How to identify motor size and type on 1966 triumph motorcycle

what alters the engine capacity is stroke length or piston diameter ( not conrod length)
what you will be checking is bearing size and conrod pin size to check for changes

the little plastic /rubber bit has come off the shut off valve ,although you have no doubt found this out by now .

http://www.pdfmotomanual.com/index.php?r=site/page&view=manuales&key=T&make=1966

Any help?

I believe that these are heat ranges. One for touring and one for city driving. The touring plugs run cooler. Someone could have put the hot plugs because of oil fouling. Another option ( I raced a 65, ) is to go with platinum plugs. More expensive but last forever and can run a hotter heat range so no fouling.

Check for a Short in that Circuit

You mentioned original engine. There are thrust bearing on the crank main bearings. If these wear out then the clutch has problems. There is a spec as to allowable forward backward movement of the crank. Press the crank pulley to the rear then press the clutch. The movement should be in thousandths.

http://www.bikebandit.com/1995-triumph-motorcycle-thunderbird-front-brake-caliper-discs/om17558sch562797/

Yes there is a washer on each bolt, size M8 stainless steel

Most oils are preferential, but don't use car or low friction special oils in your bike, and beware of detergent oils if you don't know the service history, they will break down in a bike and can dislodge accumulated crud. To be safe10/40- 20/50 Motorcycle oil for engine/ part synthetic if you like, but not a necessity sae 80s gearbox, Dot 4 clutch and prepacked branded long life coolant with integral lubricant for cooling.

Aston Martin early DBs and V8 Austin Healey Sprite 948/1275/1500 Austin Healey 3000 100-6 100-4 Austin Mini Cooper, America, Jensen Healy, Marina Buick Olds Aluminum Block V8 215 Bentley (1960's- 1987) Jaguar 3.8 Jaguar XKE 4.2, XJ6 Jaguar XKE V12, XJ12, XJS V12 Jaguar XK120/140/150 Land Rover Discovery V8 Defender V8 and others Lotus Elan, Elite , Esprit, Eclat, Europa, Seven [Caterham] MG TD TF MGA 1500, 1600 MGB [early Pre-1968] MGB [late, 68 on] MGB-GT V8, MGB V8 MGC MG midget 1275/1500 Nash Metropolitan 1500 Range Rover V8 Renault R-16 powered vehicles Rolls Royce / Bentley 1960's - 1987 Rolls Royce / Bentley Silver Cloud II and III 1959-1966 Triumph Stag Triumph Spitfire Triumph GT6 Triumph TR2,TR3 [early] Triumph TR3[late] Triumph TR4 Triumph TR6 Triumph TR250 TR5 Triumph TR8 Volvo 4cyl 1961-1984 by my online engine catalog books these calculations for a 1500 spitfire it states that these vehicle starters are applicable to the 1500 spitfire motor hope this helped