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MG MGB Technical - worn points

I changed my points this weekend. I've only been driving with them for 3000 km but they had a nasty crater on them.
The reason I checked the points in the first place was the lousy running when the engine was cold, it ran fine when warm though(now after change it is ok when cold too).

What could be the reason to the worn points other than a faulty condenser? Coil?

Jesper

I'm always a bit out of my depth on anything electrical, but did you check your gap prior to removal?

You may have put them in with too little clearance, or (more likely), the plate got loose and the gap tightened up. I find that when tightening the screw for the points set, the gap ALWAYS tightens, so I have to "sneak up" on the clearances when tightening the screw in order to get it right.

Just by replacing the points, condenser (and check the low-tension lead), you should be OK, I would think. FWIW
John Z

Jesper - Change the condenser. If you are getting severe pitting of the points it is an indication that the condenser is not the correct value. The tolerances for condensers is very wide and even though it may not be open or shorted, it can very well be the wrong value to do it's job properly on your distributor. Once you get a condenser that prevents sever pitting and allows even wear on the points, do not change it when changing points. Condencers do not wear out and will normally last for years before going bad. And yes, the coil could have gon bad also, but check the condenser first, it is cheaper. Good luck - Dave
David DuBois

John, this is one reason that so many of us have changed to electronic ignition. Someone advised many years ago to fit contact less ignition but being a die hard one for originallity I stayed with the points. After breaking down in the middle of nowhere one Sunday, which was a result of a burnt out set of points, I fitted the Petronix system. If I could recommend the best value for money that I have spent on the car for under $100 it would be to fit Petronix contact less ignition. It also fits inside the distributor so you can't tell.

Andy 74 GT
Andy Preston

Andy - If you are using an electronic ignition such as the Petronix I would strongly advise that you carry the necessary parts to switch back to a points system in case of an emergency. I have never been stranded by a points system, while I spent one whole afternoon trying to get from Grants Pass, OR to Crescent City, CA, having been stranded by a Hall effect ignition similar to the Petronix. My point being that when a Hall effect system fails, there is no way to jury rig it to get home, you are just dead in the water untill you get replacements. Having said that, I run with the Petronix system in our MGB which is used every day and for long yearly trips to Southern California, but I do have a backing plate in the trunk all set up to switch back to the points system if necessary. Cheers - Dave
David DuBois

Dave, you one hundred percent right and everyone who has a petronix or similar system would be well advided to carry a new spare standard set up. I carry a complete ignition set of points, condensor, wires, cap, leads and coil, and fuel pump, plus all the usual hoses. Leave nothing to chance and nothing will happen that you cant deal with.

Great suggestion to pass along.

Andy 74 GT
Andy Preston

Jesper - pitting/spiking of the points is the normal wear mode, how long since you changed/cleaned them last? Do you check the gap between changes using dwell? They should last several thousand miles before any significant surface damage is apparent but work perfectly well for several thousand miles more. If they are burning much faster than that the condenser/capacitor could be faulty - although I've never had one fail in 35 years - and this will be causing a weak spark at the plugs as well. Another cause of burnt points is a 6v coil us used on rubber bumper cars being used on an earlier system, or the coil ballast on a rubber bumper car being shorted out for some reason.
Paul Hunt

Thank all for the help!
I had only driven for 3000 km with them. The coil is a 12 volt without resistor. I have not checked any dwell (this dwell thing is new to me), is that the duration of time/degrees the points are open? I have actually printed what Paul Hunt have written on the subject, but haven't had the time to grasp is 100% yet.
I will change to an old capacitor and see if it work better.
My reason for waiting with capacitor shift is that I recently changed capacitor because of the wear.

Well today I got a set of points to keep in my trunk for spare, and at the same time I got some other goodies as two new king pin/swivel axle sets, two new shocks and the rear u-joint for my transmission. Lets hope for a nice ride later and that you don't have to help me on that.
Jesper

Jesper. The "dwell" is the amount of time, measured in degrees, that the points are closed. This is the "charging" cycle for the coil--it charges while the points are closed and the spark is induced when the points open. Paul H can explain the full theory behind this, if necessary. Are you cleaning the contact surfaces of the points after you install them? I seem to remember a problem with points burning when the contacts are not cleaned before use, but it has been many years since that happened. Now, I clean the contact surfaces and the points last many thousands of miles with no performance loss noted for most of them. When you start noticing a performance loss, it is time to change out the points. They can show wear, but still perform correctly. Les
Les Bengtson

Like Les I also clean the contact points as the last step before sealing them up. When new, or after insertion of a feeler gauge, you can leave a film of oil which can become an insulating layer with the effects of the spark (the condenser does not completely eliminate the spark). When cleaning I put a piece of clean paper between the points, close them, and pull the paper through them. However I do not pull the edge of the paper through the closed points as I have found that this can leave fibres behind which can also cause an occasional misfire.
Paul Hunt

This thread was discussed between 26/08/2002 and 30/08/2002

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