Auto Advance Unit Assembly and Fitting

Cerberus · Post by **Cerberus** » Sat Jul 31, 2010 12:49 pm

Bike: '61 AJS M16 coil ignition.

I am re-seating my auto-advance unit as when setting the timing I have virtually no adjustment in one direction on the contact plate as the auto-advance unit seems to be off-line (by about 5 degrees). At the same time I have fitted new springs. However, and here comes the confusion:

Part 1:

The auto advance return springs fit onto a small metal "widget" which is pivoted in the centre. Thw widget has the timing cam located into a hole at one end and has two small holes in the other, into one of which the spring is fitted. I have two different manuals for the bike and both of these show the spring fitting into the "inner" hole of the two. However, when fitted in this manner there is no tension on the spring and the auto-advance weight bobs can simply flap about. Are the diagrams wrong or are the springs too long? I can't see any disadvantage in fitting the springs to the alternative hole, unless someone has more knowledge than me (not difficult). Any suggestion / clarification?

Part 2:
When re-fitting the auto-advance unit and tightening the retaining bolt, as the bolt tightens, it usually manages to rotate the unit by a few degrees (probably the reason why it was mis-aligned in the first place). Am I trying to tighten too much? Suggestions on how I might stop this happening would be useful. I could of course assume that it is going to shift and initially seat it off-set from the desired position.

Rex

dave16mct · Post by **dave16mct** » Sat Jul 31, 2010 1:05 pm

Perhaps your springs are for an SR1 mag auto advance? I'm sure its the inner hole the springs go on (as in the manual)

Cerberus · Post by **Cerberus** » Sat Jul 31, 2010 1:38 pm

They were purchased from JSL as "Auto Adv. Springs; 350CC Alternator Models" (pt no 420421)

Charles · Post by **Charles** » Sat Jul 31, 2010 2:32 pm

Having conveniently got one the similar unit off a 1961 18S sat on my bench, the springs are on the inner position of the two holes and are under tension. The weights do not flop about so I think you must have been sent the incorrect springs or have stretched them during fitting (easily done and we all know how I know that.....).

I found the way to stop the baseplate turning relative to the inlet camshaft when tightening was to give it a really firm push once set in position to tighten up the taper and then gently tighten with a good washer under the bolt head (which does not overlap the rotor of course or it will nip that. The retaining bolt does not need to be that tight and I used loctite on it as well.

You could pop over and borrow the unit if you wished; I am only a few miles east of you, and you could take the springs if they are of use to you - I think I even have a spare set somewhere though for an 18S.

Cerberus · Post by **Cerberus** » Sat Jul 31, 2010 4:22 pm

Charles,

Thanks for the offer, however, from what I understand when I was looking round for the springs in the first place, AMC classic spares and JSL told me that the springs for the 350 are different (or at least a different part number) to those for the 500, so I'm guessing that they might have a different strength. They are also cheaper at £3.90 a set compared with £5.94. I might well have stretched them when attempting to fit, so I think I might get another set.

Cerberus · Post by **Cerberus** » Tue Aug 17, 2010 7:59 pm

Just a postscript. Thanks to Charles who lent me a set from a 500, I was able to determine that the metal bits of mine were in reasonable nick. It didn't solve the mystery of the springs. The 500 springs are very much thicker than the 350. On the basis that I might have stuffed the first set of springs, I purchased a new set just after Jampot. When inspected the previous set were slightly stretched, but even then with the new springs, on the inner hole there was insufficient tension to return the bob weights. Took all the bits to the club section last night and consulted with the great and the good. Came to the conclusion that I might as well try and use the outer hole. Did so, fitted the set, set the timing 1/2" BTDC (fully advanced). Started first kick! Ran OK static. Took out for a run 10 miles didn't miss a beat. Result and big grin. Now on to the next i to dot and t to cross.

mike.dowling · Post by **mike.dowling** » Wed Aug 18, 2010 1:31 pm

Hi
My springs were very loose and low revs top gear was always very eratic so I deceided this morning I would change onto the other hole, what a difference it made it pulls a lot cleaner and is nice and smooth pulling in all gears. Is there something wrong with springs or the drawing, I'm going to leave mine as it is because it holding the weights together properly and it works.
Regards
Mike d.
P.S Cerebus and Charles it must the air in this part of the country.

Cerberus · Post by **Cerberus** » Wed Aug 18, 2010 5:31 pm

The speculation at club night on Monday was that the reason for the two sets of holes, might have been 500 inner, with strong springs, 350 outer with weaker ones and they used the 500 drawings for the manuals. However - it worked, so I'm not going to mock it.