Flywheel, removal warning, main seal, oil pump cover, oil pump

This CAN BE CRITICAL, so Flywheel Removal is the first item in this article:

When you remove your flywheel for such as to replace a main 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 some pressure against the alternator rotor center bolt. This can be done in many ways, such as a piece of lumber such as a 2 x 4, bungeed to the cylinders or exhaust pipes and with a screw to press against the rotor bolt. Very crude, that. A small easy to make tool can 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. The 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, and this gives a bit of pressure. The tool's Allen end simply fits into the existing alternator rotor bolt head. A picture of this sort of small tool is on this Snowbum's website, at tools.htm as item #8 of that article. If you do NOT block the crankshaft, you run the risk of the crankshaft moving forward a small amount... probably it could possibly move a bit under 1/4", and the HIDDEN thrust washer COULD move off its pegs. If that happens, the washer will not align back on those pegs as you tighten the flywheel bolts, and you run the risk of MAJOR DAMAGE to the thrust washer....even the engine casting. You will find that the crankshaft will essentially nearly freeze up as you tighten those bolts. You REALLY do NOT want this happening. If you forgot or did not know about blocking the crankshaft, and you want to know IF the crankshaft has moved, Tom Cutter's sketch, below, will give you the information. The dimensions need to be as shown, in order to know that the crankshaft has not moved. The only way to see and get (however slightly) onto the hidden thrust washer, if it has moved off the pegs, is via removal of the right cylinder.....or disassembling the engine! Do NOT think that you can simply tighten the flywheel bolts and see if the crank starts to seize up, that is, if engine rotation becomes more difficult. By the time the crank gets to that point, you already have caused damage to pins and thrust washer.

If the thrust washer has already been destroyed/damaged, then disassembling the engine is your only option. This means a total tear-down, and includes pulling the front bearing and removing the right piston, enabling you to move the crankshaft forward in order to replace the thrust washer. This is very serious business, with many additional ramifications not mentioned here. So, heed my words, heed this article!! BLOCK THE CRANK!!

Below is a sketch of the flywheel and crankshaft of your airhead, sketch courtesy of Tom Cutter, with additional notes by me. 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, and does not show how the rear thrust washer is retained, and other such minor details that are of no importance here.

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, and the thrust washer has slipped, and if one tries 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 crankshaft VERY LOOSELY and 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', and you can tighten up the crank to torque specifications and the crankshaft will not be locked up. Be really careful about all this sort of thing!
_{BMW came out with a Service Information
bulletin (we call them SI's) in November 1991, this SI is
11-049-91, #2495, and this can be seen on the 12/92 fiche on page
3, G23.    Basically, it stated that whilst the
flywheel bolts were previously at 75 footpounds (100 Nm), they
were now to be at 90 footpounds (125 Nm), with cleaned
AND OILED!!! threads! BMW specifically said that the
bolt limits would NOT reach their limit of elasticity at that
torque, and could be REUSED!!!!!    I will NOT
tighten them that tight. Makes me very nervous! NOTE
also that this is in regards to the 11 mm bolts, not the smaller
/5 bolts.   There have been a lot of different
specifications on flywheel bolts over the
years.}

Crankshaft main seals came in a number of styles over the years. The latest seal, of a Teflon-like material, is quite different in design from the early seal. Early seals were very conventional looking, a lipped rubber seal (more than one type of lip and seal color) with a coiled spring backup. The 1980 and earlier models had just the conventional seal. In 1981, BMW changed the design of the flywheel/clutch, for lighter weight (faster engine acceleration and deceleration, unfortunately with more vibration). The clutch was radically changed too.... to eliminate weight, and greatly reduce hand lever pressure. The flywheel was now called a clutch carrier. The earlier flywheel had the main seal lip resting on the flywheel boss, so when the flywheel was inserted into the engine, the seal curled...well, sort of...ever so slightly inward. For those earlier designs, I always recommended that the flywheel seal area be laboriously polished with ONLY crocus cloth (in kerosene). Absolutely no fingernail felt irregularities are allowed in the flywheel sealing area...although discoloration is normal. Seals were installed sometimes to very slightly different depths to avoid old rubbed areas, but I used the crocus cloth and never had a problem.

The guide ring used on the 1981+ models (the clutch carrier fits to it, the guide ring is over the crankshaft).... has a center lug to enable it to be pulled rearward by a factory tool. 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.

To replace a main seal on a 1981 and later, you have to remove the guide ring first. You then install the seal. The guide ring (with a new O-ring!) is then moved into the seal, using the carrier bolts (probably with some washers/spacers). As the guide ring is installed, it makes the Teflon seal working part move forward. That helps the seal maintain oil integrity as crankcase pressures increase during engine operation.

***When using the bolts for that, you may need to use spacers under the bolt heads....see the guide ring installation photo, showing the bolts with some sort of junk-box provided spacers under them, to allow the bolt heads to be turned properly.

Main seals are installed using the special factory tool, but if you are careful, you can do this with a block of wood (or Ed Korn's tool). Install the seal absolutely straight and square. Install at the same 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.

The latest seal is a Teflon (PTFE) containing seal. In MY opinion it is installed oily (but need not be soaked). I personally prefer to soak the new seal (and tool!) in 150°F +- engine oil for a few minutes....the temperature helps the job of preparing the seal, perhaps softening it, perhaps not. You do not HAVE to soak the seal, you can oil it or grease it (especially oil or grease the OUTside during installation), then install using the proper installation/depth tool. If you fail to oil or grease the working part during assembly, it may squeak for a short while after engine start, until oil works its way to the seal. The area where the new seal is to be installed can be heated. Press the new seal in squarely, using a flat plate seal installation tool, or fashion something.

****Probably the best way to do a seal job, is as shown by Oak, in the MAY 2004 issue of AIRMAIL (see page 17-18)...where Oak discusses 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 need 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 (mind the OT mark and be at OTC on the pistons!!), then insert the bolts lightly, and then find the centering point of the assembly, by moving the flywheel CW and CCW, back and forth on the bolts...there will usually be a slight amount of play. Then tighten to only a few footpounds. When it has cooled, tighten fully to specifications. Mind the torque. There are two types of threads and sizes, the weaker type was used to 1974. Be very cautious about the torque used.

A tool can be fashioned to lock the flywheel/carrier, whilst the bolts are torqued. Such tools are shown in photos in such as Clymer's and Haynes manuals, BMW literature, ETC. The original BMW tool may even be available, but the tool is quite simple.

Main Seal installation tools (if you decide to use them):

The original BMW main seal installation tool was #880.
There is an article on making a fancy, nice, main seal tool that works fine with the later seals. The article is on the http://www.airheads.org website, and it is also here: http://www.gunsmoke.com/motorcycling/r100gs/mainseal_driver/index.html

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...and Ed 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, 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.

Thanks to Al Patton for supplying the original photos of a later type Airhead (type with Guide Ring), which I have modified and placed below.

That is the 5 bolt holes in the crankshaft you see, above, and notice that they are symmetrical...that is why you MUST align the flywheel/carrier for OT mark with pistons TDC!	Notice the spacers used by Al Patton here...otherwise the bolts would not turn at the hub area.
Notice that the holes all are lined-up	The 10 mm hex bolts at the bottom of the photo are the later types, and that is the oil pump cover.
NO need to tighten much!

_{BMW came
out with a Service Information bulletin (we call them SI's) in
November 1991, this SI is 11-049-91, #2495, and this can be seen
on the 12/92 fiche on page 3, G23.    Basically,
it stated that whilst the flywheel bolts were previously at 75
footpounds (100 Nm), they were now to be at 90 footpounds (125
Nm), with cleaned AND
OILED!!! threads! BMW specifically said that the
bolt limits would NOT reach their limit of elasticity at that
torque, and could be REUSED!!!!!    I will NOT
tighten them that tight. Makes me very nervous! NOTE
also that this is in regards to the 11 mm bolts, not the smaller
/5 bolts.   There have been a lot of different
specifications on flywheel bolts over the
years.

Although I do not use 90 footpounds on oiled threads on the later
/6 and later bikes, you can.   We used to install these
bolts at 75 footpounds, dry threads. I set them about
75-80, oiled threads. I check all flywheel bolts to be sure
they visually do not look stretched or damaged in any
way.   You can always purchase new ones if you are
worried!}

If flywheel bolts loosen, or come out or are sheared off, considerable damage to the threaded holes in the flywheel can occur. This most often was seen on the old /5 bikes, with the small threaded bolts, with someone forgetting they were on a German bike, and 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!!

The oil pump cover O-ring should be replaced any time the flywheel is removed. Early oil pump covers had Phillips screws, which often are a problem to remove (use of the special impact wrench listed in my tools.htm article is highly suggested!). You can install the later pump cover, with the later bolts. When installing the pump cover with its new O-ring, be sure to 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 threads; and 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).

The oil pump inner rotor INNER EDGE is chamfered. Oil pump clearances are easily measured with common feeler gauges and 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"

Rev:

02/04/2008: incorporate all previous revisions; expand and also add information from "being-eliminated" article engineinternals.htm; clarify details on mainseal 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.