Help - bike's gone bang!

[harvey mushman]

If the slipring is running loose on magneto shaft the wire connection on slipring may also be disconnected, sounds like a magneto strip job!

Hope that helps   

derek

[Worty]

Thanks Derek.  The slipping of the slipring is intermittent but definitely happening.  I even took of the mag cover to the points and observed it not going round as it should.  I'm still getting sparks, but I fear that my mag is goosed.  Next question is if anyone can recommend a good company for a complete strip and rebuild.  May be a stupid question but I'm guessing my timing is now all over the place??

[Ted_Flash]

Stripped fibre timing pinion (on the Auto advance) - sometimes turning the magneto, sometimes not?

[Triton Thrasher]

Ted’s got a good idea there.

Is it the entire armature that is not turning?  If the points don’t rotate, then that is the case.

That will be a stripped fibre pinion or the auto advance or solid pinion is loose on the tapered end of the armature shaft.

[Worty]

I think you may have it there guys!  The points rotate intermittently so it is the armature.  Is this a common thing?  Also, as I'm fairly new to Brit bikes, could you take me through the repair.  Presumably it'll need to be retimed - can I do this without specialist tools? I have an engineer pal who restores bikes so he may well be able to give some pointers (there I go again) or help out with tools.

[Ted_Flash]

Priory Magnetos site has a brilliant document going through repairing an ATD - presumably also they can supply the parts needed.

https://sites.google.com/site/priorymagnetos/tech-tips-1

[Worty]

Thanks Ted, will check it out.  Many thanks for pinpointing what I reckon is the problem.

[Worty]

Picture of slipring!

[chaterlea25]

Hi Wortluck,

From my reply earlier

Next,
I would check the timing, maybe the mag tufnol gear has failed?

If the auto advance unit comes undone from the taper with the self extracting bolt, the job is  straight forward
Make sure to clean out the remains of the fibre gear teeth, change the oil, clean the sump filter + clean the oil tank out

John

[morris]

I think you may have it there guys!  The points rotate intermittently so it is the armature.  Is this a common thing?  Also, as I'm fairly new to Brit bikes, could you take me through the repair.  Presumably it'll need to be retimed - can I do this without specialist tools? I have an engineer pal who restores bikes so he may well be able to give some pointers (there I go again) or help out with tools.

Start by taking the timing cover off. That’ll show whether the ATD pinion just came loose or (worse) the teeth have stripped.
For timing you won’t need any special tools apart from a timing disc. It can be done with the pencil down the plug hole trick, but a timing disc is more precise.
If the ATD came loose then you’d have to determine top dead centre on the right hand cylinder’s compression stroke. You’re on compression stroke when both valves are closed.
On the magneto side, you’re on the right hand cylinder spark when the brass part of the slipring is visible through the upper pick up brush hole.
Once determined those, find the exact top dead centre, fix the timing disc and create a pointer to the 0 degree on the disc.
Jam the ATD on full advance with a small wedge.
Then turn the cranck backwards by 32 degrees, put a fag paper between the magneto points and rotate the shaft (should only be a little bit) until the fag paper pulls out.
Thighten the ATD ( only slightly because you may need to loosen it again when the first attempt wasn’t entirely correct).
Once happy with the adjustment, tighten it up firmly, and you should have a working bike again

[KiwiGF]

Picture of slipring!

Although the slip ring is damaged it may not cause any problems, especially as the bike was running ok. They are not TOO hard (or expensive) to replace (I’ve done it myself, after making a special bearing removal tool) but you may want to get it done by a mag expert.

The slip ring damage was probably caused by someone attempting to remove the mag armature without first removing the screws that earth the HT when there are no HT leads fitted. I forget what those screws are called.....but it’s easy to forget to remove them and as they stick out into the space between slip ring “flanges” they can easily damage the slip ring, which goes very brittle with age.

As to the armature moving when it should not , you need to remove the timing cover and have a look at what’s going on, as per other posts it may just be normal movement from an auto advance unit, or a stripped fibre gear., or simply the mag pinion has come loose.

This does not sound expensive to me, just annoying!

[Worty]

Brilliant, thanks guys, but why change the oil and clean the tank and filter. Can debris get into the oil from where the ATD is (I changed the oil just before taking it out!).

[morris]

Brilliant, thanks guys, but why change the oil and clean the tank and filter. Can debris get into the oil from where the ATD is (I changed the oil just before taking it out!).

Yes.
Have a recipient ready underneath when you take the timing cover off.
There’s quite a lot of oil in there.
It lubricates the cam and ATD gears.
Debris from the ATD gear won’t do much harm by itself, but may choke some small oil passageways...

[Triton Thrasher]

I’d leave that chipped slip ring alone and just fix the magneto drive problem.

[Worty]

Don't worry mate, the mag was working fine and still gives a solid spark.  My philosophy, 'If it ain't broke .......'.  Just want to get the ol' girl back on the road asap - winter's for fixing things, summers for riding!