oil in frame
 

Which models and years did triumph use the frame as an oil tank?

Thank you for any answers.

1971 onwards .

The 650's and later 750's had oil in the frame frames starting 1971 until production ceased at Meriden in 1983 and was continued on a small scale under licence by Les Harris until 1987.

So, how about any of the new models?

Most modern bikes have wet sumps. This places the engine proper several inches higher. The advertising tells us consistently this makes for better handling. I don't believe it.
Mostly these days they seem to hang the engine from the frames' backbone to avoid having any frame below the engine in order to get the sump (therefore the engine/gearbox) as low as possible. The most notable exception are BMW who raise the engine even higher to allow for higher lean angles which they can't get with a lower engine because the heads will ground. This puts the crankshaft and most of the gearbox way above the wheel spindles unlike old Brit bikes which always had the centreline of the crank well below the wheel spindles. The higher mounted engine also helped increase the driveshaft angle thereby making what was a good design over stressed. Just take a look at a 1961 Velocette and then a modern (ish) bmw 1150. There is nearly a foot (300mm in new money) difference in engine/gearbox height.