MG MGB and MGB GT Tech Talk
I tried to start my 72 BGT and the distributor smoked. I found the points melted. I replaced the points, making sure they were insulated from ground. In the process I found the clamp loose and one of the mounting bolts missing. I tried it again and fried a second set? I did not repace the condensor and have no idea if the coil is good. Where do I start?
Could it be that the timing is so far off that when the points close there is no where to discharge the energy and they end up taking the coil to ground?
Too much current to the points. If you are using points with a plastic cam follower the plastic will melt. The older ones with phenolic material didn't melt, they just fried the points themselves. Work backward from the side terminal through the coil and ignition switch checking current at each connection. Also check the ground connections for the battery and the jumper strap at the left front motor mount. They must be squeaky clean and tight.
Jack
The other issue is that your distributor wasn't grounded well to the block if the clamp was loose. A bad ground will create heat. Chances are good that the ground wire at the points plate is probably burned through as well - I'd highly recommend soldering in a flexible replacement wire. make sur ethe negative coil terminal is wired to the points and that in no way is any coil wire grounding. High resistance in the cap, plug wires, or the coil will also cause a high-heat situation, so make sure your ignition system is in excellent condition. Chances are high that the problem is caused by overlooked maintenance or a faulty ignition part.
Jeff,
"distributor wasn't grounded well to the block if the clamp was loose"
I did clean and replace the mount and re-tightened the clamp.
"ground wire at the points plate"
I will check this as well. I can put a meter from the plate to the block to make sure. The car was running rough when I got it and has only been started once in the past year for about 5 minutes.
"ignition system is in excellent condition"
I have replaced the cap, rotor, and wires.
"overlooked maintenance or a faulty ignition part"
Could you elaborate on this.
Steve
The "ground wire" that Jeff speaks of is the thin and very flexible woven copper wire that is soldered to the fixed base plate and the movable contact breaker plate. Any replacement MUST be VERY flexible, otherwise a stiffness will inhibit the movement of the breaker plate. Sort of a b**** to replace reliably but with some care you can do it.
Another thing, not related to your "melting" issue is that the collar that fits the breaker plate to the base plate must not be too sloppy from wear. The real fix is to replace the assembly, but if you are careful you can "peen" the surfaces to reduce the slop and still have free movement. Excessive slop here causes erratic dwell and resultant incorrect timing.
Of course the ultimate fix is a little postage and a credit card number to get the distributor to Jeff for a full rehab. :-)
Jack
All this could be from a bad coil that's internally shorted as well.
Sure, I can rebuild your distributor if you want to go that route! Just visit my website and print a copy of my Curve Worksheet to send along:
http://advanceddistributors.com/Curve%20Worksheet%2007.htm
From that info I'll set up your distributor to be optimised for your engine, as well as check out your new cap/rotor/wires to make sure they're in good working order.
Another possibility is that the carbon brush in the center of your cap is missing. That'll cause high voltage arcing that'll ruin new points in no time. A bad condenser can cause similar damage.
