The overhaul kit should be here tomorrow, I'll keep you posted
We-heey, job done. Took it for a blast just now, the brakes brake, the gears change, everything works. First ride since November, happy as a pig in shit, teeth full of bugs.
So it was the master cylinder then, gunge was preventing the piston from coming all the way back. There was some in the calipers too, but nothing like in the master cylinder. Oh, I checked the Tell-tale clearance, it was 4.2mm in mine, I checked it with a drill from the set I have sized at 0.1mm intervals (that's four thous in old money), apart from drilling holes they are often handy for measuring gaps. Happily this gap can be easily measured when the master cylinder is in position on the bike, just you try measuring the actual gap between the piston rod and the operating lever. I couldn't anyway.
Naturally more grief was to come finding the order in which the seals and washers went on the piston rod, and how they were fitted in position, there were no instructions included in the kit. Darren from Motor Works spent about half an hour with me on the phone, bless him, trying to sort it out, asking other people and he eventually found a drawing from Real OEM.com which he emailed me. The correct order is: Spring, Piston (with the two rings/seals) the plain washer, the black neoprene(?) seal with the writing facing the plain washer, and then the ring that looks like the crush ring that goes under oil filler and drain plugs on the bike. This last ring fits neatly into the recess around the edge of the black neoprene seal. The whole lot is then inserted into the master cylinder, the spring is compressed and the washers are pushed back up to the shoulder that is about a couple of centimetres inside the master cylinder.
According to Darren people then use a suitable socket in the recess and tap it with a hammer to expand the ring that looks like the crush washer, in expanding it retains the spring and piston in the cylinder. It does the same job as a circlip but without needing a groove. I couldn't find a socket that fitted so I made one in the lathe, ten minute job, if anyone wants to borrow it then it's here for you if you want it.
One rather worrying thing was that the seal was very slack on the rod, it didn't actually grip the rod at all: put it on the rod and fell it off immediately when held upside down. I can only hope that when the crush washer is nipped up and flattened then it has the effect of reducing the hole so that the shaft is gripped, but I really doubt it. It might explain the gunge I had found in my master cylinder.
Bleeding was done with little bother with the vacuum bleeding system loaned by the BMW Club, they have all the special tools needed for working on Airheads (and for all I know, perhaps for all other bikes in the range as well) whether it really needed the vacuum bleeder or not I neither knew or cared, such was my desperation to finish the job. The Tool Hire service was the reason I joined the Club, and it really is good to have the proper tools for the job.
One of the last awkward jobs was getting the ruber boot/gaiter/bellows over the output flange between the gearbox & swing arm, that was done using a tip I got here in the Airheads Section of bending bits of welding rods into hooks, thanks for that whoever it was.
One snag I found on firing up was that there was an oil-leak from one of the rocker covers, I'd stripped the thread on the central stud. I've done search, but no luck, from what I've heard it shouldn't be too difficult to do repair in-situ. How is it done, Helicoil or drill & tap oversize? I may post another thread in the hope that more people will see it. A cut-and-paste, perhaps.
Feck, that first ride was good.
it was just a short length of steel bored out to clear the piston but reaching down as far as the thin gold-coloured washer. The stack of washers were pressed down and held in position and then tapped with the hammer as in photo 4 to expand the washer. As I said elsewhere, if anybody wants to borrow it, let me know.
