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Front main bearing cap/holder/carrier.
MAIN SEAL Installation. 
Grabby clutch.
Oil pump & oil pump cover.
Timing Chest Seals.  Rod bearings.  
Rod bolt tool.  VIBRATIONS.

Copyright, 2014, R. Fleischer
Article 60, sub-section 2


This is CRITICAL! Flywheel Removal/Replacement is the first item here!!

NOTE:   If you remove your flywheel for any reason, be sure to FIRST set the engine
to OT, top dead center, Oberer Totpunkt, and be sure that OT is STILL in the
timing window when replacing the flywheel

There are potential trouble areas when removing & replacing a flywheel (or,
from 1980, called the Clutch Carrier).  First trouble area is the moving of the
INNER HIDDEN thrust washer off its two locating pegs, which YOU MUST
PREVENT by the use of a crankshaft blocking tool, information later herein
(with a photo).  There is a second thrust washer & that REAR thrust washer,
similar-looking, but probably a different thickness compared to the front one;
it can also come off its two locating pegs.  It must be on its pegs, & not be
rotatable by your fingers (check!) before you reinstall the flywheel. 
Sometimes the pegs do not stick rearward very much.  

You can use a very thin amount of a soft grease to 'stick' the rear thrust
washer to the boss/pins.  Thrust washers are listed in parts catalogs by
that name, & also by such names as stop discs, thrust discs, or stop rings.

Below three photos show why the thrust
rings must not be allowed to come off
their two locating pegs....they will be
ruined by tightening the flywheel bolts.
FURTHER, if you continue tightening,
there is a great danger of cracking
the rear engine case.

Inside view of crankcase, showing where forward thrust washer fits onto the pegs, crankshaft removed. Three assorted thrust washers.  Crankshaft installed, but slightly forward and tilted to show some clearance at thrust washer.  Photos courtesy of Marten Walkker; with permission to use.

When you remove the flywheel, such as to replace a main seal, oil pump
seal, etc., it is CRITICAL that the crankshaft be BLOCKED from moving
forward.  This blocking is usually done by some sort of makeshift tool that places
pressure against the alternator rotor center bolt.   This can be done in
many ways, such as a piece of 2 x 4  lumber bungeed to the cylinders
or exhaust pipes; with a screw to press against the rotor bolt. 
A small
easy-to-make tool c
an be made of a piece of Allen wrench with a welded
or brazed fender washer on one end, over-all about 3/4 inch long. 
outer cover holds it in place, the tool being made just a bit too long to
allow the cover to fully bolt-up to the engine; this gives a bit of pressure
(do NOT but LIGHTLY tighten the cover bolts!!).  The tool's Allen end
simply fits into the existing alternator rotor bolt head. 

Here is a photo of how a very simple bolt method is used.
 "Source: Brook Reams,"; by permission.

8 mm bolt, of appropriate length,
placed into alternator's existing
allen-head bolt, so that the outer
cover can be NOT QUITE brought
fully-home to the engine, with
LIGHT pressure on the cover's
bolts.  ((One could remove the
existing bolt and screw one in, for
another method)).


I'm really not a fan of that...but it IS functional.  I prefer a screw-in
and therefore adjustable bolt, OR, my tool, below:

Here is what Snowbum uses to hold crankshaft from moving forward:
Make the tool out of a piece of 6 mm Allen wrench material.   Weld a steel disc
or 'fender washer', perhaps one of 1 inch in diameter, onto one end of the cut
piece of allen wrench material.  The washer should be maybe 1/16" thick (not
critical, no harm with thicker).   Make the length such that the Allen end fits
FULLY into the stock existing alternator bolt, & the disc end presses against
the inner surface of the timing chest cover.  Usually ~3/4 inch overall.  Weld
the washer squarely to the straight piece of 6 mm Allen wrench.   The last time
I made one of these, I made it to fit my 83-84 bikes; the OVERALL length was
3/4".     The length should be such that there can be some light pressure is
applied by the cover when the cover is screwed back onto the engine LIGHTLY,
but the length of the tool is such that the cover can't be brought back fully to the
engine surface. DO NOT over-tighten.     




Whatever tool you make and use, be sure it cannot rotate and thus loosen its pressure....if you rotate the flywheel (or, in later models, called the clutch carrier).

If you do NOT block the crankshaft, there is a REAL RISK of the crankshaft
moving forward a small amount. 
Very little movement will cause
forward thrust washer to move off its pegs.  T
he thrust washer will not be
aligned on those pegs as you tighten the flywheel bolts (you do not have
to tighten very much to cause damage).
to the thrust washer....
AND you could damage OR RUIN the engine casting!

BTW....the two pins go completely through, that is, you see two, & there are
only two.  They must be rearwards enough for the rear thrust washer to fit, &
not fall off....if they are seemingly just a bit short on the rearward side, but the
thrust washer fits adequately, then add some soft grease to the forward side
of the rear thrust washer during assembly...that will keep it in place, sort-of
like glue, until the flywheel (or clutch carrier) is installed and fully bolted-up.

With a thrust washer having fallen off its pegs, you will find that the crankshaft will
essentially freeze up as you tighten those bolts.  You REALLY DO NOT want this

happening!!  You do NOT want to even get near the point of the crank freezing up.  
If you forgot or did not know about blocking the crankshaft,
& you want to know IF
the crankshaft has moved, the sketch, well below, will give you the information.
If you have ruined a REAR thrust washer, that is NOT a disaster (assuming you
did not injure the bosses area).   You just need another thrust washer of the SAME
COLOR identification.   Sizes are also listed in the literature.

If you have SECURELY blocked the crankshaft before unfastening the
flywheel bolts, you have nothing to worry about, regarding the crank
moving & the forward thrust washer dropping.  
You must be careful about
the rear thrust washer coming off its pegs, when you re-install the flywheel.

The TYPICAL only way to see & get to (however slightly) & MAYBE get the
thrust washer back in place if it has moved off the pegs, but is
undamaged, is either by removal of the right cylinder.....or disassembling
the engine
(totally!).  HOWEVER, you MAY have lucked-out, so scan down
to the following section:
"Another way of explaining things:"
Probably you will NOT be lucky.

Do NOT think that you can fully tighten the flywheel bolts to see if the
crank will start to seize up; that is, if engine rotation becomes more
difficult.  By the time you tighten that much you already have likely
caused damage.  If you think you may have goofed, take measurements!

If the forward thrust washer has already been destroyed/damaged, then
disassembling the entire engine is your
only option.  This is very serious
business, with many additional ramifications not mentioned here.  So,
heed my words, heed this article!!  BLOCK THE CRANK!!

YES, I am WELL AWARE that many have never had a problem from not blocking
the crankshaft. PLEASE heed MY cautions; DO block your crankshaft.

Below is a sketch of the flywheel & end of the crankshaft of your Airhead.   
Following this section is information on main seals, etc.

Dimension B is the depth of the flywheel (or clutch carrier, as it is called on 1981+
models) where the crankshaft boss fits into.   The sketch is simplified.

Another way of explaining things:   "A" must be greater than "B" by
at least .05 mm.  If A is LESS than B, by, perhaps, 3 or 4 mm, then the crank has
moved forward; a thrust washer has slipped.  If you try to bolt-up the flywheel,
serious damage will occur.   
If the amount of forward movement is quite small, you
may be able to move the crankshaft backwards with some relatively modest
pressure at the alternator rotor. This might also be done by bolting up the flywheel
to the crankshaft VERY LOOSELY & moving the flywheel rearward by hand pressure.  
If you can move the crank by either method to the proper dimensions, A is larger
than B, you have 'lucked-out', & you can tighten up the crank to torque specifications
& the crankshaft will not lock-up.
Be really careful!   















The above original sketch was done by Tom Cutter who furnished it to
me as I was too lazy to make one.  That sketch was improved for clarity
for me by Peter Holdcroft in July 2012.

Things look a little bit different for the clutch carrier models (1981+), but
will be able to see if there is a problem by taking the measurements. 

I cannot emphasize enough how much I recommend you BLOCK THE
CRANKSHAFT, by one of the methods outlined earlier in this article......
thereby totally avoiding any problem...and you certainly will have no
need to take these measurements. 


Flywheel bolt torques :
This is in reference to a BMW Service Information bulletin (we call them SI's),
dated November 1991, #11-049-91, sub number 2495, & this can also be seen
on the 12/92 fiche on page 3, G23.   In brief, it stated that while the flywheel
bolts were previously at ~75 foot-pounds (100 Nm), they were now to be at 90
foot-pounds (125 Nm),... first you cleaned the threads,... & then the threads
were to be OILED!  BMW specifically said that the bolt limits would NOT reach
their limit of elasticity at that torque, & could be REUSED!   

I personally get more than a bit nervous, at 90 foot pounds & oiled, so I will
NOT tighten them that tight.  However, some do; I have heard of no problems
reported.  It is YOUR CHOICE.  NOTE that this is in regards to the 11 mm bolts....
certainly not to the  /5 & early /6  smaller 10 mm bolts.  These early bike 10 mm
bolts need replacement upon each use, which the 11 mm do not (unless
overtorqued).  Those 10 mm bolts in the /5 & early /6 are absolutely not be
torqued to such high values.   There were two lengths of 10 mm bolts used.

There have been a lot of different specifications on flywheel bolts over the
years.    I use (clean & dry) torques of 42-45 foot-pounds on the 1973 & earlier
engines; for the 1974 I use 52-55 ftlbs; for 1975 & later models I use about 75
to 80 ftlbs.   I am OK with any of the bolts being faintly oily.  Some aftermarket
literature will show different flywheel bolt torques for different engine sizes
for the same year.  DISREGARD such advice. The big difference is in the size
of the bolts, with the earlier 10 mm bolts using substantially less torque.

For additional the section on flywheel bolts:

Crankshaft rear main seal:  

Repeated Note:   If you remove your flywheel for any reason, be sure to FIRST set the
engine to OT, top dead center, Oberer Totpunkt.  B
e sure that OT is STILL in the
timing window when replacing the flywheel. This ensures that you have not
rotated the crankshaft.

Crankshaft main seals came in a number of styles over the years.   The very latest seal,
of a Teflon-like material, is quite different in design from the early seals.   The latest type
is 11-11-1-338-342.

A type of geese-honking noise can sometimes be heard on an engine with the old style
seals.  This noise comes from the slight vacuum created in the crankcase as the pistons
go OUTWARDS, & the atmospheric pressure, being higher in the clutch area, pushes
air into the engine.  The biggest problem is NOT THE NOISE; but that clutch dust, which
is abrasive, moves through that seal, slowly eating it away.  This is not good for the rear
of the engine, let alone anyplace else the grit gets into.  It primarily happens on old worn
seals, even if not yet leaking oil.  CHANGE THAT SEAL!

Early seals were very conventional looking, a white color lipped rubber seal (there have
been more than one type of lip & seal color) with a coiled spring backup.  For the /6 &
later, BMW ADDED an O-ring in the flywheel bore.  For the /7 & later BMW added
a metal cap ("Guide Ring"); the O-ring is inside. 
In 1981, BMW changed the design
of the flywheel/clutch for lighter weight, which gave faster engine acceleration &
deceleration due to less inertia....unfortunately with more vibration.  Other effects from
this change were to reduce clutch hand lever pressure & changed the shifting feel,
depending on throttle setting.  The light and redesigned flywheel then had a new name:
clutch carrier.

The pre-1981 heavier flywheel had the main seal lip resting on the flywheel boss, so when
the flywheel was inserted into the engine, the seal sort-of curled; ever so slightly inward.  
For those earlier models, I have recommended that the flywheel seal area be laboriously
polished with ONLY crocus cloth (in kerosene).  Crocus cloth is a super-fine-grit polishing
paper.  Absolutely no fingernail felt irregularities are allowed in the flywheel sealing area...
although discoloration is normal.  All seals before the latest Teflon type, 11-11-1-338-342,
were installed slightly different or controlled depths to avoid old rubbed areas. 

Main Seals must be installed squarely.   Main Seals often fit very tightly, & you
might have problems trying to get them into their cavity.  It REALLY DOES HELP
to warm the engine case up, considerably, in the main seal area; and this can
take quite awhile.
  Lightly oil the seal just before you install it.  Install it squarely...
it must be
installed straight & square.

The cap, or "guide ring", is used on the later models.  The clutch carrier fits to it, the
guide ring is over the crankshaft; it has a center lug to enable it to be pulled rearward by
a factory tool.  To replace a main seal, you have to remove the guide ring first.  You can
improvise.  You can use a flat punch to rotate the ring until some of each crankshaft hole
is covered, then pry to the rear....use a small screwdriver or similar, pry a bit on each
hole/guide ring.   Be careful not to damage the guide ring nor the threads.  Once
the guide ring is out, you can remove the main seal.   The Guide Ring can
deteriorate (hard coating).  If the surface appears to be deteriorating, that
surface could have teeny imperfections that would eventually tear-up a new
main seal.  Replace the Guide Ring if it has so deteriorated

With the guide ring removed, you then install the new-style main seal.  The guide ring
with a new O-ring!) is then moved into the main seal, using the carrier bolts.  When
using the bolts for that, you may need to use spacers under the bolt heads....see the
guide ring installation photos, later here, showing the bolts with some sort of junk-box
provided spacers under them, to allow the bolt heads to be turned properly.   As the
guide ring is installed, it makes the "Teflon-like" seal working part move forward.  That
helps the seal maintain oil integrity as crankcase pressures increase during engine

Leaks that seem to be the rear crankshaft seal could actually be that rubber
O-ring.   However, determining which is which may not be so simple, so most
just replace both mainseal & O-ring.

Main seals can be installed using the special factory tool, but if you are careful, you
can do this with a prepared block of wood...but I recommend Ed Korn's or similar plate
tool.  Install the seal
absolutely straight & square.  While I think ONLY the latest
seals type should be used, which is installed to full depth, if you have an
older style seal you are installing, you would install at the same original depth...
except that early flywheels with a big radius are best installed not quite fully...
maybe a mm will be proud of the surface.   See notes below.


Here is a link to a pdf file on this website that has the factory information on the new
style seals:

MORE on the new style seal:
The latest 11-11-1-338-342 seal is a "Teflon-like" (PTFE) seal.    NOTE that it
is designed so if you install it squarely, you can install it fully, without
bothering about setting the depth. ...but read the following:
There area two types of flywheel (or clutch carriers) in use.  If the front end
has a small radius, then the seal is installed to full depth.  If there is a taper,
as on early flywheels, then the seal is rearward a small amount, about 1 or
1-1/2 mm.  Oak uses rear ring gear shims for that, installing the shims, then
the seal.  I don't....because I don't have any stock of them anymore, and they
are not absolutely needed.  Early style tapered flywheels do not have to have
the seal 'preformed', but I do it anyway.

Hints: The latest version needs no oil soaking; but it is best to install it oiled
or lightly greased a bit for ease of installation.
While you do NOT have to do
this, I do:
soak the new seal & installation tool in 150F +-   engine oil for a few
minutes....the warmth helps prepare the seal, perhaps softening it.  

If you have an earlier new seal (are there any still around?)...I suggest you toss
it and use the new seal.

Using a very fine sandpaper, sand the aluminum entrance edge to the bore
in the case to allow the seal to press-in easily.  Oil slightly (or lightly grease)
the bore area of the engine case that the seal fits into & the seal outer too. 
If you heat (it takes a fair amount) the engine case around the prepared seal
bore area, then add a tad of grease or oil, the seal will press-in much easier.

If you fail to oil or grease the new seal during assembly, it may squeak for a
short while after engine start, until oil works its way to the seal.    Press the
new seal in squarely, using a flat plate seal installation tool, or fashion
something.   Install the flywheel (carrier) with a bit of oil on the nose.  Keep
in mind what I said earlier about the seal depth and taper on the flywheel nose.

Oak did an article on main seal installation in the MAY 2004 issue of AIRMAIL
(see page 17-18)...where he discusses much of this in some depth, in response to
a question posed by someone.  

Be sure the 5 holes in the guide ring are exactly aligned with the crank holes,
as you do this job.  

If you use one of the plates-type of installation tools, you do not tighten the bolts
very much.

Some recommend installing the flywheel when it has been heated fairly hot.  When
you align a 'flywheel' to the crankshaft, install by eyeball first.  YOU SHOULD HAVE
previously set the pistons fully outward; now when you reinstall the flywheel its OT
mark is in the timing window when you've double checked the pistons are fully out
on the pistons.  Then insert the bolts lightly finger tightened, & then find the centering
point of the assembly, by moving the flywheel CW & CCW, back & forth, mounted
loosely by the bolts...there will usually be a very slight amount of play.  Then tighten
to only a few foot-pounds, evenly, cross-pattern as best you can.  If the flywheel
was not heated, tighten fully to specifications at this point, in a cross-pattern.  If
the flywheel WAS heated, wait until it has cooled, then tighten fully to specifications.
Mind the torque.  As noted previously, the early 10mm bolts must be new.  The
11 mm ones are reusable, unless damaged from over-torquing, etc.

A tool can be fashioned to lock the flywheel/carrier, while the bolts are
torqued.  Such tools are shown in photos in such as Clymer's & Haynes
manuals, BMW literature, ETC.  The original BMW tool may even be available,
but the tool is quite simple.   I recommend you do NOT lock the
flywheel/carrier by using the starter teeth.

Brook Reams has an article that clearly shows using these tools:

Main Seal installation tools:
(if you decide to use them, and I recommend you DO!)

The original BMW main seal installation tool was #880; various numbers were
used in front of that one, such as 88-xx---etc.

There is an article on making a fancy, nice, main seal tool that works fine with
the later seals.  The article is here:

In the photo below, note that the BMW stepped plate can be used upside
down for flush seals, or with the step to the inside for installing to slightly
forward of flush.   The Ed Korn type tool shown uses setscrews to adjust
the depth; the tool seller provides instructions with the tool. There area
two types of flywheel (or clutch carriers) in use.  If the front end has a
small radius, then the seal is installed to full depth.  If there is a taper, as on
early flywheels;  the seal is rearward a small amount, about 1 or 1-1/2 mm. 
Oak uses rear ring gear shims for that, installing the shims, then the seal.
I don't....because I don't have any stock of them, & don't see the need.

The above type of plates (or, ~~ similar) can be modified to
add a central threaded hole, & to add 2, 3, or even 4 radial
holes.  The plate can then be used for removing the seal;
not just installing a new seal. 
  Removal is done by
installing 2 or 3 of the bolts, LIGHTLY tightening them &
thus the plate, to the crankshaft.  Then screw pointy sheet
metal screws through the plate & into the seal.  The central
threaded hole has a large diameter threaded hole. Remove
the crankshaft bolts, & then installing & tightening the
central bolt, will cause the seal to be pulled out. 

Photos below:

The above six photos, which I have cropped, were provided, with permission to use, by:
 "Source: Brook Reams,".
These photos show the seal being removed and then the new seal being prepared for installation.

Thanks to Al Patton for supplying the below original photos of a
later type Airhead (has the Guide Ring), which I have modified &
placed below; which, with the above photos, should show you all
you need to know.

NOTE thrust washer on pegs.  NOTE 5 bolt holes in the crank, symmetrically arranged. That is why you MUST align the flywheel/carrier for OT mark with pistons fully outwards!

Note the white spacers used here. Without them you could not rotate the bolts.

Note holes all lined-up

The 10 mm hex bolts at the
oil pump cover are later types.

NO need to tighten much!
When installing the flywheel, mind information early in this article on bolts & their torques! If flywheel bolts loosen, considerable damage can occur.   This most often was seen on the old /5 bikes, with the smaller (10 mm) bolts, with someone forgetting they were on a German bike, & shifting the wrong way, from, let us say, 2nd, with lots of rpm, down to first.  That sheared the bolts.  I've fixed a few of those!! If you are removing the clutch (obviously needed if removing the flywheel), MARK the position of the major parts to each other, except the clutch diaphragm spring.  Factory marks are at 120.
NOTE:   If you remove your flywheel for any reason, FIRST
set the engine to OT, top dead center, Oberer Totpunkt, and be sure that OT is STILL in the timing window, or very close to it, when replacing the flywheel.  Pistons are fully outwards, or very close to that.
If the flywheel has a groove (it will if it is 10/1975 or later), it needs an o-ring there.  It was 11-22-1-337-099, now is -093.  A long time ago the number was 11-22-1-263-798.  The O-ring is called a Seal Ring by BMW.  It is 59 mm x 3 mm.

Suppose the engine rotated some, or you forgot to mark things...or, the
flywheel or clutch carrier was miss-positioned by a previous owner. 
How do you find the proper flywheel position?
The safest method is probably this:

1. Remove the valve cover on left cylinder. Remove left & right cylinder spark plugs;
    engine is easy to rotate. INSTALL A FLYWHEEL STOP TOOL at the alternator
    rotor!!!!!   If  you use a bolt for that, use a nut on it, to be sure that the bolt
    will NOT screw inwards as you rotate the engine!

2. Place the flywheel into any bolt-hole positioning, putting in a few bolts, fully home &
    lightly to moderately tightened.  
3. Rotate the flywheel slowly in the NORMAL direction, which is CLOCKWISE as you
    face the flywheel from the rear, as you shine a light into the left spark plug hole.  You
    will see the piston come fully out, then reverse.
4. Rotate the flywheel slightly back & forth, CW & CCW, until piston is seen to be fully
    outwards.  Some might use a round tip metal rod for 'feeling' the piston, if so, Do
    NOT bugger-up the spark plug hole edges. Rotate back & forth, etc.,
    SLOWLY/SLIGHTLY.  Do NOT use a pencil, it could break.
5. With the piston now fully outward, if the OT mark is not someplace IN the timing window,
    reposition the flywheel.
6. With the flywheel now in proper bolt hole position, have its bolts LIGHTLY loosened...
    just barely enough that you can rotate the flywheel by hand JUST ENOUGH to FEEL
    the slop in the bolts/hole.  This may be negligible. If present, center the flywheel in that
    sloppiness.  NOW tighten the flywheel bolts more.  Do NOT take the chance of moving
    the crankshaft forward; remove the crankshaft stop tool only after the flywheel is in
    final position & those bolts tightened!!!
7. At this point you probably have everything ready to FULLY tighten, in some sort of
    cross-pattern, the flywheel bolts, according to torque specifications....

Oil pump and oil pump cover:

The oil pump inner rotor INNER EDGE is chamfered, in case you remove it & wonder
what direction to replace it in.....and the punch marks go to the rear. You do not have
to line up the punch marks.  Oil pump clearances are easily measured with common
feeler gauges & a machinist's or other straight edge rule, on edge.   Here are some
general specifications:
Rotor 2.22"  +0-.0009"
Housing 2.23"  +.0017" -0
Rotor end clearance .004-.007"
Rotor thickness .54" -.0066+.0013"
Rotor to housing face .001" to .0023"
Rotor to rotor clearance .0046" to .0117"

The oil pump cover O-ring may be replaced easily any time the flywheel is removed.  
Original oil pump O-ring was black 11-41-1-250-274, 0.079" thick.  That part was
discontinued a long time ago in favor of a red O-ring that is slightly thicker, at 0.084",
part 11-41-1-335-895.  SOME parts lists & on-line fiche, will show it as

Early oil pump covers had Phillips screws, which often are a problem to remove (use
of the hand-operated impact wrench listed in my
article is highly suggested!).   Early pump covers had tapered screw holes to
accommodate the flat head Phillips screws.   Early pump covers did not seal
well; the later type cover ALSO fixes that potential problem, by groove depth
& later thicker O-ring.
 If you have a Phillips-screw type of cover, I recommend you
install the later pump cover, with the later hex-head bolts.  When installing the pump
cover with its new O-ring, grease the O-ring, or otherwise be very careful that the
O-ring stays in place during the installation/tightening process.  I use Loctite BLUE
on the bolt threads.  I am careful to tighten the 4 bolts evenly, in a cross-pattern, a
bit at a time, until tight....88 INCH-pounds (that is only 7.3 footpounds).


When setting up a lower end, particularly if it is a NEW crankshaft, you must use 
BMW specifications for matching the crank color code; main bearing bushings;
bearing cap (front main bearing holder).  Generally, it is a matter of matching color
codes on these things...the Factory Manual has the various specifications. If unsure,
for the final word, ask on the Airheads List, rather than use Haynes or Clymers
manuals (which are OK for getting ideas about how things might be done).   Some
things are not in the factory nor Haynes nor Clymers manuals.  I probably have the
details later in THIS ARTICLE.

MOST of you will never have a crankshaft out, let alone be changing one.   A few
of you may have the crank out for re-shimming.  BMW lower ends are very
long-lived, providing they get clean oil all the time.

A very grabby clutch, vibration, hard shifting, & idle rpm change with
clutch lever use AFTER full warm-up usually indicates a need to re-shim
the crankshaft.  Do NOT get confused here, as it is normal for idle rpm to
speed up SLIGHTLY with clutch lever pull-back with cold transmission oil,
even in neutral. Details are in this article somewhat further down this page.


Front main bearing and its cap/holder/carrier:
Changing the front main bearing? Confused about its holder/carrier? 

Pay attention to the information in the books about properly positioning things; the
oil holes being vertical ...and about the drilling needed on the two holes through
the bearing...0.124"...right through the existing front bearing carrier.... and then
the bearing area.  A new locating pin hole....taper hole, partial at 0.156", & full
at 0.148"....there is a special ream...etc.   All this is being mentioned for you, &
not put in exacting detail, to be extra cautious in not just willy-nilly changing/doing
things.  Things are not always as you may think they are....ask questions
on the Airheads LIST!!  If you have the BMW Factory Service Manual, it
will show the front bearing carrier drilling setup.

To remove the front holder you need to use a puller, either BMW's, or a steering
wheel type for a car.  Use a good hardened bolt with a countersunk depression
(use a lathe), in the crank nose, for protection.  YOU MUST HEAT THE AREA

There is a bushing (main bearing) in the main bearing cap.  Heat the cap to sizzle
& press out the bushing. Reheat to install new bushing.  Be sure to line up the oil
hole & have the joint properly offset from vertical (the hole).
  I can supply a photo
of this.  Once the bushing is installed, you have to drill two oiling holes, & ream
properly.  The bearing cap holes are already 3.2 mm.  Details as in the factory
manual must be followed.   You will be installing a retaining pin, a taper fit; locking
it in place with punch marks.  It prevents the bushing from rotating, & cutting off
the oil supply.


Grinding crankshafts...???:

Do NOT even think about re-grinding crankshafts unless you are prepared to
re-heat-treat (maybe hard plasma coat; nitriding?) the area that was ground,
& to properly radius the sharp corners, etc.  You would need a clever machinist. 
The crankshaft has cheeks in the way hindering being re-ground.  All this
WOULD BE VERY tricky to do.  BMW offered its published/available
undersize bearings NOT because a used crankshaft can be reground,
BUT, because of RARE production use of undersized crank journals.
The nitride type hardening of the stock crankshaft is not very deep!  Due to
the weights on the crank being in the way, I don't think you will be able to
grind a crankshaft anyplace, let alone re-nitride treat it; or do plasma coating,
ETC.  If you find a company that can AND DID do all this for you, please let
me and the Airheads LIST know about it!


Crankshaft end play, spacers, etc...
Crankshaft end play is set via two thrust washers at the rear end of the
crankshaft. Photos are much earlier in this article. One each of selected
thickness thrust washers (they come color graded for thickness) is used, &
it is common to have them of different thicknesses in the same engine. 
These are the thrust washers with the oil groove and 'strange look' that FIT
ON THE two PINS at the rear of the engine case.  One thrust washer is
forward of the casting boss, one behind it. 
It is NOT a difficult job to set end play....and ALL the details are just

Fairly rarely...after huge mileages usually, one sees an Airhead that has
two or more of the following symptoms:   Shifts hard, (BUT isn't input
shaft play or lack of splines lubricant or bad clutch).  Probably has a
lurching, grabby clutch action.   Idle rpm is unstable & varies a fair
amount with clutch pull-in even after engine warmup.
There is engine
A grabby clutch can ALSO come about from clutch parts AND
from excessive transmission input shaft end-play.


If you have an airhead with such symptoms, you will want to check the
end-float (end play) of the crankshaft. You are advised to see an expert, or
to get the BMW official information, but here is likely all you need to know. 
You will have some color(s) of thrust washers on both sides of the engine
housing boss area.  It is these that set the end-float of the crankshaft.   SOME
BMW Manuals have the sizes of these WRONG (in converting the mm
to inches).
  If your existing crank has only excessive end play, you may want
to just change the thickness of the REARWARD spacer.  BMW has specifications
on end play, or end-float as they call it.  You need to understand that it
varies if oily or dry; BMW does not tell you about that. 
The end-float
specification is 0.08 to 0.15 mm (which is 0.003" to 0.0059").  This is for
  If oily, the minimum is 0.15mm (0.006").    If you have removed the
crankshaft & are installing it.... you may want to lower your labor by installing
the thinner RED spacer inside.  Thusly you likely will not have to remove the
crank again, just select the appropriate rearward spacer. 
Note that BMW has a limit for wear; it is 0.20 mm (0.0079").

Here are the real values of the thrust spacers:
RED:   2.483 mm to 2.530 mm (0.0978" to 0.0996").
BLUE:  2.530 mm to 2.578 mm (0.0996" to 0.1015").
GREEN:  2.578 mm to 2.626 mm (0.1015" to 0.1034").
YELLOW:  2.626 mm to 2.673 mm (0.1034" to 0.1052").

Crankshaft REAR bearing (a bushing type):
The case is heated to sizzle in the area; the bush pressed out.  The case
is reheated to install the new bush.  The bushes are available in oversizes
to match your existing crankshaft, if it came undersized. YOU CAN NOT
likely have your crank ground properly if the bearing area is bad. MAYBE. 
There is a oil groove & oil HOLE in the new bushing.  As you look from
the rear of the case, with the pan surface facing you, the joint of the bushing
is at the top right, & the oil hole is at the top.  That is, the bush joint is 26 to
the right of vertical.


Regarding rod bearings, caps and bolts:

I do NOT reuse the rod bolts!.....
The conrod bolt is a special type, although it looks like a Torx.   You can get
the tool from NAPA as part 2305, which is the same as K-D tools part 2305.  
Be sure
to oil these parts rather well as you assemble them & also put the tab
into the cap slot; & the rod on correctly....that is, the located pins will be facing
forward! Tighten the rod bolts slowly, don't use too much torque at first, so you
can check for smooth operation of the rod on the journal....BEFORE you
tighten to the final value of 35-38 footpounds; NOTE that the R80GS, R80R,
R100GS, and R100R are to have the rod bolts tightened in stages, by degrees.  
Initial preload on them is 15 footpounds, then you go to 40-45 degrees more.

Additional hints/notes....regarding vibration, noises, etc.:
(1) There have been instances, in the seventies, ....(& suspicions by me
      of even in the eighties in some R80 engines, possibly others), that
      some noisy engines, or engines with vibrations that have not shown
      up as being due to anything else... are caused by out-of-tolerance
      crankshaft bearing fitment. I do not mean the thrust spacers at the
      rear of the crankshaft that set end-play of the crankshaft; I mean the
      bearing shells & crankshaft journals.

      This is a complicated subject, & reference to a very technical SI is
      needed.  The main journals should have a clearance, measured by
      PlastiGauge or other means, of 0.0014" to 0.0026".  If the clearance is
      over 0.0026", BMW offers a mid-oversize bearing shell, number
      11-11-1-265-437.   This is the green one.  There are quite a few other
      such shells, of various dimensions, you would need the SI, & a fiche
      or on-line listing(s), & some knowledge. 

(2) To measure the front main bearing cap internal diameter, the
      crankshaft must be removed, but the cap bolted in place!

Timing chest seals:
There is sometimes confusion over the alternator & camshaft seals used in
the inner cover.  All models use 11-14-1-255-011 alternator seals, probably
28 x 47 x 7 mm...have not measured to confirm that exact size.
The camshaft seal up to models built in 9/1975 was 11-14-1-261-193.   It
must not be use in later models, or there will be leaks. The later cam seal is
11-14-1-262-977, is 20 x 32 x 7 mm. See the article on doing a 'timing chain'
job on this website:


For the curious, the chain size is 3/8 x 7/32, both SIMPLEX and DUPLEX.

Crankshaft bearing:   For many years, this was number 07-11-9-981-722, and
is 35 x 62 x 9 mm. The bearing number has been changed to  07-11-1-468-882.  
It is a common bearing, but you must get the correct GRADE:
The bearing is   FAG16007-C3



02/04/2008:    incorporate all previous revisions; expand and also add information from "being-eliminated"
                     article engineinternals.htm; clarify details on main seal installation.
02/11/2008:   Photos of rear seal installation.  Fix typo on which sub-section of article 60.  Edit entire
                     article A/R, for clarity and emphasis.
04/24/2009:   Minor changes to text in one photo.  Clarify the 90 foot-pounds that are only on the 1981+
05/10/2009:   Remove most of the emphasis and base colors, as experiment.
01/15/2010:   Clean up article for better clarity, less verboseness.
08/08/2010:   Add information on the crank tool from my TOOLS article
05/31/2011:   Cleanup
08/01/2011:   Add Addendum area with note on the REAR thrust washer problem.
06/18/2012:   Add minor commentary on the O-ring.
07/29/2012:   Flywheel warning sketch replaced by improved clarity version. Clean up article a bit.
09/04/2012:   Add "suppose the engine has rotated some...." section.   Add QR code; change Google ad
                     display, add language button
12/12/2012:   Insert old crank.htm article and begin to completely revise
05/01/2013:   Oil pump O-ring part numbers and description changed.
08/03/2014:   improve the description of the crankshaft and bearings tolerances description and why.
04/06/2015:   Additional information on the O-ring, and history.
12/24/2015:   Update the meta-codes.  Revise entire article for layout,  left narrower justification, and
                     reset tables orientation, etc. Clarify some details.  Combine sections for clarity. 
                     NO technical details changes.
02/23 /2016:   Slight changes to meta-codes.  Increase fonts A/R to 14 & 28.  Eliminate some superfluous
                     items.  Eliminate some repetitive items.  Narrowing of entire article.  Obtain some photos
                     from Brook Reams and Marten Walkker, permission to use, with acknowledgements.
02/27/2016:   Fix typo on the bolt Brook uses at alternator, and add comment.

Copyright, 2014, R. Fleischer

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Last edit of THIS page: Monday, May 23, 2016