Or you could 'soup up' your R65 motor. There are various ways to do this but most tuners that make a living from this sort of thing keep their cards close to their chest. Some overbore to suit a new light weight piston, some also also skim the heads to increase the compression ratio, and also gas flow the heads. All recomend mikuni's and a cam change.
You also have to start with a post 81 R65 motor for the capacity hike to 800cc and above as the earlier engine, with the iron bores, heavy flywheel, smaller valves is not as good a starting point. You cannot overbore the iron barrels too much or you'll end up with a pile of large washers. The post 81 engine is also significantly lighter - when you take these differences into account (and the weight difference between a valeo and a bosch starter motor is also removed from the equasion). And I am also told that the oilways for the post 81 cranks are improved?
There are many out there who repeat the falacy that an R65 motor cannot take a capacity hike or tune up, but it is not true - the crank might be different, but it is at least as strong as that in the R100 or R80.
I will however admit it would be easier all round to slip in an R100 motor instead, but, as already mentioned, you will have to fabricate/adapt a new exhaust to fit....
Many people who are looking for performance hikes, would start with an R100 motor, because it is easier and the power gains are bigger. But I like the more compact nature (width wise) and the reviness of the R65 motor, I just cannot justify spending the sort of money required to tune it up. Plus my motor is a 1979 motor with 100+ thousand miles on it.
But I have found 3 different tuners in the south of england who have tuned R65's before, each has their own idea of how to go about it. And each of them have very good reputations to uphold. But they are looking for business and are not going to give their tricks away for free.
Steve Hawkins
