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Alternator gap adjustment
#528672 02/17/14 1:29 am
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DavidP Offline OP
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Just checked the gap around my rotor and it is not equal, tight 8 thou on one side and maybe 10 thou opposite that spot.
So, how does one adjust this? Remove the stator and gently tap on the studs until the gap is uniform?
Thanks


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Re: Alternator gap adjustment
DavidP #528673 02/17/14 1:39 am
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0.008" is OK,but it's the minimum.If you can rotate the crank through a full revolution and it's not tighter than 0.008" at that point,you'll be OK.
You might be lucky enough to just pull it central if you loosen the 3 nuts,but probably not.I normally end up removing the stator and bending one or two studs with a soft hammer.If you bend one stud 0.003",the stator will move 0.001".

I like to have slightly more gap at the bottom and toward the clutch.Chain load will pull it in that direction.Two strips cut off a beer can and stacked together makes a good non-magnetic 0.008" feeler gauge.

Re: Alternator gap adjustment
DavidP #528792 02/17/14 7:23 pm
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The tight spot is at about 7 o'clock. I rotated the engine a few times when setting up the clutch, and it evened up a bit. Guess I'll be OK.
Thanks


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71 A65L "Zelda"
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72 T120V cafe project "Mr. Jim"
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Re: Alternator gap adjustment
DavidP #528862 02/18/14 3:22 am
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my norton as new was the same. always scared the hell out of me to "carefully set over the studs" with some sort of pounding tool so i never did it. recently it has occured to me to ream out the stator holes slightly and then use three feeler gages to centralize before tightening the stator nuts. anybody ever do this??

Re: Alternator gap adjustment
DavidP #528868 02/18/14 6:27 am
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I wouldn't go there jaycee. I would think the bolts would wobble all over the place in your enlarged holes frown. As for the feeler gauges, see non magnetic beer can solution earlier. Now, here's one for Magnetoman to get his teeth into wink. If the rotor is not running true it is cutting the magnetic field more efficiently thereby upping the current? Discuss smile

Re: Alternator gap adjustment
Adrian1 #529156 02/19/14 7:20 pm
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If the rotor is not running true,it's usually easy to fix.If you carefully file the back face of the rotor to make it square,you can tip the rotor back to central.You might only need to file off 0.0005".

Re: Alternator gap adjustment
DavidP #529777 02/23/14 2:09 am
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I took a sanding drum in a power drill and ground off a little of the stator. Instant clearance. No drilling out of the stator holes and then hoping everything stays put. ( I lost a rotor/ stator combo on my Atlas because of this). No pounding on the mounting studs and hoping they stay put.
Quick and clean. The clearance remains every time you R&R the stator.

Re: Alternator gap adjustment
DavidP #529955 02/23/14 6:52 pm
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Skimming a rotor in the lathe is just as easy.

Re: Alternator gap adjustment
downhere #530008 02/24/14 5:40 am
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Hi,

Originally Posted by SEATTLE GS
sanding drum in a power drill and ground off a little of the stator.
No pounding on the mounting studs

Originally Posted by downhere
Skimming a rotor in the lathe is just as easy.

Errrm ... why would you do any of this? confused

Given the widely-known information that pattern parts suppliers work to different standards, and a rotor and stator only work together with a clearance of a few thousandths of an inch:-

1. Why would your first check not be to ensure that the rotor fits inside the stator with the correct clearance all the way round? Only if neither rotor nor stator can be replaced to get the minimum clearance all the way round can I see any point in skimming the rotor?

2. Given this Forum has been around since 1996, do you seriously think this problem has never arisen before? The solution detailed by Adrian is the one that's been posted several times over the years; I know this because it's the one I use and I first read it on here.

3. Fitting rotor-'n'-stator as one unit means the stator mounting studs are moved the miniscule amount necessary to keep the stator Concentric with the rotor. If you move the studs individually, you'll never get it right (at least, I never have frown ).

4. If you "pound on" the stator mounting studs, you'll rip them out of the crankcase; I can move 'em with hand pressure.

5. The stator only generates its maximum output with the minimum clearance from the rotor all the way round. If you "[grind] off a little of the stator" or "[skim] a rotor in the lathe" just to get minimum clearance at one point, if the clearance is larger elsewhere, the stator coils at that/those point/s won't generate their maximum output. Yes, thousandths of an inch do make a difference when you're using magnetism to generate electricity. wink

Hth (with apologies to David the o.p. who knows the above).

Regards,

Re: Alternator gap adjustment
DavidP #530131 02/24/14 6:27 pm
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All very well Stuart, have you tried adjusting gaps where the stator is mounted in the outer primary case as mine was? It charged just as well as any after the skimming.

Re: Alternator gap adjustment
downhere #530184 02/25/14 12:22 am
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For anyone who saw my now-missing post, I decided to delete it to avoid an argument. Just center your rotor in your stator, and don't do anything to increase the gap because you will decrease the output.

Re: Alternator gap adjustment
DavidP #530188 02/25/14 12:36 am
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While the alternator is off, again, I might try swapping the studs around to see what effect that has. Be good to check for straightness in any case.


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71 A65L "Zelda"
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Re: Alternator gap adjustment
Magnetoman #530204 02/25/14 3:27 am
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Originally Posted by Magnetoman
For anyone who saw my now-missing post, I decided to delete it to avoid an argument. Just center your rotor in your stator, and don't do anything to increase the gap because you will decrease the output.


confused FWIW I thought you were right on the money smile

Re: Alternator gap adjustment
downhere #530207 02/25/14 4:19 am
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Hi,

Originally Posted by downhere
have you tried adjusting gaps where the stator is mounted in the outer primary case

With both triples and a twin, I've done it in both the timing compartment (triple) and the primary case (twin); ime, installing the rotor-shimmed-inside-the-stator as one unit works in both. What problems did you encounter?

Regards,

Re: Alternator gap adjustment
DavidP #530215 02/25/14 5:53 am
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Im a bit late coming to this thread, and probably like going to the pub after its closed, but with the 68+ engines (I assume were talking about your A65) the Alternator sits within a cast housing, as mine has always been a tight fit in here I struggle to see how you can adjust its position by moving the studs confused

However, depending on which way around your cable is exiting the alternator (and providing your cable outer hasn't gone brittle) you can remove the stator and turn it around, this should also give you 120 degrees of stator movement which may either worsen or improve the gap (which is all relative to the accuracy of the stators manufacture).

It could also be an interesting move to remove all the primary, and put a dial gauge on the crank shaft, see if that is out.


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Re: Alternator gap adjustment
Stuart #530226 02/25/14 7:45 am
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Originally Posted by Stuart


3. Fitting rotor-'n'-stator as one unit means the stator mounting studs are moved the miniscule amount necessary to keep the stator Concentric with the rotor. If you move the studs individually, you'll never get it right (at least I never have).

4. If you "pound on" the stator mounting studs, you'll rip them out of the crankcase; I can move 'em with hand pressure.

I'll still whack the studs on a Triumph.If I want a stud to move 0.003" it'll move 0.003",and I'll measure that before I re-fit the stator.I've never broken a crankcase doing it and I doubt that I ever will.Each to his own,I suppose.

Re: Alternator gap adjustment
DavidP #530240 02/25/14 9:55 am
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MMan--didn't see anything wrong at all with your original posting.

Re: Alternator gap adjustment
DavidP #530250 02/25/14 10:39 am
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Quote
 It charged just as well as any after the skimming.

As it works ,
I would say it charges well enough , but I wonder about ' just as well ' .
But an over gapped rotor will give better service whan a rubbing one

Some bikes stators mound to the primary case ,
the final clearance
As the rotor/primary assembly goes on
then becomes an act of faith ... adding a few thousandths clearance
Say to .012 ?
before fitting makes
Sense against any potential loss in output

I wonder if anyone has tested the 'Lucas gap' and charted
the loss in watts per .001 added ?
... any volunteers ?







Re: Alternator gap adjustment
quinten #530281 02/25/14 2:08 pm
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Originally Posted by quinten


I wonder if anyone has tested the 'Lucas gap' and charted
the loss in watts per .001 added ?
... any volunteers ?

I would love to set up an automotive electrics research lab.
All I need are the winning numbers for the next Lotto. laughing


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Re: Alternator gap adjustment
quinten #530291 02/25/14 2:47 pm
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Originally Posted by quinten
I wonder if anyone has tested the 'lucas gap' and charted the loss in watts per .001 added ?
This actually is a very easy measurement to make given just a lathe, bracket to hold the stator on the toolpost, voltmeter (or oscilloscope), and 1 ohm resistor.

I have all of the above(*) but I'm not going to report the measurement here. Because, the right thing for someone to do is to bend the studs (or replace them) to make the stator Concentric with the rotor, thereby giving the max. output it is capable of. However, if instead of a relatively easy fix someone would rather butcher components in order to end up with something that works worse than it should, go for it.


(*)for this measurement the rotor is held in the chuck by a steel bolt to simulate the magnetic properties of the crankshaft, and the stator held in an Al bracket that bolts to the front of the plate holding the magneto that is shown in:

http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=463824#Post463824

Since the OD of the rotor is smaller than the ID of the stator it can be translated sideways from having essentially no gap with a pair of coils on one side, to having a gap of ~0.015".

Re: Alternator gap adjustment
DavidP #530309 02/25/14 5:14 pm
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Perhaps "pound" was an exaggeration.
I have spent many hours gently trying to push a stator a few thousandths this way and that. Perhaps the rest of you have incredible luck with that method and can dial in the gap in minutes but that isn't what I have encountered. If I can get .006 all around I am happy. Or a minimum of .006 at the tight spot. I will fiddle with it gently for a short time before grinding. But expecting two different Brit companies to be dead on to the thousandth is wishful thinking. My patience ran out at least a decade ago. So I carve off a very few thousandths off the plastic and steel laminations and I can move on. Maybe I do lose a little bit off the total output. It is not a perfect world. I know that this method is far better than drilling out the three stator mounting holes.
I used to put three feeler guages .008 at 120 degrees apart between the stator and rotor and tighten the bolts hoping it would center. No luck with that either

Re: Alternator gap adjustment
DavidP #530317 02/25/14 7:00 pm
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There is simply no room to move a stator around in an outer primary case fitting. Have you ever looked at a Matchless twin and hybrid Norton case M.M?

Re: Alternator gap adjustment
downhere #530330 02/25/14 8:27 pm
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Originally Posted by downhere
There is simply no room to move a stator around in an outer primary case fitting. Have you ever looked at a Matchless twin and hybrid Norton case M.M?
I have a Matchless twin, so the answer is yes. If the stator isn't Concentric with the rotor the number of possibilities for that problem are limited: bent studs, badly made reproduction stator, or badly made reproduction rotor. In the case of unit Triumphs and BSAs the studs are long enough that they are the first place to look for both the problem and the solution.

Re: Alternator gap adjustment
DavidP #530351 02/25/14 10:29 pm
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I have a p11 motor in a trackmaster frame. It has the same system of the stator in the primary cover. very poor. No way to check it except put ink on the rotor and kick it over a few times and see if it rubs. If not, cross your fingers and bolt it up.

Re: Alternator gap adjustment
SEATTLE GS #530355 02/25/14 10:47 pm
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Originally Posted by SEATTLE GS
I have a p11 motor in a trackmaster frame. It has the same system of the stator in the primary cover.
When I got home tonight I took a look at my G12 and G15/45 engines, both of which are in pieces. The mounting system isn't bad as long as the factories stuck to the proper tolerances. The outer cover (containing the stator) is keyed to the inner cover by dowel pins so there isn't even 0.001" of play between them. The same lack of play for the inner cover to the engine case.

I have a pretty complete set of Triumph and BSA service bulletins, including ones covering the late pre-unit twins that used the same mounting system for the stator. It's been quite a while since I read most of them, but I don't recall any of them mentioning issues to watch out for when replacing stators. This seems to indicate that at least when Lucas was making the parts everything could be just bolted together without worrying about rubbing.

The fact the stator is bolted to an Al cover that is itself bolted to an Al engine means that differential thermal expansion wouldn't have been a huge issue. That said, the outer rim of the primary cover where the stator is mounted wouldn't be at the same temperature as the engine case. Still, the region of concern is fairly symmetric so there wouldn't be much tendency for the stator to be pulled in any one direction from the center line by the temperature difference.

Anyway, this means that if there isn't rubbing at room temperature, there probably won't be rubbing in operation. Still, wrapping the rotor with a layer of tape and turning the engine over to check to see if there is at least that much clearance wouldn't be overly cautious.

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