GOES ANYWHERE DOES ANYTHING
Rewinding a couple of years, a Meriden Triumph 650 twin was on the list of bikes I wanted to try. It just so happened that Chris at Venture Classics was selling a 1968 TR6P at a price I could afford. When I heard it’d had an SRM engine rebuild I was sold. Two of my bikes recently developed large, expensive engine problems so any assurance on the reliability of the mechanical components was welcome!
The TR6R is a single-carb version of the twin-carb Bonneville, or a Bonneville is a TR6R with two carbs, whichever you prefer. By the late 1960s the differences between the two were otherwise cosmetic. The paint schemes were different and the Bonnie got the best bling, but the engine internals were, as I understand it, identical, as were frames and cycle parts.
In both cases the engine is a parallel twin of 649cc with a bore and stroke of 71 by 82mm. Compression was identical too at 9:1. The TR6R output 45bhp and the T120R 50bhp, both at 6500rpm so that’s an extra 10% -- but at the back wheel or crank, I’m not sure. Interesting that these figures from the 1968 rider’s handbook are for ’straight through exhaust systems’, so both may be a slight overestimate compared to the standard, baffled road bikes.
1968 is one of the more sought-after years of unit construction. It’s late enough to have most of the development benefits of the model, but comes before production switched to the less-loved oil-in-frame in 1971.1968 is also a good year for
