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8th September 2006

Tech: Changing Contacts

Be afraid. Be very afraid. Someone has let PaulG80 back into the workshop… and this time he's adjusting things which spark!

Many of our varied and ancient steeds use the good old contact breaker to initiate the spark at the plug. It can be really surprising how quickly these items can wear and how badly worn they can be whilst still giving service.

Old points, arrowed...

The case in point (sorry) is the Black Pig, my Moto Guzzi. I thought I had better check the points one evening, as I hadn't looked at them since I'd owned her in 5000 miles. Well… you know the old adage: if it ain't broke, etc. When I did the check I was astounded that I had any spark at all as they were that badly worn. For instance, if you look at the part that moves you'll see that there is no face at all and it was striking on the metal it was made of. The next two days riding was filled with paranoia as to whether she would breakdown or not. This obviously proves the other old saying, that what the eye doesn't see the heart doesn't grieve over!

I phoned Corsa Italiano on a Friday after a recommendation from Will, one of the Gloucester Dribblers, and was confronted with a choice. Did I want the genuine points? These were £14 for one side and £28 for the other (work that out). Or did I want the cheap pattern ones. To anyone who knows me it should be pretty obvious what I went for and I got a pair for £8.51.

Saturday morning dawned and lo behold the postie shoved a small packet through my door. It was my points! So top marks to Corsa Italiano for service.

The postman always wears latex gloves when delivering to Paul's house...
Random Guzzi Stuff on

I sneaked up on the Black Pig and whipped off the tank in a blink of the eye. This exposed the distributor cover, held in place with two screws. These were removed to expose the points. The contacts are normally held in place with two screws, one is on a slotted hole to give adjustment and one is on a fixed hole. These were removed carefully to avoid dropping them either into the distributor or anywhere else. You can use a magnetic screwdriver or as I did, and put a dab of grease on the end of said tool.

I did the top ones first and once released they needed to be disconnected. These ones are connected by way of open spade terminals under a screw. Once the wires were swapped over I installed the new points but only nipped up the two mounting screws, as we will come back to them. The same operation was then carried out on the lower points.

New points in place. Maybe.

Now for the fun bit, setting the gap. You will need the following:-

  • A set of feelers in the appropriate range (imperial or metric)
  • Two screwdrivers of the flat head type
  • Three hands and pot of patience

    The next thing to do is set the distributor cam so that points will be open. This is the spinning part in the centre of the distributor. You will notice that it has an eccentric profile. Basically it's an off-centre circle, and when the highest point of the circle is under the points that's where they open.

    Now to set the points you will notice that by the screw that had the slotted hole there was a notch in the body of the points, and this corresponds with a notch in the backplate. Insert one screwdriver here, and this will allow you to adjust the points gap by twisting them back and forth.

    How do you feel about this picture?

    Next select the correct feeler gauge. In my case the points should be set between 0.30mm or 0.40mm. Always try to get the lowest setting. Insert gauge between the faces of the points -- now there is no easy way of describing the sensation you are feeling without resorting to filth so empty your minds (that was quick) and bear with me. You need to have a good sliding fit with the slightest bit of friction as you pull the gauge back and forth.

    Once this is set on the lowest setting, leave the gauge in place and take your other screwdriver to tighten the adjuster screw and the fixed screw while keeping your other screwdriver still in the slots. I told you that you needed three hands!

    Hopefully you should still have that good fit. Now take the feeler gauge off the upper setting and see if fits. Now, in the words of Dr Haynes, repeat for the next set.

    Once you've changed the points and set their gaps, you'll probably want to check the ignition timing as well. The timing can be varied quite a lot by changing the points gap. On the Guzzi the timing of right cylinder's points is set by rotating the whole distributor round its mounting and the timing of the left cylinder's set is done by moving the plate inside the distributor that the points mount to.

    To cap it all

    All that's left to do now is replace the cap and the fuel tank and start her up. This is bit I was dreading as I am to maintenance what Tigger is to sitting still and quiet. But I got lucky -- she fired up and even ran vaguely OK.

    Hopefully this has shown that something that sounds quite complex can be easy. So go on check your points and make sure that your sparks spark well and full…

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