The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: BSA500 on 11.12. 2023 13:06
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Has anyone had issues with wear on their points heel on the K2F magneto. I was trying to start the A7 this weekend just run it up and she just wouldn't start and has been a bit stubborn for a couple of weeks, I just thought it was the damp/cold. Pulled the plugs wet with petrol. No spark at the plugs. Surprising as Andrew had gone through this mag completely last summer and new leads plugs etc. I assumed the drive cog must have failed. I checked if it was turning and yes it was then I noticed that the points heel didn't seem to be touching the cam. It has completely worn away I had only ridden it for about 500 miles and had noticed she was getting more tricky to start which I put down to using a spare incorrect carb.
I have had this bike for over 30 years and never seen this before, i have never had to adjust points gaps in that time they just never changed, its just very weird??. its no biggie as the bikes off until the finer weather and I have to service the gearbox but is there a bunch of dodgy points out there?
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New points sets and baseplates are poorly made. Check carefully for a loose pivot pin. That makes the gap close up.
Even the little contact points themselves can come loose on their arm.
There should be a wick under the bottom of the cam ring, with a plug of felt that sits in the round hole in the cam ring. It should be kept oiled.
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Thanks for the reply. I can actually see that the heel has lost material and worn away in around 500 miles of use. I have had points that I used for years without having to adjust(and I admit to neglecting to lube). Its just so odd
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The newer points may have an inferior nylon heel, rather than the old Tufnol.
There is such a thing as special points cam grease, but I don’t know where it’s available. I think I heard that specialists in air cooled Volkswagens used to have it.
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Well I will have to take it out for a closer look see and eeplace at least its an easy fix. I will get a decent set from Andrew rather than the "genuine' lucas ones on ebay ;). Like I said no rush I have gearbox oil leak to sort
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Had the same thing happen to me. A newly overhauled mag got steadily worse and would only run on fully advanced. I discovered that the points gap had closed to 1 1/2 thou. I'm used to mags running without attention for years. Now checking points has gone on the the frequent checks list.
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It's quite common to see points gaps self-adjusting with the later Lucas steel-backplate cb assembly because the method of attachment of the fixed point carrier leaves much to be desired. But not so common I think for the heel to be worn down the way BSA 500 describes. (I infer that the problems recounted here relate to these later versions.)
Replica points kits for the steel backplate units have been of very variable quality and some just aren't fit for purpose: flimsy construction, serious mis-alignment of the contacts when fitted on a decent Lucas backplate, loose contacts, dodgy rivet holding the bent tin opening point carrier to the heel - all and more of what TT said.
I'm not sure what the quality is like of any of the bits that are available from the usual sources to be honest.
Ideally I'd always use an earlier brass backplate if one is to be had. Although they suffer over time from worn pivot posts and oval holes in the heel, these weaknesses can be sorted, and if needs be better contacts can be grafted onto damaged or worn parts. The heels on these parts last pretty well - a bit of lube (as also says TT) is good, using the felt strip and pimple supplied.
It is also worth bearing in mind that it is possible to fit a BTH or Bosch contact breaker unit of the correct rotation. It may (depending on the individual version) require suppression and recreation of the integral keyway/ register on the male taper to get the internal timing right (or repositioning the camring), but the design of these cb units is superior to the Lucas one in my view.
As an aside, the temptation to regard these things as 'fit and forget' has to be resisted, a bit at least!
The general advice back in the day, per any number of Owners' Manuals, was that a mag should be sent to a 'Lucas service agent' every 10,000 miles for a complete strip and replacement of any worn or defective parts, with interim maintenance such as points cleaning, lube and re-gapping every 3000 miles. I'd say these days, for the miles most folk do, that annual removal and checks to the cb unit and HT pick-ups and brushes is probably enough. Simple checks can be revealing, especially in relation to oil ingress, excess armature float or wobble etc etc and are often the stitch in time that saves nine.
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then I am really unlucky I have the brass points plate, God hates me
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That is definitely boring. But I reckon you're better off with the brass one despite this one-off problem.
The heels do wear - in the end - but if it's an original Lucas bit, it's a really gradual thing usually, even if a bit low on lube.
Is there any sign on roughness / damage on the camring that could have caused the heel to be ground down so quickly? Or any small part missing or detached and floating that could have got into the works and damaged either the heel or the ring?
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I will have a close look when time allows
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I got a good picture of the points in place and it looks like they are in fact opening but I think the plastic washer that goes under the clip that goes over the points is missing. I need to take these points out and have a good look
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I think the plastic washer that goes under the clip that goes over the points is missing.
It’s not difficult to know whether the little insulating button is there or not.
Post a photo with the clip moved out of the way.
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I have tried to find a way to reduce the image but have not found a program etc that works yet. I shall have a nose at the points later. Does this act as an insulator?
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Regarding photos, find and load the program/application “Snapseed.” Hit three dots. Go to “Settings” and set image size to 1,366. Then, after opening a photo in Snapseed, select “Export.” The reduced file will be saved in the Snapseed folder.
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The spring clip blade that holds the moving point onto its pillar should be kept from metal-to-metal contact with the rocking arm, by a small plastic button sitting atop the hole in the rocking arm.
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Does this act as an insulator?
Luckily no. The opening point is earthed on the brass cb units. The dimpled button just sits in the register and stops metal-to-metal contact as TT said. (It can help reduce wobble on the pivot if there is modest wear.)
If the clip blade is sloppy, it will slide out of position and the button will eventually fall out.
The clip is held by a simple pin. If it's loose, a fractionally bigger one - or for belt and braces, tap the hole say 6BA and use a small screw to retain it. It won't interfere with the secondary earth brush if there's one fitted up the rear face.
A button can be made from anything really, I use a bit of 'klingerite' or similar, a gasket hole-punch of appropriate size and then a pointy punch to create the dimple.
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I have found that emailing the photo to myself works well. My email has an option for image size. I just choose small works every time. A bit of a faf but it works
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The tip of a syringe or the bit you cut off the end of a 3in1 oil tin or suchlike is a good substitute.
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I have sorted the photo sizing problem *smiley4*
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Just to prove it
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I know could do better working on it
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Looks like the plastic bit has gone walkabout.I will have to remove the points plate to make sure it's not wedged anywhere it shouldn't be
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So if the points are in fact opening and closing and the plugs/leads/pick ups and the mag had a full Andrew rebuild 500 miles ago why have I lost sparks??
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So if the points are in fact opening and closing and the plugs/leads/pick ups and the mag had a full Andrew rebuild 500 miles ago why have I lost sparks??
Is the insulator button now in place?
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Can't find it it has evapourated *smile*
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I suspect it escaped when I took the end cap off. I think the clip needs to be bent in a little as well to make better contact when I replace the button
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So if the points are in fact opening and closing and the plugs/leads/pick ups and the mag had a full Andrew rebuild 500 miles ago why have I lost sparks??
Is the insulator button now in place?
So is it an insulator or just there to locate the arm on the dimple?
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Not an insulator, both the retaining spring and the moving contact are earthed to the mag body so just to hold the moving point in position.
With the original Lucas points the little nylon button is a tight press fit in the moving points and can be quite hard to press it back in. The common pattern replacement points (which fit both anticlock and clock mags) with plastic heel have a black button, larger diameter than the nylon one.
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Not an insulator, both the retaining spring and the moving contact are earthed to the mag body so just to hold the moving point in position.
I do get confused, especially with the steel plate being so different from the brass plate.
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Which adds to the confusion as to where have the sparks gone???
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Which adds to the confusion as to where have the sparks gone???
Probably not very far, but it's going to be hunt the thimble to find out. A sudden total lack of sparks both sides, not a glimmer, speaks more to a low tension / contact breaker type problem than to a failure on the High Tension side (usually).
A few thoughts:
Low Tension side:
1. Have you tested for sparks with the screw-on end cover and kill button detached from the magneto? A short between the carbon brush and the cover, or where the wire attaches on the outside, will stop it working. (Make sure when testing that the blade that is supposed to have the button under it can't touch the head of the centre screw if it's out of position - that would short out the low tension side as the screw and the brass bit it passes through are 'live'.)
2. Get the cb unit off - one screw. With the points closed, do you see as near as makes no odds Zero ohms across them? If there's a high resistance the points aren't making good contact for whatever reason - oxidisation being a common one. Cleaning to squeaky clean will often resolve that.
And then with them open, do you see an Open Line? (No good testing with the cb on the mag as there won't be an Open Line when they are open - just the half ohm resistance of the low tension winding.) If there's continuity with them open and off the magneto with the centre screw shoved up the middle, then there's a problem - which is probably a broken insulator, the one the cb centre screw passes through, or the mica flat insulator that goes between the fixed point carrier and the cb backplate.
3. Put a meter between the cb centre screw (no need to put the whole cb unit back on) and measure the resistance between it and the mag body. It should be about half an ohm. If there is no reading, then either the electrical connection to the 'nut' inside the mag which the centre screw attaches to, or the earth connection from the coil up at the condenser end, is faulty.
Low tension windings themselves fail so infrequently it's a million to one against there being a problem with the winding itself.
High Tension side:
1. Remove HT leads and check for continuity from the brass washer under the acorn nut to the spark-plug end of the lead. Should be Zero ohms. Avoid using high resistance plug caps if possible, and don't use carbon leads. Copper-cored for choice. Not a likely reason for your problem as both sides wouldn't go funny on you at once, but to be checked all the same, especially if using those flexible rubber plug caps whose screw tends to go off centre when attaching to the HT leads.
2. Remove HT pick-ups and check the brushes are there, and in good condition. Check continuity from brushes to the bit the HT leads screw up against. A modest resistance of a few ohms would be pretty normal.
3. With the pick-ups removed, turn the mag until you can see (maybe using a small mirror) the brass segment on the slipring which the brushes run on through one of the pick-up windows. Put a meter on the brass segment, and the other end to the mag body, high resistance scale. You should see about 5000 ohms. If you don't, then there's a break in the HT continuity. The HT winding is earthed up at the condenser end in common with the low tension side - so an earth problem would probably affect both. Clean the slipring if it's mucky, using a wooden rod with a bit o' rag on and a solvent. Shouldn't be mucky unless you have fitted poor quality brushes since it was overhauled. Othe problems could include the connection of the coil to the slipring being dodgy, or that there is a fault on the coil or condenser. Highly unlikely given the excellent provenance of the thing but 'stuff happens'.
I'm guessing the problem is at the contact breaker somehow, but these things are capricious and the only way to proceed is 'one thing at a time'. If everything seems good per the above, then I think you need to get back to Andrew after he re-opens for further advice and suggestions!
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Well she is a runner. Took the cb out and found the disc in the picture,must be the button, behind the cb a.ssembly at the bottom of the housing. A bit thinner than it should be. Still she would not start. Did some of the low tension and leads checks .All checked out ok. Pulled the plugs and checked the sparks and noticed they were white sparks and not across the gap. A bit sooty so cleaned them and low and behold nice sparks. Put hem back in and away she went.
Still need to put a new button in an Ben the clip down a bit as the gap is alittle wide and not holding point in properly but thanks all for the advice *smile*
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*beer* *beer* *beer*
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Wait. It runs without one of the points buttons?
Richard L.
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They often do. many is the sparking mag I have looked in to find no button present.