Auto advance/retard vs manual

[Housewiz]

What is the preferred set-up for a '58SR?  As my complete system is missing, I want to be sure I am heading in the right direction when looking for parts.  I would think manual would be more dependable?  Just another cable and handlebar lever?

Thanks,

Steve

[Topdad]

Hi Steve, never had a manual mag on any of my bikes ,I've ridden plenty with and really have never had an issue with the auto unit ,having said that I'm not riding now as I did when i was 16 to 24.
I think the manual mag became an optional extra from quite early on the RR AND SR on but may be wrong I know someone here will correct me ,certainly a mate who a 59 SR in 1966 and didn't scamp on what he paid out had auto and he thrahed the living daylights out of his for many a year anyway will be interesting to find out the true situation, best wishes BobH.   

[BSA_54A10]

The AA unit will be better than the manual as it will (hopefully) adjust itself continuously to the correct state.
manual timing tends to be left full advance once the bike is started.
I know of more than one bike with both on the same maggy

[Motoanimal]

I had a manual A/R on my RGS. It was a PITA 'cause I kept forgetting to retard before starting. My ankle thanked me when I rode an A10 with an auto! 

[alanp]

I had a manual A/R on my RGS. It was a PITA 'cause I kept forgetting to retard before starting. My ankle thanked me when I rode an A10 with an auto! 

I'm the opposite on my RGS, I start on retard and then forget to advance it until I notice that I've lost some performance.
On my manual mag. I usually leave it fully advanced on fast open roads but alter it on slower/hillier roads.
I have found that if she starts to pink, sometimes when retarding the ignition I can definitely feel a power surge, which is why modern engines have multiple sensors and ECUs to take the human out of the equation.
I think the manual unit is best for high compression engines since they are more prone to pink even when pulling hard at the upper half of the rev range.
On the auto advance unit I wonder if anyone has ever checked when it reaches full advance? I suspect quite low in the rev range.
I had a Jota with a German ignition control system on it where I could choose any one of 15 different advance curves to suit the the type of riding I wanted by rotating a selector. I expect the old classic auto units are very crude in the way they advance the ignition.

[Motoanimal]

Ha ha, Alanp is absolutely right, It's good to have on a high comp. engine and it's nice to have the means to deal with rubbish fuel that causes pinking, but it should be noted that a too far retarded ignition will cause an engine to overheat and possibly seize, like my friends RGS did in Wales many moons ago leaving a 20 foot skid mark! He was lucky to stay on. I think it's just something else to remember, but that's only my opinion.

As regards the advance curve, I also have to concur with Alanp inasmuch as once started and the bob weights fly out the ignition is probably fully retarded although some cleverer folks on this forum will be able to elucidate further

I wish I had a Jota, classic mental machine!

[fido]

I find it such a pain to set the ignition timing that it makes me prefer the manual advance. If you err on the side of having it slightly too advanced and it pinks you can get it spot on by retarding slightly with the lever.

[Motoanimal]

Good point fido, you can adjust timing 'on the fly' without so much as removing the timing cover!

Sorry I just noticed an error in my previous post:

"As regards the advance curve, I also have to concur with Alanp inasmuch as once started and the bob weights fly out the ignition is probably fully retarded although some cleverer folks on this forum will be able to elucidate further"

I meant to say " the ignition is probably fully ADVANCED" but you guys knew that !.....
Phil

[orabanda]

A tip; these days I always slot the mounting holes in the magneto, to make setting the timing an easy process. You will achieve enough rotation to give 15 - 18 degrees of variance. I punch a witness mark on the mag housing when the mag is in the middle of its adjustment , and a matching one on the crankcase. Then fit the timing pinion with the mag in this position; you will then have approx 9 degrees of advance, or retard, available from this position.

Richard

[Motoanimal]

Wow, great tip Richard! It normally takes me several attempts to get the timing spot on because of the backlash in the timing gears etc. but your method solves that problem. It also gives you some retard (albeit by the side of the road with a 1/4" Whitworth spanner) if you are unlucky enough to fill up with the equivalent of 2 star! Some purists may may balk at the idea of attacking the mag case with a file, but who's to know once it's all bolted up?

I'm off to my garage to find my rotary file!

[orabanda]

I have machined some, but allow 30 minutes if using a file.

I use high tensile 5/16" plain washers as well (then shakeproof washer, then nut).

Richard

[iansoady]

One advantage of the auto advance is that on full retard you're still opening the points at the maximum flux point so getting the best spark as the cam ring is fixed. With manual advance the cam ring rotates so full retard tends to give a weaker spark.