Project BMW
Project BMW – to pull together as one, one must first know the individual elements. The frame needs painting, the gearbox and final drive checking, and the engine stripping, so Matt asks the question – just how easy is it to pull a boxer apart?
We strip the bike in preparation for painting the frame and we have a look inside the engine. What will we find?
Ireally missed my calling as a scrap dealer. I seem to be able to build such momentum when stripping bikes, engines, cars, even houses – but said momentum falters slightly when fixing or servicing parts, then fails completely when it is time to put it all back together.
Any scrapyard owners want an aged apprentice?
The two days I'd set aside for stripping my R100(R)S started badly – how the hell do you hold this thing upright? Being tight and not exactly a torch bearer of over-the-top health and safety, I found some pallets to rest the rear of the big unit on, with the centrestand doing the rest – that'd do until I got further. Oils in the final drive, gearbox and engine were drained.
Easy goals are a good way to feed confidence, so I got the rear wheel off – which is delightfully easy on a boxer, but which also shifted the weight balance and ruined my pallet/ centrestand platform and I had to bring in my scissor jack that Nev bought me.
Moving on, we could then remove the shocks, which let the swing arm drop. I'd wanted to keep the original shocks as I like the preload adjuster, but when undone at the top the cast aluminium top had corroded – check yours, dear owners!
With subframe unbolted, things progressed with the rear mudguard, lights (handy plug in the loom for that) and battery box. The box gets a lot of crud in this area and allied to the odd acid spillage needs some TLC, as well as new rubber-sandwiched mount bolts; but I may make a shiny alloy one if I can find out if a smaller battery like the post '85 one will be man enough for the older engine/ heavier flywheel/ancient electrics. It would save weight, and add a little space for, well, stuff…
Next was the relays, coils and electrical ‘boxes' littered along the top frame rail and finally the loom, which was most stubborn to come out from around the headstock. I cleaned most parts up as I took them off and most look okay externally, with the loom feeling surprisingly flexible – I should get away with that. So far, one broken bolt head, one broken shock and all else as I'd hoped. Going straight for the heat torch or impact driver helped.
The engine needs to be lifted out of the frame, so I wanted to relieve as much girth and weight as possible (sounds like my diet). Top cover off and the starter was reviled; front cover off and the alternator and points said hello. It's a wonderful feeling when all the bolts holding one piece are the same torque after more than 40 years – even if someone has been in there, they were sympathetic. Notes were taken along with photos to help the rebuild, and the whole lot blown out – alloy and steel corrosion, dirt, dead bugs et al needed removing. This is a bike, not a bug house! The swing arm wasn't as straightforward as a chain drive one, but once the propshaft is unbolted from the gearbox, it will come. It's bloody heavy, though!
Then the gearbox was unbolted and holding underneath... by now there's plenty of room behind for you to pull it out of the flywheel centre. It's heavy, but not as awkward as the swing arm.
The clutch and flywheel looked dry – so no oil leaking from the crank seal, which is good. Just lots of clutch dust, so a new plate will go in. This has the older flywheel, which is huge! You can swap for a later, lighter one, but then you alter the engine braking characteristics and I'd rather start with a bike as was designed and modify if and when I feel it will improve things, not because forum ‘experts' say that's what you must do. The pressure and friction plates came off easily, but I will need a centralising tool to refit – I hope my universal car tool will work. Flywheel face looked nice and smooth, so I saw no reason to take it off.
Notes were taken along with photos to help the rebuild, and the whole lot blown out – alloy and steel corrosion, dirt, dead bugs et al needed removing. This is a bike, not a bug house!
I haven't touched the gearbox yet; I want to have a clear bench before I do.
Not that confident, nor experienced with them, so I want to approach it at my pace. But both Motobins and Motorworks, UK BMW specialists, keep most of the parts that may have worn out in stock, including shorter first and taller fifth gears.
Right. I am now faced with a short engine in a frame – with complete exhausts fitted. Why? Because the damn things won't come off despite being soaked in penetrating oil for a week and lots of swearing. I'd bought Motobins' excellent spanner for the finned manifold nut, but there was no way either was coming off. I couldn't pull them out of the cylinder head port; they had to be swivelled. There was no option but to cut the balance pipe so each side could be moved individually. Heat it was I turned to, mindful that while I could replace the exhaust without too much expense, I did not want to damage the cylinder head. The alloy head did its best to cool quickly and disperse said heat, but after several minutes and more penetrating spray (Rock Oil Rockeeze, if you ask), a long bar placed in between the U-bend of the downpipe started small movements – hurrah!
Thankfully Father was passing as I struggled on, so with him holding the bike, more heat and more oil led to more movements. The key was not to try pulling it out but to twist the pipe in the head and break the fit/corrosion/ whatever was holding it together. It took around 20 minutes each side and I was convinced I wold break a head – but luck was smiling.
The pipes are a good fit and the constant heat/cool cycle makes things worse, allied to the fact there is little reason for them to come off, so we were disturbing 40-plus years of fit. They're reusable once I have a new balance but I fancy making my own, so let's wait and see.
After all that exercise it was lovely to sit and pull the heads and barrels off. I'd been waiting to do this to see what condition they were in, and the job was most straightforward. The hardest part was the rocker covers which, even though I knew of the ‘hidden' two 10mm nuts (in the head fins), would not budge. Soft mallet, gentle chisel and even heat – they were glued on, and it's so difficult to not round off or dent either the cover or the head. Eventually they did pop off, revealing rocker gear that looked to have the right tolerances and good, unworn faces.
The heads came off next, which looked coked up but otherwise good. Later I'd remove the valves and springs; boxers of this age don't run valve stem seals, and the guides are certainly loose to the valve stem, so new guides are ordered. These are a much tighter fit to older British bikes, so that job can go to my friends at BDK Race Engineering! I've bought new valves too – I aim to keep this bike forever. The seats looked alright, so should just need a cut.
The barrels also slid off nicely, though I removed the gudgeon circlip so I could take the piston out inside the barrel to keep everything together. These older barrels are iron, whereas the '80 onwards are alloy with iron liners and therefore lighter. Regardless, there was no tideline of rust from the piston rings and no more than minimal wear. The pistons looked first-rate, and even the rings were still within tolerance. Apart from rusty pushrod tubes, which will clean up, I am a lucky boy!
UP, OUT AND ON THE BENCH
And so it came to pass that I could pull out the bottom end from the frame... er, once I'd got the two tightly fitting threaded bars which pass through the bottom end and the frame. Number one was a good boy; number two would not come. With both nuts off I tried using spacers to pull the bar out, but I stripped the thread. Yet again, heat and a pound hammer eventually saved the day. Pulling the short engine from the frame was a doddle after that!
Once on the bench, it could be cleaned and inspected, and the sump pan removed for cleaning and checking – they can get split thanks to being low. I'd ideally strip it completely for vapour blasting, but I feel I can get it nice enough for what is planned to be a regularly used machine.
Plus, the innards are staying in. Brian, who had owned the bike since it was five years old, is happy that there was no bottom end issues. With all the signs you get from stripping a bike, I'm happy that all adds up; so the bottom end can stay together. You can get new shells and bearings, oil pump and so on – but where do you stop? I just cannot afford nor justify that. So heads and barrels will be blasted, the bottom end cleaned, heads will get the work needed; guides, cut seats and new valves, barrels will get honed and pistons will wear new rings. Everything can have new BMW gaskets – Clint and David from local dealers Lind BMW are most helpful with the older bikes.
NOW WHAT?
I'm still really pleased how the R100 broke apart. I need to keep the momentum up and purchase and fit new valves, guides, gaskets, seals and piston rings. Blast, clean and paint the heads and barrels, hone and face, then put it all back together. After that, we can renew the timing system and service items, fit a new clutch plate (and maybe new crank seals), and we should have a newly-painted frame to fit it to.
MODIFICATIONS
There are so many modifications and fitting of later parts to improve the early R100s but if I wanted a later R100 I'd buy one (er – you have one…). I want to rebuild the (R)S, use it and find which parts I wish to improve. Let's get it going, first.