Author Topic: Ignition timing adjustment  (Read 269 times)

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Phil C

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Ignition timing adjustment
« on: 03 February, 2018, 19:10:02 »
Some of you might remember that my 1965 B40F (side points) won't run without a bit of choke, even when warm, and yet has a black sooty plug. Before I start looking at the carb, I thought I'd check the timing. Having had a look at the current setting (rod down plug hole), I think it might be a bit retarded (you'll notice I don't sound very sure - that's because as a novice I found it difficult to be accurate about piston position.) Anyway, I thought I'd advance the timing a bit and see what happened (having been advised in a previous discussion that if my timing is retarded it might result in my needing to run with choke.) Trouble is, when I've slackened the two pillar bolts, in order to rotate the points base plate, there is very little movement possible, because the bolts are very close to the ends of their slots. And what very small bit there is is hindered even further by one of the pillar bolts pushing up against the spring. Any thoughts/advice please?   Phil (novice)

PS Enjoyed the show at Shepton Mallet today - got a few old imperial spanners at the jumble, but annoyed that I bought a large secondhand Pozidrive thinking it was a Phillips.

DEAN SOUTHALL

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Re: Ignition timing adjustment
« Reply #1 on: 03 February, 2018, 19:50:34 »
Rotate the points plate so that the pillars are in the centre of their slots. Loosen points cam (centre screw) and rotate the cam to set timng. If you then need to tweek the timing you use the small adjstment provided by the slots in thepoints plate.

Phil C

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Re: Ignition timing adjustment
« Reply #2 on: 03 February, 2018, 21:08:06 »
I see, thanks very much Dean. I asked someone at the Shepton Mallet show today if I could rotate the cam, but  they said no because it was keyed. So I'm really pleased to read your advice. So I loosen the hex-head screw/bolt in the centre of the cam?  Thanks again.    Phil.

AWJDThumper

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Re: Ignition timing adjustment
« Reply #3 on: 04 February, 2018, 10:28:14 »
Phil. Unfortunately, the C15 and B40 are not the easiest singles to check the timing on. To do it reasonably accurately, you really need to fit a timing disk to the alternator rotor so that you read off the timing setting in degrees - the advanced setting should be 33.5 deg. Alternatively, you can do it by measuring the piston position which should be 7.1 mm BTDC but this can be difficult to do accurately. The other complication is that you need to use a screwdriver in the small slot in the top of the points cam to rotate it against the auto-advance springs so that you are measuring the advanced ignition timing setting. Some people use a suitably chosen washer under the cam centre bolt to fix the cam in its advance timing position to make the process a bit easier. To check the timing you need to start with the engine well before TDC on the compression stroke ( to remove backlash in the gears) and then slowly rotate it forward until the points just open (measured with a bulb and battery or ohmmeter) after which you can read off the number of degrees BTDC on the timing disk. If it's not correct, you need to carefully rotate the points plate or use the fine adjuster if fitted to move the timing closer to where it should be. A bit of a tedious process at the best of times >:(


Phil C

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Re: Ignition timing adjustment
« Reply #4 on: 04 February, 2018, 11:22:51 »
Thanks for this. But my old BSA Instruction manual tells me the normal condition for checking the ignition timing is with the timing fully retarded, which it is of course when the engine is stationary. It says the setting should be one sixteenth of an inch before TDC when fully retarded. I don't understand what you mean about rotating the cam against the auto-advance springs - do you mean only turn it one way? By the way, on my bike the auto-advance mechanism is underneath the points base plate (see photo attached). Confused,  Phil .

Phil C

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Re: Ignition timing adjustment
« Reply #5 on: 04 February, 2018, 11:59:35 »
Further to my previous entry a few minutes ago, I see that, aswell as the BSA Instruction Manual,  the Haynes manual also talks about a sixteenth of an inch BTDC, but the Haynes doesn't say whether fully retarded or fully advanced, so I guess retarded as per the BSA Instruction Manual. It goes on to say a more accurate method than a rod down the hole is with a degrees disc, as you said. It does seem very tricky to be accurate with the rod method, so I think I might try the degrees disc way - it will be a good learning experience for me. How do I set the cam to fully advanced? (as per photo attached, the auto-advance is behind the points base plate).  Thanks for your help (and your patience!)  Phil.

JulianS

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Re: Ignition timing adjustment
« Reply #6 on: 04 February, 2018, 13:47:53 »
BSA service sheet 424A for C15 may help.

Phil C

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Re: Ignition timing adjustment
« Reply #7 on: 05 February, 2018, 10:13:58 »
Regarding (as described above) the pillar bolts being at the end of their slots, and one being up against the points spring, I've just tried Dean's suggestion (above) of undoing the bolt in the centre of the cam and then turning the cam, but unfortunately it doesn't turn freely - it will only turn under the spring pressure of the auto-advance. Any other advice please?  Phil (novice)

JulianS

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Re: Ignition timing adjustment
« Reply #8 on: 05 February, 2018, 11:26:39 »
The bolt should unscrew but the cam/auto advance are taper fitted to the camshaft and to remove it the taper needs to be freed. There is a tool but you may be able to free it by unscrewing the centre bolt a little then tapping it gently to one side. Not too hard or bolt will bend. You can then remove the unit if points plate first removed.


Phil C

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Re: Ignition timing adjustment
« Reply #9 on: 05 February, 2018, 15:42:37 »
Thanks - that's pretty much just what Monty at Monty's Classics told me this morning. I'll give it a go. My whole points/timing issue is a bit on hold now as I've  ordered a replacement set of points and back plate, which might take some weeks to arrive.

Phil C

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Re: Ignition timing adjustment
« Reply #10 on: 06 February, 2018, 16:04:43 »
Points and back plate won't arrive for a few weeks, but in the meantime, out of interest,  I've just tried to get the cam to move, as advised by Julian, but without success. I assume the points cam should come away complete with the auto-advance mechanism, which would allow me simply to put it back on in a slightly different position, thus effectively rotating the points cam? Maybe I need to tap it a bit harder? Tap the bolt, or the cam? Nothing is simple!!  Phil (novice)

JulianS

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Re: Ignition timing adjustment
« Reply #11 on: 07 February, 2018, 10:00:34 »
Try the extractor bolt part 61 3761 which you should be able to source from any good dealer.

Phil C

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Re: Ignition timing adjustment
« Reply #12 on: 07 February, 2018, 12:14:47 »
Thanks Julian. Actually I got it off this morning by the tapping the bolt method. Had a look at it - springs don't seem very strong, don't exactly snap the weights back, but I've left them for now - and put it back on in a slightly different position, which will hopefully solve the problem of me not being able to advance the timing because of the pillar bolts running out of slot. Just waiting for the points and backing plate to arrive, but might be a few weeks.  Phil.