If you've ever ridden that most honourable, cheap, and above all, Communist of motorcycles, the MZ ETZ, you were no doubt struck by its amazing lack of power and responsiveness. This is because the timing drifts appallingly.
In order to remedy this, one must set the timing.
Underneath the little side cover on the right hand side of the
bike, there's an ignition trigger system. This can take one of
four forms:
Step one- remove the little side cover.
You are now looking at one of:
- Points. This looks like an ovoid cam with a plastic shoe
type thingy resting on it. These need setting up depressingly
regularly- about every 1500 miles or so.
- One of the two different kinds of MZ electronics. One looks
like a weird metal wheel with a big allen bolt in the middle, and
I have no idea what the other one looks like, but it's probably
quite similar to
- A Newtronics system, also known as a Piranha. This looks
like a metal propellor type thingy and a black plastic light gate.
There's a certain degree of red cables involved on all the ones
I've seen. These are generally maintenance-free.
- is the same as 1, only it's connected to an electronic ignition
unit. This has the advantage that you don't need to set them up
nearly as frequently, as there's no current there to erode the
points. However, they do need setting up occasionally.
And, expect the unexpected:
- Other. There's any variety of other systems out there. You'll
have to improvise if you have one of these, as I have no idea
how to set them up.
Basically the
timing process revolves (haha) around making sure that the
spark plug fires at the right instant in the cycle. How do we know this?
Because you can tell how far up or down the
piston is. How?
With the big
allen key from your toolkit,
smartypants.
Step two: take the spark plug out. Place the big allen key down
the hole. You can now turn the engine over with another allen key
inserted into the hole in the end of the crank. Note that the big allen
key goes up and down in a vaguely entertaining manner.
When the allen key reaches the top of its travel, the engine is at
top dead centre- TDC. The spark needs to fire slightly before the
piston reaches TDC, so that the wavefront of the exploding mixture
reaches the crown of the piston just as the piston reaches TDC.
But Jas, I hear you say, but Jas, the time it takes for the wavefront
to meet the piston will depend on how fast the piston is moving,
how much fuel there is in the mixture, and how fast the piston is
moving!
Well, yes, you're right (and repeating yourself!) This is why most
engines have a mechanism to advance and retard the ignition
according to the rate at which the engine is revolving. Usually this
takes the form of a bobweight and spring, or a vacuum-operated
plunger arrangement. It makes adjusting the timing quite tricky,
as the adjustment has to be right across the range.
MZs don't have any of that, because it's complicated and
expensive. Instead it has... bog all. Yes, that's right, absolutely
doodly squat. The spark in an MZ engine fires at exactly the same
instant in the cycle regardless of how fast the engine is running.
Whereabouts is that? About 2.5mm BTDC. What does that mean?
It means two and a half millimetres of allen key travel before
top dead centre.
Okay, Jas. I get the picture. How do I measure that distance?
There are two ways: with a slide gauge or with a dial gauge.
The dial gauge measures how far you turn the crank around.
The slide gauge measures how far the piston moves.You can
improvise either, or buy either.
A slide gauge is basically a graduated allen key down the
spark plug hole. You can improvise one by getting a pencil,
finding TDC, marking it with a metal rule across the head,
then measuring down 2.5mm, marking it off, attaching it to
an old AOL CD with hot melt glue and so forth. Or you can
drill a hole through a spark plug and fit it with a rod of some
kind. Or you can buy one for a couple of quid. Or you can
use a tyre tread depth gauge (the pencil type) and a G clamp.
The possibilities are literally possible.
A dial gauge is basically a protractor with a pointer on it.
You can improvize one using a protractor and the allen key
you've been turning the crank with. Hold it in place with
bluetak, by the way.
But Jas, I hear you ask. Isn't that terribly inaccurate? Well,
yes but if you're riding on points, as soon as you start the
engine it's going to drift all over the place anyway.
So, we know what we're setting, how to tell where to set it,
and what our goal is. We don't know how to set it or how
to tell whether we're doing this right or not.
To do this properly you're really going to need a voltmeter
of some kind. A cheap multimeter should be in everyone's
toolkit, the expensive one should be on the bench, so I'll
thank you to leave it where it is.
What are we doing with a
voltmeter? Well, you see, the way the ignition gadget works
is to interrupt the current to the coil. The coil is actually a
transformer- it has a thick winding of wire that takes 12 volts,
with a few hundred turns on it, and a thin winding of wire with thousands of turns that
will produce several tens of thousands of volts. Unlike a
normal transformer, though, we're after not a continuous
output but rather a sudden pulse of power.
The ignition system's normal operating mode is to whack
current through the coil. This is why leaving the ignition
turned on when the bike is not in motion is bad for the
coil- it will get rather hot. And flatten your battery. Which
is bad for all concerned.
Well, also inside that can, asides from two coils and a lot of
plastic insulation, is a bit of steel, or rather, lots of small bits
of steel, and they get magnetized by the primary coil.
When the points open, or the output transistor in the
electronic unit turns off, the primary coil no longer supplies
this current and the steel has rather a lot of magnetic field
energy floating around that it can't do anything with.
The magnetic field collapses and all the energy goes into
the two coils- the primary has a condenser to soak it up,
and the secondary has a spark plug to allow it to jump to
earth.
So, what you're saying, Jas, in your roundabout way, is that
the moment the points close is not really important, but that
the moment they open is what we're interested in?
Yes, exactly. We want the points to open at about 2.5mm
BTDC. We can tell the points have opened because the
voltage across the coil disappears.
Step three: find the coil wires (they're under the seat).
Attach your multimeter, set to the 25 volt scale.
When you turn on the ignition, a voltage should appear between the terminals of the coil,
and it should appear at about twelve volts, unless you happen to
be setting up a six volt bike. Guess what the voltage should be
on a six volt bike? Yeah. Right. Unless of course you've
stopped the engine near TDC, in which case the points
might well be open, so turn the engine over very slowly to
see if it goes on and off as the piston goes up and down
and the ignition sensor goes round and round. It should do.
If it doesn't, then you have a major problem. Still, press on.
Step four: examine the sensor for proper functioning.
This varies depending on the type of ignition sensor. If you have
straight, plain Jane points, then note that the surfaces of
the points should be smooth, flat (or rather, slightly convex) and
there specifically shouldn't be a stalagtite on one and a
stalagmite on the other side. The plastic should be clean
(or at most, a little oily) and the felt pad that lubricates the
cam should be present and not have disintegrated.
If any of these is the case, you need to get a new one- BSA
Regal, Burwin, or any Trabant enthusiast can help you out.
With a Piranha, the sensor works by sending a beam of
infra-red light between two points and interrupting it
periodically with a bit of metal. The bit of metal should be
present and correct; the sensor must be clean, or it won't
work very well. This goes for the official MZ optical system
too- it needs to be clean.
With the metal wheely dealy, the sensor is magnetic- actually
a Hall effect switch- and is triggered by a permanent magnet
on the wheel, which is poo. Be careful not to damage it,
because the only repair you'd want to do is to junk it and get a
whole new ignition module. It needs to be free of dirt and
metal filings, and preferably it needs throwing in the bin and
replacing with a Piranha.
Okay clever clogs, you know all about these things, how do
we actually adjust it then?
Well, the Piranha is easiest to adjust. (mutters)
You fit it and it bloody works and it makes no difference what the
setting is. If you do feel the need to adjust it, for whatever
reason, you loosen the screws that hold the base plate the
sensor is mounted on and rotate that back and forth. You can
tell when the notional points open because the LED on the box
turns out. You can't set up optical points in sunlight, so don't
even try.
The real points are next easiest. On these there are two things to
adjust- the point when they open and the distance they open
when they do. There are two backing screws, but only one of them
actually attaches the points to the bike. The other is a disgusting
liberal myth of a screw which is actually an eccentric adjusty thing.
You can tell which one this is because it looks funny. You need to
slacken off the other one slightly, so that the base plate can move
slightly. Now turning the adjuster will change the angle the points
foot presses against the cam. By moving the base plate under the
other screw, you can adjust the angle of the whole thing and thus
affect the distance the points open when they do open. This
shouldn't be far- there's an official specification but three folded red Rizla papers
are the right thickness.
The electronically-enhanced points, of course, are adjusted in
exactly the same manner.
The wheelie widget is adjusted by moving the sensor, same as the
Piranha except that the Piranha doesn't care if you get it a bit wrong,
and the MZ one will fail to work entirely if the clearances are wrong.
Rubbish, it is. The real pappe kak.
So, okay, how do we adjust this? Enough messing about.
Step 5: Find top dead centre. Mark it on your gauge.
Step 6: Rotate the engine round to just before top dead centre-
in fact, just before the timing 'before'- say 3 or 4mm BTDC. Ensure
that the coil is energized at this point. If you have to, adjust the
sensor
so that it's energizing the coil at this point.
Step 7: Rotate the engine, very, very slowly towards your desired
timing point- some say 3mm BTDC, some say 2.5mm BTDC, my
sweetheart Clunk wasn't happy unless he was at 2.2mm BTDC, but
I digress- and once there, adjust the sensor by the smallest increment
possible to cause the needle to plunge back towards zero on the
multimeter, the Piranha light to go out, the Rizla to fit between the
points, the spark plug to fire, and the world to be a just and happy
place for MZ riders. All or some of these things should happen at the
same point. If you're on points, check that the gap is right at this
position.
Step 8: Tighten up the screws very, very tight. Add Scotchlok if you
have any.
Step 9: Check the setting again- particularly with points, tightening
makes it drift. If it's wrong, well, rinse and repeat steps 6, 7 and 8.
Step 10: Say to yourself, cor, that wasn't half as difficult as Jas
made
it sound, and think that the multimeter trick is a good way to set up
the points. Replace the spark plug, covers and so forth.
That's all there is to it, really.