Early BMW K-Series

A Brick is not a Boxer, this is about Bricks

In the early 80s, BMW introduced the highly advanced K-series. An example is the author's K100RT shown. This was a completely new model, and a radical departure from the Boxers. 'K-Bikes' as they are know in most of the world, 'Bricks' (from the engine being shaped like a concrete block) as they are often known in the UK, are 3 or 4 cylinder water-cooled bikes with Electronic Fuel Injection and Ignition. The engine is laid 'flat', in that the pistons run left and right, with the head on the left and the crank inline, but these were a completely different style of bike to BMW's earlier twins.

 

BMW K-series, 1983 on

This article discusses Bricks mage from 1983 to about the mid-90s. Newer bikes are not covered here, since anything newer is still part of the 'new bike' market, on its way down the depreciation curve, and not usually in the hands of us tinkerers. Here we are interested in the original K-Series 8 valve and 16 valve. Lets cut off this page in the early 90s, when BMW changed from calling them K100 to K1100, K1200 etc.

Thinking of Getting One

Assuming you are thinking of getting one, but never had one before....

This is not a sportsbike. Definately not a sportsbike. If you want a Fireblade, buy a Fireblade. The K-Series is a fast bike - in a long-distance cruiser kind of way. But it is no back-road scratcher. One of this author's scariest memories is barrelling down a Scottish backroad on a K100RS, realising at the last minute that this bike at 100mph+ was not going to make it round that corner, grabbing as much brake as possible, ....and picking his spot on the verge.

Having said that, if you want a 'point-it-at-the-South-of-France-and-pull-the-trigger' bike, there are few better than a K100RS.

In 'riding style', they are like BMWs have always been. Well-made, fast, reliable. Gearboxes reward slow changes, cornering lines should be well anticipated, the forks are soft. You buy one because they are well-made, comfortable, and reliable cruisers.

Before you buy one, ride it. Duh, Yeah ! But you should have ridden a few (pester your local dealers). There is a lot of variation in the 'Buzziness'. I had a K100RS which was smooth as a peach, and a K100RT that always tingled through the pegs and bars. Nobody seems to know why there is so much variation, but from new some were worse than others. If you are looking at a bike that has had a lot of owners, maybe this is why they have passed it on quickly. (K75s don't suffer from this, they should always be smooth.)

BTW If you are short of leg, you definitely want to ride a couple before deciding you want one at all. They are heavy bikes (particularly with fairings), and you may be on tip-toe to balance it at standstill and in traffic. Lower seats are readily available, a common mod. You can adjust the rear spring to lower the ride height, though this may disturb the handling.

Viewing One

Check out the Owner. If you are buying from a Dealer, try find out about the previous owner. This is especially true of K-bikes. Many get bought as cheap hacks - especially ex-police bikes - and run into the ground without proper maintenance. Dispatch riders like them, so check the mileage matches the easy-to-change clocks.

The Owner you want to buy from is a mature rider, has toured on it for 10 years, and will be showing you a wad of paperwork for servicing and maintenance. They are selling because they have bought a newer BMW, Pan European, or similar.

Mileage is not a problem. Any K which has been looked after will run beautifully way past 100,000 miles and still take you round Europe in complete reliability.

Buying checks

(Assuming the Owner has passed inspection.....That the bike is straight, without serious accident damage, it has 2 wheels....)

Does it start immediately, cold or hot, with no throttle required. A few turns over are acceptable, but if it shows any hesitancy, and needs 'nursed' to get the engine to start and tick over smoothly - you could have any one of a hundred problems in the Fuel or Ignition systems.

Cold or hot, it should not vibrate heavily through the bars or pegs. All K100s vibrate to some extent, but anything more than normal points to anything from an out-of-tune engine, to badly repaired accident damage (forcing a twisted frame to bolt up to the engine introduces stesses in the frame, which magnify vibration). K75s should not vibrate much at all, their engines were much better balanced internally. If they do, the engine is out of tune.

When warm, tickover should be low and smooth. Snap the throttle open. It should rev quickly and cleanly. If it hesitates, the throttle bodies are out of synch, or the injectors are gummed up.

There will be a whining noise from the tank. This is the fuel pump. It is louder when the tank is nearly empty, and is quite normal. If it is very loud or intrusive, open the tank filler cap and start the engine. Make sure there is no 'whooshing' noise, which may indicate a cracked tube or hose spraying fuel under pressure back inside the tank. If the pump is particularly noisy, it may need replaced. Small hands are useful, but it is not a difficult job.

Check the final drive by rotating the wheel back and forth. It is hard to feel play in the K-series, and the gearboxes are bulletproof, but you want to know whether you need a driveshaft (£100, 2 hours to fit) or bevel box work (repair expensive, used replacement cheap).

Check the rear shock very carefully. This is a K-series weak point. Second-hand they are £100 - but don't bother, it will be just as dead. New is £200up.  They last for years, but bear in mind you could be looking at a 20 year old bike, on the original shock.

Front forks are soft and have long bouncy travel - this is normal.

Look at the bottom of the clutch bellhousing. There should be a small hole, poke it clear with a match if it looks blocked. Any oil here is the engine output shaft seal or the gearbox input shaft seals.

Check under the front of the engine, where the water and oil pump bolts to the front of the block. Any oil escaping here will be a major pain to rectify (On one of mine, I had the pump off and on 4 times before I got it sealed properly.) Listen here with the engine running. If the water pump squeals, the impeller is about to fall off. Do not confuse this with the timing chain whirring, which is normal.

Check the radiator cooling fan turns, you can get a finger to it through the right hand side fairing vents. They sometimes seize.

Side stand fulcrum pins wear badly. If it lists heavily to port on the side-stand, this is why. There is no easy cure.

Be very wary of bikes which have lain unused for a while. They may start and run fine, but problems will emerge soon. If you buy a bike like this, you must strip it to access every bit of wiring harness you can find, undo and make surgically clean all connectors, and re-assemble with water-proof grease (Vaseline or similar). 99% of problems can be avoided by doing this.

(Actually, I always used Vaseline, because it is easy to get hold of and has always worked well for me. But I am told that some brands go liquid at not-very-hot temperatures, like directly above your engine on a hot day - which is not good. Much better is 'Dialectric Grease', available from computer parts places and better bike accessory suppliers. Maplin calls it Silicone Grease, less than a fiver gets a spray can. A couple of quid gets a tube which will last for years.)

Most electrical components - fuel and injection ECUs, solenoids, etc, are long lasting. Apart from the clocks - speedometers are notorious for failing, and are very tricky to fix. (And the digital clock segments always fail with age. If you care, replace the chip. If not, live with it.)

On an RS, make sure the wee aerofoil thing at the top of the screen is still adjustable. It is a crucial component for high-speed comfort, and you want it to be there, and to be adjustable to your preference. It's mounting/adjustment points are fragile. It is very difficult to repair well.

Test Ride

Moving off should be smooth and civilised - any 'snatching' is probably the clutch splines needing lubed, or it may be more serious.

The general feel of the ride should be smooth and progressive. No K should be harsh or jerky. Get it into 3rd or 4th at just above tickover - with a long clear road in front of you - and open wide, letting it run to the redline. Pickup should be smooth and fluid throughout, with no drama anywhere.

The gearbox should be positive and smooth. If there is any stiffness or false neutrals, something is not right. It might be the box itself, though this is unlikely unless it has been abused for high mileage. It is more likely to be needing a clutch spline lube, supposed to be done every 20,000 miles, and requiring gearbox removal.

It might smoke a little on startup, particularly if it was parked on the side-stand. Oil drains down overnight down the bores and into the combustion chambers. It should clear quickly. If it continues to smoke after a test run, you want at least new rings and valve seals, and possibly new liners and pistons. This is much more involved than on the older Boxer twins, and requires a complete engine strip.

Brakes should be good. All Ks had strong brakes. They may be a bit 'wooly' in feel, this is normal.

Handling should be good, if slow. It should track nice and evenly during cornering. Any 'nervousness' or 'twitchiness' is not normal, and indicates accident damage, knackered head bearings, dead shocks, or too-stiff springs (an owner's attempt to make a sportsbike, perhaps ?).

Check the cooling fan cuts in. Let it tick over on the stand. It will get pretty hot (they do run fairly hot normally), and you should clearly hear the fan and feel a blast of warm air as it cuts in and out thermostatically.

On a faired bike, check carefully the fairing attachments. Bits of fairing will have been taken off many times during routine servicing and maintenance. A careful mechanic will have put all the fixings back correctly. A poor mechanic will have broken many, and used crude replacement oversize bolts and screws to hold it all together. The fairing should be fixed on tight all round, with even panel-gaps.

What to pay ?

(UK prices - this is motorcycle.co.uk after all ! Your Locale may vary.)

Old dog K100s are worth £500-600. This should get you a runner, maybe with MOT. Anything cheaper is a parts bike.

Somewhere around £1000 will get you one that has been looked after by sympathetic owners, with a decent length of MOT, maybe high mileage.

If you want one with unmarked paint, garage-kept, maybe a later early-90s model, maybe with ABS, heated grips, etc ...you need to be up at £2000. If it is the full enchilada LT, in exceptional condition, with radio and tasteful extras - be prepared to go above that.

There are quite a few K-bikes in Dealers' second-hand stock - pre-owned in BMW Dealer-speak - but prices are always higher. This is justifiable, because you will probably find they have been Dealer-maintained, had an owner who did look after it, and you will be expecting a decent warranty and a cup of coffee. Be happy to go 50% over private-sale prices for a good one at a dealer.

K75s are seen as less desirable (though they do have a cult following), and go for a little less than similar-condition K100s.

Ex-Police K75RT or K100RTs are common in the UK. Direct ex-police, they can be fine bikes, well worth having. But after a couple of civilian owners, they are probably well-abused. The typical ex-police K-Series is bought by a dispatch rider, winter commuter, penniless student, ... They will not have maintained it, or even washed it in most cases. (No offence to those folk - I have dispatched, I was a student, and I have commuted in the winter on a bike. And my bikes are always very well maintained, even if nobody else's is :)

Ex-Police, and ex-paramedic, bikes often go through specialist auctions. Withams-SV and Force Motorcycles are well known.

Ex-Police vehicles are often disposed of through local car auctions, but you don't know when the bikes will be included unless you ring up, or get on their mailing list.

If you want a K-bike, you have probably already have decided you want a fairing or not. Naked bikes are much less sought after, so may be found at a bargain price. (Unless it is a real bargain, it is never going to be so much cheaper that it is worth buying one and fitting a used RS/RT fairing.)

There are no rare, charismatic models of the K-Series. Good, low-mileage late LTs are the best laid-back tourers, and sought after. A pristine K100RS MotorSport with ABS and two-tone paint may attract someone who wants that particular model, but no K has yet achieved legendary-classic 'highly desirable' status.

Well, maybe the ice-cream van that is the K1. If you want a K which will become a future classic - and you can live with having 'that bodywork' and no panniers - good condition K1s are now beginning to climb in value.

Price Guides

eBay might give you a starting point for current prices. Search for K100 and 'Completed Items' and it will show you the prices for items sold and not sold over the last few months. This is only a starting point though, since a well maintained bike from a Dealer will be worth twice what something might go for on eBay.

In the US Kelley Blue Book covers most of the K-series In Australia, it is the Red Book

Where to buy

eBay is the obvious place, but unless you can view and test-ride the bike before bidding, you could end up with something much rougher than it looks in the pictures.

A good place to try is www.adtrader.co.uk. They offer free ads throughout the UK, and there are generally a few K-bikes advertised in there. In London, Loot is good.

The 'specialists' are Official BMW Dealers. They know how to charge an arm and a leg, but you have some guarantee of getting a bike in good condition. ...And you will be expecting an impressive Service History and a long Warranty.

Model Identification

In K 100 RT - K = 3 or 4 cylinder water-cooled engine; 100 = 1000cc; RT = Touring Fairing

K100

 

Introduced 1983

 

BMW K100
K100RS

Introduced 1983

Excellent fairing for high-speed touring. A good K100RS is a high-speed missile.

BMW K100RS
K100RT

Introduced 1984

Tall wide fairing with side pockets, big wide handlebars, and room to fit a radio. Much loved by long-distance tourers.

R75RT and R100RT variants

Bike advertised as 'RT' may be similar RT TIC - where TIC means 'Police Spec'. Often has crude holes cut in fairing to fit flashing lights, etc.
(DVLA now seems to call these RTIC)

BMW R100RT

K100LT

'Luxury-spec' RT.

Often comes loaded with taller screen, heated grips, radio, comfy seat, ....

BMW K100LT
K1

1989-93

Early ones red-and-yellow or blue-and-yellow. Later plain colours. Small cubby-holes in rear side-pods. No panniers.

Basically a K100RS in drag - Now becoming collectible.

BMW K1 in blue

BMW K1

K75C

Introduced 1985

3-cylinder engine identified by triangular silencer, as opposed to K100 square shaped silencer.

'C' has handlebar mounted fairing

BMW K75C
K75 Introduced 1986 BMW K75
K75S

Introduced 1986, with frame-mounted fairing, optional belly-pan.

(There was no official K75RS, though the K100RS fairing can be made to fit.)

BMW K75S
K75RT

Introduced 1990.

(Model shown has the optional large screen and side deflectors.)

BMW K75RT

Engine Types

  • '8-valve' (2 per cylinder) Leaded - 1983-1985 - requires leaded fuel. K100 has 90 hp, 135mph
     
  • '8-valve' (2 per cylinder) Unleaded - 1986-end - takes unleaded

    (There was also a change from a '6-rivet' to '12-rivet' counter-shaft from around 1986.)

  • '16-valve' (sometimes called '4-valve') from 1990. K100 has 100 hp, 145mph

ABS was available from 1987.

MonoLever / ParaLever / TeleLever

The K-series we are interested in are all MonoLever or ParaLever.

MonoLever is BMW's term for a single-shock single-sided swing-arm.

ParaLever, from about 1990, with the 16-valve engine, is single-sided, with an additional Torque Arm below the right side of the swingarm. It was designed to reduce the rising and falling of the rear of the bike 'jacking up' the rear under acceleration/deceleration. A bit of a non-existent problem really. All bikes will rise at the rear as you accelerate, and squat as you decelerate. Anyway, BMW invented the ParaLever, and claimed it did away with the 'problem'. ParaLever driveshafts run dry, and need replacement sooner than older types running in oil. And there are many more bushes and pivot points to keep an eye on. It has more benefit than on the R-series bikes, since the Ks are more powerful and do rise noticeably at the back under hard acceleration.

TeleLever came in around 1994, as a refinement of ParaLever.

Exact dates of introduction will vary by a year or two, depending on the model you are looking at.
 

A good description of how ParaLever works is here www.largiader.com/paralever

For detailed Technical Specs by model - weights, wheelbase, power, etc:

A selection of real world photos are here, to help you choose which model you like. And look at other pages there for lists of Paint Codes, engine and chassis number lists, numbers of each model produced, and loads and loads of other detailed reference stuff.

 

Working On Them

The amount of work you do will depend what kind of rider you are. You can buy one as a cheap hack, squint at the oil sight-level glass down on the right now and again, throw petrol in, and ride it until it dies. This can be a long time, which is why Dispatch riders like them so much.

Or, you can be a fastidious owner, and approach maintenance as a Zen-like pursuit of tranquility....

Frame and Cycle Parts last forever. Bearings last a long time unless the grease has dried out because it has stood for years.

Engines will run forever (if you do regular preventative maintenance), or stop tomorrow (if you haven't looked at it for years).

Exhausts are stainless steel. Discolouration can be cleaned off if it bothers you.

By comparison with the R-series Boxers, work on the rear drive is easy. Follow the 'Anton Method' described here. The bevel box can be off in half an hour, and the driveshaft out 10 minutes later.

Work on the engine or round the headstock can be awkward on faired bikes, simply because there is a lot of body work to remove, with hard-to-find fasteners. "Re-assembly is the reverse of removal", the manual says. In practice, getting the fairings back together neatly takes a few attempts and a large measure of patience.

Try to avoid having to remove the exhaust on high-mileage bikes. The headers stick fast in the head. The silencer sticks fast to the pipes. If you have to take it off, re-fit the headers with new sealing gaskets and new copper nuts. If you have to split the sytem, make careful notes which way round the pipe to silencer clamps go - or you will need a black belt in origami to get them back on in the right order and the right way round.

Try not to take the heat-shield off. Actually, you will be very lucky to get it off without an angle-grinder. Unfortunately, you may have to, since the heat shield rattling is a common annoyance. If you have to tackle this job, prepare in advance by buying new mounting nuts and bolts, not forgetting the rubber mount at the front. And probably a new rubber stand-bang-against rubber (Its obvious what I mean if you look down there.)

'Exposing the engine' is achieved by lifting the frame off the top. Not in itself a difficult process, but there are a lot of connectors to find and detach (people with small double-jointed hands will find this easier !), and the frame and everything left attached to it needs to be raised quite high to clear the engine - and then put down somewhere. You will need a workshop hoist or a couple of strong mates. 'Lubing the cluch splines' needs you to split the engine and box, which means lifting the frame. But you can get away with leaving most things attached, and just raising the back far enough to allow the box to slide off backwards.

Early instrument panel housings let in water, you will regularly get condensation on the inside of the glass. The guages being obscured is not the problem. Rust forming on the delicate electrical connections in here is the problem. Later units have GoreTex ventilation panels. Early units have a seal which can perish, which you should replace - but this is a problem you may have to live with. It will eventually lead to the electronic speedometer failing, requiring careful disassembly, cleaning, and re-assembly on a well-lit, clean workbench. (Speedos sometimes fail because the sender in the rear drive get caked with dirt, so check this first if it stops working.)

And be very careful washing the bike not to direct your hose at the clocks.

I'll not waste time rewriting complete 'how to' explanations here - For how to fix a speedo, lube the clutch, and all like that - is in this excellent list of exactly how to do everything.

Regular Maintenance.

All electrics are very reliable. Problems are almost always down to broken wires or dirty connectors. To avoid being stranded by the side of the road, once a year remove the tank and bits of fairing. Take apart, clean and re-assemble with water-proof grease all electrical connectors. Liberally treat all bits-and-pieces (choke switch, air-flow meter, ...) with WD-40 or similar water-repellant / lubricant.

Regularly oil or grease the clutch pivot on the back of the box. If this seizes, and they do, you will have to angle-grinder it apart (hitting it with a hammer will smash the casing). If it has not already been done, I would recommend removing the component, drilling it and fitting a grease nipple, then a couple squirts with a grease gun every year will keep the action nice and light for the life of the bike. I suspect that the K-bike reputation for getting through clutch cables is partly down to this pivot getting stiff. All K-bikes should have a smooth, easy clutch action.

If you have the bike apart, double up the control cables by taping spares alongside the existing ones. The throttle cable is a particularly difficult thing to fit. It is better to run a spare while you have the bike semi-dismantled at home, so if it breaks in the middle of nowhere in the rain, its less of a nightmare to attach.

Lube the clutch and rear drive splines at regular intervals. Scrupulously clean first, then apply grease lightly. Do the drive splines any time you have the wheel off.

Check the driveshaft boot regularly, replace if cracked or perished. If you don't, you will be buying a new driveshaft soon.

The timing should never vary, and there are no routine adjustments to the fuel injection, but while it is on the bench for the annual ritual, check the balance of the throttle bodies with a CarbTune or similar. The manuals say never to touch these adjusting screws, but you can and it is often beneficial.

On a high-mileage bike which is running roughly, before you strip it all down, try some snake oil Injector Cleaner to dose the fuel with. It may take a while and a few tankfuls, but I have had good results with this - and it requires no workshop time :)

Check the centre-stand. Some types rust internally, and can fail without warning. If you have the kind with bungs in the end, remove them and poke inside. The spray your favourite rust-prevention in there and refit the bungs. Replace at the first sign of weakness or cracking.

Get new or used parts from a specialist parts supplier like MotorWorks or MotoBins.

 

The Haynes Manual is good, as is the Clymer - but they both have that 'remove and take to your local dealer for servicing' mentality. Original BMW Workshop Manuals are available from the specialists for £40 or so, and sometimes come up on eBay.

If you are facing any tricky job, print out the relevant article from IBMWR. I have used many of these articles over the years, and found them always to tell the truth, and be a lot more useful than even the factory manual's explanations.

Useful Mods

If you are replacing fork springs, go for 'Progressive Springs'. On early bikes, particularly RS/RT models with the heavy fairing, the original springs will be well soggy. MotorWorks do a 'Handling Kit' including progressive springs and heavier fork oil which I have used and can recommend. More expensive (£500 !) rear shocks are available to improve handling, if you are repared to spend that much.

Very few other mods will significantly improve a K-Bike, they were pretty well sorted from the factory. Anything else is personal preference. Heated grips are available - and often fitted to RTs from new. Radios can be fitted to RT fairings, LTs had them from new. Voltmeters, temperature gauges, clocks, furry dice, ....

If you are doing work in the final drive, note that the 100RS has a slightly taller finally gearing (2.81:1) than the naked K100 and 100RT (2.91:1). If you are buying a used replacement or an exchange-rebuilt unit - getting an RS one gives more relaxed cruising.

Taller screens can be useful on the RT, and are widely available in 2" and 4" taller. (You should not need this on an RS, the original aerofoil thing was more effective than any after-market taller screen).

If you want parts in the UK, its MotorWorks or MotoBins. Elsewhere in the world, ask a local.

 

Tyres

Tyres make a difference to a bike's handling, obviously.  This author never liked Metzeler Lazer patter fronts, and throws them away at the first opportunity.  Here is some useful intelligence from someone who's done high miles on a K100RS:

Having covered over 100,000 miles on a K 100 RS (with no major attention whatsoever) and loved almost every minute of it (except the first 4000miles) ... I’m amazed that this greatly underrated all rounder has not become a classic. I and several of my KRS riding friends toured and scratched them for 10 years all over the British Isles through the late eighties and into the nineties, never ceasing to be amazed by their versatility. They were quick, capable, bullet proof and effortless to ride long and hard thanks to their comfort and torque.

However as supplied on (usually Metzler or Conti) cross plies they handled poorly, particularly refusing to negotiate fast bends and roundabouts with any sort of ease.

It took me four thousand miles (by which time I was preparing to sell it) before I spoke to my tyre supplier who advised a change to radial ply tyres before I did so.

What a revelation!

‘Radials’ transformed the motorcycle into a sweet handling paragon of fluidity more than able to give a good account of its self in almost any company. It’s no quick steering lightweight but once you develop the greater level of anticipation needed when riding a heavy machine quickly it’s a real joy to scratch and always rock solid.  

  • Dunlops were excellent in the dry but slightly suspect in the wet.
  • Bridgestones were brilliant in all conditions.

Unfortunately, its getting hard to find radials in the right sizes.

From another correspondent:

I have used Avon Road Riders on my K75C and K75RT and am very pleasd with their performance... especially in eliminating tram-lining.

References and interesting reading

A huge list of maillists is here, dig down for, KRS_OWNERS, BMW-Tech, ...

I'll add more links here as they occur to me.
 

We have concentrated here on BMW's K-series made from 1983 to the early 90, the K75 and K100 models, which are the ones we are likely to find in the classifieds and buy and ride regularly.

There are other resources out there, see in the text above or your favourite Search Engine. This has been a Guide to Bricks for the UK biker. If you know of more useful K75 / K100 resources - relevant to the UK biker - that I should add to this K-Series page, let me know.