My Norton BVR 5 Valve

Hi Al

Once again I have to disagree

I have an original 69 Rickman 8 valve kitted Triumph T120 650 engined Jim Lee framed race bike. Actual capacity is 686cc.
This is the mag alloy head, rocker boxes & barrel. When I got it it ran 14 to 1 compression ratio with alcohol needles in the carbs built for formula 750 racing.
I dropped the compression ratio & set the bike up for petrol. At Snetterton a dozen years ago I ran against two T140 Bonnies with fully kitted engines Nourish z cams 12 to 1 power Max pistons flowed heads one piece cranks. My bike got out of the corners better & was even on the straights until it got into its stride where it blitzed them at the top end. Dave nourish used to say they made 6 8 bhp more than the 2 valve engine BUT the spread of power the pure ridability is just so fantastic. Totally different to my Sommerton cammed Dudley Ward tuned pre unit Bonnie engine with 12 to 1 Power Max pistons, huge valves & lightened valve gear.
If I ever get a one piece crank sorted I will run it again.

Chris

Chris

Do your race organisers do fuel checks ? I'd love your 686cc Bonneville on methanol. Are you using Puma crankcases ? If you are using a Weslake head, you might as well go the whole hog and forget about being a gentleman. One of the things we found with 650 Triumphs - as with Nortons it is often better to set them up to pull hard, rather than rev too much. With slight modification a two valve head on a 650 Triumph motor will permit more revs than the bottom end will cop. The 4 valve per cylinder set-up will probably give slightly better breathing, however I suggest that probably it's best use is combined with short stroke. I'd go 75mm.