coseng wrote: ↑
Tue Dec 17, 2019 11:12 pm
If that was a picture of a Norton or Triumph engine you would be correct but it is a Japanese engine, they know how to design one! A neighbor is involved in racing vintage British motorcycles so I see too many 360 twins to keep track of.
The oil system you showed is a drip feed. It was also used by Rotax in their 4 stroke singles (crankcase donor for my existing engine) to oil the rod big end roller bearing. The oil drips out of the main bearing, is caught in a hat-brim shaped oil collector on the crank cheek, and then the centrifugal force from the crank spits it out to the rod big end, so not exactly pressure fed.
https://www.cosentinoengineering.com/wp ... -crank.jpg
Used in a 2T engine I would think the oil dripping from the big end bearing would throw off the premix ratio (and is also not premix oil).
Actually, no it isn't. The diagram I posted shows an 'injectolube' system in which the oil is provided
by a crankshaft driven pump, & it is quantitatively metered by a throttle-position quadrant (it may
also be pumped via discrete lines to 'pre-mix' with the fuel just prior to delivery), while at the crank,
the oil is slung by rotational force to flow through the crank-pin drillings & directly feed the big-end.
(In some multi-cylinder applications the pressure pulse from adjacent crankcases was also utilized
to redirect excess drip-pooled oil through reed-valves in each 'sump', via oil galleries & back to
the main bearings of the next cylinder, also).
As for the Yamaha, it was their 1st attempt at selling a big 4-stroke bike, so they naturally used the experience they had with 2-stroke rolling element crankshafts, but their XS 650 was way overweight, didn't offer any power/performance advantage over the British twins,
& when raced in hard-tuned form, it also proved a tad fragile, too.
Kawasaki & Suzuki both did better with their early rolling-element crankshaft 4-stroke fours,
but that's a bit more of a subject drift...