The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: RichardL on 22.03. 2009 06:16

Title: Slipring Position
Post by: RichardL on 22.03. 2009 06:16
No spark (had it before replacing the head gasket. Timed with intention of 3/8" BTDC. When the points actually open with timing fully retarded, it appears that the contact portion in the slipring has already passed by. Is this normal? How much contact portion should be visible when using an ATD at hand-turned  RPMs? Is it just that my timing might be that far off?

Thank you for your help and ideas.

Richard L.
Title: Re: Slipring Position
Post by: groily on 22.03. 2009 09:09
Hi Richard,

Just went out to have a look at a spare mag on the bench.

When the points are just opening, the HT brush is sitting squarely on the start of the brass portion of the slip ring, which has just come into view; as you advance the mag at the ATD, holding the pinion still, more of the brass portion comes into view and the points open wider. The firing point seems therefore always to be at the beginning of the brass strip. All 3 slip rings in my box of mag bits have the brass strip in exactly the same relative position.

If your brass portion has been and gone, as it were, when the points are starting to open, something's very not right. (Although it will of course be out of sight when the points are closing or shortly thereafter, also if you look through the 'wrong' HT aperture or if you rotate the mag the wrong way!)
The relationship between slip ring and contact-breaker opening has to be spot on.

It's worrying that you have no sparks at all, because regardless of whether you've got your 3/8ths bit right, there should be some, sometime!

Suggest looking at it in the following order:
thorough check of fixed and moving contacts if you've had them apart;
ditto of cb backplate to be sure it's located properly in its key-way on the armature (and that the key-way is in decent shape - see recent thread about collapsed one!).
Failing a problem there, the only other things that could have happened, if the relationship between slip ring and points/armature has been upset, are a) that the slip ring has moved on the armature, probably busting the HT take-off from the HT winding, and we don't want to go there and how could it anyway? . . . . I've never heard of it happening. Does the slip ring move if you try to push it either way through an HT aperture? Should be nicely tight.
Or b) the cam ring isn't in the correct place in the end housing. Can't imagine you've had it out as it's a fixed one, but if it's for some reason or somehow in the wrong spot (difficult to achieve given the pegging arrangement), then the points will open somewhere silly and the same result would pertain. Also very unlikely therefore.

Fingers crossed it's something minor and easily sorted. But likely nothing to do with how you set the basic timing. Best of Luck.
Title: Re: Slipring Position
Post by: bsa-bill on 22.03. 2009 09:40
Hi Manosound
I'm probably reading your mail wrong, but timing should be set at full advance. maybe your talking regarding manual advance /retard which may be different ( I have no expierence with manual set ups).
Forgive the intrusion if you already knew this *red*

All the best  - Bill
Title: Re: Slipring Position
Post by: RichardL on 22.03. 2009 12:55

Thanks, kindly, for your time and giving me good information to help get my brain organized. I just want to stop thinking, "G*d*mmit! I just want to ride it! The weather's beautiful and I'm stuck in the @#*%ing garage! AGAIN! 


Easy to misread my point. The timing was set for 3/8" (at least, intended) with the ATD fully advanced. When looking at the slipring position with the timing cover on, and just determining points-open position by when the cigarette paper slides out, that position is fully retarded. Maybe the question here is, "Does kickover RPM substantially advance the timing such that the position of the slipring viewed at points-open-and-fully-retarded is not relevant?"

Richard L.
Title: Re: Slipring Position
Post by: RichardL on 22.03. 2009 13:09
Groily (or any),

If I pull the center screw to check the keyway, if the keyway is good, will the timing stay put while I try to rotate the points-base on the armature? I don't want to lose the timing while determining that there was actually no problem with the keyway.

Richard L.
Title: Re: Slipring Position
Post by: bsa-bill on 22.03. 2009 14:32
Hi Manosound
Yes I thought I must have your mail wrong, but it does interest me as I have just set the timing on my Projest ( Rocket Gold Flash -  does that make sense ) and have "AIMED" at 3/8th, with the head off it's easy to get the pistons at the right place but then getting the a/r unit to tighten with out altering is another thing.
I think at some time in the future I will make a micro adjuster for the Maggy ( got to have something to do in the shed in winter )

All the best - Bill
Title: Re: Slipring Position
Post by: RichardL on 22.03. 2009 15:18
First, Groily,

Disregard previous. I now have spark, maybe not fat and blue (a description I might occasionally apply to myself), but we'll see if and how it runs. I can't try to start in yet, this early Sunday morning in the suburbs. Here's what I think may have happened, which I forgot to mention. Last night, upon discovering no spark, I cleaned the slipring with denatured alcohol. I gave it some time to evaporate but, apparently, not enough. I'm not sure this is the reason, but I am temporarily pleased. Consider that I owe you a pint, if ever meet up non-cybericiously.


There is a boatload of talk and suggestions here in the forum about measuring BTDC with the head in place. My own apprach, you may recall, was a straw with a taped-on graticule and which ran into the plug hole through a guide clamped to the head-steady bracket. I'd steer you to photo if need be. It seemed to work well.

About tightening the ATD unit without changing the timing, I have started to get a little feel for this and think I have made progress over the last time I did the timing which took about 15 tries.  First, I got sick of messing with the horseshoe washer so I cleaned the large washer (having two alignment holes) and the horseshoe washer with mineral ("white") spirits and sprayed one side of the horseshoe washer with a light coat of contact adhesive. This keeps it in place so you can concentrate on the hold-down bolt. (I don't think anyone can convince me that the possibility of this small amount of adhesive working its way into the oil as a clogging factor is a problem.) Once you have the timing set, finger tighten the bolt while applying back pressure at the points plate with the other hand. Now, with the socket over the bolt, and no ratchet or breaker-bar in it, very lightly tap the end of the socket. Now, with the ratchet or breaker, make a first light tightening of the bolt, to the extent you can, summon-up a lot of thumb strength and try holding back some of this turning at the points plate. Now, recheck the timing. If good, go ahead and finish tigtening the bolt. Recheck timing again.

Richard L.

Title: Re: Slipring Position
Post by: RichardL on 22.03. 2009 15:24
Engine started. Riding soon, I think.
Title: Re: Slipring Position
Post by: groily on 22.03. 2009 18:34
phew! Love it when a plan comes together! I was fat and blue, but returning to pink (and fat) with the advent of spring, official.
Title: Re: Slipring Position
Post by: snowbeard on 22.03. 2009 20:41