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[Thack]

Jojje and Norm: no disrespect to either of you, but I'm extremely sceptical that the "smoother at high revs and idles better" says anything at all about the big end!



After all, that experienced mechanic said there was nothing wrong with it. Secondly, "smoother... and idles better" are totally subjective judgements and could be as much psychological and real. Thirdly, I've never, ever, heard a claim that a new big end can improve the idle! And of course the smoother could just be because numerous things are subtly different after an engine has been out of the frame and back in again.



No, from the account Jojje gave us, it sounds like an unnecessary replacement to me.



Sorry, and I truly don't mean to disrespect anyone. I just can't ignore what my judgement is telling me.

[Thack]

Sorry - " ...as much psychological AS real"

[Norm]

Thack at 40,000ks it needed replacing, I only know of one that had those ks on it, and new main bearings means it will run smoother and probably the crank was assembled with more care, all little things which help

[Thack]

OK, so just based on mileage, like is customary for various other engine components. Fair comment.

[Jojje]

Thack, you are absolutely right!
In my opinion, the fact that my crankshaft was carefully assembled by a very experienced mechanic made all the difference. Of course, main bearings were renewed also, but nothing was wrong with the old ones either.
Concerning idle speed, my judgement is not purely subjective but based on the readings of an electronic Smiths tachometer according to which the engine can idle smoothly as low as 600 revs, previously 900. To me it says: better balance and maybe less friction. After rebuild I even had to fit a smaller idle jet as the idle was too high.