I should have added in my OP that this all started about two weeks ago but I didn't want to jump straight on the forum for fear of letting my frustration make me post inappropriate, over-emotive disparaging comments.

So a big thanks to Kev for all the "behind-the-scene" advice and being a soundboard.


@Bond: Thanks for the link. I did think about another engine but I have always been put off second hand engines for fear of the unknown. As my engine is in bits I can see what great condition the gearbox and cylinder is. Mind you at �200 it's bloody tempting - pity it's a bit of a trek from me. Interesting that there has been no bids on it though???

@66T: Good call. I racked my brain when this first happened for all possibilities and one of my thoughts was to get the water pump assembly pressure tested for that very reason. I left it hung up over night with coolant in it to see if it leaked at all. However, there was no sign of water elsewhere or emulsification of the oil. In any case when running I would have thought the great pressure in the crankcase would force oil into the coolant but I didn't see any signs of that. Can't really rule it out though as a possibility so will change the seal anyway. Afterall, the bike has done 91,000 miles.

Clearly, moisture has got in from somewhere but there is absolutely no corrosion anywhere else in the engine which made me wonder immediately about dissimilar metals and galvanic reaction between the crankshaft, bearing, drive gears, washer and woodruff key?? Surely can't be the case though otherwise there would be horror stories all over the interwebbynet.

I can only put the whole thing down to a series of unfortunate circumstances: condensation in engine (hot engine/cold garage at night) and not getting the engine to warm up quick enough in the morning due to taking too long to allow the oil to distribute before opening up the throttle and/or constantly trying to max out on fuel efficiency by chuffing along in highish gear on barely open throttle - for most of it's 91,000 miles.

If you didn't see/realise the previous link you can see pictures of the corrosion here.

Anyway, got a new bearing in the fridge that should be chilled by now so will soon find out if it is enough to remove the excessive clearance - probably not!