The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Beezageezauk on 16.07. 2009 19:37

Title: Ignition Timing...what am I doing wrong??
Post by: Beezageezauk on 16.07. 2009 19:37
Now then I hope that I can put this into words and that it makes sense to you.

First of all I am running 3 A10's, 2 of which I built up from scratch and I have never had a problem with setting ignition timing.  That is...until today...when a mate of mine asked me to set the timing up on his '57 swinging arm A10.

His engine was running fine after we set his timing up a few months ago and then all of a sudden it started to run lumpy.  We put it down to contact points so he changed them.  The engine ran fine again but soon began to run lumpy yet again.  On saying this the bike hasn't been on the road, just running in the garage. 

Anyway, we decided to work together and try to determine what the problem was.  First of all we removed the contact points, gave them a good clean and set them to a 12 thou gap.  The auto advance and retard is a new pattern part and the bob weight mechanism felt a bit stiff so we treated it to some thin oil.  This did the trick and it works fine now.

Ok, so we decided to reset the ignition timing.  After removing the rocker covers and spark plugs we set the engine at 11/32 btdc on the compression stroke and offered up the auto advance unit with the bob weights wedged open and the contact points just opening.  This was tightened up and then the timing was checked by manually moving the bob weights.  Nothing had moved and the points were still just opening.  We used one of those buzzer thingies to check this.

When we tried to fire up the engine...nothing...except an odd explosion in the exhaust system.  We then swapped the plug leads over in case we timed it up 180 degrees out and there was no difference. 

We then stripped everything down again and retimed it using the same method but on the other cylinder.  This time we used a cigarette paper to set the points instead of the buzzer.  Exactly the same results.  An odd explosion in the exhaust system!!  After again swapping the plug leads over we came to the same conclusion....we were mystified.

Now we started thinking about valve timing so we pulled off the inner timing cover and checked it out.  No problem there.  Whilst the inner timing cover was off we even removed the tab washer and nut on the camshaft pinion just in case the key had broken and the camshaft timing had moved.  No problem there either.  Even more mystified!!

Oh yes, we double checked the rotation of the magneto so the points were just opening and not just closing.

Is there anything else we can do??  I'm sure that some of the A7 and A10 Gurus on the forum can advise.  We must have missed something obvious but what is it?  Surely we can't blame it on the Gremlins.


Title: Re: Ignition Timing...what am I doing wrong??
Post by: RichardL on 16.07. 2009 20:08
I'm not the "Guru," but I have some comments (So, what's new, have you seen the ridiculous number of posts I've made? It's embarrasing.)

1. Do you know for certain the initial trouble wasn't fuel related? You could pull a carb from a properly running bike and use it on the troubled bike to eliminate that possibility while testing for other troubles.

2. Why remove the rocker covers? did you make some valve adjustment that has the exhaust valve(s) opening too early, hence the popping in the exhaust?

3. I don't think moving the bob weights is a good way to check if timing has moved during tightening. I would say, after tightening, leave the weights wedged, replace the ciggy paper in the points well before 11/32", shift into 4th gear and use the rear wheel to turn over the engine while lightly tugging on the paper, remeasure distance BTDC.

4. Perhaps obvious and not fitting your total description, but are you certain the timing marks on the pinions lined up both before and after your experiments?

5. Perhaps the mag, slipring or pickups have gone bad, or a combination thereof.

That's seems enouugh from a lowly apprentice of a guru's apprentice.

Richard L.
Title: Re: Ignition Timing...what am I doing wrong??
Post by: beezalex on 16.07. 2009 21:13
Geeza, I think you need to start with the basics: compression, ignition, fuel.

If you get good compression, I'd stop messing with the valve timing and adjustment.  It'll run.

You never said whether you are getting a good spark after all this.  There is a nice, inexpensive tool called a spark tester that will help you check the quality of your spark.  Barring that, get an old plug and set the gap to about .060".  If it won't spark over that gap, it won't fire on compression.  BTW, you did try fresh plugs, right?

Now, a fuel check is easy.  I've got some old squirt bottles one of which I put gasoline in.  Squirt some fuel directly into the mouth of the carburettor with the throttle open.  Try to start the bike.  If it starts and then dies, you have a carburettor problem.

Hope that helps.
Title: Re: Ignition Timing...what am I doing wrong??
Post by: A10Boy on 16.07. 2009 22:14
My 2 pen'orth.

You seem to have done everything corectly, so maybe the Mag is knackered, it seems to have had a rapid deterioration, first it was ok - then it ran lumpy - now it wont run at all... so maybe there is a winding gone west. Have you another mag to try ? have you checked the pick ups and earth brush ?

Title: Re: Ignition Timing...what am I doing wrong??
Post by: chaterlea25 on 17.07. 2009 09:50
Hi, All
Sounds like something that happened to me??
Check the mag slipring, if you have an ohmmeter or megger tester megger from one pluglead to the other
should read very high M ohm's or infinity
I have found that the slipring tracks and the mag is now trying to fire the 2 plugs,
pull off one lead and see if the bike will start on one cylinder???
John O R
Title: Re: Ignition Timing...what am I doing wrong??
Post by: motoloco on 17.07. 2009 14:53
hi guys ,same thing has happened to my a10 this morning ,after replacing bearings in the mag just bought the bike and it lacked power.checeed the points 12thu one side 18 on the other put mag back together gaps still very different called  mag specialist in uk . he said you must grind cam ring with your dremil to get them even  .declined to sell me new points said they were rubbish.but would rebuild my old ones,strange thou i did valves and fag paper thing,and swapped leads, even got the bang guess ill just go back out there try something else.
Title: Re: Ignition Timing...what am I doing wrong??
Post by: RichardL on 17.07. 2009 16:25

I would make a very close inspection of your cam ring before replacing it or grinding it yourself. If it has changed 0.006" on one side and not the other, I think there would be some really obvious damage. Why it would wear so unevenly is a mystery to me, so I tend to think the problem is elsewhere. Now, you are not the first to mention uneven cam wear, so, I suppose it can be a problem, but your's sounds like a large amount, to me, as I said, a mystery. Assuming you are correct and the camring is bad, you might opt for just buying a new one from a reuptable dealer. I searched "k2f cam ring" and found several, one that stuck out was

Having said all this, I am not really commenting more here about your overall problem, as the previous posts and, I'm sure, more to follow, provide some good advice, maybe even my own.

Richard L.

Title: Re: Ignition Timing...what am I doing wrong??
Post by: motoloco on 17.07. 2009 16:45
hi mano you right about the cam ring i failed to mention its the end case that holds the bearing its not machined accurately , mine had the metal three hole gasket cut in half where they had tried to get the offset specialist said he sees this alot i guess lucas had maching problems at some time.           
Title: Re: Ignition Timing...what am I doing wrong??
Post by: groily on 17.07. 2009 18:27
that is so often the problem, and the cam ring is so often blamed. All the reconditioners would, I believe, say the same - ie it's usually the bearings or the housing, and only sometimes the ring.
When I've got the other things right, in all bar one case over the years I've found that cam rings I thought I needed were wholly unnecessary. And that one had been eaten by rust, so not really its fault. If one thinks that many housings are living on mag bodies they weren't supplied with, that there's the risk of some slop in the mating faces and the registers, that the bearings have been hoicked out by nameless persons with 'orible 'tooling' over the years etc etc, it's not surprising concentricity and perfect fit aren't 100% guaranteed. And the poor cam ring as often as not gets the blame. As long as I can get within 2 thou on each cylinder, with no slop in the obvious places, I'm happy. And I'd never take a mini-grinder to one myself, I have to say, although a light 'stoning' of any rough bits or minor warts may be OK. Good idea to make sure the lube-retaining felt is in place in the housing and that the hole through which it arrives on the inside of the ring has its little felt pip in it. Set it up right, with a known good armature and modern condenser, fit and forget . . . that's been my plan, apart from periodic standard checks. Wonderful things.
Title: Re: Ignition Timing...what am I doing wrong??
Post by: A10Boy on 18.07. 2009 13:56
A decent mag specialist would sort this out no problems.
Title: Re: Ignition Timing...what am I doing wrong??
Post by: Beezageezauk on 18.07. 2009 22:33
Thanks for your replies and suggestions so far, but can I let you know the latest news on this saga. 

Whilst I was at home my mate decided to remove a pick-up and try to start the A10 just to see what happens.  Guess what!!  It fired up first kick as a single cylinder.  He then replaced the pick-up and tried again....nothing.  He then removed the other pick-up and the damned thing fired up again as a single cylinder, obviously on the opposite cylinder.

Now he decided to replace the removed pick-up whilst the engine was ticking over and the bl**dy thing cut out.  This shows me that the pick-ups and high tension leads are ok so the fault must be with the magneto itself.  It also proves that we timed the engine correctly in the first place.  So we were not doing anything wrong.

The magneto itself was rebuilt at some expense by a very reputable company in the UK and has had less that an hours running so they will be getting a phone call on Monday morning.  We don't want to play about with it and give them the excuse to nullify the guarantee but we would like to know where the problem lies for future reference.  I think they will probably ask my mate so return it for them to check it out and he is likely to get it back in good working order without a suitable explanation.  However, if we do find out exactly what the problem was (or is) I will let you all know.

In the meantime my mate has fitted one of my spare magneto's and the bike is running fine.   

Title: Re: Ignition Timing...what am I doing wrong??
Post by: BSA_54A10 on 19.07. 2009 10:39
Either there is a problem with he slip ring ( dirty or cracked or both)
Or the earth brush is not making proper contact.
Title: Re: Ignition Timing...what am I doing wrong??
Post by: chaterlea25 on 20.07. 2009 11:57
Hi Beezageeza,
This is what I said to do on my reply,!
The fault is the slipring it has tracked right around and there is not enough energy from the mag to fire both plugs at once!!!!
Try closing both plug gaps right down and see will it run?
I am convinced that there were crappy sliprings being supplied to mag refurbishers 5 or 6 years ago
I have had to change several in the last 2 years
John O R
Title: Re: Ignition Timing...what am I doing wrong??
Post by: Beezageezauk on 20.07. 2009 21:54
Hi John (Chaterlea 25),

I believe that my mate read your suggestion to try firing up with only one pick-up and you hit the nail right on the head.  Thanks very much.

I'm amazed that I haven't come across this before if it appears to be a common problem.  Maybe I've just been lucky with my magnetos!!

Anyway, the faulty item is being returned to the suppliers who will make good under the guarantee.  All's well that ends well.

Thanks also to everyone who replied.


Title: Re: Ignition Timing...what am I doing wrong??
Post by: Triton Thrasher on 21.07. 2009 08:17
There were warnings of soft HT brushes on sale.  They marked the slip ring too easily.  Another cause is a brush slewing sideways under the pickup as you fit the pickup into the mag. The carbon is easily cleaned off but be careful not to shock your finger.

With a tracked slip ring, it sparks at the plug which is not under compression.