Author Topic: Ignition timing/magneto problem  (Read 4543 times)

Offline redbeeza

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Ignition timing/magneto problem
« on: 08.08. 2010 16:18 »
Can anyone help with the following (or tell me if I'm thinking along the right lines)?

I've an A10SR with newly rebuilt engine. Bike not yet ridden but engine has been running fine: fairly steady tickover, good throttle response and settling to a steady tickover again. Rebuild/resto finally thought complete late last Autumn, but because weather was poor and I haven't ridden for some years I decided to lay the bike up until the Spring when a maiden ride could be made on roads not covered in leaves and mud!

Over the winter I removed the battery and kept the bike in the shed. I decided, probably erronously, that it would be a good idea to kick the bike over occasionally, my thinking being that it ought to move a bit of oil around and keep things freed off. So I kicked it over (plugs out) a dozen or so times once every week or two.

Spring arrived and I went to start the thing up (bearing in mind that it started and ran OK before it was laid up). It was difficult to get it started and when it did fire up it ran very roughly; one pot, then two, then one. It idled very high and very badly. The exhaust headers blued rapidly! So I shut it down.

I had fitted new plugs, leads, pick-ups, and brushes to the magneto (along with bearings and oil seal). On checking the brushes I found that they had either worn down very rapidly somehow or had broken off; one had a very rough end where it touched on the com.

I fitted new(ish) brushes and started her up again; same problem. I then checked the ignition timing (only the measuring rod through the plug hole and fag paper method I'm afraid, but it worked OK the last time). The timing seemed to be out a bit so I reset it and double checked. Started her up again; no improvement.

My postulations are these: Could this trouble be caused by a broken off carbon brush spinning around in the mag and arcing randomly? I suppose my over-zealous kicking-over of the bike during the winter could have broken off the brushes??  Could the kicking-over have moved the timing pinion also??  Could these all be red herrings and the slip-ring and/or the condenser has broken down coincidentally?? Am I mad to turn an engine over like that for such a short lay-up??!

I am in France at the moment until the Autumn and the bike is in England, so I can't go out and try anything immediately. I would just like to get a head start on probable causes of this trouble so I can rush out to the shed when I get back!

Any ideas?
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1962 A10 Super Rocket.  First Brit bike, first rebuild.

Online bsa-bill

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Re: Ignition timing/magneto problem
« Reply #1 on: 08.08. 2010 16:46 »
Can't think that kicking it over would do any harm
My last experience of non starting after winter was last year when my normally two kick start Flash just would not fire, it had for the first time been stored in a dampish environment out of necessity, turned out to be the high-tension leads had  corroded at the plug cap, cut off quarter of an inch and it fired straight up.

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1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline LJ.

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Re: Ignition timing/magneto problem
« Reply #2 on: 08.08. 2010 18:10 »
Possibly a number of things... Have you got the right spark plugs? these bikes are rather fussy about what they run on.
Had the bike wet sumped giving a sort of lumpy running until cleared?

If a small piece of carbon brush has broken off then you need to get the broken bit out, there wont be any damage done but likely it could grind up leaving a dust layer around on the slip ring that could result in spark leakage.
As you have not ridden the bike the carb may not be set up correctly, if the pipes are blueing while ticking over then the pilot jet is a bit lean, richen it up a bit, but you do need to start the bike and ride it, adjusting things as you go along.

When checking your ignition timing did you check it in full advance? It always pays to buy good quality brushes as there are some soft ones out there that do wear down quickly.
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Ride Safely Lads! LJ.
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1953 BSA B33  500cc Teles/Plunger-Maroon
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Re: Ignition timing/magneto problem
« Reply #3 on: 08.08. 2010 18:37 »
I would go with Bill on checking your HT leads for corrosion. The damp gets in everywhere so that is a very real possibility. The mag could also contain condensation droplets. Try removing the end cap and spraying some WD40. Another area to investigate is the possibility of gum deposits in the pilot jet. It is good practice to switch off the petrol taps and leave the engine running until the carburettor is empty if you do not plan on using the bike for a while. I think that it is very unlikely that the timing would have changed from when the engine was last run. The practice of turning the engine over during a lay up period is a sensible precaution to prevent the rings sticking for example. As far as your comments relating to the condition of the brushes is concerned, it is quite likely that you have a set of soft after market brushes which wear away prematurely. Contact someone like Tony Cooper and get some correct grade brushes. If you have soft brushes you might find that the magneto slip ring is contaminated with carbon dust. I will just mention that as a matter of routine I always add Redex to my fuel. It really does help to keep the carb clean. It is also good for the valve gear.

John
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Online bsa-bill

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Re: Ignition timing/magneto problem
« Reply #4 on: 08.08. 2010 20:52 »
Where do you get your Redex John? I haven't seen it for a long time (other than diesel treatment)
in the sixties we used to squirt it into the carb until billows of white smoke poured out the silencers, probably a complete waste of time but very very impressive
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1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline trevinoz

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Re: Ignition timing/magneto problem
« Reply #5 on: 08.08. 2010 22:22 »
Possibly the carby has some of the fine holes blocked with crud if you left fuel in it.
Probably a good idea to strip and clean thoroughly.
Trev.
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Re: Ignition timing/magneto problem
« Reply #6 on: 08.08. 2010 22:35 »
Bill,

Redex is available from Halfords. Your sixties recollection of squirting Redex into the carb was a common practice with Home Tune operators and other engine tuners for that matter. It breaks down carbon deposits it is claimed. The effectiveness of this is even greater if you pour it into the cylinders and leave it to soak over night. I recall an engine tuner telling me back in the sixties that the technique was used by some race teams especially those who raced/rallied Mini Coopers who claimed that it could increase engine power by a couple of BHP. I use it just to keep the carb clean, which it does. I make no other claims about its usage. Its a nice story though.

John
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Re: Ignition timing/magneto problem
« Reply #7 on: 09.08. 2010 09:19 »
Thanks John- worth a try next visit to Berwick
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1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline redbeeza

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Re: Ignition timing/magneto problem
« Reply #8 on: 09.08. 2010 16:59 »
Thank you for the recommendations chaps.  I'll check all the things over when I get back to Blighty; have a good look at the mag and clean the carb.  I can't recall the spark plug type but I've pretty much been using Roy Bacon's BSA Twins book as a bible during the rebuild, and have used his recommendations.  What type would you suggest?

The bike does wet sump, despite its fancy new blue SRM pump, But I drained the oil off before starting.

Thanks for the tip on soft carbon brushes, I think I got them from Independent Ignition Supplies along with the pick-ups but I can't be sure without the receipts to hand.  Any suggestions for a reliable source?  Where do I contact Tony Cooper and is there a particular size/grade I need to ask for?

I did set the ign timing on full advance and, as I said, it has run well previously (but only stationary).  While I'm on the subject, I can't recall the measurement in fractions of an inch BTDC that I set the timing at, but I do know that I followed some advice on using a different setting than the original BSA one for a '62 Super Rocket because of using unleaded fuel.  Could someone let me know what setting they use for a model like mine?

And thanks for the Redex tip, I'll seek some out.
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1962 A10 Super Rocket.  First Brit bike, first rebuild.

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Re: Ignition timing/magneto problem
« Reply #9 on: 09.08. 2010 20:38 »
I think most choose the recommended in the day 3/8ths but some debate as today's fuel differs from that of fifty years ago
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1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

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Re: Ignition timing/magneto problem
« Reply #10 on: 10.08. 2010 01:02 »
Quote
I think most choose the recommended in the day 3/8ths but some debate as today's fuel differs from that of fifty years ago

Bill it is interesting that you make this point because I found 3/8ths was to advanced. The bike went well enough but pinked very badly under load. 3/8ths by the way is 35 degrees. I have a friend who wrote to BSA in 1971 and BSA advised him to set the timing to 33 degrees (DA10 SR big valves and spitfire cam).  because at that time 5 star petrol was being phased out. The 3/8ths setting applied to aluminium heads with HC pistons. Iron heads should be 5/16ths (32 degrees). If you check the SRM website and navigate to the technical section you will see that they have got these degree/fraction values wrong. Which is worrying, because a lot of people will accept what SRM say as gospel. Incidentally if you are going to set the ignition timing with the head in place there is only one accurate way to find TDC. Use a piston stop and wind the engine until the piston touches it then wind all the way back until the piston again touches the stop. Divide the difference on your timing disc and you have an absolutely accurate TDC. Any other method will be at least 4-5 degrees out Trust me, sticks down the hole will not do!!!

John
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Online orabanda

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Re: Ignition timing/magneto problem
« Reply #11 on: 10.08. 2010 01:44 »
In support of John, through dyno testing some of my bikes, I have found the optimum advance for iron head A10's with 7.25: 1 pistons and 536 cams, is 30 to 30.5 degrees (both small fin and big fin heads).

By optimum advance, I mean in relation to the enginge producing the best combination of maximum torque at lower RPM, more HP, and smoothest running.

Here is 54 GF at 30 degrees:







I will be doing a couple of Super Rockets, and a Road Rocket in the next few months, and will post the results. However, i have found that 35 degrees is too far advanced for my engines, and based on my dyno experiences, expect the best result to be around 33 degrees.

I strongly urge everyone to spend the small amount that SRM want for their timing disc kit and cush drive nut, and use a strobe light for timing. It is the most accurate way to get it right, and a small investment when the engine is performing to its max, using less fuel, and causing you to have a permanent grin on your face!

I also slot the maggie mounting holes, which gives about 18 degrees of adjustment to the timing whilst the engine runs; you only need a few degrees adjustment to get it right, but it is much easier than on and off with the timing cover, and hoping it is where you want it!

My findings also contradict SRM's, although not by much. Advancing to 32 degrees results in a reduction in torque, and HP.

Richard

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Offline cotterpinkid

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Re: Ignition timing/magneto problem
« Reply #12 on: 10.08. 2010 09:31 »
Okay then, I agree with John that the use of a timing disc and 'piston stop' will accurately get you TDC (I time the Velo using this method as that's how Velo's are timed and with the Velo. I've always been told that timing is important). I also use one of those mag timing thingies that gives you an audiable 'buzz' as soon as the points open (leaves your hands free rather than trying to pull the fag paper at the same time). I'm currently waiting for my mag. to come back from a rebuild so I'm not quite at the timing stage. The last time I timed the A10 (10 yrs ago) I used the stick down the plug hole method, but will be using a timing disc this time. I was interested to see that there are several views regarding the timing setting. My machine is a '57 plunger, what should I set it to? Also, if having locked up the mag. pinion, the timing is still slightly out you can make slight changes to the timing by adjusting the points gap. There must be lots of people who use SRM's timing figures (I would have done if I hadn't read this topic), but I haven't yet convinced myself which timing setting to use - help!.
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Re: Ignition timing/magneto problem
« Reply #13 on: 10.08. 2010 09:38 »
Hi Guys (and girl) - thanks for the info, I timed it to 33 degrees as stated in the BSA little brown book for SR, with an srm timing disc ( I have their cush nut, tad more hex on it would have been good) and checked for fractions with a vernier as the head was off, as stated elsewhere I had difficulty getting the two to match, I now know why.
Mostly though I just found judging TDC by eye and finger on piston to be very inaccurate for me so used a dial gauge in the end.
Project has been tamed a bit due to protect my hip, now got 8.5 pistons and 356 cam.( 357 and 9.5 in store for now, will possible sell if bike goes well)
I'll leave the timing as is for now, I can get a bit on the points if it's to advanced.
Winter job will be slotting the maggie as Richard had done,  is this possible with laymans tools or best to get them machined?  
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1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

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Re: Ignition timing/magneto problem
« Reply #14 on: 10.08. 2010 09:51 »
cpk,
I recommend 30 degrees BTDC
BSA Bill,
the mag mounting holes CAN be filed out successfully (been there, done that); the quality of the job is in your hands.

However, I have a machinist mate who owes me a few favours (same person who has machined my crankcase bearing), so he does them in a CNC lathe.

Richard
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