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TR2/3/3A TR3 Plug gap .032 or .025?

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K

karls59tr

Obi Wan
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This question is related to my other post about carb adjust as I'm trying to track down misfire and sputtering issues. Plugs are definetly carboned fouled and I'm going to adjust the carbs from scratch but was wondering about plug gap?...Manual says.032 for TR3A(1991cc?) and .025 for TR4A(2138cc)......is the difference because of engine size? In any event, is anyone running a 3 with a mild street cam and header and what do they set their gap at?
 
It's my belief that the .032" is a misprint, and that .025" is the correct gap for all TR2-3A. For example, Practical Hints 6th ed (the factory owner's handbook for later TR3A) says:
 
It's been quite a few years now, but when I was running a TR3A with mild cam & headers, I used .025" and it seemed to work great.
 
Karl: Are you using a standard Lucas HA-12 or Sports Coil or an aftermarket high energy ignition? The Lucas coils produce a very modest high voltage, less than 20,000, so you don't want to open the gap too much. In fact, if you open the gap too much on the Lucas system, you will shorten the life of the coil.

If you have one of the high energy units, these can produce 40,000 volts or more and large gaps are required to benefit from the increase in voltage.
 
angelfj said:
If you have one of the high energy units, these can produce 40,000 volts or more and large gaps are required to benefit from the increase in voltage.
Click to expand...
However, large gaps can still shorten the life of the other high tension components, particularly the rotor.

I ran a MSD-6 for many years on my TR3A and IMO I got plenty of benefit even with .025" gaps. Opening the gap to .030" or .040" made no difference that I noticed, until the coil failed.
 
Although this article by Dan Masters addresses a TR6 ignition system, I think the comparison that he makes between using a Sports Coil and a regular 20k coil may apply. What he doesn't mention is what Randall brought up and from what I've heard on the Forums may be a contributing factor to the reports about "faulty" and failed rotors.
https://www.vtr.org/maintain/ballast.shtml
 
poolboy said:
Although this article by Dan Masters addresses a TR6 ignition system, I think the comparison that he makes between using a Sports Coil and a regular 20k coil may apply.
Click to expand...
He also totally neglected the fact that Lucas Sports coils are available in both "no ballast" and "external ballast required" versions. The part about bypassing the ballast assumes that you have the "no ballast" version.

It also perpetuates the myth about a "hotter" spark. The spark temperature is basically fixed by physics, a high output coil does NOT actually increase the temperature of the spark. And any spark at all is far, far hotter than actually required to light the fuel/air mixture. 400C is plenty to light the mixture, the spark temperature is over 4000C.
 
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