Engine Bushings

[Jordan]

I've owned 6 Ducati widecase singles, all second hand. Interestingly, every one showed wear and scoring of the crankshaft end bush. I guess the crank whips around a bit out there.
Even though left that way, I never had a problem with lack of oiling. It seems the low pressure system only needs a "restriction" rather than a tight seal, to work properly.

Jordan

[Paddy]

I agree with Stewart. Even bushes like the kick-start shaft bush that does not have a constant rotating part need to be within a tolerance, once they become slack, load is no longer spread evenly and often the supporting web in the crankcase will break, that is why i recommend oillite bearings in these positions. I have two examples of fractured cases at the kick-start bush.

[Jordan]

Oilite is an interesting choice for the kickstart bush material. I'm not sure what the advantage is, as it's not as strong as solid bronze, which gets lubricated by engine oil anyway. There's an oilite type product based on iron rather than bronze, that is stronger, if you need an impregnated lubricant type bushing.
I agree that a nice fit is to be preferred. A less than perfect crankshaft end bush isn't fatal though, which is good because they are always worn.

Jordan

[Paddy]

I dont think strength is an issue with a kickstart bush but it does sit high in the engine and is not oil fed., of course when your little beauty starts first time its not an issue but after ten kicks, a cup of tea and a fag its probably as dry as a bone and will wear quickly. a crankshaft end bush is a different matter as its oil fed anyway.

[gregwils]

Thanks all for a very thorough and beneficial discussion of the subject. You helped me and everyone down the line.

[StewartD]

Jordan,

I agree, all the ones I've seen seem to be worn, sloppy and scored. Also I'm sure there is a fair bit of deflection at the crank (timing side) half shaft end. The cyclical loading of the cam drive would result in a fluctuating separation forces at the bevel gears. The Crank bevel gear is quite 'overhung' in relation to the crank main bearings. This overhung distance results in a higher bending moment on the half shaft and therefore greater deflection.
Any amount of flex in the crankshaft webs and crankpin would result in a proportionate amount of movement at the half shaft end.

Paddy,

Thanks for the photo and comments about the kickstart weakness/fractured cases. I wasn't aware of this problem.

I've got a Mach 1 with the problematic kick start crank. Kick starting this is always a fraught exercise due to the lack of effective swing. My old 450 was always an easier starter, even though the force required was much greater. I might revert to push starting the Mach 1.


Cheers,

Stewart D