The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: AlaskaJoe on 14.10. 2025 04:09
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Hello all! Thanks for adding me to the group and for helping me tap into the collective knowledge here.
I just brought home my first British bike, a 1957 Road Rocket with the a10 motor. I am so pumped as I’ve wanted a preunit BSA for a long time.
First issue I need to fix to get it running is the manual advance. I actuate the lever on the handlebar and can see the cable flex and slack, but the points plate doesn’t move (pic attached). I suspect it’s stuck from sitting and I am seeking advice on the best and least risky/intrusive way to break it free. All advice and tips are appreciated! Thanks again for the add!
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Hi.
Would be best to release the cable from the lever and then unscrew the housing on the mag, you will then expose the spring and engagement paul, I would then remove the points via the centre brass bolt, try some WD 40 around the cam ring to try and free it off, you will see at the bottom of the cam ring a felt oiler, the cam ring should rotate quite easily and suspect it will be corroded. With the cable disconnected and the points off, you should be able to lever the cam ring out of the mag. Have a look on the Priory Magnetos web site page for detailed information, Andrew is a forum member here in the UK
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When you say the 'points plate' doesn't move, are you expecting the points to move or the cam ring? The cable is attached to the cam ring which should rotate clockwise when you move the cable to the 'tight cable' position. If the cam ring is stuck, I would expect the cable to go very loose when you move the lever to the slack position.
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Hi.
Would be best to release the cable from the lever and then unscrew the housing on the mag, you will then expose the spring and engagement paul, I would then remove the points via the centre brass bolt, try some WD 40 around the cam ring to try and free it off, you will see at the bottom of the cam ring a felt oiler, the cam ring should rotate quite easily and suspect it will be corroded. With the cable disconnected and the points off, you should be able to lever the cam ring out of the mag. Have a look on the Priory Magnetos web site page for detailed information, Andrew is a forum member here in the UK
Cheers, Billybream! This all sounds quite straightforward and I’ll give it a go and report back.
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When you say the 'points plate' doesn't move, are you expecting the points to move or the cam ring? The cable is attached to the cam ring which should rotate clockwise when you move the cable to the 'tight cable' position. If the cam ring is stuck, I would expect the cable to go very loose when you move the lever to the slack position.
Thanks for the clarifying question, Cheeserbeezer, I’m thinking that my terminology is off. If I understand the manual advance system correctly, I’m thinking that I should see the points mechanism move clockwise or anti clockwise as I actuate the handlebar lever. Not that the points themselves move, but the entire plate rotates. Perhaps that’s called the cam ring (forgive my ignorance). The picture is the bit I’m referencing. Total BSA newbie here.
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Hi Joe,
It is only the steel cam ring that's outside the points and inside the alloy housing that moves, maybe a 1/4 inch or so
John
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This method of altering the timing can seem strange as in more conventional systems the whole points assembly moves in relation to the cam. Here it is the cam ring that moves to alter the timing. The whole points assembly rotate clockwise when the engine is running.
Moving the cam ring anticlockwise advances the timing.... Pulling the cable retards the ignition for starting and slackening the cable allows the return spring in the plunger housing to move the plunger and the cam ring back to the fully advanced position. Referred to as "Slack Advance". Chances are the whole mechanism is seized but it's a simple clean up job. Points plate seats on a keyed taper, treat with care. The points assembly pulls off after releasing the center bolt with "lefty-loosey" thread. The cam ring will then draw out after freeing off. To reset the timing is a whole different ball game, let's hope just a little bit of TLC gets a runner. Static timing is set at full advance, the normal running mode. Retarding the timing by pulling the cable aids easier starting by reducing kick back.
Swarfy.
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Well, I'm surprised no one with more manual advance experience than I (really, zero expreience) would not have posted a picture showing the ring and direction of movement by now. The arrow from the outside points to the cam ring. Counterclockwise moverment advances the spark, as Swarfy notes.
Richard L.
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Oh, here's a tiny tip about a tiny tip. Looking at the retaining spring that holds the points arm in place, there's a bump out there that normally fits over a tiny tip on a tiny button that sits in the points arm. If there is even one still there (it doesn't look it), try not to lose it. I don't think it is an available part. I made myself a new one from a plastic rod on a lathe.
Richard L.
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Ok, progress report. I removed the cable from the handlebar mounted lever and unscrewed it from the mag housing. Then removed the brass screw and the points came right out. Lots of corrosion on the outside of the points (see pic) I suspect this shows where the manual advance plunger was stuck. So, is the remaining ring on the mag housing what is supposed to move? Also, that plunger where the cable end connects won’t go back down into the housing. Is there a trick to lining it up somehow? First things first, I need to get that ring moving. Thanks for the ongoing advice!
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Hi Joe.
Nearly there, pic attached will show how control plunger and cam ring work.
Suggest try some WD40 around the cam ring, then gently grip the plunger and push and pull until cam ring moves, then pull cam ring out from the housing and clean up surfaces
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The cable operated plunger lower edge engages in a slot in the cam ring, as the plunger is moved up and down the cam ring rotates in the magneto end housing...... At least that's what it should do.
There is a narrow gap behind the cam ring, just wide enough to get a pick to ease the cam ring out. As suggested WD (and maybe a heat gun) will aid removal.
BSA Service Sheet 801 provides more information about the magneto but does not include manual variant. Sod's Law indeed.
Swarfy.
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Thanks all for the detailed advice and pics. I’m moving really slow as I don’t want to damage anything. I reckon it’s a bit harder to find these parts of I break them.
One additional question for the group. I’ve gotten advice from a couple folks on using WD 40 to help break this ring loose. Is it ok to use like a PB blaster or kroil penetrating oil or are you all suggesting WD 40 because it’s easier on these parts? My goal is no damage, but I’ve had great luck in other bikes using those penetrating oils/sprays to break up seized bits.
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I think we tend to use the term WD as a generic term for any penetrating fluid, a bit like Hoover for vacuum cleaner. Sounds like you're progressing fine. You're right to be careful, some spares can be difficult to find.
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Regarding WD40, I reckon Kroil, Plusgas etc are far far better than WD at freeing things. WD is OK as a spray-on lube but useless as a release agent.
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Progress report. The ring is out! Using a pick to slowly work it out was an excellent tip! All is out and no damage. The groove in the mag housing seems a little rough, but honestly looks like it was machined like that originally. Next question, do you all recommend using grease or anti-seize when putting this all back together? Any reassembly tips or tricks to align the plunger to the groove on the ring? Thanks all! Pics for progress 😎
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I'd use a VERY light smear of oil on both sliding surfaces around that steel ring.
(Oooh and an hour or two meticulously cleaning those components wouldn't go astray).
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The square section groove in the housing holds a felt pad to retain lubricant and keep things sliding smoothly. There is matching hole in the cam ring to allow replenishment from time to time, this is also intended to lubricate the fibre heel against the cam ring. Also lubricate the moving points pivot pin.
Swarfy.
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The square section groove in the housing holds a felt pad to retain lubricant and keep things sliding smoothly. There is matching hole in the cam ring to allow replenishment from time to time, this is also intended to lubricate the fibre heel against the cam ring. Also lubricate the moving points pivot pin.
Swarfy.
Well, this felt pad was missing when I disassembled, I reckon it wore out ages ago. Is that something I can make or repurpose from another bike? I doubt I can buy it, but if so does anyone have a link or a part number?
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To put it back together insert the plunger in the housing so the mushroom head is about half-way down the fenestrated bit inside the housing. It will then align with its notch while the BIG notch will slip over the peg that limits camring movement. There's a fair bit of wiggle-room and it's usually easy. In some cases it's wise to hook the plunger to the cable first, in case space is tight.
However, with this one I'd pay particular attention to make sure that at each end of the arc of movement of the ring the plunger can't disengage when you operate the cable to full extent either way. Normally, the notch for the plunger is a V shaped one, and a snug fit over the mushroom foot of the thing. Not quite sure from the pic what form yours takes but I'm thinking the camring has been in the wars over the years. Many of them have.
Worth checking too, when you have the camring, plunger and cable all hooked up, that the camring can't chatter at full advance. Ie that when the plunger is fully down in terms of cable movement, the ring is firmly against its stop. You don't want the ring to have more movement available than the range of the plunger.
As far as a bit of felt goes - something from an upholsterer's offcuts or whatever will do. A slivver cut with a scalpel, and that's sorted. You can even make a pimple of the stuff to ram in the hole in the camring if you like - this'll transfer a tiny amount of the grease on the strip through to lubricate the heel of the opening point.
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To put it back together insert the plunger in the housing so the mushroom head is about half-way down the fenestrated bit inside the housing. It will then align with its notch while the BIG notch will slip over the peg that limits camring movement. There's a fair bit of wiggle-room and it's usually easy. In some cases it's wise to hook the plunger to the cable first, in case space is tight.
However, with this one I'd pay particular attention to make sure that at each end of the arc of movement of the ring the plunger can't disengage when you operate the cable to full extent either way. Normally, the notch for the plunger is a V shaped one, and a snug fit over the mushroom foot of the thing. Not quite sure from the pic what form yours takes but I'm thinking the camring has been in the wars over the years. Many of them have.
Worth checking too, when you have the camring, plunger and cable all hooked up, that the camring can't chatter at full advance. Ie that when the plunger is fully down in terms of cable movement, the ring is firmly against its stop. You don't want the ring to have more movement available than the range of the plunger.
As far as a bit of felt goes - something from an upholsterer's offcuts or whatever will do. A slivver cut with a scalpel, and that's sorted. You can even make a pimple of the stuff to ram in the hole in the camring if you like - this'll transfer a tiny amount of the grease on the strip through to lubricate the heel of the opening point.
Cheers Groily, this is a fantastic explanation. Just so I’m completely certain, my little square of felt sits in that groove under the cam ring? Pic attached. It seems kind of wild that it just sits there!
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Yup, the strip sits flush and grease-impregnated in the groove, and the camring keeps it there.
The felt also helps reduce chatter between ring and housing.
The points end cover should prevent in-and-out chatter, probably with the aid of a gasket.
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The end cover also carries the ignition cut out brush. This bears on the rotating centre bolt, and by completing a circuit to earth with the cut out switch bypasses the points and the engine stops.
I'm wondering if this bike came with a cover.... Those bolts securing the end housing look well established.
There are three basic design of end cover.
"Bell Push" Alloy dome with centre push button. This is the early type.
Bakelite cover with side mounted retaining clip. Easy access to the points, found an early '50's bikes.
Alloy screw on type with serrated edge which engages with a spring steel retainer on the end housing. Later type.
These latter pair have a connection to the handlebar cut out switch.
Magneto identity plate carries a month and year of manufacture. Long number identifies the actual build specification, down to the smallest screw, such was the Lucas way to keep track of numerous variations to a basic unit.
Swarfy.
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Well, this felt pad was missing when I disassembled, I reckon it wore out ages ago. Is that something I can make or repurpose from another bike? I doubt I can buy it, but if so does anyone have a link or a part number?
I packed the groove in the housing and the hole in the cam ring with snippings of felt and dripped oil into it, not grease.
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Yup, the strip sits flush and grease-impregnated in the groove, and the camring keeps it there.
The felt also helps reduce chatter between ring and housing.
The points end cover should prevent in-and-out chatter, probably with the aid of a gasket.
Very helpful, thanks! One last question, how long should that piece of felt be? Should it be half the length of that groove or much shorter?
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I cut them to fill the groove, no reason not to.
Originals were full length and width, flush, and retained a useful dob of grease (or oil for them as prefers).
I normally add a fresh dob when doing regular maintenance of contact breaker and camring (every two or three thousand miles probably) and wipe an oily rag round the whole camring while I'm there. Also, I clean and grease the plunger in its 'ole - moisture can get in even with a decent rubber sleeve over the cable adjuster.
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The end cover also carries the ignition cut out brush. This bears on the rotating centre bolt, and by completing a circuit to earth with the cut out switch bypasses the points and the engine stops.
I'm wondering if this bike came with a cover.... Those bolts securing the end housing look well established.
There are three basic design of end cover.
"Bell Push" Alloy dome with centre push button. This is the early type.
Bakelite cover with side mounted retaining clip. Easy access to the points, found an early '50's bikes.
Alloy screw on type with serrated edge which engages with a spring steel retainer on the end housing. Later type.
These latter pair have a connection to the handlebar cut out switch.
Magneto identity plate carries a month and year of manufacture. Long number identifies the actual build specification, down to the smallest screw, such was the Lucas way to keep track of numerous variations to a basic unit.
Swarfy.
I’m glad you brought this up, Swarfy, as it was one of my next questions. I do have the cap for this which is held in place by a moveable arm as seen in the pics below. What isn’t immediately clear to me, is how the kill switch wiring attaches to the metal bit inside this cap (other pic). Is there a special kind of wire end connector to this that presses on? The prior owner included a new Lucas harness so I’m rewiring the lot.
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Is there a special kind of wire end connector to this that presses on? The prior owner included a new Lucas harness so I’m rewiring the lot.
Feed a bit of wire through the 'acorn' nut that screws into the cover, put a washer over the bared end and splay the strands back against the washer - solder it if you like - and screw the acorn nut back in to retain it. The little split brass washers commonly used to secure HT cables to the magneto pick-ups are the normal thing, as they have a suitably small hole.
If rewiring the machine completely, it's the time to be thinking about your options. 12v or 6v? Electronic regulator? Earth polarity?
Loads of threads on here, and plenty of opinions and preferences, some strongly held! You're spoilt for choice, but some of them are a lot better than others . . .
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Progress report! The cam ring is reinstalled with a nice slice of oiled felt in the groove, and with plunger hooked back up to cable I’ve confirmed it is moving as required when the lever is moved. This feels like a great step closer to running!
Follow up question since I’m still learning about this system. I’m struggling to understand how the movement of the cam ring changes the time A/R, since the points plate itself is fixed in the mag. When I retard the timing via the lever and the cam ring moves, how does that actually change the timing? Does that really change at what point before tdc the points open?
Thanks in advance (no pun intended) for the knowledge 😎
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When I retard the timing via the lever and the cam ring moves, how does that actually change the timing? Does that really change at what point before tdc the points open?
It does, yes. The points plate is fixed in position relative to the crank and pistons via all the many bits in between. So if you move the cam you'll change when the points open relative to everything else.
If the cam was fixed and the points backplate was the movable bit as I think you expected, the result would be the same. That's basically what the often-mentioned ATD or ATU (automatic timing device /unit) found on the driven end of the magneto on probably the majority of these machines does - it moves the magneto armature and points plate relative to the crank and pistons, according to engine speed, while the cam is held in a fixed position.
All very "rub your guts and pat your head at the same time", but you'll get used to it!
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I'm sure Joe has found "The Cams".... they are the small humps on the inside of the cam ring and can be felt on the unmounted ring. The small rise is magnified by the leverage ratio of the moving points arm so a small movement is turned into the points gap. Moving the cam ring against the direction of the rotation of the armature and points plate moves the hump and so advances the the position at which the heel rides up the hump.... and opens the points to give the spark...... like MrG says.
Swarfy.
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Cheers to you both for this clear explanation. I woke up at 2am thinking about this last night and couldn’t wrap my head around it. I’ll sleep better tonight, or more accurately I’ll ruminate on something else. 😎
The last piece of the puzzle now will be setting my timing. I’ve got a tdc tool and am very confident in getting to the point before tdc on compression, but I am less confident in how to move the points at that stage without moving the entire engine and thus losing my point before tdc. Do I need to unscrew and disengage the gear in this photo? That seems to make sense since it’s what rotates the mag.
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Ok Joe, theory of setting the timing is easy, doing it simple, getting it spot on first time...... Slim chance.
Here's a quick way to get a rough check of the timing.
First step is to set the magneto at full advance, (slack cable) then bring the crank up on compression and adjust the points gap as you would on a normal contact breaker system.
Now reverse the crank and once more turn forwards to the firing point... This changes for model year, different compression ratios and camshafts mean there are various recommended piston heights, and where available crank angles BTDC. All found in published data and on the forum.
You should now find the points are just opening and that will be good enough to try and get it to start.
If it's miles out then yes the timing gear has to come off the magneto, using an extractor to avoid damage. Magneto is once again set, turn the points plate clockwise until at full advance the points are about to break. Crank again brought forward to firing point...... And the timing gear pushed onto the plain taper of the magneto shaft.. The hard part is making sure nothing moves as the bolt is tightened. Plenty more to explore already on the forum of the finer points of the operation.
Swarfy
Additional. Recommended ignition settings apply to fuels in use years ago. Modern fuels may require slightly different settings to avoid pinging. That drive nut for tacho is a normal lefty loosely thread, original gear is relatively soft fibre.. Treat with care.
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Cheers Swarfy, I’ll give this a go tomorrow and report back!
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Joe, I'll have a go at this. The rotating armature of the magneto is 'locked' with the engine rotation by those gears in the timing cover.
The other, points end, the armature rotates with the engine correspondingly. The camring is independent of the armature and is ground with a thicker section and thinner section, and so if the camring is rotated, (by the advance cable), the 'heel' of the points which is 'riding' on the camring, will open / close the points earlier or later. Advance / retard the spark in relation to the rotated position of the piston.
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original gear is relatively soft fibre.. Treat with care.
Additional additional: If there's the slightest doubt about the state of the pinion - can't see all the teeth clearly in the pic - Replace!
Shedding teeth out on the road requires dentistry you can't easily do sitting in a ditch!
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Hi Joe and All,
Check the timing às found before trying anything else.
Be very careful when installing the points rotor make sure it is engaged in its keyway in the armature before tightening the centre bolt..
A trick that I have found very useful when setting the timing is to
1 make sure the tapers are clean and degreased thoroughly.
2 put a little chalk dust on the magneto shaft taper, then when engine and magneto are in the correct position use a socket or such to give the pinion a light "tap" so it bites onto the magneto shaft taper.
John
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Progress report: she’s a runner!
Unstuck the cam ring, installed new points, adjusted valves, checked timing (was within spec) and it started in the second kick! I removed the sump plate cleaned it all out and installed a new SRM stainless filter for good measure and the oil return is flowing like a champ. Now I just need to wire it up for lights, tune the carb, get new tires, install new fork seals, and I can ride it! Time to go read up on Amal Monobloc carbs…
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Nah.... That will be just fine on the Alaska Highway. Has all the character of a Yukon Truck*
Swarfy
*A description of vehicles which have somehow slipped through the net of authority and where health, safety and compliance with anything is marginal.
Swarfy
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original gear is relatively soft fibre.. Treat with care.
Additional additional: If there's the slightest doubt about the state of the pinion - can't see all the teeth clearly in the pic - Replace!
Shedding teeth out on the road requires dentistry you can't easily do sitting in a ditch!
I'll second that!! I had two fibre gears strip and one ATD collapse when the rivets failed. Lots of debris in the engine and broke a tooth off one of the timing gears (read all about it in Worty's A10 Engine Rebuild thread). When the well-esteemed Bergs rebuilt my knackered motor, I bought a brand new ATD unit off him for peace of mind.
As with any critical piece of kit, always replace new when you have the chance. Don't do what I did and trust very old bits and pieces in critical applications.
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Replacing the fibre wheel isn't too difficult if you follow Andrew's illustrated guide. My bikes run on alloy ones. There are arguments for both. My Velo runs on a steel pinion since it stripped the fibre wheel a long way from home.
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Replacing the fibre wheel isn't too difficult if you follow Andrew's illustrated guide. My bikes run on alloy ones. There are arguments for both. My Velo runs on a steel pinion since it stripped the fibre wheel a long way from home.
I've come to like the idea of alloy wheels, after my ATD woes!! As I've said, don't rely on knackered mechanisms and fibre wheels that are decades old. I know new ATDs are expensive, but I'd rate them alongside SRM pumps, etc, a critical component. Having said that, I still have one of the original mazac oil pumps which is still going strong.
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Replacing the fibre wheel isn't too difficult if you follow Andrew's illustrated guide. My bikes run on alloy ones. There are arguments for both. My Velo runs on a steel pinion since it stripped the fibre wheel a long way from home.
Personally, I wouldn't use an alloy wheel. The fibre wheel is described as a 'sacrificial component' for a reason. If the armature breaks (and they can) and the mag locks up the back of the crankcase might break off. Back in the day when people took their BSA to the local dealer for a service, the condition of the fibre gear would have been inspected. The reason they strip is because they've been used beyond their service life and the teeth have become sharp and weak.
However, the teeth on a Velocette fibre gear are so fine that it is hard to believe they last more than a couple of thousand miles from new! I, too, would use a steel wheel.
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Been running my Velo (which ain't a plodder) for many years with those fine teeth, and rarely heard of failures there. I wonder if the fact that the Velo teeth are finer, effectively 'spreading the load' thereby less loading on individual teeth, therefore fewer failures? (I'd of course bow to your extensive engineering knowledge Andrew).
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Been running my Velo (which ain't a plodder) for many years with those fine teeth, and rarely heard of failures there. I wonder if the fact that the Velo teeth are finer, effectively 'spreading the load' thereby less loading on individual teeth, therefore fewer failures? (I'd of course bow to your extensive engineering knowledge Andrew).
I’ve met Velocette owners who shout and swear if you remind them of the “bloody Tufnol gear!”
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Or the mag gear that splits because of the hole for the adv/ret spring ....
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OK here is my current setup. At the start of this years biking season I had an issue with the manual A/R "mushroom" which operates the cam ring disengaging, causing the timing to retard too far causing very rough running and heat. This happened when out and about a few times, I tried a different mushroom but I think the housing in the end cover is worn so I made up a special mushroom to lock the cam ring in the fully advanced position. Starting and tickover are both good and reliable, this is my short rod motor with flat top pistons, 357 cam with twin carbs, timing set as per Eddie Dow recommended "twin tips" 5/16 BTDC. I will get around to changing the end cover and cam ring to the fixed type one day. Might be a different story with a 9:1 motor.
Chris P
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Been running my Velo (which ain't a plodder) for many years with those fine teeth, and rarely heard of failures there. I wonder if the fact that the Velo teeth are finer, effectively 'spreading the load' thereby less loading on individual teeth, therefore fewer failures? (I'd of course bow to your extensive engineering knowledge Andrew).
The slightest run-out on the armature shaft and they're knackered!
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BSA's become "knackered" while Velo's require the slight ministrations of an engineer.
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hello Forum,
here is an Info from the www. Translated by Google from German.
"Fine teeth in a gear drive offer smoother running and more precise torque transmission, while large teeth allow for more torque at lower speeds. The choice depends on the application: fine teeth are suitable for applications where smooth and quiet operation is important (e.g., for precise control), while large teeth are advantageous where high power (torque) is required at low speeds."
Best regards, Manfred
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Large teeth mean I can get through my burger quicker *smile*
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Allegedly Bert Hopwood described the timing and gearbox pinions on BSA's and Triumphs as "mangle gears".
You have to be of a certain age to understand the reference. *eek*
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Allegedly Bert Hopwood described the timing and gearbox pinions on BSA's and Triumphs as "mangle gears".
You have to be of a certain age to understand the reference. *eek*
When I read that I could hear the mangle gears turning. 😁
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I can picture my dear ol' mum turning the handle now.
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In addition to my an the previous posts I would like to post a good example for smooth (?) and quiet (??) operation and therefore precise control on the left side and high power (torque) on the other - Made by Triumph *smile*.
Best regards, Manfred
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FYI. The spelling of 'mangel' on the machine is, apparently, the Dutch spelling of the word from which we get our 'mangle'.
I do like those cogs. *dribble*
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What... about 20rpm? *eek*
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It looks just like the etching press we used at Art School too.