BEEFY BENELLI & BEESA BEARINGS
I read the report on the smart looking Benelli Tornado 650S with interest. To avoid confusion, I would suggest that a bore of 84mm and stroke of 58mm would be described as an over-square engine configuration and not under-square as is stated.
As Paul Miles says, a smart, well handling motorcycle is as relevant now as then. But at 465lb dry, isn’t the Benelli a bit lardy for a 650 twin when compared to a late 1960s unit Bonneville at under 400lbs? If a motorcycle looks right, sometimes it is right. But look again at the Benelli’s high centre of gravity with the disjointed appearance of the engine sitting tall in the frame... quite a bit of that weight is well above the wheel spindles. Although I must admit the steering geometry looks about right to the human eye for straight line stability. Not for me though, those 1970s and 80s Italian big twins. These later designs lost desirable Italian style and flair when compared to 1950s and early 60s Latin single cylinder lightweights.
There was an enthusiastic letter from Barry Huron about the weak timing side bearing on the A65 which was I believe a bigger diameter than on the A10. If my memory is accurate, when Mr Hopwood redesigned the Herbert Perkins A7, he would have preferred a ball journal on the timing side, but production costs and accountants put paid to that. With similar plain timing side configurations on the C11, C12, C15 and the Terrier and Cubs, the amount of development and strengthening needed over several years to make these engines strong and reliable and customer proof is now legend.
Again, if my memory is correct, Mr Hopwood got his timing side ball race journal in the similar Dominator engine by eliminating the manufacture of some expensive timing gears, substituting cheaper to make timing chains and sprockets.
The nearside big end on the A65 or A10 will nearly always suffer due to the loss of oil pressure from a worn main bush. It’s right at the end of the oil supply chain. Frictional losses when fluid is pushed through tubes and holes affect oil supply. Does the water at the end of your garden hose exude as quickly as at your sink tap? Most probably not, solely because of frictional losses within the hose.
I’m not sure about the A65, but the A10 has a small hole in the nearside conrod just above the big end eye. This should face toward the centre of the engine to chuck a little more oil up the nearside bore to avoid piston seizures. So a little less oil and more leakage for the nearside big end shells. Shells of course rely on continuous oil flow and pressure. But in slow-revving engines, a plain bush or shell bearing can survive happily on splash feed, as in some Panthers and many industrial engines. When BSA went racing they had many failures in long distance events. At least one factory employee was already privately developing the timing side needle roller bearing to counteract this hard use.
Yes, regular oil changes are vital to a clean sludge trap. Modern mineral multigrade oils with about half a pint of additives in each gallon have the phenomenon of suspending muck within the oil. This comes out in an oil change. Cheap mono-grades without proper additives leave all that muck behind in the engine, but the oil will drain out looking relatively clean and cheerful.
One final question: when does a roller bearing become a needle roller bearing? Answer: when the length of the roller is four or more times the diameter of said roller. Then it is termed a needle bearing. Dave Blanchard, member 4809