BMW R1100 S
Poor Ralph. This tired old boxer wants to step out of the ring once and for all – but will Ferrand let it?
Ralph Ferrand battles this Boxer twin!
The torturous Teutonic twin with 160,000 hard miles on the clocks is back at its belligerent worst!
This bike just seems to be fighting me at every turn. Whilst I have fettled a number of members of the R1100 family in the past, I have never stripped one this far apart, and whilst I have worked on an R1100 RS that had been properly abused some years ago, I never had to strip it back as far as this one. That one was a case of sticking plasters on to keep it functioning; it only ever got serviced if something broke. This one has had a harsher master, but has been regularly serviced, which is the key to high mileage. The plan this month is to strip the remainder of the engine, remove the gearbox and clutch and see what state the key components are in.
I started by removing the engine oil pump cover and releasing the engine oil feed pipe banjo bolt and securing cap
screws. At this point BMW helpfully tell one to ‘remove complete oil pump (2) together with cooling pipe (3), and disassemble’. Well, I could loosen it a bit, but removing it wasn’t a goer at all; it simply would not come off. Why I don’t know, as it was hardly suffering from corrosion given its environment, but it would not come out even after being bombarded with a collection of the finest and most obscene Anglo-saxon oaths ever assimilated. I decided to leave it be until I split the engine cases.
I then turned my attention to the cog swapper box and clutch. This was a job I’d done before, though not on an S. With all the other R1100s you remove everything behind the gear box, i.e., the swingarm, bevel box, rear wheel, etc., and then when the lower rear sub-frame bolts are removed the sub-frame swings up and out the way, giving access to the gearbox.
The S is a very different animal and has a more traditional frame leading to superior handling over its siblings, but a more complex job to change the clutch I should imagine.
As I am stripping this bike down to its last nut and bolt, the order is somewhat less important. I was unable to take photos whilst separating the gearbox from the engine unit as all the parts were large and heavy and only having two hands was enough of a challenge, without trying to take pictures with a heavy DSLR leaving only a left hand to work with. Other than the habitual reluctance of the corroded fasteners to be removed it was reasonably straightforward. Removing a gearbox from a Beemer, as with many other components is more akin to a car. The gearbox is held on to the engine with a bell-housing and once all the bolts are removed the gearbox is pulled away from the engine.
The input or first motion shaft of the gearbox has a spline that slides into the centre of the single dry clutch plate. Once the unit was separated, I could see that the spline on the shaft was totally buggered, which meant the gearbox would need to be stripped and rebuilt. Given the number of special tools required to achieve this task and the apparent difficulty, I suggested to the bike’s owner that he entrust that job to a specialist. Likewise, the bevel box required a host of expensive special factory tools I do not have or want, so that went off to the same boys. Once stripped, the empty cases were to return to us for paint treatment. As on a car, the main clutch outer housing is bolted to the fly wheel, which came off without too big a battle. The fly wheel is bolted to a flange on the crankshaft by
five high tensile bolts that are apparently done up by an eight-foot Bavarian body builder with a 12-foot breaker bar.
They consumed a good few calories of heat from my propane torch and only parted company from their beloved crankshaft after I bullied them off with the mind-warping torque of my Aircat air impact wrench.
You may remember that in January’s issue I mentioned that one of the screws securing the ignition stator to the casing had to have the head drilled off. This month I had to remove the remains. With the stator plate carrying the delicate pick-ups and wiring I could hardly start waving gas torches about, but with the case removed and divested of anything delicate or combustible, I could start to show the fastener who is boss. It was soaked in penetrating fluid for some considerable time, which obviously didn’t work, so I broke out the propane torch yet again and heated the little sod up ’til it was bright red, but still it wouldn’t move with pliers. I removed the machine vice from the bed of my milling machine and bolted the casing to it. For maximum accuracy I milled the top of the screw flat with an end mill. I then fitted a small centre drill into the chuck of the milling head and very accurately positioned exactly in the centre of the screw and
centre, drilled it. I then used a 3.1mm twist drill to make a hole through the middle of the threaded remains. Again, I employed warmth from the propane torch to heat it all up to red hot again and then this time I fitted a professional 1/8” screw extractor into the hole and turned it with a cranked ring spanner, and this time it finally gave in and came out. I had set it
up in the mill accurately so that had it not given in I could have drilled the whole lot out and Heli-coiled it, but fortunately that wasn’t required.
Splitting the cases was comparatively straightforward, wrestling out fasteners reluctant to leave their abode of several decades. There was one M6 cap screw that would have been easy to miss inside the bell housing, but over the years I have a mantra of looking for the last screw that is hiding and often you can look around cases several times before finding the bugger; there’s always one! I saw a set of Z1000 A2 cases destroyed by a bloke who had missed one and instead of questioning why the two halves were so reluctant to part, continued adding more and more extra tightness to the separator bolt until he destroyed the cases. Remember, there’s always one hiding! Old Zed factory manuals tell you how many crankcase bolts you need to remove, which is really helpful, so if it says 15 and you only have 14, keep looking!
Once divested of the full complement of fasteners, a few taps around the cases with a hide faced hammer exposed the engine’s vital organs. The crankshaft is very short and fat, with not inconsiderable mass. There were two plastic funnelshaped oil pick-up funnels with plated perforated steel grilles to prevent the
sucking up of large pieces of detritus into the bosom of the pump. At this point the oil pump was still attached to the shaft that drives the cams and I was now able to lift the pump out with the shaft and take them to the bench vice to be separated into the individual components. The pump should have been removable with the lump in one piece, but wasn’t having any of it. I removed the melted remains of the plastic cam-chain tensioner blades.
I decided to measure the cylinder bores to ascertain how much wear the bores had suffered in 160,000 miles. I dug out the manual to find out the wear limits and discovered that there were two sizes of bores produced: A 89.992-99.000mm and B 99.000-99.008. I can only guess that they are not able to produce them all the same size and therefore measure them post production, and depending on size designate them as either size A or B. The pistons are also specified as A or B to match, but I could find no markings on them to work out which size we had. One of the pistons had a small section below the oil control ring broken off, presumably through metallurgic stress fracturing during its long and hard life, so was sadly a scrapper anyway. I was to measure the bores with a cylinder bore gauge with a DTI (Dial Test Indicator). I fitted a suitable anvil to the measuring head and set up a metric 75-100mm micrometer screw gauge, very gently clamped in the soft jaws in my bench vice, to read exactly 99.000mm.
The trickiest part of the job is to hold the bore gauge perfectly perpendicular to the micrometer. The easiest way is to rock it until the dial gauge reads the smallest dimension and then set that to zero. I use a digital one and so zero it by pressing a button. Despite being a very expensive Japanese instrument, the button requires quite a hard press, which makes it difficult to use. On a traditional analogue gauge the bezel is turned, which moves the face to set zero. I then put the cylinder bore gauge in the barrel and rocked it until the smallest measurement showed on the DTI, which indicates that the measuring head is perpendicular with the bore. Whatever is displayed on the DTI is added to 99.000mm, i.e., if the DTI reads 0.012 then the bore at that point measures 99.012mm. I always measure the bores at three positions, ½” down from the top of the stroke, the middle of the stroke and ½” up from the bottom of the stroke. I take these measurements in-line with the con-rod and at 90° from it. Were this an A bore then the wear limit would be 99.050mm and 99.058 for a B.
As all the measurements were well inside this limit, despite 160,000 miles, the cylinders were still within the specified tolerances, which impressed me.
Even though the pistons had bits broken off, they, too, were well within the specifications. Beer for me now – see you next time!