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Mag timing

In view of the fact that we now use 95/97 octane petrol is it still applicable to use the original 7/16" timing figure or is there a better figure. I need to reset my timing.
regards Jon

Re: Mag timing

It may be advantageous to alter the ignition timing to suit modern fuels...

However, the only accurate way to assess the effects of any changes would be to get the bike on a Dyno with an operator that knows what he's doing...Incremental changes to the settings followed by a test each time would determine the effect on the power and torque curves and the optimum setting could be found....

Anything else would be an inaccurate 'shot in the dark' with ill defined effects...Ian

email (option): ian@wright52.plus.com

Re: Mag timing

7/16" it is then.
regards Jon

Re: Mag timing

I set mine to 12mm these days, it seems to work fine for me, I noticed the difference on my jeep so I give most of my old vehicles an extra bit of advance. A lot of these vehicles were designed for 68 octane so it’s quite a jump to 95 octane without any timing adjustments

email (option): davmax@ntlworld.com

Re: Mag timing

I've played about with the timing on my 16H, it should be 7/16" but I've found that even a fraction under that and the bike is running retarded. Riding 2 up on a ride out the bike slowly overheated and wouldn't pull. Set the timing more advanced than 7/16" and it loves it. I'm now setting it at 1/2" so similar to Dave's setting of 12mm. 7/16" is the most retarded the bike will run.

email (option): horror@blueyonder.co.uk

Re: Mag timing

Hello Dave, I think you mean 86 octane. John

email (option): john.kater@chello.nl

Re: Mag timing

I think Dave is right. 68 was common for vehicles with 80 for aviation. I've heard as low as 40 around 1930. Ron

email (option): ronpier@talk21.com

Re: Mag timing

My understanding was Pool Petrol for vehicles during the war was approximately 68 octane and when I was a student running my M.20 back and forth to College I used to run it on two thirds petrol 95 octane to one third paraffin with a naphthalene ball (moth ball) chucked in the tank to kill the smell of the paraffin. Got me back and forth to College - 60 mile round trip - for 3 years without any major issues although one or two unkind folk said the bike smelt like their granny's wardrobe!!.

email (option): keithchandler@clistandchandler.co.uk

Re: Mag timing

Took the advice of advancing the ignition point to 12mm before tdc.There is a noticeable difference in operation now -the bike does accelerate better and when at rest after a run there is not so much heat radiating from the barrel compared to before.I set the timing whilst I got the head off to fit a solid copper gasket.I think both of these mods are well worth doing.
Jon

Re: Mag timing

Interesting this

Ian
Did your ever manage to finalise your timing tool experiment

It would be interesting to get an update

Job

email (option): jonnyob1@googlemail.com

Re: Mag timing

I am about to check the timimg on my M20, suspecting it could run a tad more advanced. (runs a bit hot and gutless).

I would like to try 12mm but I need a lesson from you experts.

The difference between 7/16 and 12mm is 0.9mm. How on earth do you time that accurately? Is it a head off and dti? Even then, how do you measure the points gap to equivalent tolerance?

Re: Mag timing

So far I stick to the makers timing settings but would accept a tiny bit advanced but never at all retarded. I set the piston to the required advanced position either with the head off or through the timing hole or plug hole with a marked stick or some other guage. I set the points on full advance and just breaking with a 1 1/2 thou feeler gauge and then nip the pinion nut.

I then turn the engine over at least two revolutions and check that the points have remained at just breaking when the piston arrives at the pre determind place. In my experiance it never does first time and I can spend ages re-doing it untill it's accurate.

Ron

email (option): ronpier@talk21.com

Re: Mag timing

As Ron says it is a bit fiddly, and you will be lucky to get it right first time. Years ago i brought one of those magneto timing light and buzzer, since then i have never looked back makes the job a lot easier. 2 wires out of the box one to earth and the other to the cental points fixing screw if it is a ring cam. If a face cam as M20s i clip it across the spring points arm. Light and buzzer sound when the pints just break. If you have the mag off the bike lightly lap the drive gear to the shaft, this will help stop it slipping when you tighten the nut.

email (option): t.j.walker@btinternet.com

Re: Mag timing

When setting my timing to 12mm I had the head off to fit a solid gasket anyway.I clamped a steel bar across the cylinder after cleaning the piston crown and used feeler gauges between the piston and bar to obtain a slight pull on the gauges at TDC.Using this measurement added to 12mm gave conveniently 12.7mm.Searching through various toolboxes found a die that was 12.7mm thick and used this as a setting block.I too used a timing light on the points.

Re: Mag timing

I use an electronic 'gizmo' box with a light and buzzer to determine the point of opening for the contact breakers...A great tool that provides certainty every time...I measure down the bore with a depth micrometer to set the piston position...

I don't generally bother to accurately locate the exact dwell point at TDC...I get that as best I can by 'feel' which seems to work out OK for the M20...Ditto the comments about lapping in the drive gear and taper before commencing...

To date I have stuck with the standard 7/16" BTDC fully advanced timing figure, though I'm getting more interested in doing some experimentation in that area...Ian

email (option): ian@wright52.plus.com

Re: Mag timing

Cheers guys, these are the method/s I've used although I have not tried the black box timimg light yet as that arrived after I'd used the fag paper method.

No one mentioned strobing to double check although in my experience a strobe is never reassuring!

Re: Mag timing

Well at least an amount of over advance can be corrected at the handlebar lever if the engine was to pink. I also have one of those buzzer light gizmo's but one of the little crockodile clips fell apart the second time I used it.....I need to replace the clip sometime but it's nothing I have knocking around. Ron

email (option): ronpier@talk21.com

Re: Mag timing

Well at least an amount of over advance can be corrected at the handlebar lever if the engine was to pink. I also have one of those buzzer light gizmo's but one of the little crockodile clips fell apart the second time I used it.....I need to replace the clip sometime but it's nothing I have knocking around. Ron

email (option): ronpier@talk21.com

Re: Mag timing

Interesting article,

If someone had a lot of free time...:grinning:

https://open.uct.ac.za/bitstream/handle/11427/8286/thesis_ebe_1991_bleimschein_ge.pdf?sequence=1


Noam.

Re: Mag timing

I got fed up of taking the mag sprocket off and trying to get it right so I bought a vernier mag sprocket. I think it had 15 holes in the sprocket and 16 in the centre so each position of the pin moves the timing a couple of degrees or so. I wasn't happy with the 2-3 degree jump between positions so I've made my own for the Model 18 with 27 holes. I never have to take the centre off the mag and the timing can be advanced or retarded just by moving the pin 1 hole. Then the cover washer and nut go over the pin and tighten the sprocket onto the centre. I haven't worked out how much in degrees each position is but I think about 1 degree. I can take the mag off and put it back without having to re-time it.

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email (option): horror@blueyonder.co.uk

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