The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Black Sheep on 02.05. 2025 07:00
-
Has anyone replaced the fibre pinion on their Lucas ATD? It's not obvious to me how you get it apart.
-
check out the wonderful resources that Andrew has published.
https://docs.google.com/document/d/19LiHsh0ALtF7z0ttQZYofWhsS_3ZIsIv/edit?tab=t.0
His repair manual re the Auto advance is excellent.
Worked for me.
Cheers,
Richard
-
I can vouch for that BS.
Col
-
Excellent guide! Now to buy an appropriate bearing puller. Hours of fun to follow...
-
A further question.
With the unit fitted to the engine, is it ok when operating the bob weights by hand there is not enough spring tension to return those bob weights all the way back remembering that they are now turning the mag armature and points unit. I have only previously used manual control so this might be a dumb question.
Chris
-
If the springs pull the weights back OK on the ATD before fitting back onto to the magneto, that's fine. Once assembled things are different as you say but as long as the armature can rotate slightly relative to the drive gear the ATD will do its job.
Weak springs, worn pivots, along with plenty of slop and rattle are par for the course, despite which the things work well enough to prevent kickback on starting. Once running most time is spent fully advanced, it's only on slow tickover when wear manifests itself as an annoying rattle. Frighten yourself with a listening stick, sounds terrible but will continue to run happily.
Swarfy.
-
Thanks for that Swarfy.
I can now go ahead and button it up without any doubts.
Chris
-
Excellent guide! Now to buy an appropriate bearing puller. Hours of fun to follow...
I take it you mean a puller to remove the collar on the rear of the unit? Instead of a puller, I heated it gently then drifted the unit out of the collar. To replace, heat the collar and gently tap it into place so that the top of the collar is flush with the shaft. Use a punch to secure it in place.
For those that know, I had four repaired/second hand ATDs fail, one of which disintegrated and broke a tooth off one of the timing gears. With the other three, they spread ground up fibre gear round the engine - you know the rest from Worty's A10 Engine Rebuild.
The best thing for me was to buy a brand new ATD (courtesy of Bergs) - the bike has never missed a beat since.
-
"Instead of a puller, I heated it gently then drifted the unit out of the collar. "
The puller won't move it so I'll try the heat and drift next. As I mentioned, hours of fun!
-
"Instead of a puller, I heated it gently then drifted the unit out of the collar. "
The puller won't move it so I'll try the heat and drift next. As I mentioned, hours of fun!
It can be difficult to get a puller set up right as there isn't much room under the collar. It sounds as if your unit has a properly tight collar (which is good). My logic was that if the collar is a shrink fit on the shaft, a bit of heat and some judicious drifting should do the trick - which it did (make sure you have a pile of old rags to catch the bits as, from memory, all the bits and pieces tend to fall out).
As for rivets, I ordered some, measured them against the old rivets, cut them down then tapered the ends (they can be a bugga to get through all the plates and the fibre gear - the taper helps).
In hindsight, after repairing about three or four of the blighters, I opted for the new one from Bergs ( *respect*). The reason was that most of the one's I bought were very worn and didn't look that reliable (and weren't). The one that disintegrated prompting the engine rebuild actually lost one of the posts the bobweights move on - you can imagine the carnage (it was wedged solidly in the inner timing case!!)
Andrew's instructions were absolutely invaluable!!
-
Oh, and don't get RM on the job *ex*