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TR2/3/3A TR2/TR3 spark plug gap setting??


Senior Member
Hi, I am curious what spark plug gap I should run on my 1955 TR2...

The Moss catalog specs section states .025 for all TR2/TR3/TR4 and original manual and Haynes states .032 for TR2/TR3 and .025 for the TR4.

I recently installed new plugs set at .032 but had a lot of carbon on the rotor and distributor contact, as well as the points. I have developed a very slight miss even after cleaning everything up.

Should I set it to .025 or at least a bit smaller than .032?

Can carbon build up on the rotor and points be linked to the plug gap?

Thanks for any thoughts!! Tim


Country flag
Hey Tim,

Use .025". The voltage in the system is only as much as is required to jump the gap. If you increase the gap, the voltage required goes up exponentially. So yes, larger gap means higher voltage, which means faster wear to the parts.



Great Pumpkin - R.I.P
The Haynes manual has a lot of misprints (even different misprints in different versions of the manual).

I agree with John, set the plugs to .025" as given in the owner's manual.

Since you have run the wide gap until it caused problems, I would consider also changing the rotor and distributor cap; at least as an experiment. The extra-high voltage can sometimes force its way through the inside of the plastic, leaving a trail that makes it easier for the next spark to follow the trail instead of jumping the plug.

There is a copy of the owner's manual in the reprint of the factory workshop manual, both of which are good things to have on hand. PN 502602/SC at

Or there is a PDF scan at https://docs.google.com/open?id=0B2H2NJt34OffYWZiN2VlZGMtNTkxMi00NGUzLWE4NzMtMGRkODRkYzU3MDU1
(download to your hard drive, it's too big to look at over the web)


Senior Member
Hi, thanks for the fast answers!

I do have the new ignition parts on order already, it was time regardless. The extra gap was really hard on the points too.

I was confused because the original Triumph manual does spec .032" for the "Champion L10S" plugs, that second link like Randall posted above has it on page 65.

So basically all the manuals I have, original or not, spec'd .032 but just happened to browse the Moss catalog and noticed the .025 while I was thinking about the excess carbon on the rotor, oh well.

I will go with the .025, the .032 even looked too big now that I think about it...

Thanks again, take care!!


Great Pumpkin - R.I.P
The wide gap should not have had any effect on the points. Is there any chance you have the wrong ignition coil?

Geo Hahn

Country flag
TR3driver said:
The wide gap should not have had any effect on the points. Is there any chance you have the wrong ignition coil?

Or have the coil connections reversed for the polarity of the car?


Senior Member
Hmm, the coil does read 2.2 ohms between the two outer connections, is the coil failing or the wrong ballast? Factory spec is between 3.1 and 3.5 ohms.

The car is positive ground, should the + side of the coil be attached to the distributor or to the wiring harness?

Thanks again guys!!

Geo Hahn

Country flag
TimK1955tr2 said:
Hmm, the coil does read 2.2 ohms between the two outer connections... The car is positive ground, should the + side of the coil be attached to the distributor or to the wiring harness?

Sounds to me like the wrong coil with that resistance.

White wire (wiring harness) should go to the - post, White/black (distributor wire) on the +. The engine will run fine if that is reversed but it will greatly shorten points life.


Jedi Hopeful
Country flag

My original TR2 factory service manual calls for .032"

but my original factory owners instruction booklet, that came

with the TR2s, specifies .025" instead. So even Triumph had

mistakes in their info.

Me I've used the latter with no problems.
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