Author Topic: Can ignition timing go faulty during use?  (Read 1411 times)

Offline RichardL

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Re: Can ignition timing go faulty during use?
« Reply #30 on: 14.02. 2019 14:15 »
...and let me fill in where Groily is obliged not to. Assuming you have the magneto off, or maybe perfect reason for taking it off, put in an EasyCap from Brightspark Magnetos in place of the original (or, maybe even, standard replacement) cap.

Richard L.
Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.

Online chaterlea25

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Re: Can ignition timing go faulty during use?
« Reply #31 on: 14.02. 2019 15:04 »
Hi All,

Quote
Fourth, a quick HT test  . . . if you put a meter on the Resistance scale from the brass of the slipring with a pick-up off, and the other probe to mag body or a good earth, what do you see? Should be c 5000 ohms typically on a K2F. Open Line says a break in the winding, or that slipring-to-coil contact is absent. There should be no problem in this department  . . . but you never know.

Digital meters are a poor choice for this test, more often than not they will show open circuit, the connection at the slipring is just a push fit
The very low voltage applied by a digital meter, most often sees this as an open circuit
Something like the old AVO Mk8 analog meters are needed to get a real reading

John
1961 Super Rocket
1963 RGS (ongoing)

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Re: Can ignition timing go faulty during use?
« Reply #32 on: 14.02. 2019 17:16 »
Not with you on that John. A digital meter will do the measurement just fine. They don't 'more often than not' show an open circuit on a continuous coil - at least none of the four such meters I have here does! (Nor does the analog one, perfectly true.) This applies to still-good original windings from eg Lucas, Bosch, BTH and the rest, as it does to rewinds.
The slipring to coil connection on rotating coil mags is a lousy bit of work really, but the push-fit has been with us as the standard method since before WW1, and never really got improved. A plastic grub screw (or something) might have been a good idea, maybe, but there's norralot of playspace and the angles of dangle are awkward.
Absolutely crucial to test continuity when fitting sliprings, as it's all too easy for there to be an open circuit, and then arcing inside the slipring, which does things no good. We want to see exactly the same resistance from armature earth (spindle) to brass on slipring as we see from spindle to the bare spike on the coil before the slipring is fitted. Always a very good idea to clean out a slipring that is to be reused with a small number drill - but better still to replace with a decent modern job, as they're not expensive in the overall context, and the dielectric strength of old ones may have degraded: putting seemingly-good ones in the HT line off a coil tester and heating the ring up will often show how badly, as the current required to get a spark through often goes much too high with temperature.

But I'm pretty confident I haven't come across a continuous coil which any of my digital meters shows to be open line. Hundreds of coils with a break will work on an independent tester due to the spark jumping inside, indeed they'll work often almost to the makers' specs (eg Lucas' "2 amps at break for 5.5mmspark across  three-point test gap") which confuses things, but a break is a break for a' that as Rabbie Burns didn't say. And a break only gets worse until it doesn't allow the spark to get through.

Ref Richard's kind comment, not in the least in selling mode, honest! A WIMA 220nF job as fitted by Dave Lindsley and many others, the caps used by Andrew Beezermac, and the caps used by a number of others do a really good job. Rolled paper, ceramics wired or solder-mount, whatever. And some of the old mica ones from way back remain good almost indefinitely as far as I can see, having tested them from all eras, back 100 years or even more.

I have a graveyard of extracted modern capacitors chez moi, though (hundreds of, literally) and it is sadly the case that a lot of repaired mags with perfect rewound coils and other parts are let down by the use of capacitors which aren't that great in this application. 
Whether that's the case here remains to be seen when other causes of grief have been eliminated. As I said, hopefully not, cos it's a pain in the backside to fix  . . .

Bill

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Re: Can ignition timing go faulty during use?
« Reply #33 on: 14.02. 2019 20:14 »
Hi Bill,
The slipring connection as you say is the weak link
I have found that this will show open circuit on the armature when tested with a digital meter from the brass segment to the core
If you remove the slipring and test from the HT "spike" the winding will read OK
My experience has shown me that the higher voltage applied by an analog meter will "make the connection" and get a reading through the push in spike where a digital will not

In use I believe that centrifugal force will make a good enough connection so the "spike" and slipring segment do not burn away ????

Digital meters can give false readings when circuit testing on 6 or 12v electrics  *problem* where a simple test lamp
would show up a dodgy connection
I own 2 Fluke meters which were at the top end of the price scale when new, luckily they were supplied my my job
plus an assortment of analog testing stuff gathered over the years

John




1961 Super Rocket
1963 RGS (ongoing)

Offline owain

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Re: Can ignition timing go faulty during use?
« Reply #34 on: 14.02. 2019 21:11 »
Thanks for all the tips guys, I really appreciate the advice. I'll try out the tests suggested on the magneto this weekend. I tried cleaning the slipring today by removing the plug and taking a clean cloth to it. Still no change in the symptoms. I recorded a video as well which may help to illustrate the problem as well (https://vimeo.com/317319823).

I need to sort out of the circuitry on the sidecar before making the decision to swap to an electronic ignition instead. i.e. the battery charges fine without the sidecar attached but when I've plugged the sidecar up, there is a huge amount of resistance in the circuit and battery dies not long after but that's for another time! First port of call is to get the bike going! Plus I sorta like the concept of an independent ignition system that doesn't rely on a battery (I remember the stator cables vibrating loose from my stator on my Triumph trophy and the battery died in the middle of nowhere!  *lol*)

New carb, Reconditioned mag and plenty of compression...It should be running like a dream!  *problem*

Failing the tests, I'll take the mag off the bike this weekend though!
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

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Re: Can ignition timing go faulty during use?
« Reply #35 on: 15.02. 2019 08:07 »
Hi John,
Thanks for the additional comments. I shall have a play next time I'm faced with an open circuit on an armature, and see whether the analog jobbie will show continuity when one of the digitals doesn't!
But as a general comment, there are lots of slipring connections that are bad, with a small gap inside due to the design's not being so hot. I would never continue with reassembly of a mag if I couldn't see absolutely the same HT resistance with the ring on as with it off, using any meter, because arcing in there leads to failure over time. The number of rings with pinhole damage caused by this is significant - not so much with K2Fs, but certainly on a lot of others. In extreme cases there's a complete breakdown of insulation between ring and armature spindle or between the boss on the ring and the surrounding brass of the armature end cheek.

Sometimes HT spikes have been cut too short to suit a replacement ring; sometimes it's necessary to tin the HT spike to get a bit better fit in the tiny inner hole in the slipring; sometimes things are just filthy dirty; and sometimes the insulation on an original coil's HT take-off is too thick to slip into the outer hole of a replacement slipring (and that section of the ring needs opening out to allow full penetration (!)) - but in the end I strongly believe every armature should conform to the 'no difference' requirement and be tested for it after the bearing race and any shims/flinger etc have been fitted, as well as before. Rotating forces and vibes may well make good a connection that isn't so brilliant, but it's not a place to take chances as it's a PITA to revisit. This particular thing can drive a bloke mad sometimes, and take up disproportionate time, but I reckon it's worth the effort to get to 'happy'!
Bill

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Re: Can ignition timing go faulty during use?
« Reply #36 on: 15.02. 2019 09:15 »
...This particular thing can drive a bloke mad sometimes...
Yup, I think he is nearly there!

Offline owain

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Re: Can ignition timing go faulty during use?
« Reply #37 on: 17.03. 2019 21:25 »
An update on the A10: Sadly still no sign of life. I removed the mag and tested for a spark on the workbench. I was getting a good bright and consistent spark with a flick of the wrist on the bench. Placed the mag back into the bike...No spark.  *problem*. I took the spark plug out of the cylinder and grounded the spark plug directly to the mag with an electrical cable. Nice spark again. Placed back into the cylinder: No spark.

The slipring is new from having the mag recently renovated and don't think the mag is the issue (Although I could still be wrong). It seems to me that the spark plug isn't grounding when in the cylinder. My theory is that oil has leaked from the rocker box cover onto the the spark plugs and ran down the threads. Insulating the plug from the cylinder. Although this sounds a bit too unlikely to have happened to both spark plugs at the same time.. The pain in the ass is that I then cleaned the cylinder and spark plug threads with degreaser and used fine grit sand paper to expose bare metal. Still no spark! I even secured a piece of electrical cable from one of the cylinder base studs to the magneto to guarantee a path to earth the spark plug to the mag. All to no avail. I'll repeat these steps again tomorrow and hope for a different result but at this point I feel like I'm grasping at straws  *sad*

Just re-read  RichardL's post about easycap from Brightspark magnetos. Sounds interesting, there is no capacitor on my K2F as it is at the moment.
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Online Triton Thrasher

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Re: Can ignition timing go faulty during use?
« Reply #38 on: 17.03. 2019 21:46 »
How do you know there is no spark inside the cylinders?

That issue of the plugs failing to conduct through the threads never happens.

Offline Swarfcut

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Re: Can ignition timing go faulty during use?
« Reply #39 on: 18.03. 2019 08:44 »
Owain..The Thrasher is right, the plug/cylinder joint is not where the problem lies. You should get nice big fat sparks from the end of a bared plug lead to any part of the engine unit. The system will only generate sparks that will fire a plug under compression if a capacitor of the correct rating is in the circuit.  So, looks as if the magneto in its present state is the weak link. Once you have sparks, making sure they appear regularly and at the right time and place is your way forward.

    Easycap is a very cost effective and reliable alternative to revive an otherwise serviceable maggy.  Or a case of  talking things over with whoever renovated the mag....If it was you, get a second opinion, 'cos something basic is not right.

 Good luck.

 Swarfy.

Offline owain

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Re: Can ignition timing go faulty during use?
« Reply #40 on: 18.03. 2019 09:08 »
Thanks again for the tips!. Of course, It is an assumption that there is no spark in the cylinder as I'm not getting any sign of combustion when kicking the bike over or running down the street and dropping it into 2nd gear. I fitted a new concentric carb onto the bike as I initially thought a worn carb (bought from an autojumble) was the original cause of poor starting. Even if the the air/fuel mix is way off with the new carb fitted, I thought there would at least be a pop from the engine...

Taking your advice on board. I'll twiddle with the carb settings this evening and see if that makes any difference. Failing that I'll send the mag off to be looked at by a different company for a second opinion!
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

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Re: Can ignition timing go faulty during use?
« Reply #41 on: 18.03. 2019 13:29 »
Hi Iain,
The fault you describe can be due to loose bearings in the magneto and or bad earth brushes,
I have seen cases like this but really cannot offer a great explanation as to why it happens
I am presuming that you checked the fibre mag drive gear ?

John
1961 Super Rocket
1963 RGS (ongoing)

Offline owain

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Re: Can ignition timing go faulty during use?
« Reply #42 on: 18.03. 2019 16:15 »
Checked the fibre gear and it looks solid. I just tried turning the air/fuel mixture screw in and out sequentially (half a turn at a time) on the carb with no success. Worth trying a different main jet before I remove the magneto? Otherwise, I'll just take the magneto off and send it to again to a different mag guy.
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Offline Klaus

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Re: Can ignition timing go faulty during use?
« Reply #43 on: 18.03. 2019 17:02 »
Hi owain,

get off the fibregear and look for scratches at the rear side. Sometimes the the tapers are in such way ,that the gear is just against the timingcase. In this way you can fit the gear and the magneto turns, only for a few turns you have the right ignition point, but the taper doesnt fit proper.
I had this, and it drive me mad.

Cheers Klaus


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Online RDfella

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Re: Can ignition timing go faulty during use?
« Reply #44 on: 18.03. 2019 17:44 »
I have read several of the posts on this thread but maybe not all, so forgive me if I’m re-covering what others have said.
Owain says no spark in the cylinders. How does he know? Is the head off to see? He says there’s a good spark on the bench, so I suspect this is not a magneto problem. If he lays a plug on the cyl head (or any metal part that’s earthed) he should get a spark. If not, try holding the end of the HT lead ¼” away from the head. If still no spark, try another HT lead – maybe his are carbon instead of copper core, or the plug caps are resistor type.
Oh, and BTW, his magneto has a capacitor / condenser - it wouldn’t work without one It’s inside the armature.
Given there’s a good spark on the bench, is the magneto timed correctly when on the bike? It is actually turning when the engine turns over? Do the plugs come out wet, indicating fuel is getting to the cylinders? Is the fuel fresh? I once spent an hour or so trying to start my B31 to no avail. Wouldn’t even fire with a push start. Reason? The petrol was about a year old. Fresh petrol and it started within a couple of kicks.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.