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#1
06-28-2003, 08:01 AM
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Melting Distributer caps
I have a 1969 GMC C910 that I changed ignition on. I changed to a crane hi-6 multi spark box, PS-92 coil and MSD cap adapt. This was working fine until about a year or so ago when I noticed that the cap was melting where the button goes that touches the rotor tab. I was running a stock cap first then tried a MSD and Accel caps and the same result. It is on a 383 stroker motor, Taylor ignition wires (spiral core metering about 100ohms resistance+- on each wire), my coil wire is about 10" long and running NGK V-groove plugs. The truck doesn't seem to miss but does have trouble at high rpm but I think that is a carbration problem. I asked at the race shop that I deal with and they are stumped and that is why I am posting here. This is the first forum that came up in a google search. So I hope someone out there can help. Thanks in advance.
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#2
07-04-2003, 11:14 AM
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I am an electronic technician, so I have a little insight as to why this is happening.
Heat in an electrical connection is a sign of resistance. This connection would seem to be the high-resistance point in your spark system. I can think of two ways of dealing with it: 1) you need to improve the contact between the center button of the cap to the rotor. I haven't seen or handled an old-style distributor cap in a long time, so I am wondering if there is a way to put a stouter spring in the cap(?) OR possibly some device (something spongy but heat resistant) underneath the contact in the rotor to make it bear against the button a little harder. 2) you may need to do something to increase the resistance of your plugs...maybe go to a resistor-type. I am speculating that opening the spark gap may even work. The bottom line is that there is high resistance at the point where the melting is occurring and it is producing heat. You want the high resistance to ALL occur at the spark plug, which is where you WANT the heat. Hope this helps!
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#3
07-04-2003, 05:01 PM
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thanks for the suggestion. I have also talked to Crane Ingnition since my posting and they also said to check the phasing of the cap and rotor. This also gives me something else to try cause melting caps sucks and it can't be helping 5000+ rpm performance.
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#5
07-20-2003, 06:52 PM
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Yes just solved the problem last weekend. I phoned Crane and talked to one of the ignition techs and he said that the button/bushing that was in the cap had to much resistance and to find one that was a solid brass one. He said that MSD or ACCEL should have one. I went to a local speed parts store (MOPAC in Edmonton Alberta thanks guys) and they had a low resistance one from MSD. It is more for race only ignitions, 7AL and higher that produce HIGH voltages. The problem was even in the MSD cataloge that this would cure this problem.
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#7
07-27-2003, 06:39 AM
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The caps themselves wasn't the problem it was the little buttopn/bushing that runs throught the cap carying the voltage from the coil to the rotor. There was too much resistance in it for the voltage my coil puts out. Now I can work on the next problem, and that is tunning the carb and fuel system. It seems like a neverending cycle, always something to fix. When I get it dialed in it should scoot nicely.
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