Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board spark plugs changes

Hello; trying to understand some changes over the models.
For example in the 67 models you have Monoblocs 9:1 and N4; however, the TT had the Monoblocs with the same jetting as the T120R, 11:1 and N5


Thanks

the TT with 11:1 will have higher cylinder temperatures than the 9:1 engine.

Spark plug choice is not about the jetting used.

You're right, but the 11:1 should then need a a harder (colder) plug, and the N5 is a hotter plug - not sure of the scource of Reverb's info, mind you.

...the info is in the 67 parts manual that I was checking to buy some parts.
Regarding high or low compression, you have the low compression T140E with N5

N58R

Yep, plenty of info on the web about N58R (circa the same heat range as N3), which makes sense.

Hi; I see; thought that was me and the old print because do not sell those N58 here; hence thinking in N5 so the doubt.

Thanks

If you got the N5 info from a shop manual it could be a typo. There are several errors in the manuals. N5 seems way to hot for an air cooled motorcycle. My MGA runs M5’s.

N5 is the recomended plug on many plug charts for the parallel port E 750....
the improved chamber turbulence can use a hotter plug...as said by John Healy..
These are NGK 7's out of my 79 T140 D from a fast ride...You can just see the grond strap discoloration indicating just a touch cold... This engine has 9.2 static compression, 100 degree intake lobe center an 32mm Mikuni TM carbs....

Hi Tony; I used the NGK BP6ES as main plugs for about 10000km (plus other 3000 testing the B6; BP7; B7; B8) for the dual plug head with bathtub chambers; 8.6:1; 2 Mikuni 32 VM with all the internal new and following the set up that Kevin sent me (Triumph/Mikuni carbs)
My bikes are transportation; the commutes are all on the road and the engine is firing for about half and hour to 3 1/2 hours without stopping at mid range strong speed (freeway constant speed)
NEVER had the plugs like that. More like between brown/grey and sooty

Fernando, the plugs in the photo have about 100 miles on them, non ethanol fuel. They do tend to darken a bit with more miles but not fluffy black...With new plugs after a few miles, the ground strap should show a noticable lighter color for 2/3 of it's length if the spark plug heat range is reasonably correct .You are using a projected tip BP type plug...generally, you can run a hotter heat range because the projected tip run cooler....Example, I used a Champion N7Y projected tip in a 650 Triumph for many years instead of a N3. This engine had 10-1 compression...Never had plug fouling in the city and no problems with fast riding..So maybe try the BP7 and check it after 15 miles...But be careful with projected tips because a higher lift cam may cause the valve to hit the spark plug electrode..
This plug from my BSA A10 is just slightly cold and shows the often subtle color change on the ground electrode