The engine in my project also goes a long way back. It was originally developed by a company called Weslake Research & Development which was founded by Harry Weslake. The company was involved in mainly cylinder head designs for high performance engines like Jaguar, Ford GT 40 and the Rolls Royce Merlin aircraft engines. In the 1970’s, the company developed and manufactured a parallel twin cylinder engine for motorcycle racing use. The design was very much the same as the ones made by BSA, Matchless, Norton and Triumph
in that the twin cylinders are in parallel, and the crankshaft resting in a ball/roller bearing in each one of the vertically split crankcases. A very simple and strong design. As Weslake were cylinder head specialists, this is where we see a deviation from the traditional designs. Weslake used two camshafts, located in the crankcases behind and in front of the cylinder block and the cylinder head sports 4 valves per cylinder, operated by push rods and rocker arms.
I can recall a chap called George O’Dell who used the Weslake in his racing sidecar in the 70’s. George was a 4 stroke fanatic and drove like an accident just waiting to happen but he still could not keep up with the 2 strokes of the time. He finally gave up and switched to a German ( Berlin ) 2 stroke racing boat engine made by Dieter König. After that the Weslake disappeared from my vision and only turned up again in classic motorcycle racing.
The whole business was picked up by Dave Nourish who ran it until January 2015 when he decided to retire early at the age of 82. Dave’s business was called Nourish Racing Engines and from this their current name NRE comes. I spoke to Dave a couple of years back about buying an engine and I got him to mail me a price list. I asked him if he had an email address and his reply was “no I don’t believe in those things”. Well, nothing came of this at that time and only early this year when I read about Chris Bushell having bought the business from Dave did my interest wake up again. At least Chris has an email address but he is not very efficient at answering to my queries. I guess he is busy organising Nourish Engineering as he now calls the company.
I had a hard time choosing between a replica Norton 750 and the Weslake, sorry NRE, but finally decided that the NRE must have a potential for being the faster engine, simply because of its 4-valve design which should be 10-20% “better” than the Norton’s 2 valves. And, I wanted to do something different than the “big boys”, read NYC Norton, Minnovation Racing, Steve Maney, JS Motorsport et cetera. That I will not be able to use all that power is another story. The knowledge that it is there is enough.
One hard decision had to be made immediately and that was which bore and stroke I wanted. Chris gave me 4 alternatives for a 750 motor and they were:
73 mm 88,5mm
76 mm 82 mm
77,8 mm 77,5 mm
80,5 mm 72,6 mm
My old Norton sidecar engine was a standard unit with an 89 mm stroke. It would rev to 7200 rpm which translates to a piston speed of 21,36 meters / second. In the days when these engines were originally made, 20 meters / second was, as a rule of thumb, a number that one should keep as a maximum. Now, as maximum power is a function of, among other things, revolutions per minute (rpm) I wanted to give my NRE an additional advantage of being able to pull more rpm’s than the Norton. After much deliberations I settled on the 77,8 times 77,5 millimeter dimensions. At least the 77,5 mm would allow 8000 rpm and still be just below 20 m/s piston speed. And, I could miss a gear change and over rev by 500 and still not break piston rings. POWER & RELIABILITY is the name of the game. That translates into being the fastest on a straight line, slow in the corners and making it all through the race. There is no use in being the fastest and having to retire halfway through the race, or finishing all races in a season but always as number 10.
Next decision was carburettor size, I guess because Chris needed to finish the inlet ports to fit the carb adapters. He told me that the ports would be 34 mm and the adapters could open up to 36. More about this under “CARBURETTORS”. I think I made a very good but maybe unconventional decision.
Compression ratio is going to be somewhere around 10,5 – 11,00, Ignition has been selected by Chris to be RTD and as for exhaust dimensions it looks like I have to resort to my engineering background to calculate something to suit an 8000 rpm maximum output. The good thing with this German club Grab the Flag, whose races I intend to take part in, allows unrestricted exhaust systems. Again, this means maximum possible power, maximum possible noise and maximum possible fun.
The “old” NRE engines had a cast iron barrel but Chris has now developed an aluminium unit that is lighter and can dissipate more heat = theoretically more horsepower. That is what I am getting. We have had no time to discuss camshaft profiles, influencing valve lift, opening and closing timing, overlap degrees, valve acceleration, valve jerks ( change in valve acceleration rate), These are all things that I know about and I am afraid Chris not ( too much). On the other hand I don’t know a thing about e.g. wine, does not matter red or white, but that equals out. Although I find that at dinner parties there are fewer people interested in discussing valve timing than a red wine bouquet. Such is life. Maybe Chris understands both. However, as he is a Ducatisti ( a fan of Ducati motorcycles ) I suspect that he best understands Ducati’s and Barolo’s. Which is a whole lot better than understanding camshafts only.
Another feature that we are getting is the 90 degree crankshaft. Japanese have always favoured a 180 degree layout while the British have always opted for a 360 degree layout. In the 180 degree engines, one piston moves up and the other down, with a 180 degree separation. In a 360 degree layout, both pistons move up and down simultaneously. Primarily, the different designs are aimed at reducing vibration. However, late research in Formula 1 engine design has revealed that a certain cylinder firing sequence, or rather spacing, results in a different power profile which again means getting away quicker from where one is to where one wants to be. The 90 degree formula of the NRE engine is getting us the best of two worlds, a minimum of vibration and a kick in the back that it will take a very determined horse to copy.