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Re: C2 Ballast Resistor question
The ballast resistor changed to GM 1957154 (Delco short number D1110) for all cars without TI ignition in 1965. In the 63L-64 era, the 'hot' version of the ballast, GM 1931385 (Delco short number D1111) was used on high horse, solid lifter, engines (without TI)that used an '091 ignition coil. The 'cold' version of the ballast was matched to '087 and '202 coils.
The 'hot' ballast is usually referred to as having an 0.3 ohm nominal resistance while the 'cold' version is usually spec'd at 1.8 ohms. But, Delco specs provide the acceptable range of resistance and there WAS unit to unit variance.
Measuring the resistance of either ballast is relatively tricky since you're 'pushing' the lower limits of resolution on your VOM. Factors like probe wire resistance and getting a solid probe of the ballast's terminals are fighting you in getting an accurate reading.
The very best way to measure resistance is to compute it... With current running through the ballast, measure the current and the voltage drop across the resistor. R= V/I.
But, if you're actually able to measure 0.8 ohms with the ballast cold AND lead wires DISCONNECTED, I suspect your ignition problem doesn't lie in the ballast. Your car should have a '202 ignition coil which the '65 Corvette Shop Manual spec's as having a 1.24-1.46 ohm primary resistance and 6500-9500 ohm secondary resistance.
Why so much variance in winding resistance? Simple, winding resistance means very little to an ignition coil's performance. What is important is the effeciency of energy transfer from primary to secondary windings which is a function of the coil's inductance ratio and core coupling efficiency.
Since few are equipped to measure this, spec books list winding resistance as it's easier to measure for a simple 'go/no-go' test. Bottom line, few actually care about the STATIC characteristics of ignition system components. The rubber meets the road during dynamic operation where energy transfer is taking place repetitively under the stress of component heat loading.
The easy way to validate what's going on with your car is to take it to a competent garage and put the ignition system's waveforms up on an engine analyzer and you'll learn a LOT in pretty short order! -
Re: C2 Ballast Resistor question
I think your ballast is okay. It would help if you would describe the tests you ran and the results.
The ignition circuit is a very simple DC circuit. The points make and break the ground. With the points closed there should be continuity between any point in the circuit and ground and open when the points are open. Run these checks with the ignition OFF.
I have no data on a Delco 172 coil. What are the measured primary and secondary resistances?
With the ignition on you should have voltage at the coil + terminal.
The breaker plate has a ground wire, and after 40+ years these can break due to constant movement of the plate by the vacuum advance control. If it breaks there is no ground circuit - as if the points never close. The low ohm ballast is also known to burn points because it allows higher primary current.
DukeComment
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Re: C2 Ballast Resistor question
If you are trying to eliminate the ballast as your source of no spark jumper it out, then try to start.Comment
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Re: C2 Ballast Resistor question
Spark dwell is a function of the ignition coil and the condenser in the distributor. When the points open to fire the plugs, electrical energy on the primary side of the coil 'ping pongs' between the coil and the condenser (the two components play a game of 'catch' with the energy stored in the coil). That's was causes the spark to 'persist' or 'dwell'.
Without the condenser, you get a 'one-shot' delivery of energy to the spark plugs which won't last long enough to light off the air/fuel in the combustion chamber. Plus, you'll see the 'funnies' you just observed...spark without dwell.Comment
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Re: C2 Ballast Resistor question
The shop manual does not account for the "low ohm" resistor that was OE on SHP engines of your year, so that explains the "out of spec" voltage condition.
I suggest you use ONLY ignition components made by Standard Motor Products. These include Standard, Blue Streak, NAPA, BWD, and Echlin brands.
Use the high breaker arm tension points (28-32 oz.), such as NAPA CS89 or BWD D112HP. You can cross reference to other brands from their web sites if you wish. High revving SHP engines need these points to prevent high rev point bounce.
The NAPA condenser is RR175SB.
My recommendation is to always use name brand OE replacement parts, such as the above and avoid aftermarket hot rod brands if at all possible.
But keep in mind that the low ohn ballast and higher breaker arm tension will wear the rubbing block faster and also increase contact material transfer, but they should last 15-30K miles, and you should check dwell and initial timing every 5-10K miles.
DukeComment
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Re: C2 Ballast Resistor question
Duke,
Thanks for the advice on part numbers. I will stop by NAPA today. I always thought Accel had quality parts but maybe not since I had a problem with the condenser and points after such a short time in use. In the decades I have worked on cars this is the first time I had a condenser go bad. I agree I will stay away from the "hot rod" parts. Thanks again to you and everyone else who provided advice.
RodComment
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