| Author | Message | ||
     Kenb |
i don't quite understand why the big end bearing on the harley twin has to be a roller bearing. why wouldn't a plain bearing journal work with the knife and fork con rod layout ? most v8s have 2 rods per journal. i would think a solid forged crank would be much more durable than the pressed together design. i know there is a company called sputhe that makes a plain journal v-twin but the rods are side by side not knife and fork. does the complexity of the forked rod and endcaps outweigh any advantages ? | ||
| Diablobrian |
High torque loads at start when combined with a dry sump will wipe plain bearings in short order. | ||
| Whodom |
Ken/Diablo- there actually was an aftermarket plain bearing replacement sold for Sportsters back in the early 1970's. I used to subscribe to some chopper rag when I was a kid, and I remember they did an article on it. The mag claimed vibration was substantially reduced, which seems to have been the only benefit claimed for it. I'd guess Brian's analysis is on the money; I don't think anyone produces anything like that now. Edit- on second thought, I don't agree with Brian's analysis. Why is a dry sump engine worse than a wet sump in this regard? In either case, there is no oil flow to the bearings until the crank starts turning. The bearings in a wet sump engine are not submerged in oil unless you've got WAY too much oil in the crankcase. There's undoubtedly some reason that roller bearings are preferred for this application, but dry sump/high starting loads are not it. Those factors apply to lots of engines that successfully use plain bearings. (Message edited by whodom on March 15, 2006) |
