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Bike Review - Posted 24th September 2014
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BMW K100 Buyers Guide, Part 2

Dave Simmons shares his thoughts on buying BMW's K100, an emerging classic occasionally known as the Flying Brick. This time; common faults and all-round advice...

K100 gearboxes are hand-carved by Bavarian dwarves from a single piece of indestructium deep in the heart of the black mountains and I can't remember any tales of woe. Some say a bit clunky but I think it's just lovely and a conventional one-down / four-up arrangement. Drive is transferred back their way by a dry car-type clutch and delivered to the back wheel by shaft. Ah yes, the shaft. Some say it is an Achilles' heel (I think we'll steer clear of discussing Achilles' shaft) as it has been known on more than one occasion to fail.

BMW K100 Buyers Guide A BMW K100RS drive shaft, yesterday

This can happen in one of two ways; the splines can strip or the coupling can break. In general, these failures are due to a lack of maintenance and this in turn is because the infrequent task of greasing the shaft is a bit of a pig, or at least it's intimidating enough a task to encourage neglect. If you are considering a K then ask about shaft maintenance. It should be greased with a high molybdenum grease every (insert your best guess here but when you change the tyres is a good rule of thumb). That said, replacements are easily available so a bike with a bust shaft can be a good buy. Worth mentioning here that the later 12 rivet shaft is better than the earlier 6 rivetter so if you are an optimist then failure can be seen as an opportunity to upgrade.

Continuing with our theme of weaknesses, the other one worthy of mention is the electrics. Nothing fundamentally wrong with them but there are rather a lot and old connections will be grouchy, won't they? The oft-repeated advice on the most excellent K100 forum is to undo and treat with contact cleaner all electrical connections. Given that the K100 was a technical tour de force and Bimmer threw every newfangled odd and sod at it there are many connections to go through and this can be a time consuming process, albeit one that will cure many ills.

BMW K100 Buyers Guide

Earlier bikes had L-Jetronic fuel injection and later ones Motronic. Both systems are bulletproof which is good news as a secondhand Motronic ECU is £300 (an L-Jetronic a measly £70). Nuff said? Not quite, they may sometimes be overpriced for secondhand items but Motorworks, Bins and James Sherlock are all good for the new stuff and you can get just about anything. This is of course a double-edged sword if ever there was one. My K was in need of work when I bought it and quite quickly I had a pile of invoices for parts that I dare not read and far surpassed the value of the bike. Sound familiar?

There are not many other downsides to speak of. One-piece 16-valve exhausts crack at the weld between downpipes and silencer and, although they can be fixed, repairs never last. Fortunately later K1100 exhausts also fit. Earlier 8-valve bikes do not have this problem, the silencer and pipes being separate items. As an aside, one easy differentiator for the uninitiated between 8 and 16-valve machines is the silencer; the former having a square profile and the latter round (and the K75 triangular). The whole range is cat-free (we're not talking felines here).

BMW K100 Buyers Guide A BMW K100RS brake pedal, yesterday. Some corrosion is evident

Servicing is mostly straightforward although valve clearances on the 16-valve are by shim and so time consuming. Fortunately this needs to be done very rarely indeed due to the robust design and build of the head. The timing on both models, which uses a Hall sensor arrangement, is best done using a BMW tool (available to hire from the UK club) but the rest, fluids and so on is pretty much the same as any other bike. The driveshaft spline lube has already been mentioned and must be done. In terms of literature, the K100 Forum has downloads of workshop manuals and the Clymer manual is very good as well.

There were a few extras that were fitted as standard or available as upgrades. Heated grips are one and work well, another is ABS, fitted to some late 8-valve and all 16-valve bikes. As a child I marvelled at the K with its giant ABS accumulators; they just looked so cool and space age, proudly pronouncing their technology in bold white letters. Many owners see the flashing light of ABS doom on the dash and strip the system out. I am not sure why but a prime candidate has to be the intensely irritating flashing dash-mounted fault light that can only be temporarily disabled without radical surgery.

BMW K100 Buyers Guide
K Series BMWs on Now...

Unusually, I have persisted and my ABS system now functions perfectly. First I changed the ABS computer (which resembles half a ZX81) and then after 18 months of searching (yes really) and with the help of an expert from Japan I found a simple wiring fault. I like things that were fitted as OEM to work and there is nothing fundamentally wrong with the ABS system. It just needs a bit of commitment.

Of course panniers and frames are a must and widely and quite cheaply available. A fully loaded RS with panniers is a handsome and purposeful machine. The bellypan also looks good. If you want one then it's best to buy a bike that already has one as they are costly to buy used, and finding one in the right colour could take a long time.

BMW K100 Buyers Guide

Let me end on the issue of size. These bikes were built and tested by German folk. When I was in said country I observed their stature, on the whole, to be somewhat greater than my own admittedly under average frame and this seems to be reflected in the proportions of the machine. It is big. The wheelbase is long for autobahn stability; the seat is only moderately high at 810mm (31.9 inches) but it is wide which steals valuable inches from the femurally-challenged. Although a low seat option was offered it is a kit of many parts that is rare secondhand, and when fitted ruins the lines of the bike by doing away with the sidepanels.

The K100RS is also heavy at 249kg (548lb) wet. As is often the case, once on the move the weight vanishes but it really is a heavy brute at rest and pushing it around is inadvisable for those who have or do not wish to acquire a lower back condition. Should you have the misfortune to drop it (most do, its engine mass is perched quite high up) then lifting it up again can be difficult.

Quality though. Yes, quality, everywhere and we do like nicely made things, don't we? No part of this machine appears to me to be made to a price… although of course it was. From the aluminium petrol tank to the monstrous frame tubes and solid fairing panels, it seems that pretty much the best of everything has gone in to the mix and that is no doubt reflected by its longevity. We need to remember this bike was a gamble for BMW and a lemon could have spelled the end for their motorcycle division so they did a good job with the engineering.

My advice? If you want one then buy now while they're cheap because the number on the road has dropped off a cliff in recent years and appreciation is growing. Buy the best you can because a bad one will be a money pit of Siberian proportions. It's a big bike with a lot of road presence and subtle character that still looks good. And if you're a short arse with a bad back? Think twice!

Photos: Dave Simmons / RC archive

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