Auto advance cam position

[courtney]

Hello,

Bike is a 1965 C15F.

I've rebuilt the motor and am attempting to sort the timing on it. The auto advance cam thing is on a taper and I am unsure how to position this on the shaft. I've read various service sheets but they don't really say how to position this unit as far as I can make out.

I have found a couple of old topics on here and realise that the position of this unit can be altered to adjust the timing, but I'm just struggling working out where to put it.

I've confused myself and can't get my head round it. Any help would be appreciated. Many thanks.

[Blackthou]

Hi,

Does this help at all?

You need to work backwards. Set your piston to the BTDC as described. Loosely position your points assembly on the tpaer, rotate the cam anticlock until the bob weights are fully expanded. Rotate the asssembly until your points are just opening then press more firmly onto the taper but not too hard so as as to secure tightly.

Rotate/rock the engine forwards and back over TDC to see points opening etc. If all looks ok, nip the centre bolt or adjust on taper then nip the central bolt. It should give you a good place to start. Once that's been established, set up as instructions.

It's quite straightforward but you've probably over analysed and confused yourself.

Good luck.

[courtney]

Thanks for your help. That page you attached was the one I'd read and, like you say, over analysed it and confused myself. There's been times I thought I made sense of it and then confused it again.

Giving it a couple of hours and seeing your reply I think I finally understand it, so thank you very much. I'll give it a go after work tomorrow and see how I get on.

Thank you for your help again.

[Blackthou]

You're more than welcome. Good luck. Just take you time and I'm sure all will be well.

[courtney]

I still can't get my head round this.

I don't know visually what half the terms are when I try to do this from what it says in the book of service sheet. I can't visualise what fully advanced and all the other stuff means.

I've spent nearly 2 hours trying to understand it. It's driving me barmy.

[Blackthou]

Hi,

Poor you. Have a break to clear your head and take it one step at a time. Hold your points assembly in your hand and become familiar with advancing the weights by turning the cam so that you understand the function. Once familiar place to one side.

Remove your spark plug. Make sure you're on TDC first by removing the tappet covers to ensure both valves are closed Insert a rod through the plug hole and mark it level with a fin or some reference point to indicate where TDC is. Remove the rod and make a mark 7mm lower or whatever the correct dimension for your model.

Then with the bike in gear rotate the back-wheel to get say 10 -15mm before TDC. Next set your piston to the correct distance before TDC using the  rod down the spark plug hole.

Rotate the wheel  until your 7mm or whatever it should be mark is visible and aligned with your reference point. You are now at the correct timing position for the piston.

Take your points assembly and using the method you learnt and perfected earlier, advance the bob weights. Hold the assembly advanced and position it on the taper. Move it around until the points are just opening with the bob weights advanced. Once achieved push and secure on the taper.

Rock the back wheel and with the weights advanced the points should just be opening. Fine tune the points backplate to achieve the opening of the points in line with your 7mm mark with the weights advance and hopefully you'll be there.

[courtney]

Many thanks. I've left it for a day or so and will probably end up looking at it over the weekend. Hopefully some elves will have done it by then like that book with the elf and the shoemaker - I can't remember what it's called.

For now, I understand what you're saying and reading it again you have explained it well, so thank you. With regards to the position of the points breaker, it can be positioned differently on the plate - is there a particular way that it needs to be positioned in the first instance?

[Blackthou]

Hi,

Re points on backplate, just set in the centre of its adjustment i.e. midway in the slot. It's only a starting point.

Good luck. I'm sure you'll get there and be really chuffed when you do.

[courtney]

I'm having another go at this today, so hopefully I will get it sorted.

Just a question, is it supposed to be difficult and fiddly to hold the weights advanced while the backplate is fitted?

[courtney]

How are you supposed to turn the cam to hold the weights advanced when the points plate is in the way? It seems impossible.

[Phil C]

I'd help if I could, Courtney, but I'm just a novice. The instruction manual I got with my 1965 B40F has an "errata" sticker in it giving a measurement when fully retarded. That's what I used and it seems to start and run okay. The manual doesn't have a year written on it, and I have another - again no date - which gives a measurement for fully advanced.   I'm sure someone on the forum will help you get it sorted out.  Phil

[Pete A10]

Is it possible to make a small timber wedge to hold the weights in the advanced position leaving you hands free to make the adjustment. This works an A10 auto advance unit but I'm not sure of the exact layout on the C15

[hoogerbooger]

I've been having the same mental struggle with working out how to set/reset the timing ( on my B40F). So I'd like to know the answer as well.

One of the many references I used to confuse myself ( in this case the Haynes manual) says " revolve the cam using a pair of slim nosed pliers"  " but be careful not to mark the cam"

Not keen on using pliers myself. I can twist the can by hand anticlockwise. Only moves 3 or 4 degrees though, but I can see the bob weight mechanism move out.  Should it turn more than that ?

However would need 6 hands if holding cam in this position, to then rotate contact breaker plate and set at points just opening. So how's it done?

Is the cam bolt supposed to be loosened ? or not ?

[courtney]

I'm glad it's not just me!

[Phil C]

Could this be why one of my booklets had an errata sticker giving a measurement to use when fully retarded? I guess not.  Phil