Planning for reserve capacity on my cross country trip. What is the typical highway milage of a mid-teens 2 3/4?
A veteran 2 3/4 in good mechanical order has a touring speed of about 25mph, and if the terrain is not too hilly you could plan on maybe 80 mpg. Here the "g" is an imperial gallon, 4.54 litres. If you ride the bike at Canonball speeds it will blow up in the first 80 miles, so you won't need to worry about extra fuel.
Leon
My son manages to run ours out of fuel regularly - assume about 80-100kms
Our 1913 one seems to manage about 75 mpg. I used to carry a 2 gallon Pratts petrol can on the carrier (seemed appropriate) but some lovely woman stole it. She shot up an alleyway and disappeared clutching it. Is anything safe?
Thanks all...in the limited amount I had run it I didn't get a mileage check. I am going through the motor (and spare) machining new parts for improved performance and reliability. I hope to coax a cruising speed of 40mph out of her and also avoid blowing up in the first 80 miles. Wish me luck.
The "touring speed" to win the Isle of Man TT in 1914 was 49 mph.
Leon
Agreed - 40mph would be very optimistic on a 2 3/4hp for any amount of time. I can sit on around 40mph on the 3 1/2hp, but around 35mph is kinder.
Hi Steve,
I can confirm that my 2¾ (1913 TT model) returns about 80-85 mpg on the Pioneer Run and is capable of about 60mph in 'level flight'. The engine was fitted with modified postwar pistons some time back in the 1970's. Other than that, and a big cam, the engine appears to be pretty standard and has now done thousands of miles in the hands of it's various owners (I have the full history of the bike). The main criteria when rebuilding the engine is not to over-engineer it! Being a splash fed oiling system, the bigends need enough slack to let the oil in (say 3thou clearance) and pay particular attention to getting the bronze shells correctly fitted so that they are trapped by the keep plates while the conrod cap seats properly on the end of the rod. If the cap (and keep plates) is just sitting on the ends of the shell bearing, it will eventually work loose due to the different rate of expansion of the bronze.
When you have the bike up and running - and bedded in, don't be afraid to give the engine it's head. The 2¾ engine is a very free revving unit and is much happier just buzzing along than being made to slog.
Regards,
Eddie.
Thanks everyone...Eddie that is a ray of optimism I needed. I was thinking 2 thou on the slop but sounds like I can be even sloppier. :-). I will be getting CNC engineered aluminum pistons and concave H beam style con rods for better strength. Once I know they are working and reliable I will be happy to share the supplier and engineering specs with any who may need them.
Cheers!