Bsa crank bushing size?

[DerekAnderson8]

How do you calculate the size of bush reqd for crankshaft plain bush. I have measured the crank at 1.475" but confused as to what size of bush i will need, i know it has to be reamed to give a 0.015 clearance.

thanks

derek

[JulianS]

This page from the A65 manual may assist.

You do need to check that the journal is perfectly circular.

[DerekAnderson8]

Thanks Julian.

I have ordered a ready made to size on ebay!

will let you know how i get on.

[MALCOLM.JOHNSON]

I will be very surprised that your timing side crank shaft journal is both truly round and truly cylindrical, commonly known as ovality and taper respectively. However if it is within wear limits (which involves measuring at the front of the journal across diameters at 90 degrees to each other and then the same at the rear), that is good, but you will still find that your "ordered to size" bush will still arrive undersize to enable it to be "line bored" to size after fitting. The actual fitting process will distort and crush the hole very slightly, which is why they bored after fitting and that process also ensures that not only is the bush of correct size but also both main bearings line up exactly. I suggest that you locate an engineer in your area to fit and size the bearing for you. It is a job that you simply cannot buy the part and expect it to fit correctly.

[DerekAnderson8]

a local motor engineer?

i don't think there are too many left now!

Bush is supplied undersized and needs honed to fit correctly.

[JulianS]

I think the point to consider is if you journal is within limits of ovility to give proper fit in the bush.

[DerekAnderson8]

Update after a few months, the bush purchased was undersized as expected and after a bit of work on the lathe (ok i know its not textbook but needs must) I finally have the bike running again!

The wet sumping has almost gone completely about 20ml after a month has seeped through. The engine has a lot less vibration than before and starts a lot easier.

Time will tell if its going to last but seems ok so far.