement.

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LAB wrote: You cannot just do that on the Mk3 (see above) as metal also has to be removed from the outrigger as mentioned.

Step 2 in my earlier response deals with obtaining clearance between the stator body and the outrigger plate.

dobba99 said:

Some carriers prevent the stator sitting flat especially when a new stator is used. The stator potting compound around the bolt holes is smaller than the original Lucas stator.

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This just jogged my memory - in the CNW estart fitting instructions, Matt warns of after market stators having less space around the mounting holes than original Lucas ones. He advises carving away some of the potting around the holes in order to achieve proper stator/ rotor clearance. I can see the same thing being an issue here.

The last CNW I did had a Sparx stator, and it needed relieving. I used a finger sander - worked perfectly.

Stephen Hill said:

LAB wrote: You cannot just do that on the Mk3 (see above) as metal also has to be removed from the outrigger as mentioned.

Step 2 in my earlier response deals with obtaining clearance between the stator body and the outrigger plate.

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Yes, as had been mentioned in the 1st and 5th posts of this thread.

LAB wrote: "You cannot just do that on the Mk3 (see above) as metal also has to be removed from the outrigger as mentioned."

I never said you could just move the stator over. I said you would need to also relieve the outrigger.
If you are going to quote/paraphrase/summarize/chastise/etc, please do it accurately.
BTW, is LAB's job to moderate this forum, or answer all the questions?

Stephen Hill said:

LAB wrote: "You cannot just do that on the Mk3 (see above) as metal also has to be removed from the outrigger as mentioned."

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Yes, "as mentioned" by me in my first reply.

Stephen Hill said:

I never said you could just move the stator over. I said you would need to also relieve the outrigger.

If you are going to quote/paraphrase/summarize/chastise/etc, please do it accurately.

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If you'd read through the thread properly you should have seen I'd already mentioned that so it shouldn't have been necessary quote you at all.

And please don't accuse me of quoting you inaccurately as you edited your message after I posted my reply.

Stephen Hill said:

BTW, is LAB's job to moderate this forum,

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Yes.

Stephen Hill said:

or answer all the questions?

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It's no business of yours what questions I choose to answer.

The lady doth protest too much, methinks.

Stephen Hill said:

The lady doth protest too much, methinks.

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Only...I'm not the one protesting.

Update: I have tried a combination of suggestions, including removing some wax behind the stator, slightly reducing the diameter of the studs (chucked in a drill press with a fine file to bring down a couple thousandths, and next will be modifying the outrigger with a dremel. I’m going to try to avoid reducing the stator so I don’t get a power loss, and focus on things that equalize the gap over making it more extreme.

But all this got me thinking that I should as suggested check the crank shaft while I have things apart. I picked up a dial indicator at a yard sale yesterday so perfect opportunity. And I am finding a reading of about .015” wobble on the shaft, which telegraphs to about .03-.035” with the rotor on. There is still the same tight zone between the alternator and stator, but this may be the thing pushing it over the edge where other commandos do fine.

I’m afraid to ask, but how big of a deal is this wobble? Is it something to be expected on this bike or do I have a serious issue (beyond the scope of my current undertaking)?

Thanks,
Anthony

Anvill said:

And I am finding a reading of about .015” wobble on the shaft, which telegraphs to about .03-.035” with the rotor on.

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L.A.B. said:

What is acceptable runout at the crank/rotor end?

I was doing some other work on my bike the other day and decided to check the crankshaft runout at the alternator rotor. I had posted a question earlier about checking the runout with the engine running but it didn't seem there was a reasonable way to do that. So I ended up just putting a dial...

www.accessnorton.com

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Thanks. I’ll double check my dial, hopefully I was reading .0015” rather than .015”. As I said, the dial is new to me so it’s entirely possible.

.0015” is the correct measurement. So I should be okay to not need a fix for that, though it will need to be accommodated in whatever clearance I am able to ultimately get to.

Anthony

Anvill said:

.0015” is the correct measurement. So I should be okay to not need a fix for that, though it will need to be accommodated in whatever clearance I am able to ultimately get to.

Anthony

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Please re-read post #24. Although I doubt the stator is the problem, as far as I can tell, you have not verified that the problem is not a bad (improperly made) stator. The test will take less than a minute if you already have it off.

Also, if you have the original rotor and stator it would be interesting to see if the problem always existed to the degree it does now (very doubtful).

marshg246 said:

Please re-read post #24. Although I doubt the stator is the problem, as far as I can tell, you have not verified that the problem is not a bad (improperly made) stator. The test will take less than a minute if you already have it off.

Also, if you have the original rotor and stator it would be interesting to see if the problem always existed to the degree it does now (very doubtful).

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Yeah, I have checked the Wassell stator as well as the original Lucas stator. They are the same OD and behave identically when bolted up. I have tried rotating the motor in multiple positions and the larger asymmetry remains. The runoff in the crank likely affects it a bit, but the rotor and stator are always incorrectly centered regardless of crank orientation.

Anvill said:

Yeah, I have checked the Wassell stator as well as the original Lucas stator. They are the same OD and behave identically when bolted up. I have tried rotating the motor in multiple positions and the larger asymmetry remains. The runoff in the crank likely affects it a bit, but the rotor and stator are always incorrectly centered regardless of crank orientation.

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I understand, but did you try the stator in the three possible places? That will tell you if the stator is made off center.

Ron Hulton said:

I had the same issue with my bike ...The first thing needed to know is if the rotor is running true on the crankshaft. Do the clearances remain the same throughout a full revolution of the rotor ?? Is the stator parallel to the rotor ??

On mine , i opened up the holes on the stator ever so slightly . I loosened up the rotor and then took a piece of .010" brass shim and wrapped it around the rotor . I found that i eventually had to put a bit of shim under the top left side of the stator . Doing this closed up the larger gap on the left and opened up the right . Snug everything up evenly and go from there .. If lucky you might even get it the first time .

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I'm coming late to this thread. From what I've read, Les [L.A.B.] and Ron are the people offering you knowledgeable, useful advice. If, as Ron suggests, that your rotor O.D and stator I.D. are not parallel [left to right axis], then perhaps the issue is that you do not have the chaincase [inner primary] support stud properly adjusted. See

Chaincase Support Stud

It might be worth the effort to make a small adjustment to this support. Just a suggestion and worth what you paid for it.