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This is only the start of this
page. I have "stolen" this from Boxerworks and it was written by
Ted from Portland. As time permits, I hope to add more info about the
earlier models. If you feel inclined to add more info, please feel free to
do so. I will add it in and give you credit at the end. I imagine
that the info could have many contributors and get all mixed together. It
will be impossible to give credit for each sentence. Send submissions to
my email address below and put the word "Models" in the subject line. I will store them
till I get around to it.
1970-80 twin shock bikes.
These would include the /5 and /6 series...plus the /7s from 1977 to 1980. The
/7 designation officially ended in 1980, but you'll often see the entire 1977-84
stretch called /7s (in catalogs, etc.)...
-Often called the "heavy flywheel" bikes...this can be a
benefit or a detriment. The benefit is the legendary "buttery smooth"
idle and the smoothness at highway speeds...the heavier flywheel dampens the
firing of the cylinders. The detriment is acceleration...a heavier flywheel
resists change in speeds more than a light flywheel. One must learn to be
patient when shifting a heavy flywheel bike. It was/is a fairly common "hot
rod practice" to lighten the flywheel by machining holes, etc.
-The 1970-80 bikes will have a points and condenser ignition
system (unless it has been replaced by an aftermarket unit such as the Dyna III
or the Boyer system (there are others...those are the two most common
aftermarket units in the US, at least)). In 1979-80, the points were
changed to a "points-in-a-can" set-up...where the points set is
contained within a canister that helped to protect them from gunk, etc. (side
note: the camshaft drive is the same from 1979 on...the "points in a
can" system will fit the later bikes...this has been done for various
round-the-world bikes...the "points in a can" system uses very
commonly available VW beetle points...making road-side repairs in the middle of
nowhere a possibility. Similarly, the later, factory electronic ignition can be
installed in place of the points canister).
-All but the latest 1980 bikes will be without the pulse-air emissions system.
-1970 to 1973 bikes (the /5 series) will have a 4-speed gearbox with a
kick starter. The 1974 to 1980 bikes will be 5 speeds...the kick starters
on the 5-speeds are notoriously unreliable and
considered useless by many (note: after 1974, very few gearboxes will have the
kick starter...mostly ex-police models and the G/S series). 1970-77
will have a "direct link" shifter...where the shifter lever is attached and
pivots directly on the gearbox. 1978 and later bikes will have a "kinematic"
linkage...where, the shifter is attached to the foot peg and is joined to the
gearbox via a linkage rod (either the earlier "bent wire" type...or,
the stronger "ball joint" type). During the 1979 model year, the external
appearance of the gearbox changed...reinforcing ribs were added. The "new
gearbox" with the revised input shaft and shift plate changes came
later...the 1979-80 'boxes are (practically speaking) identical to the 1974-78
version, with the exception of the reinforcing ribs.
-1970-80 bikes will have the "round" air box and
"smooth" starter cover...with the choke lever (if applicable...some
early bikes had ticklers) mounted on the near-side of the air box. 1980 was the
transition year in this area...some 1980 bikes will have the later air box.
-All bikes up to 1977 will have wire spoked wheels...with the cast
"snowflake" wheels becoming available during the 1977 model year for
the "flagship" model...the R100RS. Supposedly, only ONE R100RS
actually had cast wheels in 1977...so, it should be considered a 1978 and later
feature. The rear disk brake first appeared in 1978...coinciding with the
cast wheels (the cast wheels were available in a drum version, too...the disk
version has a slightly wider rim).
-The switchgear went through many revisions up to 1978. In 1979,
the switchgear stabilized (for the most part) into the "small button"
switchgear.
-All front disk braked bikes from 1974-80 will have the front master
cylinder mounted underneath the fuel tank. They work quite well if
maintained properly,...but, due to the "inconvenient" location,
the maintenance was often ignored or overlooked.
-The 1981-84 bikes (and, all subsequent boxers) had a new "clutch
carrier" as opposed to the heavy flyweel. The carrier is essentially a
stamped steel plate and it weighs much less than the earlier flyweel...allowing
the engine to accelerate and decelerate faster. This kept some of the sporty
feeling that was lost due to emisisons requirements. (Don't tell anyone, but
a well tuned, stock 81-84 R100 will pull wheelies fairly effortlessly).
-Along with the new clutch carrier, a revised input shaft was used in the
gearbox. This prevents the early and late gearboxes from being directly
interchangeable...the flywheel/clutch carrier and associated parts must be
swapped ,too.
-In 1982, a "shift kit" was introduced as standard
equipment for the gearbox. This was a revised shift plate that had steeper
ramps between gears...this helped to prevent false neutrals. The kit can be
retrofitted to the earlier gearboxes.
-1981 and later bikes have the factory electronic ignition. A
fairly reliable system...the biggest problems seem to be sticky advance units or
a failed Hall Effect Sensor. Sometimes, the ICU will overheat due to poor heat
management...cleaning and reapplying heat-sink paste will go a long way towards
preventing this.
-Late 1980 and later bikes will be delivered with the pulse air emissions
system. Many folks remove the plumbing and seal the holes with various drain and
timing plugs.
-1970-80 bikes will have a "rounded" final drive housing...the 1981
and later bikes will have a "square" housing with cooling fins.
-1970-72 bikes will be Short Wheel-base (SWB) bikes. In early
73...the factory added a few inches to the swing arm to mask/hide some
handling issues...all subsequent bikes are Long Wheel-base (LWB). I don't
know much about /5s...there's plenty of info re: this change...see Duane's
website. Additionally, the swingarm changed again in 1977...to be
slightly stronger (coinciding with the 1000cc engine). In 1981, the
swingarm changed to the "big tube" version...and, had a cushioned
driveshaft (basically, a big spring that dampened things between the gearbox
output and the final drive).
1974 bikes will have a 14mm front axle...that changed to
17mm in 1975. *I think the drum braked R60/6 kept the smaller axle...my '75
has a 14mm axle.*
-1970-80 bikes will have aluminum cylinders with a cast iron liner.
In 1981, the cylinders were changed to a plated bore...often
referred to as Nikasil or Galnikel. The plated cylinders are noticeably
lighter than the iron lined version...and, the plating tends to wear much better
than the iron.
Okay...I'm getting tired. These are just some highlights...I missed a lot,
I'm sure. Also...one of the great things about the 1970-95 BMW boxers is the parts
swap-ability. This creates a lot of flexibility as far as updating,
repairing, or maintaining a bike. It can also add a lot of confusion when shopping
for a bike. For instance, it is very easy to drop a 5-speed gearbox into a /5. It's very easy to put a dual disk fork on a /5 or /6 that originally came with a
drum brake. Etc.
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