The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: UncleD on 08.12. 2018 08:17

Title: Points gap question
Post by: UncleD on 08.12. 2018 08:17
1958 Super Rocket with K2F magneto.

I am in the intiial stages of checking the timing for the first time (new procedure to me). Timing cover is off; magneto lock nut is loosened.

As I rotate the real wheel in 4th gear, maximum open points gap measures .012 on the right cylinder (bottom of the magneto) but 2.0 on the left cylinder (top of the magneto).  Shouldn't these be similar (nothing's perfect).  Is this a sign of warped internals?  Can it be accommodated or is a new magneto required?

Interestingly the right cylinder plug runs black sooty but the left is good. 

I suspect that the timing is out just by looking at the points movement in relation to piston travel.
Title: Re: Points gap question
Post by: UncleD on 08.12. 2018 08:45
..answering myself a bit...(or possibly just confusing myself / everybody.

The bike starts (not easily but that could just be my lack of familiarity with it) and runs reasonably well (comparing it with my fully reconditioned A65)...if something were majors wrong, this would be unlikely and my experience says that most problems are simple.

I'm thinking the huge difference in point gaps might be due to the cam ring being out of position?  Is this possible?

Can anyone point me to some relatively simple information (preferably with pictures) on adjustments to the points, cam rings etc?  It's clear to me that there is a lot of adjustment required in this bike's timing.

This is all new to me so please excuse my musing.
Title: Re: Points gap question
Post by: JulianS on 08.12. 2018 09:13
Variation in points gap can be more than a cam ring issue.

There is often a difference between gaps.

Lucas put a tolerence of 3 thou gap variation.

There is a lot mechanically going on in a magneto.

The points assembly retaining screw needs to be straight and the right one for your points assembly. The taper in the shaft and on the points assembly needs to be good, Sometimes substituting a different complete points assembly will give you closer gaps.

The bearing housings and cam ring housing need to be square and concentric.

The armature needs to be true.

The bearing inners need to be square on the shaft (it is easy to damage the brass shaft wen dring on the bearing inner) and the bearing outers need to be square in the insulators and the housings. Sometimes, on assembly, the insulator is damaged allowing the outer to sit off centre.

The bearings need to be shimmed properly.
Title: Re: Points gap question
Post by: duTch on 08.12. 2018 09:26

 
Quote
...... maximum open points gap measures .012 on the right cylinder (bottom of the magneto) but 2.0 on the left cylinder (top of the magneto)..........

 I guess that's another typo ?

 As Julian said, (apparently) common to have variation (Lucas claim is just to cover their butts)...If there's any slop in the camring as was mine, I packed it out with strips of tin-foil, which worked ok until I had another issue....(variation 0.012"-0.016")
Title: Re: Points gap question
Post by: Swarfcut on 08.12. 2018 09:42

  Julian has covered more than I could ever have anticipated!

   Quick check......see if there is any wobble on the points retaining bolt as the engine is running, indicating a bent bolt/ and also that the points fit into the armature shaft taper with no rock. These factors will affect the relationship of the cam ring and the points heel.

 Swarfy.
Title: Re: Points gap question
Post by: UncleD on 08.12. 2018 10:06
No, not a typo, those were the feeler gauge measures of the two gaps. 

I will check again tomorrow, looking for any movement.  I will remove the centre retaining bolt and make sure it's straight.

Will the fact that the locking screw (in the timng case) is loosened make a difference /allow movement or wobble?
Title: Re: Points gap question
Post by: JulianS on 08.12. 2018 11:16
I would suspect the spark timing between cylinders to be quite a bit out with such a variation in points gap. 1 degree at magneto = 2 degrees at crankshaft.

Most mags are a few degrees out between cylinders.

Below an exploded K2F. The insulators parts 28 and 43.
Title: Re: Points gap question
Post by: Swarfcut on 08.12. 2018 11:58
UncleD....Can you describe what you mean by "The locking screw in the timing case". This makes no sense to me. If you mean the scabby bolt holding the ATD in place, this has no effect on the points.

 The magneto can be fitted with either of two types of contact breaker.    Early type with a brass backing plate. This type comes in two different configurations for clockwise or anticlockwise rotation. This has a long retaining bolt with a taper under the head. The later type of contact breaker is of steel construction and can be assembled for either clockwise or anticlockwise rotation. Has a shorter retaining bolt with no taper but a more snug fit into the points plate. This is the one in Julian's post above.  Disregard the information about the distributor clamp plate, that is not about magnetos.

 These bolts are specific to the contact breaker fitted.  Fitting the longer early bolt to a later steel contact breaker risks damage to the coil in the armature, as it will enter deeper into the armature shaft. So check your bolt is correct for the points plate.

  As a general rule, the cam pivot should lead ahead of the cam heel, so here again is a possibility of incorrect contact breaker application or assembly. Julian's picture above shows the later points, with the magneto  set up for clockwise rotation of the points. As an added confusion, magneto rotation type is classed from the driven end. So you have an anti-clockwise magneto (as defined), but in use the points rotate clockwise as viewed when working. Note the gap between the cam ring and the points spring blade. One of the quirks of this later design of contact breaker is that the points can be earthed if the blade touches the cam ring, miss-firing is a sign. The earlier type does not exhibit this behaviour and you often come across them with nicely marked spring blades, but still running fine and polishing the cam.

 Welcome to the Wonderful World of the Prince of Darkness.

  Swarfy.
Title: Re: Points gap question
Post by: groily on 08.12. 2018 14:02
The earlier type does not exhibit this behaviour and you often come across them with nicely marked spring blades, but still running fine and polishing the cam.

Yup indeed.
Because the earlier brass type had the fixed point connected to low tension live via the centre screw and the sprung point earthed by the screw on the tail of the spring blade.  So kissing the camring doesn't kill the sparks - but it can cause spring breakage in the end if severe enough.
With the 'low inertia' later steel type, the opening point is live via the screw and the fixed one is earthed. So if the spring kisses, bye bye sparks  . . .
That said, if you test-run the same magneto with the two different types of cb assembly, you'll very often find the steel one will give sparks that match the Lucas test specs at fractionally lower rpm, owing to slightly snappier opening. So one step forward and one step back - and no doubt the steel jobbie pleased the corporate beancounters as it's cheap and cheerful.
Title: Re: Points gap question
Post by: RichardL on 08.12. 2018 15:15
Can we get claricication regarding what "2.0" means (see the photo of feeler gauges). (Photo sized with Android app "Snapseed" set to export 1920 px.)

Others have decribed the various possibilities for gap asymetry. Here are a  couple of examples. In my own case, rotating the cam-ring housing 180 derees cured a substantial asymetry. In a10gf's case, shimming the insulated bearing race cured it. Here is s link to his excellent work on this: https://www.a7a10.net/forum/index.php?topic=1375.msg9862#msg9862

Richard L.
Title: Re: Points gap question
Post by: UncleD on 08.12. 2018 20:39
Thanks all,

Swarfy...I have a brass backing plate / clockwise rotation at the points.

Yes, the timing locking bolt is the scabby bolt holding the ATD in place.

I'm not sure of the terminology (cam pivot /cam heel) but the points seem set up in the same configuration for clockwise rotating points compared with other photos.

RichardL,
I will check again the feeler gauge readings (as you have rightfully entered some doubt in my mind), but if you asked me now I'd say .012" and .020" ...but it's now 5am the morning after so I'm making no bets about my memory....it was late and we are in the 'build up'...very hot, sweaty so I could have thought/written anything (including 2.0").

The bike is runnng reasonably well notwithstanding the colour difference in the plug (right cylinder /timing side is blacker with soot). The only quirk that inhibits riding is difficult starting and when idling it will give a woman's fart (Pffft) out of the carb and stall after about 10 seconds.  I tend to think this is a carb tuning issue perhaps exacerbated by poor timing.

I'm making allowances for an old and unfamiliar bike but my initial impressions after getting her to start is that she runs strongly.  In terms of starting, she seems to need priming but floods easily but as I said I put this down to some carby fine tuning perhaps combined with timing that is slightly out.  I can caused her to pink under load but in general running there is no sign of this and the plugs do not suggest a lean burn.  The carb is a 389 monobloc (310 Main, 106 needle, 25 pilot)

For some reason the computer has accepted a photo that yesterday was too big (trick must be to load the photos earlier before the "No" lady starts work.  This photo is the points at the lesser of the two openings (0.012")...I'm thinking this is the left cylinder (as it is closer to the bottom HT lead which runs to that cylinder)...faulty logic?
Title: Re: Points gap question
Post by: UncleD on 08.12. 2018 20:52
This is the wider of the two openings
Title: Re: Points gap question
Post by: Swarfcut on 08.12. 2018 22:56
UncleD....Your magneto has the later screw on cap, so I would expect it to be a later unit and have the later steel points as in Julian's post. Your points are the early type and may be fitted with the later retaining bolt (no taper under the bolt head). If so this is incorrect for your points, allowing a slight sideways movement from centre as the bolt is tightened.

  Easy to check, undo the bolt, have a look and maybe wiggle the points off with some needle nosed pliers. They locate on a small keyway, so you cannot upset the timing as they will go back in the same place. The points pivot will be self evident, the heel of the points arm is the hard plastic brown bit that bears on the cam. Your points look correct for the direction of rotation.  The bolt should have a taper to match the one in the points plate.

  The scabby bolt on the Auto Advance Unit (ATD) is supposed to break the taper as it is unscrewed from the magneto armature but is rarely successful, and more violent methods have to be used. Yours looks like a standard bolt crudely modified to drive the Tacho gear. Make sure it is tight before start up, otherwise the ATD will move on the smooth armature taper and the set timing will be lost.

  On a twin cylinder maggy, the pick up slip ring is not continuous, and the cylinder which fires will be the one with the brass contact strip under the pick up brush when the points break. Easy to check, set the maggy to fire, remove the rearmost pickup and look down the hole with a small mirror.

Swarfy.
 
Title: Re: Points gap question
Post by: UncleD on 09.12. 2018 00:15
The bolt is tapered and straight.

I remeasured the gaps and this time got 0.19" and 0.06"!  I took these measurement as the heel? rode up onto the cam ring ramp (ie the whole heel was on the ramp).  I was careful not to force the points open with the gauge which may explain the new numbers...either way, still a sizeable difference.

I had an initial tug at the points (with bolt removed)...unsurprisingly they didn't want to move!  Any tips?

Title: Re: Points gap question
Post by: UncleD on 09.12. 2018 02:17
Righto, please excuse the previous wobbly figures!

I slowly and carefully measured the points gaps...moving and measuring in tiny increments as the heel moved across the two ramps.  The maximum gaps I measured were 0.10 and 0.20". With both of these readings there was a slight stick of the gauge.  If you were after smooth feeler gauge movement across the gaps you would say 0.09 and 0.19"

So tell me docs, how bad is it?  Can she saved or do I join Berger at the pub?
Title: Re: Points gap question
Post by: groily on 09.12. 2018 07:03
Several things Uncle D.
First, the centre screw is correct for the brass type.
Second, on any anti-clockwise drive K2F the upper cam lobe fires the pick-up next to the engine, the lower one fires the one the gearbox side. Which goes to L and R plug is up to you when you time the ignition.
Third, I also don't think those teeth are meshing deeply enough, but could just be the pic. If in doubt, hold off running things until doubt dispelled, as the teeth have a habit of stripping.
Fourth, the variation in gap is too big.

Rather than join Berger at the pub (it's shut now anyway!), you could try loosening the screws that hold the camring housing on. Wiggle it a bit and retighten. You might be surprised.
If OTOH that does nothing useful, you could take the screws out again and take the whole housing off to see whether the race for the bearing looks central and that there is a decent insulator washer behind it. Poor seating is a common reason for error. If the outer race comes or falls out of the housing easily, that is bad. They should be buggers to extract, needing gentle heat and a careful line of attack.
(Am assuming there is no up and down or axial wobble on the armature due to wear or poor assembly, with everything screwed up tight. Also that the camring isn't loose.)

You could also fit a different set of points if you had one handy, to see if the problem persists.

The cb will come off in the end - wiggle and wiggle some more with the centre screw, the needle-nosed pliers or whatever..

(Generally speaking, any wobble in rotation of the cb unit on the armature will affect both sides the same. You could waste a lot of time trying to make it turn as true as you like, without solving the gap variation problem. Getting the firing interval between sparks correct on a K2F is one of the hardest jobs.)

Title: Re: Points gap question
Post by: Swarfcut on 09.12. 2018 08:32
 Bill.. Well said.  A good few tricks to try there.  Sometimes the search for true perfection is just not worth it. Chasing the last 5% will be the aspect that swallows the bulk of the cash, so I would assemble carefully with what is to hand and have a basic runner. Chances are a better maggy will come along at some stage.

  UncleD... Keep on spannering, almost there now.

   Swarfy.
Title: Re: Points gap question
Post by: UncleD on 09.12. 2018 10:30
Thanks to both of you.  I am a person who drives for perfection but also makes rational decisions.

One of my benchmarks is that I don't leave the shed & tools 'in process' and don't like to leave bikes open/ half done.  So, with no pathway forward I reassembled the mag and put the timing cover back on (albeit without sealant on the gasket so it will come off easily) and gave the bike a kick.  She started second time so I took her for a run to see if I could find Berger and send him home.  She ran beautifully, unbalanced points gap and all.

Whatever it is both pisses me off and is not a burning priority...don't you love the world of the in between?

Groily, I will think about and pursue all that you have suggested because if I have one priority it is to learn as much about this bike (and my A65T) as possible. The next best thing to riding is learning.

On a Sunday night however, with two running Beesa's in the shed, the rain bucketing down and a cool 29 degrees, I am sipping on my single malt feeling very satisfied.

Be prepared for a barrage of questions next weekend!
Title: Re: Points gap question
Post by: JulianS on 09.12. 2018 10:40
If you get inside the mag you may find that the bearing insulator at either end is damaged. They are either flimsy paper or stonger plasticised material, but inserting them into the case or points end cover with the bearing outer sometimes either displaces them or damages the petals, causing the bearing to sit off centre and gining you a variation in points gap.
Title: Re: Points gap question
Post by: UncleD on 09.12. 2018 12:04
I have to say that I am reluctant to dismantle beyond the points both because this is very new to me but also because the bike seems to run OK at present.

If she would not start or was runnng poorly, I'd jump in but at the moment it seems a risk.

I'm not sure if you are following my post in the Engine section but theer has been some question as to whether the mag gear is meshing sufficiently with the drive? cog.  The tips of the mag gears do connect but not deeply.

Could this be related at all?
Title: Re: Points gap question
Post by: JulianS on 09.12. 2018 13:21
Mags run with all sorts of issues.

One last suggestion - just remove the points assembly and check that the key on reverse does not protrude too far causing the assembly to seat at an angle, check the taper on it and the one in the armature at the same time.
Title: Re: Points gap question
Post by: groily on 09.12. 2018 14:35
Don't think necessarily related Uncle D - but having blown the pic up to see the lack of tooth engagement  . . . I'd worry a bit and I'd rotate everything a full turn to see if it's always like that or if there are tight spots as well.  (Maybe loosen the mag fixing bolts and nudge things?? I know you've put the cover back on  . . . . but many of us  have suffered fibre drive gear failure, and it is a pain when it happens.)
Title: Re: Points gap question
Post by: beezermacc on 09.12. 2018 20:19
mod edit: post split from "ATD fibre teeth". Lots of cross-topics ongoing these days...


No dammit, I can't go to sleep ( sorry dear, I'll turn the light off shortly).

HOW THE HELL CAN THE BIKE RUN WELL WITH ONE POINT GAP OF 0.09" AND ONE OF 0.19"??!

(You may need to read my parallel post in the electrical section).

Surely it should be running like a bag of poop?  I JUST DONT GET IT! *pull hair out*

The critical issue is the timing, not the points gap. It may be that, even though the gaps are uneven, the timing is OK. Check the firing position on both cylinders with a degree disc or plug hole probe. You may find that the firing points are virtually the same, in which case the bike will run fine. Even if the firing positions are slightly different the bike may run fine but slightly hotter on one side. They're very forgiving, these A10's!!     A .010" imbalance is quite extreme and the points on the wide side will suffer from 'hammering' as 0.019" is a bit too big and it means the points are working like your hands clapping very loudly, i.e they'll get sore after a while. 0.009" is not so bad as Lucas were happy with 0.010" anyway, but if you get down to less than 0.008 (ish) you run the risk of arcing when the points separate, then it will run crap!
Title: Re: Points gap question
Post by: a10gf on 09.12. 2018 22:13
My old research into uneven points gap \ uneven timing >
https://www.a7a10.net/forum/index.php?topic=1375.msg9862#msg9862
Title: Re: Points gap question
Post by: beezermacc on 09.12. 2018 22:40
A10gf's previous article makes good reading and it is certainly true that by fitting the bearing in an eccentric position can resolve the problem. An imbalance of 0.010" is worth redressing. The fundamental cause of the problem is either a poorly machined cam ring or a poorly machined cam ring housing. In most cases the cam ring is OK. However the cam ring housing can be poorly machined a number of different ways..... including offset bearing housing, crooked, i.e face and back not parallel, offset cam ring housing, loose cam ring in housing (often the case with manual mags). Another common problem is that the cam ring housing is a poor fit on the body which causes the armature to run out of line with the body.
Title: Re: Points gap question
Post by: a10gf on 09.12. 2018 22:53
In my case, the mag was seemingly made from some parts of different sources, resulting eccentricity was not an unexpected find. To be clear, camring, bearing and points were fine, the camhousing itself was what was slightly out of line with the magneto body.
Title: Re: Points gap question
Post by: RichardL on 09.12. 2018 23:25
My old research into uneven points gap \ uneven timing >
https://www.a7a10.net/forum/index.php?topic=1375.msg9862#msg9862

A "must read" for anyone with asymetrical points gaps, even if not due to this particluar cause.

Richard L.