O-rings fitted to the tops and bottoms of the intake and exhaust pushrod tubes are available under two part numbers:
The 70-7310 and 71-1283 o-rings have exactly the same dimensions. The only difference between them is the material of which they are made. The 71-1283 o-rings were more resistant to high temperatures and were introduced in 1971 to replace the 70-7310 rings at the tops of the intake and exhaust PRTs.
Triumph supplied the 71-1283 in two different materials. The earlier ones were red and performed very poorly. Later, the 71-1283 o-rings became available in Viton, which stands up to high temps much better.
Therefore, a sensible upgrade for all the 1969-1972 650 models is to fit Viton 71-1283 o-rings to both the tops and bottoms of the intake and exhaust pushrod tubes.
For more information, see "Pushrod Tube O-Rings" in "The Bonnie Ref".
