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My 1974 BMW R75/6 Project Bike

 
A Journal of 'stuff' I'm interested in and currently working on in my spare time. - bc, 2008-2012





1974 BMW R75/6  (shown at right)
    This page is my journal for a motorcycle recondition project.


Brief Background/History:
    Picked up the bike in May 2008 as a project bike. One of those craigslist finds that I simply couldn't pass up; even included a 12hr road trip to grab it. I really wanted a toaster-tanked airhead, and this was my way of learning more by doing *most* of the work myself...

    Long story short, I eventually broke the rusty pistons free, disassembled/inspected many components on the bike (not tranny), shipped off the heads/cylinders for re-conditioning, replaced many of the rubber parts, rebuilt carbs/petcocks/forks/brakes and reassembled the engine/bike, and it came back to life (started) August 26, 2009 about 11:15pm..  I'm currently gently riding the refreshed bike around during it's recommended break-in period.  I have thoroughly enjoyed the project and its challenges, but it may "blow" tomorrow.  But that wouldn't matter to me at the moment.. I'm better prepared to maintain my other airhead, or any future airhead I may encounter.

 

Completed 1974 R75/6


Bike Condition when Found:
    It had sat in a few garages and had been passed among 'riding buddies' after spouses had grown tired of it just sitting 'round.  It was listed in the online ad as a "parts bike", but it had potential to live again, I thought...  Plus, I really dig toaster tank BMW Airheads and this odd-ball '74 model /6 had a toaster tank on it.   Such a sucker.. I know..
 
Anyway, here's the run down regarding the bike condition when it was purchased:
        Siezed engine; missing both carburetors and related
        connections; no battery or battery box; tool tray or horn.
 
         Oh, and of course it had No Toolkit, Owners Manual, or Ignition Key.
 
    Rumor has it that the bike was sold from Bedell's Cycle (an out-of-biz BMW shop) in Topeka, KS.  The shop closed in the late 70's and the owner has since passed.  I may not ever know for certain why the bike had sat for so long, or the events that led to it's engine seizure, but it's not that important, really.  I'll eventually determine the relative condition of all parts and whether it's worth the $$ and the time required to refurbish this beast and save it from the scrap yard (more likely, flea-bay).
 
What Next?
    Got busy in late May 2008 breaking down the cylinder heads to see if those pistons could be broken loose.  Long story short, it took approximately nine weeks to get both pistons gently released from the rusty cylinders. Kano Labs Kroil, heat lamps, heat guns, a modified timing gear press and PATIENCE was the key to success.  See pics for better idea of what was involved, but needless to say, I nearly gave up and went looking for a cutting torch numerous times, but I'm glad I waited while the penetrating fluid and heat/cold cycling did the work.
 
Then in late Sept 2008...
I shipped off the heads/cylinders to Rubber Chicken Racing Garage  in Yardley, Pennsylvania so that Tom Cutter could diagnose the condition and refurbish as necessary.  The cylinders were way too rusty and required a rebore and therefore new pistons were required (to match the bores).  The cylinder heads were updated for unleaded fuel with valve guides/seats, and generally freshened up to like-new condition..  Better than new, actually.  The refreshed heads and cylinders look great; too bad the rest of the engine case isn't as clean and shiny... maybe later after all of the potential expensive checks and hurdles have been crossed. :)

Spring 2009, Heads return from Pennsylvania..
Can't recall the date the heads returned but it seemed to correspond with Turkey season so not much happened until May 2009.. I finally worked up the courage to begin the re-installation process.  May 9th I believe is the date I had
completed a final re-torque of the heads and valve clearances check after a 24hr wait period per the guidelines set forth within Oak's "Top End Manual".  The top end manual, airheads website tech articles (www.airheads.org), and various other online references such as Snowbum, Anton, Scot and many others have made this project possible, but frequent help from the Airheads listserv (http://micapeak.com/mailman/listinfo/airheads) was required, and greatly appreciated.

That doesn't mean it's been super straight forward..little details like the selection of 'base sealants', oils, grease, tools, etc are constantly debated and argued among the group so us 'newbie's' that are attempting to earn our keep as an Airhead member have to struggle through the rant's and rave's and eventually make a decision...not knowing whether these online guru's are full of it or not. Typically, they're not full of it and it's pretty easy to tell, but they are a passionate/spirited group.. :)

Original Craigslist Ad and Email Responses:

> Sent: Thursday, May 15, 2008 1:23 AM
> Subject: 1973 BMW 75/6 parts bike
>
>
> Hello
> I'm prepared to buy, and pickup as soon as possible.  Do you have any
> additional images?   What about a VIN number?
>
> Will I be able to roll onto a trailer?
>
> Thanks again,

>> CRAIGSLIST Ad from May 15, 2008
>>> 1973 BMW R75/6 motorcycle parts bike. No title. Friend got as parts bike
>>> but
>>> gave to me due to storage issues. Motor seems frozen. No carburetors. No
>>> left side cover (if there is one). Must be picked up. Would prefer to
>>> sell
>>> altogether but might be willing to sell (and ship) tank/fenders, wheels
>>> or
>>> all turn signals, etc., if good offer received. Call xxx-xxx-xxxx or
>>> email
>>> replies. Other photos available


Useful Resources / Related Pages:

What's involved in restoring an old BMW motorcycle?
go here to read one person's detailed account of the tools/time/space/knowledge required to complete such a project, as well as a very detailed accounting restoration expenses.  This is a very good read for anyone considering a similar project.

How a motorcycle transmission works.  Examples using animations of BMW gearboxes.
Great overview of how this gadget functions. 


Work in progress

 
To Do/Done List:
  1. DONE: Break Pistons Free.  Carbs were off and pistons were rusted to the bores when Bike was picked up in Topeka, KS.  $350.00 original purchase price.
  2. DONE Purchase Carburetors, battery box, tool tray, ignition w/Key
  3. DONE Evaluate Condition of Pistons/Cylinders/heads
  4. Identify what work will be required of top end and who will do it.
  5. Tom Cutter reconditioned the heads; rebored cylinders .050; replaced pistons, valves, valve guides, etc.  Shipped parts out on Oct 1, 2008 and completed heads returned to my door Feb. 6, 2009
  6. Evaluate condition of electrical components/charging system.
    1. Oil discovered within bottom of points pot. 
      1. Wiped up the oil
    2. Clean up the interior of front cover; replaced speedo rubber grommet.
    3. Test Diode Board and Charging components w/multimeter.  It appears to have checked out OK. but I replaced the diode board with a ThunderChild anyways..
    4. Purchased a Thunderchild diode board and will probably replace the original diode board with this one plus the solid mounts for it.  Check, did just that in June 2009.
    5. Some wires have been disconnected/labels by previous owner.  Two wires are disconnected w/out labels.  As of July 2009, I've hooked those wires back up..Two going from the front cover into the Starter Compartment. (one hot wire; one solenoid).
  7. Replaced the Ignition switch with one from Ebay that had a key with it. Also realized the headlight bulb and parking light bulbs were missing so I put those on the list of stuff to order from hucky.
  8. Repair Front Brake Master Cylinder and Brake Pads.   As of July 7, 2009 the Front Brake Caliper has been removed and cleaned up. A replacement piston is not required (I think so anyways) and a rebuild kit has been purchased.  A braided brake line and used replacement master cylinder are awaiting reinstall as soon as the front caliper is recompiled.   The brake disk has also undergone a good degreasing.
  9. Rear Output Flange from Transmission was missing 2 flange bolts!!
    1. Search for missing hardware in drive shaft housing.
    2. Discovered one washer down the swing-arm.  Extracted  it with a "magnet on a wire".  Will have to remove the rear Drive to double-check for the bolts.
    3. Pick up a rear drive housing gasket; plus replacement bolts due to the original ones being so rusty.
      1. Update: 7/7/09:  I've removed the rear drive and degreased it; checked for additional bolts/washerss but found none..  REASSEMBLED THE REAR DRIVE and updated the 4 output flange bolts to the new style (shorter; without washers) using blue loctite.  retightened the driveshaft boot.
    4. Order replacement Clutch/Throttle Cables, Carb Hoses/Clamps, and Choke Cables, Fuel Line/Connectors. from Hucky's BMW in Vero Beach, FL..(good service/shipping/prices so use him). 
    5. Over the July 4th Weekend 2009, I cleaned up the airbox area and removed the dirt dabber nest and old air cleaner attached to it.  Washed out the air box area and degreased the clam-shell engine cases and crankcase pressure hose that extends into the right-side air tube.  Scrubbed the rear drive, wheel and tire with Simple Green, but the crusty white chalk is still attached to the alumninum wheel...more on that later.
  10. Clean Gas Tank; reseal if necessary; rebuild pet cocks.  Scrub the header pipes and exhaust nuts in preparation for reinstallation.
  11. I've Purchased a Karcoma Petcock rebuild kit and have rebuilt the to petcocks and replaced the in-tank fuel strainers.
  12. The Gas Tank was cleaned using Simple Green and water mix, followed by Kerosene, and finally Iso-Alcohol.. original lining looked good and I let it dry in the sunshine.
  13. Replace Seat/Seat pan  (found a good seat with chrome bar)
    1. Had to cut one hinge on old seat to remove it. darn it.
  14. Removed the Original Bosch Starter for cleaning, condition checks and possible rebuild. 7/5/09
  15. Ran the new Fuel line through tht  Airbox and Attached the Carbs to the heads with all new rubber parts and clamps.  Re-attached the front cover and the top, starter cover to get a feel for the final product
  16. Disassembled, Cleaned and reassembled the Choke Lever and installed new Choke cables to the lever.
  17. Added the Battery Box, and Chrome Side panels back to bike just for kicks and giggles..
  18. Changed Engine Oil and Filter.  also scrubbed/cleaned the exhaust header nuts and gasket rings. 7/7/09
  19. Completed re-assembly Sunday 8/23/09 and connected the battery.. waited for sparks and smoke but nothing out of the ordinary.. All lights except the Neutral light and the left rear turn signal worked immediately..  The neutral light started working after it was started (3 days later) and the turn signal required a quick blast of contact cleaner; then it worked fine..
  20. Started the bike at 11:15pm Wednesday, August 26, 2009.  The delay in the initial start-up was due to mis-adjusted carb floats and timing/points gap settings being way off after re-assembly..   I let it idle for 3-4 minutes and then road it back into the garage that first night and then shut it off and cracked open a cold one. :)
  21. Applied for a Title and Antique plates using the "Bill of Sale" from out of state, and only hurdle was a trip up to the local state police shop to confirm the VIN numbers matched on the frame/engine.  There might have been a background check, but I doubt it. I think they just wanted a State Police officer to give it a look and check numbers on the bill of sale.  A new Title in my name is in hand. What a relief.. :)
  22. I have replaced the front/rear tires with Avon RoadRiders. The original tires had a lot of tread left, but were old and cracking on the sidewalls, so off with the old and on with the new modern looking tires..
  23. Center stand threads failed (where the stand bolt's are threaded into the frame lugs...stripped).   So I replaced the previously repaired stock center stand with a used Reynolds Ride-Off stand... Mainly because the Reynolds is far more stable from side to side, but since it doesn't fully lift the wheels off the ground, the bike can and will roll away in steep parking lots..   I'm aware of this limitation so I had a few additional welds added to the bottom of the stand, plus I intend to be very careful parking it. we shall see. :)  Those stands also extend outward from under the frame so they are not a good choice for 'spirited, canyon carving' riders.. just us old and slow folk...
  24. Well, back during the summer of 2011, I was on my way to work and after leaving a red light my /6 wouldn't shift out of first gear..  Broken pawl spring in the transmission was expected.  So I putted to work and then home again that night; fortunately I live close to work.
  25. I began conversing with my colleagues on the Airheads mailing list (micapeak.com) and the Kansas Airmarshal decided to host an Airhead Gearbox Tech Day in december of 2011, so I jumped at the opportunity to learn a new task and meet other members.  I picked up a 1978 5-speed gearbox from ebay and acquired parts/tools/accessories and traveled to Kansas City, KS in late december for a weekend of garage work.. a looong weekend of garage work with 15 or so other like-minded folks and their gearboxes crowded into a 2 car garage.. what a time we had!!  it's been fully documented in the BMW ON magazine as well as Airmail newsletter of the Airheads (Airmail, March 2012) so I'll spare the rehash here.  Long story short, I have the original gearbox and the newer '78 both reconditioned and ready for install.  BUT...what about that rear main seal and oil pump o-ring?  I've replaced those while the R75/6 has been in the garage.
  26. With the gearbox out and clutch/flywheel removed to access the Rear Main Seal and Oil Pump (cover upgraded to hex bolts and new o-ring installed), I decided to ship the clutch assembly off to Southland Clutch for resurfacing and friction disk refurbish while I'm at it..  So that's where we are now (April 21, 2012)..  My clutch assembly is on its way to southern California via UPS and I'm replacing flywheel bolts (10mm) but dealing with the 2 different lengths of 10mm bolts issued by BMW in the early /5 and /6 year models..  my micapeak lifeline was also hacked recently so the airhead mailing list has been down for 2 days.. what's a newbie to do??!!!  ha!!  :)  I'm lost for sure..  will be back soon tho with more pics.. :)

Photos from the Gearbox Tech Day (Dec 2011):