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MG MGB Technical - No points gap! How does it run?

I didn't think it was possible, but my A with an early 1800 engine has been running with zero gap in the points. The idle was really rough and weak but at highway speeds things were fine. Is this due to the advance in the distro?
Steve Simmons

Steve,

You must have one of those "magic" engines, as well as running without a spark it probably use no fuel either!
Seriously, there must be a slight gap. Even almost a gap, which would at least give a primary current drop, if not a complete primary current interruption. Even a drop in primary current would would give a weak secondary current output.
As to the running improving at higher RPM, the cam touching the rubbing block at high speed would probably open the points a little more.
Your idea on the advance affecting it could also be correct. As the baseplate moves it could bring the rubbing block slightly closer to the cam.

Mick
M F Anderson

Perhaps the gap was microscopic, but as I turned the engine back and forth, I saw no opening of the gap whatsoever!
Steve Simmons

I betcha the distributor bushings are worn-out.

Be certain that the screw that is in the recess on top of the distributor spindle is tight.

Position the distributor cam so that it is holding the points open.

Grab the distributor cam with your hand and jiggle it about.

There should be little or no change in the points gap.
Daniel Wong

In the words of Arkwright "Ger-Granville, jir-jir-jir-jiggle it a bit"
Simon Jansen

Hi all..

I'm ashamed to admit I once ran a set of points in my B for so long a large hole actually burned through one of the contact plates! Still ran though..

cheers
mike donaldson

Folk's it really doesn't matter what the gap is, but the dwell reading.
Even if there is a hole or burn spot in the points.
My best advice is, replace it with a 'pointless system' Such as a Crane or a Pertonix system. Also Mallory makes a 'hall effect' distributor. But the pertronix system is the one I have in my '77 B. It also has the advantage of being hidden, so it looks stock.
Dyno tests show an increase of 2-3 bhp, plus it should give better fuel mileage. And timing will never change like it does with point wear. and it should outlast a set of points by at least 10 to 1.
Safety Fast
Dwight McCullough
Dwight McCullough

My 1275 midget started running rough one knight on the way home, a 60 mile trip. It never stopped but it was hard to keep it going. Next morning it would not crank, and like Steves, there was no visible gap. Thats why I like old tech cars, Its a slow dying, not the quick death that a computor based car would give you. :)
Stan Williams

Dwight, I thought those Petronix units were supposed to last forever?
Steve Simmons

Nothing lasts forever and Stan is correct, one can always limp home with a bad set of points whereas, when any kind of an electronic ignition dies, you just sit there until it is repaired. I put the pertronix system in our MGB and am well pleased with it, but I carry a spare mounting plate, complete with preset points and condenser installed for the day when the pertronix unit dies on us.
Cheers - Dave
David DuBois

My B too has no points gap as such there must just be one that is too small for one to register. I find my cars misses a beat some times and ir terriable cold. Also a lack of power and poor mpg. So the no points gap opion is one i would only recommede through nessisity mine being waiting on replacement parts.
jim

I had a problem when I first bought my Roadster driving it 400 miles home (one does daft things when young with a bank loan and first job!)
The spark was too fat and actually melted the plastic cam shoe thus reducing the points gap. I got it home, just, but had to replace the coil and fit a ballast resistor, and new points of course!
Martin

Re: "Perhaps the gap was microscopic, but as I turned the engine back and forth, I saw no opening of the gap whatsoever!"

As you note, the gap was probably microscopic. If you had the cap off and turned the motor enough to see the points move or not, then you probably should have turned on the ignition to see if the points would spark. That's a better test of zero gap vs. small gap, yes?

It's my guess that your distributor shaft has warped, and that the lobe you happened to inspect was the one most "bent away" from the cam lobe. Given that hypothesis, your motor may be running on three cylinders, in which case the idle would be bad, but would smooth out at speed (though lack power).

Just a thought.
Matt Kulka

With the proper gap the engine seems to be running perfectly at idle and at speed. I'll consider checking all four points though.
Steve Simmons

At one time points were made with a hole through the middle of each contact. The theory was that this was where the spike and pit developed, so if there is no material there there will be no spike or pit. Of course, the spike and pit develops where the contact is actually broken, which was somewhere round the edge on the 'holey' points, which still developed a spike and pit. Exit one theory.
Paul Hunt

This thread was discussed between 05/07/2003 and 08/07/2003

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