Setting Timing Using The Points

[b40rt]

Its alot easier to change the timing by opening/closing the points, rather than taking the flywheel off and moving the back plate. But, is there any reason not to do it this way ? Thanks

[pschrauber]

As I know are the Points and the contact/Points runner subject to wear.

Every time when the contacts/points are opened again, the current flow will tear off producing a small electric arc.

This arc will wear the contact surfaces, the distance of the points will increase.

But also the contact runner, - he is responsible for opening the contact -, wear off in the course of operation, so that the "breaker-contact distance" will be decreases with the time.

With the gap of 0.04mm the system is balanced out, and readjustements have to be made in terms around 5000km for a street bike.

If the opening of the points/contacts is adjusted longer then there will be more wear to the contact/points runner but less to the points/contacts and vice a verse. So you will have to readjust the ignition more often and too replacing the points.

(As I understood ... I'am not an engineer in engine technics)

Edited August 18, 2013 by pschrauber

[bestrcpilot]

By changing the point gag, you are changing the dwell. The dwell is the time that the points are closed. Why is dwell Important, when the points are closed the power is building up in the Condenser. Think of the Condenser like a Battery that has to recharge so the the dwell is the Length of time that a condenser has to recharge. The shorter the charge time the weaker the spark. When the points open the power is sent From the condenser to the high tension coil and then to the plug. The system that is used in these bikes is AC not DC. I hope this helped answered your question.

[pschrauber]

Mmmh ... isn't the dwell time much more depending to the rpm of the engine?

I have been told - so far - that the coil is set / prepared for charging within the maximum revolution speed of the engine here can be a "bottle neck".

The capacitator on the old fashioned magneto ignition is for reducing the sparc / arc bow between the points so they don't wear too fast.

The charging time of the condensor which is used is much faster as the same model is used also for SWM Enduro and MX models where the max rpm of theses bikes compared to the SWM Trials bike are around 2000 rpm higher.

[b40rt]

Thanks for the answers Patrik and bestrcpilot, both make sense. Not to concerned about extra wear on the heel of the points as they generally last year's anyway, the dwell can only change by 10 / 20 degrees, will that make a significant change on a single cylinder engine ?

[2stroke4stroke]

If you have a Yamaha then adjusting the points is the only way to adjust the timing. But eventually you run out of adjustment. Moving a movable backplate gives more scope for adjustment.

Personally I used to set the timing by using the backplate, having set the points to about the middle of their range, then tweaking the gap to fine tune, then again every couple of trials to keep it right using a dial gauge (and doing it that often definitely helped on the 348). As long as the timing was bang on and the points gap was within tolerance then I was happy.

Dwell? The manufacturer's gap figures were designed to optimise dwell to get the points opening at the peak of the magnetic flux insofar as the relatively crude nature of a trials two stroke ignition system permitted. Nowadays of course it can all be programmed, which is great, but a programme won't push the bike off the hill when it packs in and you have nothing to tweak.

Edited September 10, 2013 by 2stroke4stroke