BMW dictionary

BMW motorcycle dictionary, lexicon, vocabulary, idioms, terms, and slang

by Duane Ausherman

This dictionary of motorcycle terms is mostly specific to BMW and/or related to motorcycling in general.   The list will never be finished or completely accurate.   Each word or term can have volumes written about it.  Many of the definitions have links to something directly related.   To learn more about many of these terms, use Google.   Here is an American to British dictionary. 

What do the three letters BMW stand for?

Second Rule; Keep two seconds between motorcycles when riding in formation.

2-Stroke; A two-stroke engine is one with two strokes or movements up or down per cycle.

4-Stroke; A four-stroke engine is one with four strokes, or movements up or down, per cycle.

Abrisz;  Related to getting the maximum spark with a magneto ignition system.   Also called the E-gap.

ABS Motorcycle Brakes;  The same as a car, Anti-lock Braking System

Aftermarket;  An accessory, or part, made for your motorcycle by someone other than the original manufacturer.

Air/fuel ratio;  The mixture of fuel and air produced by carburetion or fuel injection.  A comparison between the amount of air and the amount of fuel going into the combustion chamber.

Airhead;  A BMW that is mostly cooled by air and not by water or oil. The name of a major BMW club.

Allen key, or wrench;  A type of hexagonal-shaped wrench.

Altitudinal changes;  This refers to the change in combustion mixture when changing altitude.   This is more of an issue with the older bikes using slide carbs.

Amps;  Short for ampere, the term for the amount of electrical current.

Anti-seize compound;  A somewhat greasy paste that is added to threads to keep them from sticking.   The best example on a BMW is the exhaust threads on the head.   One of the many products available.

Ape Hangers;  Really high handlebars, mostly on choppers, but I have seen them on a BMW.

ATE;  The huge worldwide company that made the first disc brake for BMW in 1974 with the /6 series. They were known for not working well.  The single-disc did not work nearly as well as the former drum brake of the /5 series.

Babbit;  The bearing compound found in plain crankshaft bearings.

back roads;  Off the main highway, often preferred by motorcyclists.

Balaclava;  A head and neck “sock” with mouth and eye slits. 

Balancing carbs; The procedure for getting two or more carbs tuned properly to allow the smooth running of the engine.

Barn queen;  A motorcycle that has been stored in a barn or other outbuilding for many years.

Basket case;  A motorcycle that has been taken apart.   For the person who still expects to put it back together, it is a project, but the buyer calls it a basket case. 

The bearing has flat spots;  See “bearings are notched” below

Bearing preload;  The slight pressure holding tapered bearings together.   Commonly used on BMW.

Bearing race;  One of the two bearing surfaces that balls or rollers ride against.

Bearing spun;  A bearing can spin in the case that is supposed to hold it.   This may damage the case or aluminum hub.

Bearings are notched;  Ball or roller bearings can get worn spots on them that are felt easily.   Those are flat spots.

Beemer; a slang term for a BMW motorcycle.   Often confused with Bimmer, the car

Bench seat; or banana seat;  A long seat for two people.

Big Ends;   The larger ends of the connecting rods which attach to the crankshaft of the engine.

Biker;   An “image” of a person who rides a motorcycle, often limited to those fitting the outlaw image.

Bikini fairing;  A very short and small fairing, more for the style than function.

Bill Mayer;  Known for making large comfortable seats for motorcycles, especially BMW.

Bimmer;  A slang term for a BMW car.

Bottom end;   The crankshaft, crankshaft bearings, journals, webs, and connecting rod lower ends of an engine.   An engine is considered to have a top end and a bottom end.

Bowman;  A manufacturer of aftermarket oil pans and other engine accessories for BMW motorcycles in the late 60s.

Boxer;  A slang term for a horizontally opposed engine where each piston has its own crank pin.  The term comes from the image of the two pistons traveling toward each other and looking like boxers fighting.

Brain;  The small computer which controls fuel, engine, and ABS brake functions on BMWs after 1984.

Brake pads vs. shoes;  A disc brake uses pads for the friction material, and a drum brake uses shoes.

Brake squeal;  A loud squeal coming from the brake.   Certain models are more prone to this malady.

Brembo:  BMW began using the Brembo brakes in 1981 (I think), and they worked far better than the former brakes by ATE.

Brick; Refers to the water-cooled inline BMW motorcycle engines that came out in 84.  Also slang for a very hard stock seat.

Brights;  The high beam of the headlight

Brushes;  The carbon electrical parts that rub against the commutator

Buffeted buffeting; Refers to the wind experienced while riding a motorcycle, often coming around a fairing.

Bump start;  A way to start a motorcycle by turning on the ignition, placing it in gear, disengaging the clutch, then running alongside the motorcycle, jumping on, and engaging the clutch suddenly.  Hard on the drive train and clutch, but will start a bike with a dead battery when no one is around to provide a “jump.”

Bun burner;  A long and grueling ride that makes the posterior sore.

Bungee Cord;  A stretch cord for attaching things to a motorcycle.  

Burning rubber;  Starting out quickly and spinning the rear wheel.

Burning up miles;  Just going down the highway.

Bushing;  Usually, a bronze part acts as a bearing.

Butterhead;  A term coined by Duane Ausherman to describe the heads on certain years of /2 BMW motorcycles where the alloy of the cylinder heads is too soft.

Cables, or Bowden cables, are the mechanical cables that operate the clutch, fuel, and brakes of a motorcycle.

Cafe Racer;   A lightweight fast motorcycle designed for style or going fast in curvy areas.

Carb;  Short for a carburetor, the part that mixed fuel and air on older motorcycles.

The center of gravity, or just cg, is that point on the motorcycle where there is equal weight all around.  A balance point.

Center stand;  The mechanical stand that holds the motorcycle vertically upright.

Chair;  A common term for a sidecar.

Chilton manual;  One of the common workshop manuals for BMW motorcycles and other vehicles.   It was probably the worst of the manuals.

Choke;  A device to assist in starting a cold engine by making the fuel/air mixture “richer” in fuel.

choke/enrichment circuit;  The part of a carb used for cold starting

circlip;  A type of fastener that looked like the letter “C”  It snapped into a groove on a shaft to retain something.   Sometimes called a C clip.

Classic;  A period of time for a class of car or motorcycle for showing.

Clear title;  Having a legal title of ownership of a vehicle.

Clip-ons;  A type of handlebar that is very low for road racing.

Concours;  Short for the French term “Concours d’ Elegance,” and it is a car show.  Also used to refer to a standard of excellence of condition for vehicles, as in, that old BMW is restored to Concours.

cone;  The inner part of a tapered roller bearing.

Corbin;  A manufacturer of aftermarket saddles for BMWs.   Provided OEM custom seats for BMW for a few years in the late 80s and early 90s. They are still in business today.

Corrosion;  Oxidation or rust on a part.

Cotter pin; a part that goes through a hole in a shaft and is then bent over.   It will keep the nut from backing off.  Example

Countersteering;  This is a highly controversial term relating to the steering of a motorcycle.

Crank it over.   To turn an engine over in the process of starting it up.

Crankcase breather;  The term for the part of a system of exhausting the gasses out of the crankcase or lower end of an engine.

Crankshaft;  The main shaft of an engine to which the piston connecting rods attach.

Craven;  A British manufacturer of aftermarket luggage for BMWs.

Crosswinds; Wind flow at an angle to the direction of travel of the motorcycle.

Crotch Rocket;

Cruisers.   A style of a large motorcycle.

crush-washer,  A copper washer used on a drain plug to “crush” as it is tightened to ensure a good seal.   On this page, you can see an example of a  new (uncrushed) crush washer.

CS;  The suffix of a few models of BMW for sport.

cupping, or scalloping;  This is the natural wear on a motorcycle tire that is mistakenly thought by some to indicate a problem.

CV, or constant vacuum carb;  In 1970, BMW began using a CV carb on the R75/5.   The older type was called a slide carburetor.

Damper, or Dampener;  Commonly a hydraulic piston or friction assembly used to lessen vibration or oscillation.

Day-Long;  A type of custom motorcycle seat made by Bill Russell often found on BMWs.

Dealer;  A seller of motorcycles authorized by the factory or importer.

Deep oil pan;  A type of oil pan that either increases the supply of oil or increases its cooling, or both.

See Bowman;  The firing of the mixture in the combustion chamber before it should.   Not a good thing to see Pinging or pre-ignition.

Diaphragms;  The round rubber “skin” found in a CV carb.   They first came out on BMW in 1970.   It also applies to the flat clutch spring used on the /2 and later.

Ding;  A nick or scratch in the paint.

Diode, or diode board;  An electrical device that allows current to flow in one direction only.   Usually, as part of the diode board and the rectifier of the alternator system.

Dipstick;  The long slender piece of metal that goes into the oil collection point of an engine, or sump, to check the oil level.

Disc (Brit) = rotor (Yank)

DOHC;  Acronym of Double Over Head Camshaft.

DOT Helmet Rating;   An acronym of Department Of Transportation.   A motorcycle safety helmet standard. 

Double-leading shoe brake;  Relating to a type of drum brake with both shoes having leading edges during braking.   Used by BMW from mid-50s-late 70s on the front wheel.

Dresser;   A motorcycle “dressed” with many accessories – luggage, fairing, trunk, trailer…etc.

Dropped valve;  The head of the valve broke off and is in the combustion chamber.   Usually, great damage occurs.

Dry Clutch;   A type of clutch system usually found on cars but is normal for BMW motorcycles.

Dual plugging;  Adding a second spark plug to the head of a BMW motorcycle.   It was/is popular on the /5 and later
motorcycles due partly to poor fuel and/or wanting more power.

Dual shock;  Relating to the older models that had a shock absorber on each side of the BMW.   In 1981 BMW came out with the first single-shock R80GS.

dwell;  Relating to the amount of time that points are closed in the older battery coil ignition system.  Don’t waste your time measuring it, as it is not needed for a BMW twin.

E-clip;  An E-shaped clip fastener.   Used in a few places on a BMW motorcycle.

E-gap;  Also called Abrisz; see above.

Earles;  The name of the man who invented the leading link forks used on BMW motorcycles from late 55 through 1969.   Especially good for sidecar rigs.

earth (Brit) = ground (Yank), Referring to electricity.

easy/eze/ezy-clutch;  An invention to give the clutch lever more leverage and allow the easy pull of the clutch hand lever.   One example.

EFI;  Electronic Fuel Injection.   Used on BMWs with the introduction of the K models in 1984.

Engine casing;  The external case that encloses all the parts of an engine.

Everbest;  A type of fuel petcock used on BMWs from 1955 until 1974.

EZ Berg;  A manufacturer of custom saddles for BMW motorcycles in the 1970s.

F;  The prefix for a line of 650 cc single motorcycles with a chain drive.

FAG;  A major company that makes bearings found in BMW motorcycles.

Fairings;  A protective covering over the front and sometimes sides of a motorcycle to make it either more aerodynamic or protect the rider from wind and rain, or both.   They are typically one of two types.  The best and safest are the frame-mounted fairings.  More prone to wobbles are the handlebar-mounted fairings or windshields.

False neutral;  When one shifts gears and finds neutral accidentally.   It is a sign of poor technique or a technical problem.

Fan blade;  The blades of the fan behind the radiator of a water-cooled K bike.

Fan Shroud;  The cooling which encloses the fan on a K bike.

Faulty ground;  A poor ground (earth) connection

Feathering the brake;  Gently applying the brake

feathering the clutch;  Gently allowing the clutch to engage.   This makes for a slow smooth start.

Final drive;  The last item in a BMW motorcycle drivetrain where the energy gets turned 90 degrees to the wheel.   Often mislabeled (due to similarities to a car) differential or rear end.   It is known to “gain oil” and have the wheel drive splines wear.

Flat spot;  As the throttle opens up to increase rpm, sometimes one will find a place, just off idle, where the engine seems to hesitate.   That is a flat spot.

Floating disc;  On a disc brake, the actual disc may “float” and not be fixed.

Float bowl; a chamber that holds a specific amount of fuel and keeps it constant.   In it is usually some type of float.   The “bowl” may be removable for easy cleaning.

Footpegs;  The resting place for one’s feet on a motorcycle.   The passenger footpegs often will fold up and out of the way.

Foot pounds;  A term for describing how much to tighten or move something.   So many pounds of pull on a lever of so many feet.

Fork rake; The angle between the vertical and the fork legs.

Forks;  The mechanism on the front of a motorcycle that holds the wheel, allows steering, and provides shock absorption.

Frankenbike;  Since BMW would keep many interchangeable parts for years, it is common for people to assemble a BMW out of parts over many years.

fuel tap (Brit) = petcock (Yank)

Gas cap;  The cover for the fuel inlet on a tank.

Gasket;  A paper, rubber, or cork part that goes between two metal parts to become a seal.

Gasoline foot;  The result of fuel dripping onto one’s foot.   Not unknown for a BMW to have a float stick or leak and allow some leakage.

Gearbox (Brit) = transmission, tranny, box (Yank)

Gear lash;  The play between two gears.

Gear whine;  The noise made by gears that aren’t spaced correctly or are worn.

Gremlin;  A gremlin is blamed when one can’t find the defect or cause of some malady.

Ground;  The return path of an electrical circuit, “Earth” in Brit-speak.

Grounding the plugs;  During certain ignition tests, one must remove and lay a plug against the engine.   This is to observe the existence of a spark.

GS and G/S;  The acronym for Gelande Sport, or terrain (land) machine.

gudgeon pin (Brit) = wrist pin (Yank)  That is the pin where the piston pivots on the rod.

H4;  A quartz halogen bulb used commonly in a BMW headlight.   Introduced in 1974 on the /6 models, it was the first motorcycle in the USA to have the approval for street use.   All about bulbs.

hack, side hack;  A common slang term for a sidecar.

Hall-effect;  A type of ignition system introduced by BMW in 1980.   Info for the ever-curious.

Halogen;  The type of headlight bulb used since 1974 by BMW contains an inert gas.  Will be damaged if the glass is touched with your finger.

hand painted stripes;  The typical pinstripes found on a BMW motorcycle that were hand-painted by women at the assembly plant.

Handgrip;  The rubber grip on the handlebars makes a more comfortable hand control.

Handlebar fairing;  A type of windscreen that is mounted directly to the forks.   Not recommended on an older BMW.

Haynes manual;  One of the main four workshop manuals for BMW.  Depending on which manual is used, double-check for accuracy.

Headlight bucket, or shell;  The enclosure that holds the headlamp, usually metal.

Head;  The portion of the engine that sits atop the cylinder.   It is the part that holds the spark plug.

Heated handgrips;  Electric hand grips can be fitted to help keep hands warm in really cold weather.

Heavy floats;  Carbs have floats to regulate the fuel level.   They can become soaked with gas and sink.   That is a heavy float.

Heinrich;  Manufacturer of aftermarket accessories for BMWs, notably fuel tanks and motorcycle fairings.

High speed wobble;  An oscillation of the forks at a high speed.   It is extremely dangerous and often results in a crash.

High side;   A crash where the motorcycle slides out, and rather than just skid to a stop, it flips, and the rider and bike start tumbling.  A high side is more dangerous than a low side crash.

Highway pegs;  Extended foot pegs which allow the rider to stretch out the legs once underway.

Hit the pavement;  An idiom for crashing a motorcycle.

Hit the road;  Get on the bike, and start riding.

hone;  A special type of stone to treat the sides of a cylinder.

Horsepower;   A measure of the power put out by an engine

Hoske;  Ernst Hoske was the manufacturer of aftermarket accessories for older BMW motorcycles, notably fuel tanks and mufflers.

Hydroplaning;  When riding in the rain at too fast of a speed, the tire can skip over the top of the water and lose traction.   The same as in a car, but less likely on a motorcycle

Hylomar;  The brand name of a type of non-hardening gasket sealer.   Many favor it for use in certain applications on a BMW.   BMW has authorized its use.

IBMWR; An Internet national BMW riders organization.   Highly recommended.

Idle mixture;  The fuel/air mixture at a low rpm is called idle.   See “flat spot” above.

Idle stops;  The mechanical part of the carb that keeps the idle up high enough so that the engine doesn’t quit.   On a BMW motorcycle, it is easily adjustable.

Ignition leads;  The special wire that connects the ignition coil to the spark plug.   Also called high-tension lead.

inline;  Usually describing the type of engine layout.   The K100 and K75 are examples of the inline engine.   The opposed (boxer) is not.

Intermittent shorts;  About the worst type of electrical problem to have, as it is usually hard to diagnose.   See “short” below.

iron butt;  A very long, hard ride.

JB weld;  A commonly used epoxy glue that is so good it can be machined.

Jesus clip;  This is the “E” clip that holds the handlebar switches together.   It is very hard to install this tiny part.   The name comes from the phrase that is commonly uttered when it flies away and gets lost, and then the person says, “Oh Jesus.”

jet needle;  This is a carb part that meters the fuel going through a jet or hole.

jet;  A carb part that has a very precise hole to restrict fuel flow

Jugs;  On a BMW, the cylinders are commonly called jugs.   Shame on you for thinking that.   Real jugs are on the left side.

Jump-starting;  When the battery is too low to start the engine, one can jump-start it from a good battery.   It takes a pair of large size electric cables and some knowledge to do so safely.

K bike;  The prefix of several models of BMW.

K&N;  An aftermarket company that manufactures air filters.   They are washable and reusable.   While that seems to be economical, it is well proven that they don’t filter as well and will shorten the life of the top end of the engine.

Kicking Tires; Slang term for standing around motorcycles and talking about them.

Kickstart;  Before motorcycles had electric starters, they all used kick starters.   A lever that one would kick to turn the engine.

Knock;  Just as in cars, it usually refers to a noise made by a loose rod.   Not a nice noise to find.   It usually means expensive engine work.

knurl;  An often misunderstood process applied to a piston to make the skirt larger, usually to make it a better fit.   See example.

Kompressor;  German for a supercharger.   A few high-performance BMW twins were known as “Kompressors” in 1939.

Krauser;  Manufacturer of aftermarket removable luggage for BMWs in the 1970s and 1980s

Lash;   A term for play or looseness, often related to the valve adjustment.

Lean;  1.   A carb mixture that doesn’t have enough fuel in it.  2.   To go around a curve, the motorcycle must lean.

Leaning into crosswinds;  As a crosswind hits a motorcycle, it naturally leans into the wind to stay about on the same track.

Leather;  This usually is used when referring to riding clothing.

Lid;  Safety helmet.

Light the fire;   Slang term for “start the engine”.

Linkage;  A mechanical connection between two things.   For example, the parts that link the foot shift lever to the inside parts of the transmission.

Locktite;  The brand name of a very common glue to hold something in place.  It is used on motorcycles to keep nuts and bolts together.  It is made in many varieties for various uses.

longitudinal;  A directional term meaning along the center line of the motorcycle from back to front.  BMW flat twins have the
crankshaft and driveshaft aligned in a “longitudinal” direction.

lower end;  An engine is usually considered in two parts, the top end and bottom or lower end.   The lower end is the crankshaft and related parts.

Lowers;  The portion of a fairing that protects the legs and is commonly removable for summer weather.

Low side;   Where the motorcycle slides out sideways with the wheels going down the road first.  Far better than a high side, where injuries and damage to the motorcycle are greater than a low side.

LT;  A suffix on some BMW motorcycle models, usually large touring bikes.   Some claim it means light truck.

lube (Brit) = grease (Yank)

Luftmeister,  A manufacturer of accessories and fairings for BMW motorcycles.  Well known to be unscrupulous.

Luggage;  The storage space for clothing and other things in a touring motorcycle, usually removable.

LWB; Acronym for Long Wheel Base.

Magneto; self-powered ignition generator.   Commonly used on BMW until 1970.

MC; Acronym for Motorcycle.

Main Bearing;  A large bearing that supports a portion of the crankshaft.

Main Bearing Journal;  The part of the engine case where the Main Bearing attaches.

MSF; is an acronym for the Motorcycle Safety Foundation.   A group dedicated to safety through well-planned motorcycle riding lessons. 

Naked Bike;   The basic model of a motorcycle without fairing or bags.

Naval Jelly;  A Loctite product and a liquid that removes rust in preparation for paint.

needle bearing;  A needle roller bearing is a special type of roller bearing that uses long, thin cylindrical rollers resembling needles.

needle jet;

needle valve;

NIB, The acronym for New In Box.

NOS;  An acronym for New Old Stock.   While the part was manufactured many years ago, it is new, original, and not a reproduction part.

Nyloc;  A type of nut for a bolt that has a plastic insert to keep it from backing off from vibration.   It replaces the lock washer.

O Ring;  A rubber sealing part.

OEM; An acronym for Original Equipment Manufacturer.   The BMW factory only assembles parts that are purchased from subcontractors.   Those companies are OEMs.   BMW puts these parts in its own packaging.   The part may be available from the OEM also but in different packaging.

Off-road;  Riding that is not on a legal road.   Usually used for sport.

OHC;  Acronym for Over Head Camshaft.   Having the cam overhead means that it is located above the head rather than in the lower end.   It reduces the reciprocating mass and allows higher rpm.

Ohms law;  The electrical term for resistance.   It is named after George Ohm.

OHV;  Acronym for Over Head Valve.   This arrangement allows for better fuel flow into the combustion chamber.   That means more power.

Oil pan;  A BMW engine has a wet sump.   That means that the oil is in the bottom of the engine.   A cover is bolted on the bottom of the engine, and it is the oil pan.   It is possible for the oil pan to leak a bit of oil.

Original owner;  This would be the first owner of the motorcycle purchased from the dealer.

Out-tracking;  The process of breaking the straight-ahead wheel alignment of a motorcycle in order to turn.  See “counter-steer”.

oversquare;  If the diameter of a piston is larger than the stroke, it is considered to be “oversquare”  This allows higher rpm and more power.

Owners manual;  The book supplied with a new BMW motorcycle.   It has riding information, warranty, and minor service work explained.   Some BMW manuals are available online, such as the /2 owners manual.

pannier;  Brit-speak for saddlebags

Patches;  The cloth “patches” are sewn onto a jacket or shirt to signify a club, brand, or something of note.

Perch wedge;  The small part of older BMW motorcycle handlebar controls to keep them from rotating on the handlebars.  In the photo, it is the small part with the teeth.

Petcock examples.The valve that turns off the fuel to the engine.   My article on BMW petcocks Petcock;

Petrol (Brit) = gasoline, or just gas (Yank) = Benzine (central Europe)

Pillion; A pillion is a mostly British English term for a secondary pad, cushion, or seat behind the main seat or saddle on a horse, motorcycle, bicycle, or moped. A passenger in this seat is said to “ride pillion” or may be referred to as a “pillion.”
Pinstripe; The hand-painted lines that so distinguish a BMW.

Pinging;  Knocking (also knock, detonation, spark knock, pinging, or pinking) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder does not start off correctly in response to ignition by the spark plug but one or more pockets of air/fuel mixture explode outside the envelope.

Piston slap;  The noise a cold piston makes as it hits the cylinder sides.   It is usually because the piston skirt is too small for the cylinder.   Often it goes away when the piston expands due to heat.   In severe cases, it never stops making the slap.

Play;  The “looseness” of parts.

Plugs fouled;  If the fuel isn’t entirely burned during combustion, then it is common for the unburned carbon to deposit on the spark plugs.   This can short out the ignition spark and stop the firing of the cylinder.   The plug must be cleaned, and the reason for it to foul is found out before all things are right.

Plugs too cold;  A cold plug doesn’t have a hot enough spark to burn off carbon deposits and will foul (see above)

Plugs too hot;  A hot plug produces a spark so hot that it will fire the air/fuel mixture before the valves are shut and the piston is in the proper position for the down stroke.  The result is pre-detonation or pinging, which can burn a hole in the piston.

plunger-frame;  In 1937, BMW came out with a rear sprung wheel.   It had no dampening, but at least it would move up and down to stay with the uneven road surface somewhat.

PO;  Acronym for the Previous Owner.   This is the unknown person on which to blame all defects of a used BMW.

Points;   The switch of the older style ignition system is called “battery coil” or Kettering.

Poker Run;   A common social activity of motorcycle groups.   The group rides to different checkpoints, and each rider “draws” another card.   In the end, the one holding the best poker hand wins a prize. 

pop the bead, or break the bead;  This relates to fixing a flat or changing a tire.   It is pushing the edge of the tire off of the edge of the rim.

Pot; cylinder, with or without the head.  A Brit term

Rubber Cow;   Comes indeed from the German “Gummikuh” (which sounds a lot better-pronounced goo-mi-kooh, but with slightly shorter oo’s).  It wasn’t given to our bikes as a reference to their extreme comfort or to describe an oscillation on long sweepers.   The term “Kuh” was bestowed upon our bikes by a famous German motorcycle journalist somewhere in the third quarter of the previous century, who had immediately noticed the pinion drive effect and commented that the bike behaved like a cow.   Cows, as some of you may well know, raise their hindquarters first when they decide to stand up and go for a walk, exactly like our bikes do when you open the throttle.   The same effect makes the rear end squat when you close the throttle.
When you do that in a turn, the bike suddenly feels as if it’s made from rubber or is hinged in the middle.  It may have to do with frame stiffness.   Hence the term “rubber cow.”

Popping the clutch;  Letting the clutch out quickly to make a fast start.

Porous wheel;  a cast wheel made for tubeless tires that has a defect where the air leaks out.

Pre-ignition;  The ignition of the compressed fuel ahead of time.  See detonation.

Pre-load shifter lever;  A trick in helping the BMW shift smoothly and quietly, with less of a clunk.

Progressive spring;  The name of a company that makes front fork springs for BMW

PSI;  Acronym for Pounds per Square Inch.

Purring;  Referring to a smooth-running engine.

quad-leading shoe;  A drum brake with 4 leading shoes, not ever supplied on a BMW

R;  The Prefix for all years of BMW up to 1984.   It is short for Rad, the German term for a wheel.

race; This could mean a race for speed or a part of a bearing.

Rake and Trail;  Bicycle and motorcycle geometry parameters; wheelbase, head angle, fork offset, and trail.

Rally;  A group meeting of like-minded individuals, usually on a weekend and commonly at a camping place.

Rat Bike;  A really tattered motorcycle, sometimes describing a BMW, that is just used for transportation.  

Reading plugs;  A close examination of the spark plugs to determine the mixture of fuel/air.

Rear main seal;  The seal at the rear of the crankshaft keeps the oil in the engine and the air out.

Rear sets;  Foot controls that have been relocated at the rear of the motorcycle.

rebound damping;  Related to the damping of a shock absorber during the extending portion of the cycle.   It would restrict the spring somewhat.

Renovation;  A bike that is renewed mechanically/cosmetically and hopefully in good taste.   Often improved over the original and frequently called a restoration, but that is an error.

Resistance;  An electrical term measured in Ohms.   See Ohms law above.

Resister caps;  A type of (often metal-covered) spark plug cap found on BMW that has a resistance of about 5 k Ohms.   Designed to reduce radio noise, the metal-covered caps were collectors of humidity and often shorted out the ignition voltage.

Resister plugs;  Spark plugs with some built-in resistance to reduce AM radio noise from the ignition system.

Restoration;  a BMW restored back to original specifications, not some improved later technology.   See renovation.

Reynolds;  Reynolds Machine Tool Co. made a variety of BMW accessories out of steel: Luggage racks, ride-off R-bike center stand, and pillion backrests.  Salt Lake City, UT.   Now out of business.

rich.   Usually refers to the fuel/air mixture when it has more fuel than desired.

Rick Mayer.   An aftermarket BMW motorcycle seat manufacturer, now Bill Mayer.

Ring(s).   A number of rings surround a piston to seal the combustion gasses from escaping past the piston.   Worn-out rings will allow the engine to burn oil.

Road rash;  The injury from sliding down the pavement.

roller;  The rolling part in a roller bearing, as opposed to a ball.   Common to BMW wheels, swingarm, and steering.

RS;  Acronym for Renn Sport, or racing sport.

RT;  Acronym for Road Touring.

S;  Acronym for sport and used as a suffix on some model designations.   Ex.  R90S

Saddlebags;  Luggage mounted at the rear on the sides of a motorcycle.

Safety wire; a springy wire used to keep a part from falling off.   Not used by BMW in production but by racers.

Sag;  A term to describe springs that have lost some of their original lengths.

Scalloping;  Also called cupping, is normal front tire wear on a motorcycle.

Seized;  Related to what happens to a piston when it expands from heat and becomes too large for the cylinder.   It was more common on the /2-era bikes.

Setting timing;  Adjusting the ignition timing to occur at the best time in the engine cycle.

Shaft Drive;   The drive shaft is how the power gets from the engine to the rear wheel.   Historically, motorcycles used chains.   

Shaft splines;  A series of grooves cut along the length of a shaft, usually to allow it to transfer rotation through a counter fitting ring or keyway.

Shimmy;  Another term for high-speed wobble. See above.

Short circuit;  A term meaning that a hot electrical wire is touching ground, or another part of the circuit.   Not a nice thing.

Shorts;  See above

sidecar;  An outrigger attached to one side of a motorcycle for carrying passengers or freight.   Also called a chair or hack.

Sidestand;  The stand that props up a motorcycle at an angle.   BMW has been well known for poor side stands.

Silicone;  A type of plastic rubber.

single/double/four/six Piston Caliper;  For disk brakes, the caliper holds the abrasive brake pads so that they are on either side of the brake disc.  hydraulic pistons in the caliper squeeze the pads against the disc, causing braking of the disc’s rotation.
Single-leading shoe,  The front drum brake of a motorcycle has two shoes.   If one is leading and the other is trailing during the application of braking, then it is called single leading.   The best braking is when both shoes are leading.   The twin-cylinder BMW motorcycles since about 1955 have all been double leading.   The R25 series, R26, and R27 were the single leading type.

sissy bar;  The near vertical bar that originally was used for the rear of a motorcycle seat commonly used on a chopper.   Over time the term has evolved to be any backrest on a motorcycle.   The Reynolds Back Rest was often used on a BMW and is similar.  This backrest was invented by yours truly.

Skid;  As in skidding the tire.

slide;  As in sliding the tire.

slider;  A Brit term for the leg or lower casting on the forks.

Slop;  A term for “play” or “looseness” in an assembly.

snap-ring;  Used to retain something on a round shaft.   BMW used them in several applications.

Snell Helmet Rating;  A long-time standard for helmet testing and safety.

Snowflakes;  A term applied to a style of cast wheel on a BMW starting in 1978.   The first ones were defective and recalled.

Solo seat;  A seat for one person that was common on older BMW motorcycles.

spline;  A series of longitudinal grooves like key seats in a hub or on a shaft so that while one may slide endwise on the other, both must revolve together.

Spoke tension; Refers to how tight a nipple is tightened on a wheel spoke.   BMW motorcycle wheels were all made with spokes up to 1978 and some since then.   The BMW is well known for not losing spoke tension because they are straight spokes, not having an angle at one end.

Square Engine;  An engine whose cylinder bore size and piston stroke are equal.   A number of early BMWs had square, boxer engines.

Spun wheel hub;  This refers to the wheel bearing spinning in the wheel hub.   Especially common on the rear of the /5, /6, and /7 models.   It usually ruins the aluminum hub.

Squirrelly handling;  A slang term for a feeling of less than full control on a motorcycle.

ST;  An acronym Sport Touring used as a suffix on some models.   Ex.  R80ST

stanchion;  A Brit term for the fork tube.

Standing on brakes;  Application of a lot of braking power, usually in a panic stop.

Starter dragging;  This refers to an electric starter that has high internal resistance due to bearings or bushings.   They must be replaced to return to easy starting.

Steering damper;  A system for adding resistance to the motorcycle steering.   BMW has used two styles, hydraulic and friction.

Stiction;  A “new” general engineering term.   The term for the resistance in motorcycle telescopic forks starting to telescope.   A lot of stiction is not good.   Caused by bent, twisted, or out of alignment of forks.

Stoppie, stoppy;  Stopping so quickly with the front brake that the motorcycle rises up on its front wheel.  A reverse Wheelie.

Stripped threads;  Threads that have been damaged and are mostly gone or won’t hold.

sump (Brit) = oil pan (Yank)

swage;  A way to fasten something.   It is done with pressure rather than welding or fasteners.

SWB;  Acronym for Short Wheel Base.

Swing arm;  The arm holding a wheel and allowing it to go up and down on a motorcycle.   The Earles fork series, from late 55 thru 69, had a swing arm in the front as well as the commonly known rear.

Synchronize;  On a BMW, this term refers to having the two carbs work together so as to provide smooth operation.

tachometer; (rev counter in Brit-speak)  A meter showing the number of revolutions of a shaft.   Usually, the revolutions per minute of the crankshaft.

Tank slapper;  Another term for high-speed wobble The forks oscillate back and forth so much that they hit the tank with a slap.  Rarely is the tank large and wide enough for that to happen, but it seems like it hits the tank when it is really just the fork stops.

Tank;  Gas tank or fuel tank.   Some of the history of the /5 and /6 fuel tanks.

tank bag;  A bag, or luggage, of some sort that mounts on the top of the fuel tank.   The Harro was the best one of the era.

taper fit;  A type of connection between rotating parts.   The BMW uses it on the output of the transmission and at the rear of older drive shafts.

Tapered bearing;  A special type of bearing common on BMW wheels, swing arms, and steering.

Throttle return;  This refers to the system for allowing or preventing a BMW throttle from returning to idle automatically.   Sort of a crude cruise control for the /2, /5, /6, and later years.

Timken bearing Timken is a USA company famous for making tapered roller bearings.

Tire bead;  The edge of the tire that seats against the rim.   BMW had a special rim for keeping the bead on the rim in a blowout.

Tire direction;  Unlike car tires, motorcycle tires have an arrow on the sidewall showing the direction of travel.

Tire plugs;  A system for fixing a flat tire.   Not recommended for a motorcycle.   It involves sticking a plug in the nail hole to plug up the leak.

Toolkit;  BMW is famous for supplying the best toolkit of any motorcycle company. 

TDC; is an acronym for top dead center.   This is the time in the cycle of the engine when the piston is the closest to the head.  

Top end;  This refers to the portion of the engine that is above the crankshaft.   The cylinders, pistons, and heads make up the top end.   On a BMW boxer, the top end is not at the “top” but out to each side.

Top hat spacer;  A part of the wheel bearing system used on older BMWs.  

Torque;  A measure of how tight something is or should be, as in turning a bolt or nut.

Torque wrench;  A tool for showing how tight a fastener is while it is being tightened.

Totaled;  This refers to any vehicle that is in a crash.   The insurance company finds that the vehicle isn’t worth repairing.   The wreck is a “total”

Trail;  A measure, in degrees, of the geometry of motorcycle forks.

Trailer Queen.; a motorcycle that is towed to events rather than being ridden.   A derogatory term.

Transverse;  Directional terminology for an imaginary line across the motorcycle from side to side.  BMW flat twin engines have cylinders in a transverse direction.

Trickle charging;  A way to slowly and gently way to charge a battery on a BMW. 

Triple tree;  The part of the motorcycle fork assembly that holds the fork tubes.

Troubleshoot;  Logical process to locate some issue or problem.

Turkey gobbler;  A noise that is loud and embarrassing to the rider of the /5 BMW motorcycle.   The name is because it sounds like a turkey gobbler.   It is related to the crankcase pressure.

Twisties.   A term that describes the roads that many BMW riders really like.   They are full of twisted curves and, therefore, the name.

Two up;  This means riding with a passenger.

Undersquare;  The design when the diameter of the piston is less than the length of piston travel.   Useful for high torque at low rpm.

Universal joint;  A method of transferring power from the transmission to the rear wheel.   Traditionally, BMW has used a drive shaft, while most other motorcycles used a chain.   The drive shaft must have a flexible part to allow for the travel of the suspension system.   This part is the universal joint or just U-joint.

Valve clearance;  Also called valve adjustment or valve lash.   This is the space between the valve stem and the rocker arm.   It is part of a regular maintenance program for your BMW.

Valve lash.   Same as valve adjustment or clearance as shown above.

Valve seat;  The part of the cylinder head that the valve head rests against during combustion.

Valve tuliping; refers to a process of failure of the valve head.   Soon the head may fall off and greatly damage the BMW head and piston.

Vetter;   Manufacturer of aftermarket fairings and luggage for motorcycles in the 1970s and 80s.   Craig Vetter

Vibration;  While the BMW twin is considered a smooth motorcycle, they do vibrate at some speeds and rpm.

Vintage;  An old BMW motorcycle.

Viscosity;  The measure of the thickness of any oil.   One must use the proper viscosity for different times of the year due to temperature changes.

Voltmeter to a battery;  Some of the later BMWs had a voltmeter mounted in the fairing.   They were notoriously inaccurate.

Voltage drop;  The loss of voltage due to resistance in a wire or connection.   Not a good thing.   

Volts;  A term for electrical pressure.   All BMWs had a 6-volt system up to the introduction of the /5 in late 69 for the 1970-year models.   Since then, they have all been 12 volts.

VOM, an acronym for Volt-Ohm Meter, is a very handy test instrument for electrical diagnostic use.

Waste spark;  A term for the type of ignition system used on the BMW twins.   One side or the other gets a “not needed” spark, so it is called a waste spark.

Watts;  A unit of electrical power.   Commonly used by owners of older BMWs, as they didn’t offer enough power to run modern accessories.

Wedding ring spacer;  An important part of the BMW wheel bearing system from 1955 thru 1984.

Weinman;   Manufacturer of alloy wheel rims for BMW throughout the 1970s

Went down;  Another common idiom for crashing.

Wet Clutch;  A common clutch type for many motorcycles.

Wheelie;  How to do a wheelie.
Windjammer;  A fairing manufactured by Craig Vetter with brackets to fit a BMW.   Significant in that this one product completely changed the industry in the early 70s.   This fairing was copied (stolen) by many others, most notably the Luftmeister.

Wires are fried;  Some, or all, of the wires in the wiring harness, were overheated and burned up the insulation.   Usually, it must be replaced.   On the unfused /5 from 70-71, it was common.

Wiring harness;  The term for the collection of wires that are usually bundled up in some protective tubing.   On an old BMW, they typically go from the headlight shell to all other points on the bike.

Woodruff key;  A small part that positions one rotating part on another one.   It goes into a keyway or groove.   Ex.  to position the flywheel on the crankshaft.   Used on older BMWs.

Update on 30 March 2023