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MG MGB Technical - Point Gap
|Getting my 67 GT ready for GOF West here in California. Given the car was restored in 2006, I was impressed with how well it cleaned up.
Motor was restored about 5,OOO miles ago. Did a check of the points (Jeff Schlemer points). Found they were nearly closed. Reset to 0.15.i Tip of the points looked smooth and clean. No burn marks.
Of note is that the car has been running fine. Plugs are light brown.
What effect does a smaller gap have on the motor?
Also, I retorqued the head at 500 miles. Is there a need to retorque it again?
|A small gap passes current through the coil for longer and allows it to 'charge' for longer at high revs, but it only has any effect at around 10k rpm or so hence irrelevant on an MGB. The down side is that instead of breaking relatively cleanly it could arc for longer burning the points more, but that doesn't seem to have happened with yours.
As the gap closes up the timing is effectively retarded slightly as the cam has to turn further before the points open. This is why replacing, and even resetting the points, means you should check the timing even if you did it with the distributor in-situ.
Having retorqued once I'd say no.
|I find that the points close up after time (cheap points?), to the extent that when the car starts playing up, becomes more difficult to start etc I go straight to the culprit. |
As an aside, as somebody who wants to persevere with points, what a pain the dizzy is in that location from an adjustment aspect. You can pull the whole unit out which makes it easier to gap the points, but if you want to check with a dwell meter it's got to remain in situ.
|Agree on both parts of the second para, although I don't find they close up over years on either of mine.
Regardless of the number of miles if the dwell meter shows they are in tolerance I leave them be. If they are out after a long time I change them anyway - on the bench, where I use a simple ohmmeter and twiddle the shaft to set the dwell. That's on the roadster, V8 couldn't be easier to access being at the top front of the engine, the irony being there is a hex bar sticking out the side of the body to adjust the dwell anyway!
|I am also a fan of points ignition, and much prefer them to aftermarket bolt on bits, with reference to poor quality points, I buy genuine Land Rover ones, you can buy these for 25D and 45D distributors, and the cost is about £2-50p/£3-00 a set, like most people I check my points gap with a dwell meter, but I also set them with one, and you don't need to remove the distributor, it is better with the plugs out as it allows the engine to spin over faster,as I renew my points on service, I will already have removed the plugs.is all you need is a remote starter button, fit the points don't fully tighten the screw connect up the dwell meter, and crank the engine over and watch the meter and adjust while still cranking, when correct stop cranking tighten the screw and recheck, simple, |
|Went to GOF West where John Twist was the guest. At his tech session I asked about the effects of point gap on timing. John stated that each degree of point gap is similar to 1 degree of timing.|
I had him check the timing during the rolling tech session and found it was off.
This thread was discussed between 09/09/2018 and 15/09/2018
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