Author Topic: polished B40 crank cases  (Read 148 times)

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polished B40 crank cases
« on: 08 November, 2017, 14:34:39 »
Hi again chaps.
                      Being a bit strange, I've always been slightly niggled by the sight of rough cast crank cases sandwiched between bright shiny primary drive and timing side covers.
Can anybody out there think of a good reason not to polish them?
I presume the rough cast will cool slightly better than a polished surface, but I can't imagine that being a problem at all.
There's a fair amount of material to remove, but the theory applied to con rods etc is that the result is stronger, due to the absence of stress nodes, and that the raised bits do nothing for rigidity.
My guess is that the only logical objection left is that the castings may have imperfections below the surface, but that seems unlikely.
Of course there's always keeping them shiny to consider, but finishes like Zoop seem to work well in other places and it should actually be easier to clean than the rough surface, as there's no key for muck to stick to.


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Re: polished B40 crank cases
« Reply #1 on: 10 November, 2017, 07:37:24 »
My guess is that the extra work of polishing the main case, and the possibility that some areas would be near impossible to polish,
would be against the idea, from the factories point of view.
Should be no problem if you do it yourself, but it will be hard work.


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Re: polished B40 crank cases
« Reply #2 on: 10 November, 2017, 09:56:34 »
As Mick says it will be hard work. If you do it be careful not to remove any of the engine number. Beware of thinning the castings which could weaken them.

I dont think there is a strength issue with B40 cases as standard.

If you seek to sell the bike sometime in the future you may find prospective buyers would not like the departure from standard resulting in a lower value.


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Re: polished B40 crank cases
« Reply #3 on: 10 November, 2017, 11:31:55 »
I did my top end and carb, it took a long time and sore fingers.
My bike is a 1958 A7SS