Yes. It’s back to work on The Racing Rhino. In my last V7Sport post I described adding vacuum take off points to the inlet manifolds so that I could balance the carburettors. I’m chasing the cause of the blue right-hand exhaust header. Before I playing about with the carburettors all the rest of the engine tuning needs to have been done. I’ve checked valve clearances but need to check the contact breaker points gaps and ignition timing next. I wrote in February about doing this but have decided to repeat myself.
First you need to get access to the contact breaker points.
- Disconnect the right hand fuel line from the tap.
- Disconnect the fuel tank retaining strap.
- Raise the rear of the fuel tank on a block. You need to do this to be able to get a screwdriver straight on the various screws later.
- Remove the 2 screws holding the plastic cover on the points housing.
- Remove the plug lead and take out the spark plugs. This is to make it easier to turn the engine over.
- Remove the 4 screws securing the alternator cover so that the engine can be turned over with an Allen key in the rotor securing bolt. You can put the bike in gear instead and turn the engine that way, as I did last time.
This is what it’s like inside the contact breaker housing. Each cylinder has its own set of points and you can’t do the timing until you’re sure the points gaps are right.
The top set are for the right cylinder and the lower set for the left. Start with the upper set of points which fire the right hand cylinder. Turn the engine forwards, that’s clockwise looking at the alternator, with your thumb over the plug hole checking for compression as the piston makes its way to the top of the stroke. Despite what the original Guzzi manual says, the points cam turns clockwise. keep turning until the top points are fully open. The gap should be 0.37 to 0.43mm so I reset them to 0.4mm using a feeler gauge. The gap is adjusted using the screws marked in my picture above.
The lower points gap is then checked/adjusted in a similar manner – compression stroke, points fully open etc. I found that both sets had closed up significantly. I’ve never had this happen before.
For an engine to work efficiently, the spark must be delivered at the correct time. That’s what ignition timing is about. I set timing statically. As I’ve already said, it’s very important that the points gaps are adjusted correctly first.
Pull the rubber bung out of the right hand side of the clutch bell-housing so you can see the marks on the flywheel edge.
You have to begin with the right hand cylinder again. Fit a bulb between the contact breaker spring and engine block. Turn the engine forwards until the right hand cylinder is on the compression stroke. As you look at the flywheel the teeth and marks will be moving upwards. Keep going till you get to the “D” mark (destra for right). This is TDC on that side.
Now you have to turn the engine the wrong way (teeth going downwards) until the next line comes into view. This is the static advance mark. Go slightly beyond it then back again to take up any backlash. Be careful when turning the engine the wrong way as the rotor bolt can come undone! It can be tightened again by jamming a screwdriver in the teeth on the flywheel to hold it still. At this point the bulb should (ignition on) come on as the points are just beginning to open. In my case the points had already opened. The timing was too advanced.
To adjust the timing of the right hand points you need to slacken the two bolts that clamp the contact breaker housing in place on the engine block. These two bolts are really hard to get at. There is a special tool to get at these bolts which makes the job easy but, in the past, I’ve managed to do without it just struggling with various 13mm spanners encouraged with a bit of swearing.
This time I took the easy way out. No one in the UK had the tool in stock and it’s expensive for what it is so I made my own. A 13mm combination spanner was sacrificed by being cut up and welded to some bar.
Using the proper tool it’s easy to undo those flippin’ screws!
Now, with the ignition switched on, I turned the housing until the light went out and then back again until it just came on. Then I did the bolts up again using my new tool. As a check I turned the engine over until the light came back on again. The correct mark lined up in the access hole.
To do the left hand side you turn the engine forward again till you get the “S” this time (sinistra for left). Then, like last time, back to the mark above, then back a bit more, then forward again to the mark to take up the backlash and reach the static timing point. With the bulb between the spring of the points set and earth the bulb should have just come on as the points start to open. Again mine needed some adjustment.
The timing for this set of points is adjusted by moving the sub-plate they are fixed to in the contact breaker housing. Again, I’ve shown the screws to loosen in the picture above. One of the screws is hidden under the wire. Move the plate till the bulb just lights then lock everything in place. Once again I checked the timing by turning the engine forward until the light came on and saw that the correct mark lined up.
Everything was then put back together and the engine started to make sure it would run.
One thing I was reminded of when I did this job was that all the screws in the contact breaker housing are quite damaged and it would be a good idea to replace them. The spare ones I have are no better.
Finally I gave that tool I made a couple of coats of paint before putting it away till next time. It made the job so easy that I would never try to do it again without.
The spark on the right being too advanced could have made the right hand cylinder run hot and contributed to the exhaust blueing.
Carb synchronising next.