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Old 10-07-2014, 12:54 PM   #1
sam906 OP
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Location: Toronto, Canada
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R90/6: Tear-down and Restore

Hi all,

I am planning on tearing down a newly acquired R90/6 and getting the pieces cleaned up and repainted. Having never owned one of these bikes (my history is with Japanese twins and fours), I wanted to get general information as to if there is anything important I should know, especially in terms of removing the engine / transmissions / drive shaft from the frame. (the part of the job that makes me most nervous)

The bike is in good running condition with what only seem like aesthetic imperfections (rust on frame, pipes etc). So aside from a carb rebuild / adjusting valves etc, I wasn't planning on doing too much mechanical work. I just want to get it down to the frame for painting and cleaning up as many of the pieces as possible.

Since I've been dreaming of owning an airhead for a while now, my plan is to keep this for hopefully a long time to come and figured a tear-down / reconditioning is also a good way to better acquaint myself with the machine.

Attached below are some pics of the bike in its current condition.

I've been sourcing this blog and both Haynes and Clymers manuals for a while but wanted to get some project specific hands-on advice from all the freakishly knowledgeable owners on this site. Aside from bagging and tagging as necessary (and tons of photos of course) Is there anything to look out for when removing or assembling pieces on these bikes?

Thanks in advance! (I'll be documenting the restoration here as soon as I gather up the courage to dig in :)









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Old 10-07-2014, 12:58 PM   #2
AndrewSJC
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Welcome, Sam!

Generally, you want to ride a bike for awhile (to find any faults it may have), and do full diagnostics on engine, electrics, etc., before you begin a teardown.
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Old 10-07-2014, 01:11 PM   #3
WNYBMW
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Hey ! I don't have anything to contribute, haha, As I am new here also but I see you are pretty close to me and having acquired my father 76 R90/6 we will have to meet up next summer. I'm in the Burbs of Buffalo
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Old 10-07-2014, 01:22 PM   #4
sirsethro
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I would just follow Brook's incredibly well documented rebuilds on his /6 and his /5. He's done a really nice job of documenting the process and sources most/all of his material from the Airheads techlist as well as other reputable online sources for BMW repair.

http://brook.reams.me/bmw-motorcyle-...ild-s-replica/
http://brook.reams.me/bmw-motorcyle-...build-project/

Personally, I say just do the basic repairs and ride it for a bit. Who knows, maybe you like its beat up charm? It's kind of hard to know what to fix if you haven't put some miles down.

Congrats on a sweet bike.
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Old 10-07-2014, 01:56 PM   #5
silverhead
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I'm the sort of person that rarely puts something back together once it's been torn down to parts that live in boxes, so I'd totally ride that thing as is. I'd pull the swingarm to re-paint it or whatever, but it looks too good to restore to me :)

I like fixing parts piecemeal as opposed to losing track of what bolt goes where.
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Old 10-07-2014, 02:18 PM   #6
disston
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Your R90/6 seems to be either a 1975 or a 1976 model. There are differences between the two. The /6 bikes have multiple changes every year.

How many miles on the bike? It seems to have been cleaned well, maybe just before you bought it? The oil up front on the oil pan seems to be the oil pan gasket but it could have other leaks. The advice to do this bike piece meal for now is good advice I think. Ride the bike for 500 miles or so and see where the oil is leaking then. Pay particular attention to the front cover, where two seals are under the points plate and the alternator rotor.

The shelf under the trans may be wet now. Few noobs know to check this. The rear engine seal is in front of the flywheel and when it leaks the shelf under the trans gets wet. Replacing this seal means taking the trans off and taking the flywheel off.

Quote:
I've been sourcing this blog and both Haynes and Clymers manuals for a while but wanted to get some project specific hands-on advice from all the freakishly knowledgeable owners on this site. Aside from bagging and tagging as necessary (and tons of photos of course) Is there anything to look out for when removing or assembling pieces on these bikes?
Good to know you have manuals and are researching. But compliments about the inmates will get you no where.

Start with rebuilding the swing arm and the wheels this Winter. Take care of any seal leaks and then after another year of miles you may be ready for the Resto job you envision.

One big thing about Airheads. Anytime the flywheel is removed, usually happens when the rear seal is replaced. make sure the front of the crankshaft is blocked to prevent movement. Fairlure to understand this and do it properly could ruin your week.
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Old 10-07-2014, 02:25 PM   #7
CafeDude
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Congrats! Looks like a very clean bike to start from. Compared to a Japanese bike, these airheads are way easier to work on, disassemble and re-assemble.....by design!

You're getting great advice here. Good luck, and keep posting progress pictures so we can come along for the ride!
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Old 10-07-2014, 03:29 PM   #8
sam906 OP
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Thanks for all the replies... definitely makes me re-think about a complete tear down...

I had the bike out a handful of times while the weather here was still decent and everything seemed good as far as I could tell.

Quote:
Originally Posted by WNYBMW View Post
Hey ! I don't have anything to contribute, haha, As I am new here also but I see you are pretty close to me and having acquired my father 76 R90/6 we will have to meet up next summer. I'm in the Burbs of Buffalo
Ha! Small world (or forum). WNYBMW, the bikes current condition is definitely a testament to your father's care and attention. These bikes are few and far between in my neck of the woods in such a condition, which is why I want to keep it as minty and original as possible.

Quote:
Originally Posted by disston View Post
Your R90/6 seems to be either a 1975 or a 1976 model. There are differences between the two. The /6 bikes have multiple changes every year.

How many miles on the bike? It seems to have been cleaned well, maybe just before you bought it? The oil up front on the oil pan seems to be the oil pan gasket but it could have other leaks. The advice to do this bike piece meal for now is good advice I think. Ride the bike for 500 miles or so and see where the oil is leaking then. Pay particular attention to the front cover, where two seals are under the points plate and the alternator rotor.

The shelf under the trans may be wet now. Few noobs know to check this. The rear engine seal is in front of the flywheel and when it leaks the shelf under the trans gets wet. Replacing this seal means taking the trans off and taking the flywheel off.
Thanks for the tips disston - the bike is a '76 having had 3 previous owners before me - approx. 60,000 miles on the odometer.

I'm now considering doing things piecemeal, as few here have mentioned - I think I just liked the idea of owning a clean airhead (not to mention filling the cold winter nights turning a wrench)

I still have to flush the fluids / do filter changes etc and might get some minor surface pieces cleaned up.

I also want to get some wider handlebars with a slightly higher rise to them. Anyone know what the stock bar size (width, pullback, rise) was for these 76 R90/6's? I can't seem to find this info anywhere.

Thanks!
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Old 10-07-2014, 03:33 PM   #9
Bill Harris
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I'm in the camp of "ride for a while. bond with it", then refurbish it next Winter.

Hop into a project all excited, it's easy to get burned out and end up with boxes and boxes of parts...

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Old 10-07-2014, 03:46 PM   #10
disston
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Those bars you have now look like S bars. They may also be CS bars. But the ones you probably want are the USA bars.

Or you might be happy keeping the bars you have and just getting a set of bar backs. Bar backs may be the cheapest way to go because USA bars usually need longer throttle cables, or something.

There are many 7/8 inch bars on the market and sellers will tell you these fit your bike. Not so. The bars on a BMW Airhead are 22 mm (surprised? A metric sized part on a European bike) So you end up having to modify the control perches to fit the larger 7/8 bars. This ruins the perches to be used some later day on the properly sized 22 mm bars.

A lot of riders have been happy with aftermarket bars from Flanders. They sell a 22 mm bar. But I think they sometimes also don't fit as well as advertized. Maybe somebody who has done this recently will say it was a good experience?
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Old 10-07-2014, 09:36 PM   #11
Thorazine
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Hey Sam! Welcome to the nuthouse. That bike looks damn good for being 40 years old. I've seen lots of 40 year-old people who would love to look that good. Nice pickup.

I'm glad to see you're gona follow the advice to work on your bike piecemeal, though your badass 'Toronno' winter is just around the corner. Will there be rideable periods up there, or is winter usually a wash? If there's no winter riding, maybe you can do one little project, finish it, then on to another (if it isn't too frigid in your garage).

Disston--those look like S bars--just like the ones I have.

Again, welcome.
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* Posts submitted under the moniker Thorazine are for entertainment purposes only, and may include exaggerations, prevarications or bald-faced lies. -- Thorazine - '74 R90/6
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Old 10-08-2014, 02:33 AM   #12
chasbmw
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I would go down the full service and I mean full, then riding the bike for a while and seeing how you get on with it.

Those bars are the euro bars, as standard on euro specced bikes. They give a very comfortable classic bmw riding position, very good for riding without a screen. The wider US bars turn your body into a sail! But it's a very personal thing.
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Old 10-08-2014, 03:45 AM   #13
Bill Harris
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The Euro bars are not that bad-- when I switched over to a Hannigan full fairing, there was interference with my stock US bars. Been riding with them for almost 40 years and (at my age) had concerns that I wouldn't be comfy with the "hunched over" riding position. I was wrong-- the Euro bars allow me to lean a bit further in with my arms closer together and the position is actually more comfortable, even behind the windscreen.

Try them, you can always change later.
Quote:
I'm glad to see you're gona follow the advice to work on your bike piecemeal, though your badass 'Toronno' winter is just around the corner.
Working on it bit-by-bit over the Winter will work out well. Don;t rush, prioritize what need to be done, and tackle it project-to-project. You'll get a lot done and not have a "bike in boxes" when you run out of steam and go "feh". And you can buy parts for future phases over times, and p'haps find used/fleamarket/eBay parts as they come available.

Do post a Build Log when you get started...



Here is a suggested maintenance list:

Quote:
I would do the services on your R75/6 in this order:


1) Change ALL oils.

2) Torque cylinder heads (25 foot pounds, loosen each nut 1/2 turn,
then torque, use crisscross pattern)., adjust rocker arm end play (zero
play, no rotational binding), adjust valve clearances (cold engine) to
.006" Intake, .008" Exhaust.

3) Service auto advance unit (don't snap the thread off the end of the
cam, tighten GENTLY!), grease point cam felt with a smear of grease.

4) Set points gap to 0.016" (0.40 mm) using a good feeler gauge, or
better yet a dwell meter, look for 39 degrees on the four cylinder
scale (gives you 78 degrees on a two cylinder).

5) Set ignition timing static setting to S mark on flywheel.

6) Check full advance timing at 3200 RPM, the dot (or hole if the paint
is gone) above the F mark should be steady in the center of the timing
hole, aligned with the machined groove in the side of the hole.

7) Service the air filter, i.e., put a new one. DO NOT blow out air
filter with compressed air, do not leave a K&N filter in at all.

8) Drop carb float bowls and clean the tiny jet in the little well in
the corner of the bowl using a single strand of wire from a wire brush,
held with needle nose pliers. Make sure contact cleaner will spray
through the jet into the bowl.

9) Remove the main jet and jet holder (make a mental note of the depth
of engagement of the jet holder), drop down the needle jet and emulsion
tube, (keep your finger over the hole so they don't fall out and get
lost.) Use some Gumout carb cleaner spray to clean the gunk that has
accumulated above the jet holder. Spray the jets and emulsion tune
clean, then reinstall the emulsion tube, needle jet and jet holder.
Visually align the jets onto the needle carefully. As you screw the jet
holder up in with your FINGERS, if it doesn't seat fully (remember the
mental note?) then back it up about 1/32 of a turn and wiggle it as you
screw it in gently (FINGERS ONLY!) You will feel when the emulsion tube
finds its way up into the carb body hole. If you can;t get it , remove
the air tube from the air cleaner housing and visually see that the
emulsion tube projects up into the venturi about 3-4 mm. You can wiggle
the needle to help align it as you screw it up in with your FINGERS.

10) Check the float level setting by lifting the float gently with your
fingers. When the needle seats, BEFORE the spring loaded part begins to
depress, the seam in the float should be parallel to the float bowl
gasket surface. Reinstall the bowl carefully, making sure the gasket is
fully seated in the groove all the way around.

11) Check that the throttle cable has a tiny amount (1-2mm) free play
when the throttle grip is all the way back. Get the two sides as close
to the same free play as possible.

12) Check that the choke cable fully seats the lever on the post when
the lever is in the horizontal position. At half choke, the lever on
the carb should be halfway between the posts. At FULL choke position of
the hand lever, the choke lever should be all the way up to the top
post.

13) LIGHTLY screw the idle mixture screw IN until you feel the screw
seat. Now back the screw OUT by 3/4 turns (this setting varies for
other models).

14) Turn the idle SPEED screw OUT until it does not contact the
butterfly lever at all. Now screw the screw IN until it JUST touches
the lever, now turn it IN one FULL turn.

These are the baseline settings. Now take the bike for a LONG test
ride, at least five miles, to get it to FULL operating temperature.
Riding around the block or starting and revving on the stand will NOT
work.

At this point you need to synchronize the carburetors. This is
accomplished either by shorting one cylinder at a time (this takes some
practice to get right, usually you need somebody to show you once) or
using a vacuum gauge on the vacuum takeoff ports on the side of the
carb. Set the idle mixture on each carb at the point that gives best
running, usually between 1/2- 1-1/4 turn out. Balance the idle speed
screws, then balance the cable pull off idle. Recheck to be sure that
you still have a tiny bit of free play of the cables. If not, readjust
the cables.

This should get the bike running pretty well. Idle speed should be
at 1000-1100 RPM. DO NOT set the idle for a super low "tickover", as
this will severely reduce oil circulation in the engine and make the
transmission rattle like a bag of rocks.

--
Tom Cutter

--Bill
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Bill Harris screwed with this post 10-08-2014 at 03:52 AM
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Old 10-08-2014, 05:04 AM   #14
SohoPhil
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Quote:
Originally Posted by AndrewSJC View Post
Welcome, Sam!

Generally, you want to ride a bike for awhile (to find any faults it may have), and do full diagnostics on engine, electrics, etc., before you begin a teardown.

+1 on riding it.
I bet you'll still have another month or two up your way before winter
locks you in. In that time you'll discover a few things that you can address over the long northern winter and be ship-shape come spring!
Plus....these bikes really love the cool fall temps.
Best riding season IMHO!
Good luck!
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Old 10-08-2014, 06:29 AM   #15
Beemeup
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Looks like you have one in pretty good shape to start with. I also agree with the ride it first camp. Fix what needs fixing for now, it isn't an eyesore.

I also agree that the S bars are the way to go. Mine has US bars on it. Mine went through a number of modifications, I even had pull backs at one point behind a Luftmeister. It then had a Rabid Transit and mostly an RS fairing but I found the S bars to be right for me. I cut #/4" off the ends to make it work in a RS cockpit.

It's naked now but the S bars still feel right, especially with nothing to break the wind.
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