Tag Archives: removal

Disassembly of an airhead R75/5 BMW final drive

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Here is a photo essay of sorts detailing the disassembly of a 1973 BMW Final drive. The same applies to all 1970’s era BMW’s (R90 R100 R75 R80 /5 /6 /7 S etc). The seals were shot inside causing leaks. The splines are decent so no need to weld on a new set of splines. I plan to have the drive blasted and powder coated to match the rest of the bike for an upcoming build.

The image descriptions have notes on the disassembly.

  • Final Drive missing a spring
  • Final Drive brake shoes removed
  • The next step is holding the drive gear in place, flattening this washer down, and removing this nut with a good impact gun.
  • Nut off
  • Gear removed
  • BMW tool used to remove the threaded ring inside this shaft area
  • Threaded Ring removed with seal inside.
  • Seal Removal 28x55x9 Part number 33 12 1 231 542
  • Note the orientation of the shoulder of this washer
  • Notice the orientation of the shoulder on the washer
  • removing that large washer
  • Removal of the M8 nuts with a 13mm socket
  • Removal of the M8 nuts with a 13mm socket
  • I’m pretty sure this was a M5 screw I had lying around. Ignore the red locktite looking stuff at the tip. These screws are needed to push the cover off the housing.
  • Two halves apart
  • Notice the shim/washer. Also take note of that small pin in the casting just above the gear. That pin needs to be removed to remove the needle bearing nested inside the housing.
  • There is that same shim from the last photo
  • Press out the axle bushing/tube
  • bushing comes out this side
  • Differential gear is next
  • Press out the differential / crown gear
  • Notice the giant shim/washer
  • Press out the seal from the cover plate.
  • Press out the seal from the cover plate. 65X85X10 part number 33 12 1 233 528
  • spring side goes towards the oil.
  • This housing was put in the oven at 350 degrees for about 20 minutes
  • Removed gear and bearings – HOT TO TOUCH!!! They practically fell out of the housing
  • Unfortunately this pin broke preventing me from removing the bearing. It is common from what I understand. I ended up covering it up with silicone to prevent media from getting at it when blasting.
  • Final Drive Disassembly Gallery
    Seal Removed – 30x42x7 part number 33 12 3 004 337

Ed Korn Cycle Works Swingarm seal removal tool

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Removing these seals is a frustrating process.  Prying them out usually doesn’t get you anywhere.

I bought Ed Korn’s tool a while back and it can be used for pulling both the races, and the seals.

Here is how you use it to pull the seals.

Here is the tool assembled

photo-1

 

I first cut out some of the seal’s rubber with a razor blade.
It was easier to get the tool installed that way.

 

photo-2

photo-3

Then you tighten the threaded rod with the allen fitting at the end of it.  By doing so, it expands the nut against the screws and presses them outward so they ‘catch’ under the metal part of the seal.

photo-4
Then you install the collar, plate and washer and nut.

photo-5

Once you begin tightening that nut, it will pull the seal out into the collar.
image_1
You can then loosen the nut, and break the old seal free with a few taps with a hammer.


image_2

 

 

Rotor Removal

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Once again, I had to return to the old donor engine block for some spare parts. The rotor on the engine to be rebuilt was a rusted mess. The rotor on the donor engine looks brand new. I will test it with an voltmeter to be safe, but being that it is so clean, i am not too worried.

To remove a Rotor, you need to have the rotor puller bolt.
BMW sells it, Huckey BMW sells one, Motoelekt.com sells one… it is between $5-$10. Or, you can search online on how to make your own. (click the photo to enlarge it)

Once you removed the alternator,
To remove the rotor, all you will need is a 6mm hex bit and a 13mm socket.

Loosen the rotor bolt with the 6mm hex bit and remove it completely. You may need to block the engine from rotating.

Then screw in the puller bolt.

Begin slowly tightening it with the socket until the rotor pops off the crank. That’s it. Done.

BMW Airhead Clutch and Flywheel Removal on the Cheap

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It’s been about 5 years since i have pulled a flywheel and a clutch from an airhead engine. I do remember the process being slightly ‘dangerous’ in that if you don’t remove the clutch properly, the force of it could cause harm to yourself or your motorcycle.  I don’t have the BMW ‘special’ tools at my disposal to do so safely… so i figured i would make my own. Total cost – $10 from my local Ace Hardware store (which happens to have the best spare bolt, nut, screw selection i’ve ever seen).
No need for the BMW Special tools.

Clutch Removal

You will need to purchase three M8 x 1.00 thread (fine thread) bolts about 2 inches long.
i also purchased a small piece of aluminum tubing that fits around the bolt:

M8 x 1.00 bolts and aluminum tubing. Bolts cost $1.50 each(damn pricey metric fine thread bolts)and tube was $2.20

 

The first step is to remove every other bolt on the clutch disk that secures it to the flywheel:

I cut the aluminum tubing into three sections about 3/4 inch.
Then screwed in the 2 inch long bolts with the tubing on it into those every other holes:

Bolts with spacers on them

The reason for the bolts with the spacers is to safely alleviate the pressure into a ‘second’ stage.  When you remove the three remaining ‘factory’ bolts, the disk’s pressure releases itself outward, safely, onto the spacers:

Clutch pressure now lessened and on the bolts with the spacers.

Now it is simply a matter of removing the remaining 3 bolts, evenly, until the clutch disk is released.

If your bike has these spacers, Keep them! Some clutch disks don't.

Clutch bits, friction plate, etc...


Flywheel Removal:
To remove the flywheel, you have to prevent the engine from turning while removing the flywheel bolts that secure it to the crank shaft.
Also, without securing the flywheel, you can also run a risk of knocking the inner thrust washer (around the camshaft) off the pegs within the inside of the engine block. SERIOUS damage could occur within your engine case if that happens.

BMW recommends a ‘special tool’ but it is merely a device that locks the flywheel in place.
I made my own from a piece of steel for $2.00.

12" piece of steel.

After some quick cutting and drilling, I have my very own version of the ‘special tool’.
Use the original flywheel bolts, and finger tighten them as much as you can and you are now free to use a nice breaker bar, a 17mm socket(i think) and crank out those flywheel bolts.
Some suggest using a center punch and making a small score on the crank shaft and another on the flywheel so you can put the flywheel back in the exact same position and your TopDeadCenter mark is still accurate.  Using a permanent marker might do the trick for a short term solution.

Piece of steel, cut and drilled out to prevent the flywheel from moving.

That’s it!  Now that the flywheel is removed, time to send it off to get lightened!
Another note while the flywheel is out… some people put white paint on the timing marks so you can see them better when timing. Just a tip….

Oh… and remember to THROW AWAY the 5  flywheel bolts. They are torque specific bolts and once they are torqued to spec, the can’t be used again. If so, they may wiggle back out and cause some SERIOUS damage.

For more info on clutches and flywheels, look here:
http://bmwmotorcycletech.info/flywheelremovalwarning.htm
http://bmwmotorcycletech.info/clutch.htm
Measure your clutch parts – http://w6rec.com/duane/bmw/clutch/index.htm

Northwoods airheads sells a $4 crankshaft blocking bolt to prevent the crankshaft from moving forward when removing the clutch / flywheel.
it is located here. http://www.northwoodsairheads.com/Tools.html