The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Nomad54 on 12.11. 2024 00:26
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Had the mag refurbished on my 1963 A10 goldflash and when I fitted it to the bike I tried to set the ign timing. Using a degree disc fitted to the crank with a TDC pointer fixed in place. Set the left hand side to 35 deg BTDC, points set at 12thou. Checked the right hand cylinder and the points crack open at 39 deg BTDC. Any idea how I rectify this problem or is it a return to the guy who refurbished it.
Tom
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2 degrees difference is acceptable, 4 is not. I would get back to the refurbisher. You can spend time grinding the cam ring but it's tedious.
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For a discussion on this, you could look at the thread here:
https://www.a7a10.net/forum/index.php?topic=16557.0
A good repairer should / would have ensured most of the causes of inaccuracy have been eliminated or reduced to the minimum - but it might help you to understand that there is a range of possible reasons for the problem. With a fixed cam ring and ATD (I assume in this case?), the common reason of wear between camring and housing doesn't arise, but others are possible.
It is also possible that if you hooked up a strobe and ran the motor you'd find that at some speeds the error changes, or goes away even . . . it's a fiddly business and dynamic testing is a better indicator than a simple static test.
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I think you have to go back to the refurbisher first before you make any changes. It may be a simple fix but its for them to do it not you. They should have a test rig which makes this a lot easier for them. You want equal timing but you also want and equal spark and messing with one can affect the other.
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I had my magneto refurbished and had the same issue with a worn cam ring. The mechanic who was working on my bike fixed it with adhesive stainless steel strip which was used to compensate for the worn part of the cam ring.
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Poorly seated or damaged bearing insulator could be another cause of uneven gap.
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I had my magneto refurbished and had the same issue with a worn cam ring. The mechanic who was working on my bike fixed it with adhesive stainless steel strip which was used to compensate for the worn part of the cam ring.
If Mr Nomad54 ends up fixing it himself, sometimes shim stock can be squeezed in between the cam ring and its housing like that.
The other bodge is to put a shim between the bearing housing and the magneto body, around one of the screw holes, so you actually cock the housing off the straight. Very bodgy, but can work a lot better than you’d think.
Grinding the cam ring ramp with a Dremel type tool or a slip stone is a proper fix, but hard fiddly work.
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Spoke to the guy who refurbished the magneto and it is on the way back for him to rectify so cheers for all the comments guys.
Tom
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Had some fun working on getting an even L-R, see https://www.a7a10.net/forum/index.php?topic=1375
Any paid-for magneto work should include and result in excellent l\r timing.
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Having "rebuilt" (OK taken apart and put back together..) a few mags I find it hard to understand how the L-R timing goes out. The end cover could be out of alignment but its all shouldered to line up, the bearing insulator could be thicker one side than the other, but its all clasping at straws. The cam rings are quite hard, the end cover is turned. Since we know they do go out, I can only assume that there was more selective assembly and we've mixed and matched parts over the years or they were never right when they left the factory. My current mag is the best bits from at least 3 and it works fine.
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Having "rebuilt" (OK taken apart and put back together..) a few mags I find it hard to understand how the L-R timing goes out. The end cover could be out of alignment but its all shouldered to line up, the bearing insulator could be thicker one side than the other, but its all clasping at straws. The cam rings are quite hard, the end cover is turned. Since we know they do go out, I can only assume that there was more selective assembly and we've mixed and matched parts over the years or they were never right when they left the factory. My current mag is the best bits from at least 3 and it works fine.
It doesn’t readily “go out.” It’s out from the start. Lucas didn’t care and nor do many magneto repairers.
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It doesn’t readily “go out.” It’s out from the start. Lucas didn’t care and nor do many magneto repairers.
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Which ones? Don't tar us all with the same brush, please?!
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well for what its worth before i bought a very expensive new cam ring from norway -- i think it was, some years ago that fires correctly on both cylinders i was running it with one that was way out of tune, no damage done, the cam ring was 100£ many years ago, betsy has been running and thrashed with one piston 10 thou below the other one after the rod had to be bored after some pillock had filed it down to take the play out of a big end on a bike years ago.
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Which ones? Don't tar us all with the same brush, please?!
Many isn’t all.
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On my shelf of disasters is a cam ring which came from a mag I bought. Timed up one side to 32 btdc and checked the other which was 57 btdc.
I was but a spotty youth when I bought this and made the elementary mistake of only setting up the timing on one side. The result was a holed piston and a con rod which let go at the small end.
Freckenham Red Lodge is an oddly named place to be stranded in the pre-mobile phone pre-recovery era and was only 200 miles from home...
Ever since then I have been very careful to check the timing on both cylinders.
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On my shelf of disasters is a cam ring which came from a mag I bought. Timed up one side to 32 btdc and checked the other which was 57 btdc.
I was but a spotty youth when I bought this and made the elementary mistake of only setting up the timing on one side. The result was a holed piston and a con rod which let go at the small end.
Freckenham Red Lodge is an oddly named place to be stranded in the pre-mobile phone pre-recovery era and was only 200 miles from home...
Ever since then I have been very careful to check the timing on both cylinders.
....almost certainly from a V-twin
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Which ones? Don't tar us all with the same brush, please?!
Many isn’t all.
I know, but 'many' cast suspicion on all.
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Freckenham Red Lodge is an oddly named place to be stranded in the pre-mobile phone pre-recovery era and was only 200 miles from home...
Ever since then I have been very careful to check the timing on both cylinders.
Was a very good 24hr caff though BS, with an excellent juke box back in the day - I'm talking 50 years back. But still there the last time I passed that way. Oddly named, yup - just down the road from Six Mile Bottom . . . where I came to an involuntary halt one time with a holed crankcase on an A10. Not so great at 2 in the morning . . . . .
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So is the conclusion that this is caused by an eccentric end cover or inaccurately machined cam ring? I've never seen any significant wear in either so what they are now is how they were made?
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Too early for conclusions Rob - could be a number of things. But camrings wear and 'things' happen to housings, including the consequences of mix and match. But a few other areas to look at too depending on what the refurbisher did or didn't do. Have to wait to hear back I think.
Inaccurate firing intervals and unequal points gaps are just extremely common on K2Fs, especially - but far from only - on those with manual advance. (Not the case here though, I'm guessing.)
It can take longer to sort out these sorts of issues than it takes to do almost anything else on these mags. I always let out an inward cheer if a reassembled one comes in at under 1° of error on the mag across the speed range on test, and a loud groan when the thing is miles out and is going to be a time-consuming bore.
For reasons of their detail design, I've almost never come across the same issues with KC2 BTHs, or indeed with Bosch twins.