I recently
decided to replace the original coil and mechanical regulator on my MZ ETZ251. So,
to that end I acquired a coil, designed for use in an old style Mini, and HT lead for it
from Halfords, along with a Lucas electronic voltage regulator
(part no. NCB 403), as fitted to various cars and bikes like BMWs and Moto
Guzzis.
One Saturday morning with the parts in hand, a copy of Hints & Tips
Vol.2 for reference, a couple of bottles of beer and a new CD that I’d just
bought for inspiration I made for the shed. I had nothing else planned and was
determined to get everything done in one go.
The
instructions for fitting a replacement regulator in H&T2 are pretty
straightforward. In fact, there are three or four different lots from which to
choose, but for those of you who don’t have a copy (and why not?) I’ll repeat them
here with my own observations
thrown in for good measure:
With the seat
off the first thing that you should do is disconnect the battery. This is in case
you accidentally short-circuit anything. Pull the wires (5 terminals) off the
regulator (don’t forget the earth wire, bottom left as you face the front of
the bike). Remove the old regulator by pushing the rubber spigot (bottom right)
through the clip on the frame with a screwdriver (be careful with this as we’ll
need the clip later).
Make a small bracket to attach the new regulator to the
bike. Connect the brown, green/blue and green/red wires to the new regulator.
Bolt the regulator and bracket in place. I fitted the regulator with its rear
against the petrol tank and the terminals facing backwards. That way there’s no
need to fiddle with the various wires for length. Next fit an inline fuse holder
with a 15A fuse between the red/yellow and red wires (the thick ones). On the
original regulator the connection between the red/yellow and red wires
(terminals D+ and 51) is a current limiter which cuts out if the current goes
above 15A. This would only normally happen if a short circuit occurred. The 15A
fuse in the inline holder would blow if this were to happen now. However, from
talking to others recently it seems that the fitting of the inline fuse is a
bit of overkill and is strictly speaking unnecessary. However, I fitted one as
a precaution and because I had one to hand.
MZ
regulator Lucas
regulator
D brown D-
DF green/blue DF
61 green/red D+
D+ red/yellow across 15A fuse
51 red
across 15A fuse
The longest
job I found was making up the bracket to attach the regulator to the bike. I
cut a small square metal plate to the size of the regulator and drilled a
couple of holes in it to line up with the ones on the regulator. A small bolt
through the hole on the left of the regulator, a longer one through the one on
the right when viewed fitted as described before. I then bent the clip that the
original regulator was mounted to so that the longer bolt could run through it
and tightened up the bolt with a couple of large washers. This holds the
regulator in place and the shape and size of the square plate prevent it from
moving around.
Next up was
the coil. Remove the original coil by loosening the bolts which mount the
bracket around the coil to the bikes frame. The new coil, designed for a car,
is quite a bit larger than the original MZ one and, no surprises, it won’t fit the
original bracket so you’ll have to make up another one. Luckily the coil I had came
with a metal bracket which I re-shaped (hit with a big rubber mallet until it
was the right shape) before attaching it to one of the original mounting points
on the bikes frame. There are also a couple of additional spade connectors attached
to the terminals on the car coil. These can be safely removed as they won’t be
needed. Connect the wires to the terminals.
MZ coil new coil
1 green (-)
15 red/black (+)
Be careful
when mounting the new coil as it’s a bit of a tight fit under the seat. Make
sure that the terminals don’t touch anything metal or you’ll start blowing
fuses. If this happens when you’re riding along the bike will simply cut out on
you and you’ll lose power and all your lights. This is what happened to me when
I originally mounted the coil using cable ties instead of a proper bracket. Not
too clever at night on the motorway, I can tell you. Copious amounts of insulating tape would be a good idea too at this point, or you could use some old inner tube as a make-shift rubber boot to protect the terminals..
Right, that should be the
coil attached to the bike. Connect one end of the lovely new orange HT lead to
the coil, cut the metal clip off the other end and screw on a standard (NGK)
plug cap. You can’t re-use your old HT lead because it needs one of the clips
which are attached to the new lead to connect to the coil properly. The one on
the other end is surplus to requirements so it can go to make way for the plug
cap.
Reconnect the
battery, and you’re in business. However, before I finished up I dressed and
adjusted the points as well since doing all that work and having it all come to
naught because you couldn’t be bothered to take five minutes to check the
points seems a bit of a waste. If you’ve got electronic ignition then this bit
isn’t necessary, obviously. Everything was then treated to some silicone
sealant to keep out the weather.
Time taken? About 3 hours from start to
finish, but that included taking off all the bodywork, the seat and the rack, doing the work including making all the brackets from scratch, before
putting it all back together and running the bike up and down the road to make
sure everything was working properly. I’m sure that if I’d been better
organised it could have been done in half of that time, but I wasn’t it any
particular hurry and it was better to get it done right than get it done fast.
How does it
all work now? Well, it’s not that much different except that the spark is a lot
fatter (which is good), acceleration is a bit crisper and it idles better.
Nothing too dramatic. Only time will tell with regards reliability, although I
believe that using a high output car coil in this way means that the points
wear out faster. However, I can live with this. It just means checking them a
bit more regularly in the future.
Note: when messing around with non-standard
bits you do so entirely at your own risk. If you follow these instructions and your bike explodes, don't
blame me.
(Originally posted in Thistledown: Journal of the South of Scotland Section MZRC, Apr. 2005)