Advance/Retard - Reconditioning

[Phil-UK]

My CB72 is showing all the symptoms of wear in the advance/retard area and when checked with a strobe is giving me about
45 degrees of advance; so if I have a tickover its too advanced, or if I set the full advance its a pig to start.

I've looked at my collection of used spares and most have wear in the rivet/pivots. The wear in the rivet part lets the
cam move relative to the backing plate and the wear in the pivot part lets the advance retard "arm" move realtive to the points drive.
Also most of the cam sprockets have seen better days.

Anyway, to my questions :-

1) I intend to turn up new rivets/pivots and was thinking of using 303 grade stainless steel bar ( as I have some )
so has anyone tried this ? Do people think I should go for another material ?

2) I am going to see if I can get new sprockets made or adapted ( 100 Kawa apparently is same form and number of teeth )
has anyone found a suitable replacement ?

3) Bill Silver's book suggests that the holes in the cam sprocket effectively limit the advance range and can be welded up
to limit the advance -has anyone done the "mod" and was it worth it ?
It seems odd to use the sprocket to limit the movement of the bob weights, but that would explain the fabled neoprene sleeves.

Any advice welcome,

Phil

[davomoto]

Phil, if you have one with a good sprocket you can weld the sprocket to the base. I've had a friend that is an incredible welder do this to a couple of mine. He welds where the flats are on both sides of the base, and all 4 rivets. It neds to be a fast weld so as not to heat thing up too much and melt the neoprene. Tim McDowell seels new advance springs, though usually a bit of tweaking with needle nose pliers will get your origionals tight again.

Davo

[G-Man]

Phil

That grade of stainless may not work too well as a rivet and may crack when you try and peen it over. I had that problem when I was making some new brake linkage pins.

316 may be better if you are going to make rivets. Then again you would probably be better off with normal low carbon steel anyway. It's not going to rust inside the engine.

http://www.metals4u.co.uk/products.asp?cat_id=83

I'm going to have a go at doing the same job soon. I've got a 1960 C72 motor with teh big A/R unit which is in need of attention.


G

[bikedoctor99]

when I assembled my '63 cb77 motor a friend welded the stakes (when I got the advance home and looked, there were tiny cracks and required a re weld). The advance works fine- timing light hits on the "f" at idle and advances to the "full advance mark" at throttle for both points- no problems!

[Phil-UK]

Hi All

Thanks for the suggestions, I think the cam thats in the bike at the moment was welded up so the excess movement may be down to wear in the pivots hence my thoughts about making new ones.

I'll check for suitable steel at the next autojumble ( Kemtpon 29th ) or maybe use some old engine studs, or ask about 316 s/less.

When you look at how the movement of the advance/retard bobweights seems to be limited by the hole in the cam sprocket it seems odd. The only point in the neoprene would be if the bobweights were expected to hit the inside of the hole when the springs wear, in which case they would dampen the "clacking" noise. Most other set ups only use the springs with the mechanism sitting in an open space .. oh well who am I to question Honda's wisdom.

cheers

Phil

[GORDON BROWN]

Hello everyone

Just a thought here, when fitting the vernier sprockets for racing we use 6mm bolts. The holes in the ( boss plate ? ) are suitable for tapping to M6. There are no space problems and you could make simple bushes ( possibly in bronze ) this should last for ages ?
Now I must say I have not tried this as on the racer we dont use the advancer however no problems with the bolts when loctited in, In even found a old one in with some spares that had nuts on the back and there was space for them.
I should have a decent std. one, if none of these "solutions" sort it out.

Gordon

SAFOJ

[Phil-UK]

Hi Gordon

Thanks for the offer, I've got a couple of numbers to ring about getting new sprockets made up so will post any progress.
Debating if I should pull the 250cc motor and fix or build up a 350cc ( have all the bits but haven't opened up the CB77 cases yet ) as I'd like to do the Coupes Moto Legendes again this year; its about a 1100ml round trip including the track sessions.

Phil