Author Topic: Magneto bad all of a sudden, and then, only sometimes?  (Read 2330 times)

Online beezermacc

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #15 on: 18.07. 2014 06:35 »
You could drill the cam ring housing 180 degrees from the existing peg, tap the hole maybe 3mm and fit a screw to act as a new peg then fit your cam ring 180 degrees from its original postion. If you mark the cam housing with the position of the lift on the cam ring before removing it you can be sure of drilling in the right place for your new peg. The old peg can be removed and the hole plugged or just grind the peg away.
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Offline RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #16 on: 18.07. 2014 08:14 »
Thanks, Andrew. I think the original eccentric stop pin should work now, now that I know it is an eccentric stop pin. Just wondering, would it make a wit of difference where the cam ring was rotated to in an automatic advance machine? It seems not. but as always, I'm pro at missing something.

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.

Online Triton Thrasher

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #17 on: 18.07. 2014 20:36 »
The eccentric pin is used to keep the cam ring in such a place that the points open at the ideal armature/magnet relative position for strongest spark.


Offline RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #18 on: 18.07. 2014 21:11 »
That makes perfect sense TT, thanks. Now, I am still assuming that 180 deg. rotation  of the cam housing doesn't matter. My eccentric pin was at the bottom and unadjustable.

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 RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #19 on: 18.07. 2014 21:56 »
Also, would suggest you make up a gasket or seal thick enough for the end cover of the cb housing to pinch against the camring, to stop it fretting if it's so inclined. Often, the seals supplied or fitted don't actually engage the camring at all.

Bill, et al,

So, looking at the fit of the cam ring versus the bakelite end cap, it appears that the o-ring (which is missing from mine) only serves as a dust and water blocker. The cam ring then appears to be held into the housing by three shoulders formed within the cap inside the inner diameter of the o-ring groove.  It then seems possible that if you use too thick an o-ring you space the hold-down shoulders away from the cam-ring, maybe making a problem if your eccentric is not protruding (hmmm, that's one way of saying it).

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.

Online groily

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #20 on: 18.07. 2014 22:49 »
With the plastic covers Richard (as opposed to alloy domes or screw-on types), there's always going to be a question about the strength of the clip that holds it on - whatever else you do. I guess the best you can do is make sure the plastic feet and/or the rubber or other seal don't leave a gap  . . .  Hard to see I know, when the end cover is on, and against the slight pressure of the kill button strip as well. If you've now got your camring pegged in place (whichever way round) then it shouldn't rotate in ways you don't want, and it shouldn't move axially if there's any sort of contact keeping the darn thing in place. Assuming these things are OK, you can then start to discover whether you get those errant sparks back  . . . fingers crossed.
Bill

Offline duTch

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #21 on: 19.07. 2014 00:11 »



Not sure if I read that wrong, or you didn't write what you were thinking....or...?

 Maybe you can rotate the whole housing as a unit, but with no net advantage, ?...(on mine the two opposing interface screws are different sizes)

  The camring being symetrical, disregarding locating pins, can be rotated exactly 180˚ for same net result, and hypothetically without any rotation, you could make a new locating slot wherever you desire, with corresponding pin- but why.... if you can just rotate it if need be and relocate the pin.

 I think, as it was running ok before (original bike? not new project?), it should in theory be ok, and you may hopefully be addressing a non existent or incorrect issue, or agonizing unnecessarily...?

 either way I hope you get it sorted... *beer*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #22 on: 19.07. 2014 05:39 »
Dutch,

You gave me a scare when you said the screws might be different sizes. Mine are not (see photo showing the two from my second mag). In my case, the net advantage is having access to the cam ring stop pin, rather than having it completely inaccessible on the underside of the mag. As far as I can tell, no need for me to add a different stop pin location or an additional slot in the ring.

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 duTch

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #23 on: 19.07. 2014 09:36 »

 Yep, ok sorry didn't mean to do that-  *smile*
 I'd say mine are maybe 1/4 & 3/16, but keeping in mind mine's an earlier(circa '50) maggie as determined a while ago by Trev. I think...

 maybe post a pic of the overall offending area so we can all have a nitpick. *smile*....no I really just mean to get it in perspective, particularly for future enquirers *smile*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online beezermacc

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #24 on: 30.07. 2014 12:32 »
The threads of the screws which hold the cam ring housing on a K2F are 2BA, and 1/4 whitworth on a K2FC.
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Offline RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #25 on: 30.07. 2014 13:15 »
Andrew,

Hmmm. So, because Dutch's housing screws are two different sizes, maybe one hole in his mag was stripped and repaired at 1/4". That would imply that he has a K2F.

You must have been back-reading a lot of posts to dredge up this topic. It pains me to say that work deadlines (those already missed and those forthcoming) have kept me from working on the bike since discovering the loose cam ring. All I can say is that I hope winter comes late in Chicago.

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 duTch

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #26 on: 31.07. 2014 00:17 »

 Ok Richard, you better dig out that green 'cone of silence'- when I read your post last night, I realized I was talking about the outer cover, threads I measured up as 0.1830" & 0.2365"- don't have a BA gauge, but as far as I can determine are 2BA & 0BA respectively, with the inner cover screw(1 of in pic), being also 2BA. *red*- will match the green hat *smile*
 0BA 25.4 tpi, close as to 1.0mm
 2BA 31.4 tpi, close as to 32 tpi

 As an aside, I'm curious how the BA pitch is calculated, as the only pitch with an even number- no decimals- is 5BA 0.126"@ 43tpi, kind of wonder if it's somehow based on a metric scheme or other??
 I guess I could do a web search, maybe later.....
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online morris

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #27 on: 31.07. 2014 17:36 »
I guess I could do a web search, maybe later.....

Have a look here Dutch. Helped me out a few times already;

http://www.britishfasteners.com/threads/index.html

And if you understand the explanation of how it's calculated, then please explain it to me in normal language *countdown*
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Offline duTch

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #28 on: 31.07. 2014 22:12 »

 Thanks Morris- I think *eek*. I'll check it out later
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #29 on: 15.09. 2014 22:55 »
Hi guys,

 I want to close off this story before moving to the next. Besides, I feel like I owe it to you after getting good advice. About three weeks ago I had a fairly detailed story written out on my iPad (don't blame me, family decided it was a good gift for a milestone birthday). That story disappeared with an errant screen touch, so you may consider yourselves lucky to be spared even more tedious detail than I give here. So, I'm going to try to do it in shorthand so I can move on to my latest issues.

After all-winter engine rebuild, started once or twice, then: no start. So, struggle, time, kick, struggle, time, kick, etc, etc. etc.

Replace plugs wires and caps with great quality parts, re-time, starts a couple of times on first kick, put everything back together, then: no start. So, struggle, time, kick, struggle, time, kick, etc, etc. etc.

Discover lock pin not keeping cam ring in place. To access lock-pin adjuster, decide to rotate cam-ring housing 180 deg. Easy to do. Re-time. No start. So, struggle, time, kick, struggle, time, kick, etc, etc. etc.

Comb cobwebs of mind to recall the need to check point gap for each lobe. Gack! Rotating the housing led to the cam ring being well off center. Removed the mag, rotated housing back the way it was, gapped points for both lobes. Turned out very close. Reinstalled mag (duh, but thought I was on Candid Camera while trying to reinstall the long nut). Timed. Success! Put everything back together. Still success. Starting regularly on three or fewer kicks, often, one.

All of the above covering about three months, what with other things going on in my life and a limited amount of knee cartilage available to contribute to the cause at any one time.

With the rebuild running apparently fantastic, put about 200 miles on her before doing something I had not done before, specifically, get on the open highway and run her fast, briefly up to about 80 MPH (I know, not fast compared to racers here). Well, something happened. Now, if you want to read more, head over to my "Piston Melted?" topic in the "Engines" section.

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.