The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: trevinoz on 22.03. 2025 20:55
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I managed to destroy a couple of fixing bolts, there is no way that they would ever come out.
I made a 3/8 B.S.F. shaft and mounted the unit on it on the lathe. I drilled through the bolt until it was almost completely through then knocked the shell out.
My question is for anyone who has played with these things, is the left hand thread 9/16" B.S.F. 16 T.P.I?
There is not much thread on these and it is a bit iffy when measuring.
I have several A.T.D.s in a shocking state and am hoping to refurbish some of them.
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G`day Trev by my reckoning it is 9/16 BSF by 16
TPI . good luck, Jim [
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+1 for that.
Measuring worn bits isn't that easy as you say. (Has to be BSF at that pitch I think.)
I've found that where the innermost thread of the yoke is bruised / abused (as more often than not) the male part can take a bit of fitting.
Beesa-type ones are available new for not much; the shorter ones for Trihards etc must also be I'd have thought.
However, as there's never a part to hand when we need it . . . we take the pain.
Good luck indeed!
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I've just removed a good, working ATD, but as it's from a Velo I think the gear pitch is much too fine for other lesser marques... ;)
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Further to the thread, it isn't BSF. I ran a tap through the unit and offered up a bolt. It screws almost down.
Possibly the thread is a 14mm of 1.5 or 1.75 pitch, very hard to determine with only a couple of threads.
Next step is to get a die and run it over the bolt.
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I have the correct tap in the workshop so I'll check the thread tomorrow. Please remind me if I forget!!
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Thanks Andrew.
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Andrew, don't forget... ;)
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9/16 - 16 BSF LHT
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....available at Tracy Tools.
https://www.tracytools.com/product/9-16-x-16-bsf-hss-l-h/
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Andrew, I have tapped 9/16 BSF LH but the bolt will not run completely through, it binds before it can free.
I will get a die to run over the bolts which do thread into untapped units. I feel that the thread is not quite 16 TPI.
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I've just removed a good, working ATD, but as it's from a Velo I think the gear pitch is much too fine for other lesser marques... ;)
Guess whose Velo has just stripped the fibre gear...
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Not mine. The ATD was removed as I bought an original Stevens tacho kit, and that requires a manual mag. Some have fitted the kit to an ATD-equipped bike but the drag on the cable/tacho head tends to retard the ignition timing as it's driven from the centre nut.
Good thing that the fibre-geared ATD didn't strip as apparently it if does you're looking at an engine strip to clean all the oilways of bits of paxolin..
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Andrew, I have tapped 9/16 BSF LH but the bolt will not run completely through, it binds before it can free.
I will get a die to run over the bolts which do thread into untapped units. I feel that the thread is not quite 16 TPI.
That's strange. I've been using these taps for about three years and not had a problem. The only one of the set I use is the plug tap.