Thanks for the replies.
There is a cover on the LHS that can be removed and shows the chain and sprocket, the other side of the 'wall' from the bevel gears and that is turning with the engine, but the impeller doesn't. I know from it's history that this low mileage engine has eaten one of the nylon gears in the past, so I'm reasonably sure that it will be buggered. I was posting in the unrealistic hope that someone could suggest an easy way to do the job without taking the head off, but I am as certain as I can be that I have no option really. She does smoke a tiny bit, so I'll examine the guides while she's apart and at least change the valve stem seals. I'll also measure the bores while I'm at it. I know the bike had new rings when she last ate and spat out the bevel gear, which might suggest she drank a bit of oil then. Maybe time for a rebore. I'm reluctant to pull the barrels though, as it looks like as though it would be a right bastard of a job refitting them. I have to date managed to avoid the fun of fitting a six cylinder block
Were the lump not so fecking heavy I would pull the whole lump out, powder coat the frame and paint the engine ... but it is
