Author Topic: A10 Golden Flash Timing  (Read 2582 times)

Offline AWJD

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A10 Golden Flash Timing
« on: 12.05. 2015 10:14 »
Hi to everyone - I've just joined the forum.

I'm presently restoring a 1961 Golden Flash and am at the stage of trying to complete the re-assembly of the engine in the frame.

I currently own 11 BSA motorbikes but am not used to setting the ignition timing on a bike with a magneto. Rightly or wrongly, I used the approach described in the Haynes manual for this machine using a piston position of 11/32" BTDC at full advance. I checked the settings on both cylinders and ensured the mean value was 11/32".

I put the head back on before I realised there might be a problem with the way I'd set the ignition timing. What I failed to check was that the top of the piston was level with the top of the cylinder at TDC since the measurements I'd made were relative to the top of the cylinder.

I'm hoping that the approach I used was ok and would be grateful if someone could confirm this. Also, can someone tell me what the angular crankshaft setting is that corresponds to the 11/32" piston position.

Cheers,
Arthur

Offline AWJD

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Re: A10 Golden Flash Timing
« Reply #1 on: 12.05. 2015 12:21 »
I've just done a quick calculation and I believe the 11/32" BTDC corresponds to an angular setting of 33.7 deg based on what I believe is the piston geometry for an A10. I'll now try to measure the current ignition settings and see how they compare with the spec?

Offline AWJD

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Re: A10 Golden Flash Timing
« Reply #2 on: 12.05. 2015 13:49 »
Just measured the ignition timing using a timing disk which confirmed the mean setting was 34 deg BTDC with a deviation of +/- 3 deg between cylinders. This seems to confirm the original approach was correct based on piston position relative to the top of the cylinder.

Not sure whether the timing variation between cylinders is within spec but I don't intend to worry about it.

Offline Topdad

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Re: A10 Golden Flash Timing
« Reply #3 on: 12.05. 2015 14:34 »
Hi, if you do a search of past posts you'll find many many on this subject. Remember these beauties were designed in an age where repairs/adjustments needed to be able to be done with minimum tools and knowledge often at the side of the road . I always set mine in the same way and usually get first second kick start and an acceptable running engine for my need's ,others use more modern variations.
Once you've established TDC back the engine to 5/16 btdc ( or 11/32 depends on engine spec) , I always check that the tappets are rocking , set mag points to 12 thou ,check gaps are within a couple of thou of each other set with a cigarette paper between points is just beginning to move if pulled , manual ing set to full advance on handlebars lever if auto keep at fully advance with a suitable piece of wood etc . push onto mag shaft ensuring it doesn't move ,if auto tighten nut don't forget the mushroom washer and that's it done, check to confirm still set as was and away you go if moved do it again , Hope that's of help, Bob
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Online RichardL

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Re: A10 Golden Flash Timing
« Reply #4 on: 12.05. 2015 14:43 »
AWJD,

Welcome to the forum. *welcome* and thank's for the introduction. It would be great to see photos of your A10, including work progress, because that is always interesting. Also, the other bikes of members, especially BSAs, are of interest here, being siblings of the members' A7/A10s.

As for the timing question, it seems you have gotten it nearly dead on. I'd be curious how many attempts it took, since it always takes me several. If you have any other questions about the angle or piston position, just hold on a few minutes and, I believe, AWJD will chime in with an answer.

Richard L.

Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline AWJD

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Re: A10 Golden Flash Timing
« Reply #5 on: 12.05. 2015 18:46 »
I bought the Golden Flash about 4 years ago but have only now got round to restoring it. However, in the interim, I've restored about 8 other BSA motorbikes most of which are singles (C15, B40, B44, B25 and B50's).

The enclosed pictures show the current state of restoration. The gearbox restoration was fairly straightforward with all bearings and seals replaced. The main problem with the engine was damage to the cylinder fins which required a replacement barrel. Valves and pistons were all within spec but valve seats and piston rings were replaced and the barrels rebored. Timing side main bearing was replaced but drive side bearing was ok. Magneto and dynamo had been reconditioned prior to me buying the bike and were therefore both ok.

I expect the rest of the restoration to be relatively straightforward although I still haven't decided what colour to paint the tinware though Nutley Blue is currently my favourite.

Carrying out the ignition timing was relatively straightforward, although a bit Old School. The main complication for me was carrying out the measurements to determine the precise difference between the 2 cylinders and then working out the distances BTDC for each one in turn to give the correct mean distance of 11/32". 


Offline muskrat

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Re: A10 Golden Flash Timing
« Reply #6 on: 12.05. 2015 20:59 »
G'day AWJD, welcome to the forum.
34 degrees is correct for 11/32" but with the modern fuel you might need to back it off a couple of degrees. The difference in timing between the two cylinders is caused by uneven wear of the camring. A couple of degrees is OK but set it to split the difference (left +1, right -1).
Cheers
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Offline AWJD

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Re: A10 Golden Flash Timing
« Reply #7 on: 13.05. 2015 07:27 »
muskrat - thanks for the advice. I'd split the difference between the 2 cylinders but will back off a couple of degrees as you recommend.

I'm surprised the difference between the cylinders was +/- 3 deg in my case because I believe the magneto was re-conditioned not long before I bought it and would have assumed this variation would have been brought back into spec?


Online orabanda

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Re: A10 Golden Flash Timing
« Reply #8 on: 13.05. 2015 08:04 »
Lucas' manufacturing tolerance seemed to be up to + / - 5 degrees for the mass produced K2F.

Offline AWJD

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Re: A10 Golden Flash Timing
« Reply #9 on: 13.05. 2015 10:12 »
Thanks - looks like +/- 3 deg falls  within the normal tolerance range so I won't worry about it!

Online groily

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Re: A10 Golden Flash Timing
« Reply #10 on: 13.05. 2015 18:01 »
Don't know what the Lucas tolerances were myself but it is usually possible to get the magneto to within 1° of 180:180, ie within 2° at the crankshaft. Sometimes, worn mags show far more. But as often as not it is the bearing/insulator and/or housing at the contact breaker end which is responsible for the discrepancy. Slop on manual camrings, funny wear patterns on moving points, and knackered pivot posts all contribute too.
It is also not uncommon for the static setting to mislead - in both senses. Ie 'false sense of security', or 'unnecessary alarm'. The only acid tests are dynamic unfortunately. What is happening to the firing interval under about 400/500 magneto rpm isn't the be-all and end-all although it is indicative -  but what happens thereafter matters quite a lot. It's a great feeling when a mag sparks rock steadily at 180:180 from zero to max speed!
Cheers, Bill
Bill

Online RichardL

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Re: A10 Golden Flash Timing
« Reply #11 on: 13.05. 2015 18:53 »
...often as not it is the bearing/insulator and/or housing at the contact breaker end which is responsible for the discrepancy.

Can't say how many degrees difference it made, but when I rotated my end housing 180 deg. (for better access to the cam- ring position-locking screw) it caused a big asymmetry in points gap.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline AWJD

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Re: A10 Golden Flash Timing
« Reply #12 on: 19.05. 2015 16:37 »
One further question on setting up the timing on my A10: How do I work out which HT lead output from the magneto goes to each cylinder. Is it just a question of taking off the HT pickups after rotating the engine to give TDC on the compression stroke of a particular cylinder, and then checking the position of the slip ring underneath? Or does the magneto fire on both cylinders at the same time?

Online groily

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Re: A10 Golden Flash Timing
« Reply #13 on: 19.05. 2015 18:16 »
Doesn't fire both at once, and you could look at the slipring as you suggest.  But easier just to know that the lower lobe of the camring fires the rear pick-up on the magneto (gearbox side). So when the points are just opening at about 10 or 11 o'clock (looking from the primary drive side as it's the only side you can see from!), the heel on the moving point is opposite, about 4 or 5 o'clock, and the rear pick-up is firing. So, if (say) the rh cylinder is on compression, piston set before tdc as desired, and points just opening with heel on lower ramp, you're most of the way there.
With the spark plugs out you can see if you're on compression or exhaust stroke, as open valves are easily visible with a small torch.
If you get the sides wrong but everything else right, swapping the plug leads sorts it out. There's no law that says one pick-up should always go to one cylinder. I go 'rear to the right' but that's just preference. Cheers, Bill
Bill

Offline AWJD

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Re: A10 Golden Flash Timing
« Reply #14 on: 20.05. 2015 07:26 »
Thank you - that is very helpful advice and should be easier to do than trying to look at the slip ring. I didn't take this into account when I did the original timing and so it will be a 50:50 chance which pick up will go to which cylinder.