Thats a decent point Limy but "jobs more trouble than its worth" is pretty much the story of my life. Right back to when I was properly gainfully(???) employed by MoD as a Scientist / R&D engineer.Seriusly, I wouldn't touch it, that's a specialist machining job for those who have the kit and fixturs etc etc, plus it will have to be balanced.
While Iunderstand your interest and helping a mate tc etc, some jobs are more trouble than they're worth
Another thought, has the crank to be machined been crack tested, we all know how BMWs get treated n the UK and some of the mechanics ar little better - my ex neighbours - the engine shop used to avoid them when ever they could.
Okay Clive I get your point, but having lived 5 yds from an engine rebuilders for over 20 years with a very good view of their yard etc, the way I've seen so many engine parts handled is nigh unbelievable, ........... and while your ''source '' may have handled it properly - you don't know how many animals have been before him.Thats a decent point Limy but "jobs more trouble than its worth" is pretty much the story of my life. Right back to when I was properly gainfully(???) employed by MoD as a Scientist / R&D engineer.
Fixture to mill so the sides can be taken off is straightforward, basically four half bearings and caps on posts correctly arranged on a baseplate.
Having slept on it doing the sides of the webs is probably best done by following a template fixed across the lathe bed, flip over for the other side. Pair of round nosed inset tools on left and right offset holders should handle the interrupted cut easily if I take it steady. Setting the template up still needs some thought but nothing apparently insurmountable.
The crank to be done has got several racing seasons under its belt so I figure that if it was gonna break it would have done by now. Especially as lots of balancing metal removal has been done on the front three cylinder cranks suggesting the original forging was way out. Lightening ought to give the centre main bearing an easier life as thats where all the forces resolve. If I were building a racer I'd have looked for a more even crank to start with.
Intrigued by the idea of using a grinder to shift most of the metal quickly. Not something I'd risk. It seems very hard to ensure equal amounts of metal are taken off each web. Setting up in the lathe afterwards to clean up and equalise things looks to be difficult too as the initial grading will surely have taken out everything that can be used for reference.
No, but we have a problem with streets turning into deerEG I suppose in your country people only drive on the Wong side of the road.
yes, but if were possible to lubricate the engine with a permanant non-liquid lube, the engine would likely overheat. You could argue that in a race motor, the primary role of oil is cooling and lube is probably secondary. Crank splash and/or squirters take a lot of the heat from the piston via the back side. Change the oil dynamics and you change the cooling."Even if it's dry sump, there's a hefty wall of oil flinging off the crank, which causes a ton of drag. Much more than you would think. "
Story is, if you have a motor with a view port on the side, and watch while it's running, the crank is pretty much obscured by an oil-colored football churning around in there.
They don't work well. No roller bearing crank works well at high rpm. (Jeff Bratton made a career out of doing nothing but grand prix two-stroke cranks, $$$, and they only had rollers because they had to, being two-strokes and all). There is too much inertia involved; speeding up and slowing down the rollers every revolution is hell on the cages and rollers skidding and races scuffing ... it's something that sounds good but works bad. XR's that will run all season at 8,000 last two races at 9. There was only one guy I can think of rebuilding the roller bearing hirth porsche cranks and he charged a fortune (rightfully so). It's not a good idea.BMW motorbikes with pressed-up cranks and roller bearing bottom ends have clearances around a couple of tenths to work well.
I suspect that a pressed-together, a shorter crank might be easier to manufacture and maintain accuracy then a longer crank like a 4 Cylinder or 6 cylinder.
Which was why the racing 2 strokes of the 70s (Yam TZ , Kawa etc ) ate cranks, (and they would only stand so many rebuilds before they'd fall to bits and scrap an entire engine)It's not about the construction. XR's are the simplest possible, two forged flywheels with integral shafts, a pin and a rodset. The problem is that the speed of the rod bearing is not constant as the crank revolves. In fact, the rod bearing speeds up and slows down continuously as the crank rotates. Look at an animation of the rod as the crank revolves and you can see what's going on.
That's okay at slow speeds but when you wick it up, the inertia becomes tremendous. Cages have to be steel (but that makes them heavier which is going opposite to the way you want), you want light rollers but that makes them skid easier and you need more if they are smaller; everything you do to make it better actually makes it worse, the whole setup is just bad at high rpm. Plain bearings kick butt for this.