Auto Advance Unit Run Out Tolerance

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Lovel

Lovel

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Dec 28, 2021
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Folks,

Using a basic form of measurement with a feeler gauge While checking for run out on the advance retard unit I am getting 0.014” run out and would like to know if that is typical/acceptable given the the points gap should be in the region of 0.015”. Perhaps a stupid question as it’s probably an obvious answer to junk it or try truing?

Auto Advance Unit Run Out Tolerance
 
It could just be that the AAU isn't seated correctly in the camshaft taper.



Edit:
Lovel said:
I am getting 0.014” run out
Click to expand...

If the clearance is changing from 0.00" - 0.014" - 0.00" as the AAU rotates then the runout is 0.007".

Lovel said:
and would like to know if that is typical/acceptable given the the points gap should be in the region of 0.015”.
Click to expand...

Even with the AAU running eccentrically, as the points gaps are adjusted independently then it should still be possible to set each gap to 0.015".
 
Last edited:
I’ve tried reaseating a number of times and making sure both tapers are clean and burr free. Perhaps I didn’t torque fully up yet as i thought might need to remove
 
Lovel said:
I’ve tried reaseating a number of times and making sure both tapers are clean and burr free. Perhaps I didn’t torque fully up yet as i thought might need to remove
Click to expand...

I can only suggest you try to keep it centralised by tapping it as you tighten the bolt.

Sometimes tapping on the end of the AAU with the bolt removed will centralise it
 
400 miles on since I fitted the points system and she is running as sweet as a nut, no popping, banging, misfiring, plug colour excellent, and really nice idle, starts on the button 1st time, not sure how long that will last, lol as I’m led to believe that this old fangled technology should be dumped. Also took the opportunity to adjust my timing marks with primary cover removed with engine timing plug in place, now strobed for a real 28deg. ;)
 
Lovel said:
400 miles on since I fitted the points system and she is running as sweet as a nut, no popping, banging, misfiring, plug colour excellent, and really nice idle, starts on the button 1st time, not sure how long that will last, lol as I’m led to believe that this old fangled technology should be dumped. Also took the opportunity to adjust my timing marks with primary cover removed with engine timing plug in place, now strobed for a real 28deg. ;)
Click to expand...
Nothing wrong with this technology
But the springs do become slack
And the bob weights can wear rapidly in the slots ,try and lube them regularly
Also the points need maintenance but if you don't mind a bit of work it's a great system that doesn't depend on the battery being fully charged all the time
 
baz said:
Nothing wrong with this technology
But the springs do become slack
And the bob weights can wear rapidly in the slots ,try and lube them regularly
Also the points need maintenance but if you don't mind a bit of work it's a great system that doesn't depend on the battery being fully charged all the time
Click to expand...
I’m with baz on this - have yet to install my electronic ignition because the old school system works just fine . Plus , it has the added advantage of actually being able to see what is happening with it which is helpful when one is a dinosaur like myself.
 
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Lovel said:
Folks,

Using a basic form of measurement with a feeler gauge While checking for run out on the advance retard unit I am getting 0.014” run out and would like to know if that is typical/acceptable given the the points gap should be in the region of 0.015”. Perhaps a stupid question as it’s probably an obvious answer to junk it or try truing?

View attachment 94000
Click to expand...
Odd choice of screws for the timing cover!

Like most I have fitted hex key/allen heads in place of the original cheesehead screws. It is simply easier to get a good tight and even clamp down on the gasket.

These seem like the worst of both worlds in as much as they are the type also replaced by hex key/allen heads on other bikes!

As for retaining points, it's a choice, they work. If your mileage is low and you aren't revving to over 7000 much, they will do.

I have retained the magneto on my AJS, everything else I have including my '56 MG has some form of electronic ignition, not for reasons of dogma, they start better, particularly are standing idle for very long periods when points can get a little dirty.

The ignitions used on Nortons are hardly new fangled, most of the ones used are based on designs from 20 to over 40 years old.

And that wear in the bobweights? Even without a lot of wear the worst case is that at high rpm the bobweights can catch on the points mounting plate bosses in the cover and explode, twisting the AAR off in the end of the cam....messy....I only let it happen once!
 
SteveA said:
Odd choice of screws for the timing cover!

Like most I have fitted hex key/allen heads in place of the original cheesehead screws. It is simply easier to get a good tight and even clamp down on the gasket.

snip
Click to expand...
Those screws are the OEM posidrive screws that are standard on Mk III Commandos
 
SteveA said:
Odd choice of screws for the timing cover!

Like most I have fitted hex key/allen heads in place of the original cheesehead screws. It is simply easier to get a good tight and even clamp down on the gasket.

These seem like the worst of both worlds in as much as they are the type also replaced by hex key/allen heads on other bikes!

As for retaining points, it's a choice, they work. If your mileage is low and you aren't revving to over 7000 much, they will do.

I have retained the magneto on my AJS, everything else I have including my '56 MG has some form of electronic ignition, not for reasons of dogma, they start better, particularly are standing idle for very long periods when points can get a little dirty.

The ignitions used on Nortons are hardly new fangled, most of the ones used are based on designs from 20 to over 40 years old.

And that wear in the bobweights? Even without a lot of wear the worst case is that at high rpm the bobweights can catch on the points mounting plate bosses in the cover and explode, twisting the AAR off in the end of the cam....messy....I only let it happen once!
Click to expand...
Just a little nip up is all I use for the posidrive screws, imo socket head screws can easily overtightenedmore than they need be.
 
baz said:
Nothing wrong with this technology
But the springs do become slack
And the bob weights can wear rapidly in the slots ,try and lube them regularly
Also the points need maintenance but if you don't mind a bit of work it's a great system that doesn't depend on the battery being fully charged all the time
Click to expand...
I replaced the springs when fitting as the Bob weights were not returning fully upon checking so yes the springs do lose their ability over time.

Weirdly I found setting the points and timing up from scratch very satisfying, should I be concerned?
 
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Lovel said:
I replaced the springs when fitting as the Bob weights were not returning fully upon checking so yes the springs do lose their ability over time.

Weirdly I found setting the points and timing up from scratch very satisfying, should I be concerned?
Click to expand...
Where did you sorce the springs?
 
L.A.B. said:
They are, however, the original 850 Mk3 Pozidriv timing cover screws.

andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
Click to expand...
Well I never....you really do learn something every day :oops:
 
Thinking a bit more about the lack of concentricity identified by Love......
My first thought was that this could be addressed by adjusting the breaker point gaps correctly, as long as the adjustment did not exceed the point gap.
But on second thought, if you did this, even if you got both point gaps correct, I think the dwell would not be equal.
Which as I recall, is important.
Do I have this correct?
Feel free to wade in with lead boots.
 
Stephen Hill said:
Thinking a bit more about the lack of concentricity identified by Love......
My first thought was that this could be addressed by adjusting the breaker point gaps correctly, as long as the adjustment did not exceed the point gap.
But on second thought, if you did this, even if you got both point gaps correct, I think the dwell would not be equal.
Which as I recall, is important.
Do I have this correct?
Feel free to wade in with lead boots.
Click to expand...
I would have thought the dwell would be unequal before getting the points gap equal, with equal points gap the dwell also becomes equal as both sets of points are open for the same length of time they must be shut for same length of time.
 
There often clapped out junk , due to lack of maintanance . Clean & lube ! .

Was given a doggey BSA one , the pieces wernt worn wot my Norton one was & V c V . So got one good 12 / 24 Deg Adv. unit . and 500 rpm Idle . Mk II Amals though .

THERE SHOULD BE NO SLACK AND RATTLE . 9 In he A.A. unit Assy .
 
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