Alternator rotor spacing

olympus · Mar 9, 2019

Hi all
Couple of question please
1. behind the rotor is a recessed spacer that requires the recess facing out & against the rotor, what is this for as i see no reason for it??
2. In addition to the spacer 10th & 36th shims are available, i can see these are to centralise the rotor within the stator, but how accurately does this centralisation need to be?? as i already have two 36th shims fitted and its still a way of being centralised ... the crank was skimmed at rebuild and this was fitted on the timing side.
3, on the back of the rotor a number of scribed line emanating from the centre axis, and against the lines are the letter A & B are these timing marks for other makes??

guest76 · Mar 9, 2019

I put a piece of plastic laminated card between rotor and stator when everything is loose - it’s just over 8 thou thick.

As I tighten down the stator, it ensures there is an even air gap all the way round.

When everything is snuggled up tight, a pull the plastic out.

I have heard of others using plastic drinks bottles and tennis ball containers with good results too.

The markings on the back of your rotor are for timing up triples, so should be disregarded.

olympus · Mar 9, 2019

I'm referring to the centralisation of the rotor between the stator when looking down from above

marshg246 · Mar 9, 2019

olympus said:
Hi all
3, on the back of the rotor a number of scribed line emanating from the centre axis, and against the lines are the letter A & B are these timing marks for other makes??

Is there a peg hole also on the back of the rotor?

olympus · Mar 9, 2019

marshg246 said:
Is there a peg hole also on the back of the rotor?

No peg hole?

L.A.B. · Mar 9, 2019

olympus said:
on the back of the rotor a number of scribed line emanating from the centre axis, and against the lines are the letter A & B are these timing marks for other makes??

Yes, they're timing marks for BSA and Triumph triples.

marshg246 · Mar 9, 2019

Sounded like an ET ignition rotor. If no hole for a peg, then it's not.

PeterJoe · Mar 9, 2019

olympus said:
Hi all
Couple of question please
1. behind the rotor is a recessed spacer that requires the recess facing out & against the rotor, what is this for as i see no reason for it??
2. In addition to the spacer 10th & 36th shims are available, i can see these are to centralise the rotor within the stator, but how accurately does this centralisation need to be?? as i already have two 36th shims fitted and its still a way of being centralised ... the crank was skimmed at rebuild and this was fitted on the timing side.

1. The recess in the spacer is to ensure that it does not bump into the rotor's woodruff key.

2. You would shim the rotor so that it would be close to but not actually touching the timing marks in the primary cover. Also you need to consider the side to side movement of the crankshaft when using the shims.

The way Norton made it, the rotor is not centered with the stator. On my bike I even made shorter stator spacers just for looks sake.

Peter Joe

acadian · Mar 9, 2019

olympus said:
Hi all
Couple of question please
1. behind the rotor is a recessed spacer that requires the recess facing out & against the rotor, what is this for as i see no reason for it??
2. In addition to the spacer 10th & 36th shims are available, i can see these are to centralise the rotor within the stator, but how accurately does this centralisation need to be?? as i already have two 36th shims fitted and its still a way of being centralised ... the crank was skimmed at rebuild and this was fitted on the timing side.
3, on the back of the rotor a number of scribed line emanating from the centre axis, and against the lines are the letter A & B are these timing marks for other makes??

Centering the rotor in the stator is important, usually this requires a combination of shims behind the recessed spacer, and shortening the spacers on the stator studs, I found that turning down the od of some 3/8" nuts brought the stator inline with the rotor while still giving adequate clearance to the belt pulley

marshg246 · Mar 9, 2019

PeterJoe said:
1.

The way Norton made it, the rotor is not centered with the stator. On my bike I even made shorter stator spacers just for looks sake.

Peter Joe

I like this idea. When I get a chance, I'll see if it makes any difference in the output of the stator - I'm thinking it should be better with the magnets centered on the coils of the stator and they aren't on a Norton.

texasSlick · Mar 9, 2019

Centralization is preferred, but slightly off center will not suffer the stator output significantly. You would have to be off by a country mile to measure the loss.

Make it look good, and that will be good enough.

Slick

Time Warp · Mar 9, 2019

With the Mercedes Benz duplex primary chain, maybe the stator and rotor could be moved inward.

Fast Eddie · Mar 9, 2019

texasSlick said:
Centralization is preferred, but slightly off center will not suffer the stator output significantly. You would have to be off by a country mile to measure the loss.

Make it look good, and that will be good enough.

Slick

If that’s the case, then for some I’d say moving the rotor more inboard might be preferable.

I’ve been looking closely at mine, when assembled it had .010” gap all round. Even so, it has clear signs of the rotor rubbing in the stator, not uniformally, only in places.

My best guess for the cause of this is crank flex (the bike does get revved hard).

Moving the rotor more inboard should, to my thinking at least, make that end of the crank less prone to flex.

Any thoughts on this folks?

olympus · Mar 10, 2019

marshg246 said:
Sounded like an ET ignition rotor. If no hole for a peg, then it's not.

What is the peg hole for??

Nortoniggy · Mar 10, 2019

Fast Eddie said:
If that’s the case, then for some I’d say moving the rotor more inboard might be preferable.

I’ve been looking closely at mine, when assembled it had .010” gap all round. Even so, it has clear signs of the rotor rubbing in the stator, not uniformally, only in places.

My best guess for the cause of this is crank flex (the bike does get revved hard).

Moving the rotor more inboard should, to my thinking at least, make that end of the crank less prone to flex.

Any thoughts on this folks?

I think that much crank flex is unlikely. Have you tried measuring the clearance with a spacer on the outer chaincase central fixing bolt and the nut fitted tight? This simulates the condition when the case is assembled. You may find the clearance changes when you tighten the nut. Pay particular attention to the clearance towards the front. If it does change you need a shim behind the inner chaincase on the mounting stud. When I fit the alternator I always have the centre mounting tightened.

Ian

Fast Eddie · Mar 10, 2019

Ian,

No, I haven’t tried measuring with the case nut tightened, I’ll try that next time (currently disassembled).

I’m not overly confident it’ll make that much difference though as I had the case shimmed up flush, no noticeable ‘pulling in’ when tightened.

But it might help, and is certainly something I’ll do upon reassembly.

I’ve also got the new stator being measured up for concentricity to the mounting studs, and I’ll be turning the rotor down to give a .020” gap (.040” difference).

Hopefully, that’ll sort it.

L.A.B. · Mar 10, 2019

olympus said:
What is the peg hole for??

The ET (Energy Transfer) rotor is retained by a pin/peg on the engine sprocket instead of a woodruff key. The ET rotor has three holes allowing the peak output position to be adjusted by setting the rotor to a different pin/peg hole.

https://www.motorcycleclassics.com/tech-corner/triumph-energy-transfer-ignition-zm0z16mazhur
"The rotor is placed as it is in relation to TDC so that the sine wave output will be highest when the points are to be opened."

https://jrcengineering.com/technical-support/electrical-tech/lucas-et-ignition-unraveled/
"Alternator rotor can be identified by the 3 holes in the back marked “S” meaning standard, “R” standing for Racing and “M” for mid position."

marshg246 · Mar 10, 2019

olympus said:
What is the peg hole for??

On an ET ignition, the peg in the front primary sprocket sets the rotor timing. You must time the stator pulses as well as the normal timing. There's not any other difference in the rotors so an ET rotor can be used on a normal battery bike.

Alternator rotor spacing

olympus

guest76

Guest

olympus

marshg246

olympus

L.A.B.

Moderator

marshg246

PeterJoe

acadian

marshg246

texasSlick

Time Warp

.......back to the 70's.

Fast Eddie

olympus

Nortoniggy

Fast Eddie

L.A.B.

Moderator

marshg246

Similar threads