ET: Engine (Twin) oil holes in Crank pin?
- Thread starter Vincent Brake
- Start date
I think you are right. Hardened flywheels so that they do not require the hardened washers each side of the crank pin and they do not distort if it is necessary to remove and then replace the crankpin., The extra holes not for balancing but to allow the alignment of the flywheels when pressing in the crankpin. Same thickness of flywheels all over for less machining and to allow plenty of metal to take the pressed in crankpin. I always thought it was a very nice design.
You don´t really need hardened cranks - like in 60 HRC hardness, just perfectly machined conrods and crankpins, no tapers or too tight clearances in bearings permitted. Nobody does hardened cranks since decades and most have no hardened washers both sides of conrod. High tensile cranks are a must anyway, so no washers a necessity. Twostrokes may be different with washers from bronce etc . Yes, holes in each crank half at opposite from crankpin will help for reducing bashing time after pressing the lot up. But even so the long distance at start of press action will not produce a good alignment even with tungsten rods. Even with my jig and 20 mm pins - I think - it ended up with 0,06 mm runout on shafts (2 thou ) with both cranks that I then bettered for 0.01 - 0.01.5 on the metric indicator in the YT clip, no imperial type with half thou increments !
As to full circle or part chopped crankwebs: My view is I don´t see any benefit from them. You either get less mass and poorer idle speeds - or you up the weight for having same effect . But Moto Guzzi got it right, they had an external flywheel with waisted inner diameter and a fat "rim" at outer radius. So you had a nice mass for idle and startoff from standstill BUT a comparatively light flywheel at same time. A flywheel with same thickness all over the complete wheel and same mass momentum (?) will be smaller but very heavy all out. Not a good and purposeful idea !
Back to press jigs: I tried to go the shortest way in order to have both mainshafts at same aligned positions without having faith in other holes that might be there for positioning or not at all. So the logic: Do two plates doweled by long pins and bore mainshaft holes at same setting. No way to be way off then - but accept not absolute perfection due to long distances to go under the press. Same plates can be adapted to other mainshafts by boring or bushing as required. And often you need some plates for your press anyway so not much money waisted. Yes, when I was younger , with BMW boxer twins you got some more facts to take care of: Crankpins have to be 180 degrees spread with two pins pressed in separately. Only solution have exact scribes on crank halves at zero and 180 degrees and a good flatsided square on the press table for correcting positions before you´ll be too late and it is a messy job later.
Vic
As to full circle or part chopped crankwebs: My view is I don´t see any benefit from them. You either get less mass and poorer idle speeds - or you up the weight for having same effect . But Moto Guzzi got it right, they had an external flywheel with waisted inner diameter and a fat "rim" at outer radius. So you had a nice mass for idle and startoff from standstill BUT a comparatively light flywheel at same time. A flywheel with same thickness all over the complete wheel and same mass momentum (?) will be smaller but very heavy all out. Not a good and purposeful idea !
Back to press jigs: I tried to go the shortest way in order to have both mainshafts at same aligned positions without having faith in other holes that might be there for positioning or not at all. So the logic: Do two plates doweled by long pins and bore mainshaft holes at same setting. No way to be way off then - but accept not absolute perfection due to long distances to go under the press. Same plates can be adapted to other mainshafts by boring or bushing as required. And often you need some plates for your press anyway so not much money waisted. Yes, when I was younger , with BMW boxer twins you got some more facts to take care of: Crankpins have to be 180 degrees spread with two pins pressed in separately. Only solution have exact scribes on crank halves at zero and 180 degrees and a good flatsided square on the press table for correcting positions before you´ll be too late and it is a messy job later.
Vic
Thanks for the info Vic, Its certainly not an easy one.......well without these special jigs for sure.......I'm more than happy to assemble stock Vin cranks and true up, but the heavy press fit parrallel pin set up looks difficult.......Cheers.