Tuesday, June 14, 2016

GS550 - Fitting New Points and Condensers.

Fitting what?
Contact breakers, remember them? It appears that many of the younger mechanics coming through don't really know what points and condensers are. Maybe they don't teach them the basics of ignition systems in college anymore, maybe they take no notice because they've never had to fit any.  Probably the latter.

Maybe I'll start with how they work.

To get a spark to fire across the spark plug's air gap, we need a pretty high voltage (20,000 - 30,000 volts), for which we use a coil. Everyone's familiar with those, but just how do you get a spark out of one?  Without electronic jiggery-pokery CDI and transistorised ignition systems?

Simply, you need some sort of switch. To get a spark out of a coil, you just need a way of opening and closing the primary circuit. There are two sets of windings in a coil — the primary, and the secondary. In simple terms the primary windings are connected to the battery/ignition switch, and the secondary's to the spark plugs. 
The primary side is "charged" when connected to the battery, creating a magnetic field around the secondary coil. When the switch is opened, the field collapses and a high voltage is induced in the secondary coil, firing a spark across any available air gap to earth. And if you're the easiest path to earth, you get the shock!

Confused? It's clear as mud.

So the simple mechanical switches we use are called contact breakers, or points. And a small cam opens the points at the exact time we need to ignite the air/fuel mixture in the cylinder. When the points open, a spark occurs across them (just like a light switch at home) which would soon cause them to pit and wear out. A condenser placed in series absorbs the voltage, reducing the sparking. Always replace them together and, if you're getting excessive sparking cross the points, your condenser has probably failed.

So new points and condensers were obtained via wemoto.com.au (really pleased they're in Oz now) and all that was left to get the GS running perfectly was to put them in and time them up. The ignition timing was way out before, so this was the ideal time to get it all perfect.

Kokusan points and condensers are fitted to this Suzuki GS550E — two screws in the points, and both condensers joined together. Nippon Denso points have only one screw, and the condensers are separate.

I gapped both sets of points at 0.016" and then used the fag paper method to set the timing. There's two "F" marks on the advance mechanism behind the mounting plate. One is for 1 and 4, the other is for 2 and 3.

Turn the crank until the "Fire 1 4" mark lines up with the line on the crankcase, then turn the points mounting plate to the exact position the points open. And because you can't really see that by eye, we use a fag paper in between the points or, as I'm using, a piece of a thin plastic supermarket bag. Turn the mounting plate while keeping pressure on the fag paper, and when it starts to pull out of the points you have the right spot. Tighten the mounting plate and do the same with the other side using "Fire 2 4" (that has a separate adjustable plate for 2 and 4).

I'm pleased to say the GS is running really well now, and a quick check with a strobe shows the timing is spot on, with the correct amount of advance:

17° BTDC below 1,500RPM
37° BTDC above 2,500RPM

Here's a slow motion video of the points, where you can get an idea on the gaps and how much sparking between them is normal. A large spark is a good indication of a faulty condenser.

Dwell Angle.
You may have heard that points need to be set using the dwell angle and not by feeler gauge, which is true to a point. The dwell angle is basically the duration that the points are closed, and can be measured with some multimeters. It is useful when one set of points is being used for all four cylinders, and it gives you the ideal duration needed for a strong spark. Being old school I've nearly always used feeler gauges and, for a simple switch, let's keep it all simple. 

Electronics ignition.
Some people don't like to set up and maintain points, and think they should be replaced by electronic units. There are plenty of aftermarket systems to do this, and I'm sure they'll all claim better starting, better fuel economy and 60% more horsepower, but I love the simplicity. Strewth, they'll have traction control and ABS on bikes next! 

Each to their own, and coming right up... why my garage has been turned into a sea of red!