Bringing 74 R90S back to life after sitting 30 years

Discussion in 'Airheads' started by _cy_, Sep 30, 2011.

  1. bringenufgun

    bringenufgun Been here awhile

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    amazing.
    i just got my newly purchased 8100 mile 74 r90s back on the road today. been stored in a basment for six years, two previous owners. serial #4950982, don't know where that puts it in production or u.s. distribution.

    i have owned it for two weeks. new tires/tubes, carb clean, master cylinder rebuild, steering stem bearings, fluids changed, wheel bearings repacked, rear brake light switch, clutch cable, air filter, odyssey battery and a few things i can't think of right now. my mechanical ability is nil (as my signature states) so i had a trusted mechanic at a small independent bmw shop do it.
    original paint, seat, etc. nice enough not to re-furb. got the original owners manual, tire pump and one correct mirror. plus a box of parts that included air filters, oil filters and other service related parts. no service records, but i think the spares are a good indicator.
    like you my initial thought was sell it to buy a more modern mount. but how many chances do you get to own/ride an original r90s? in forty years prior i've had none. heres a couple of pics after its first quick wash today since being stored.
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    fwiw, i have never seen a r90s or for that matter, a bmw airhead with the engine painted black from the factory. i've owned beau coup /5's, /6's, and /7's along with three gs' and a gspd.
    [​IMG]
    #21
  2. Renner

    Renner combustophile Supporter

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    If you anticipate running the R90S where the necessary octane isn't available, you may be able to lower the compression using a shim at the cylinder base.
    From Snowbum's site at http://bmwmotorcycletech.info/techindex.htm

    The stock cylinder base SHIM, during 1970-1975, was 1/2 mm (about .020"), and are not to be used for 1976 and later. For 1976+, TWO SHIMS were available, and these are ONLY for 1976 and later....the so-called Step 1 compression lowering gasket was .7 mm (.028"); and the very low compression gasket was 1.2 mm (.047"). BMW HAS used the word GASKET for these SHIMS. The original part numbers were 11-11-1-257-092 for the /5, for lowering octane requirements. Used on /5 and /6 was the 11-11-1-255-001. Use of the 11-11-1-335-650 base gasket will lower a 9.2 CR to about 8.6.

    I think the R90/6 shim would work on your S, and installation/removal isn't terribly difficult.

    Is this your first Airhead? Do you subscribe to the Airlist?
    There must be an R90S-specific forum somewhere... yahoogroups or similar.

    the 'bum has about 25 pages concerning the DellOrtos alone, including links to factory manuals & etc.
    You may go blind looking for it, but most of it is there somewhere.
    http://bmwmotorcycletech.info/dell.htm
    #22
  3. bringenufgun

    bringenufgun Been here awhile

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    over the years i've had a few mega motored japanese four cylinders including a 160+ hp suzuki gs1150/1229 and a 150+hp bandit 1200/1216 both running 11.5:1 compression. none had a problem on 93 octane pump gas.
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    #23
  4. danedg

    danedg Horizontally Opposed

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    [​IMG]


    Please don't scream too loud, when you find out you're not this 37 year olds' second date....:evil
    Toss the tires and tubes...
    #24
  5. DoktorT

    DoktorT BigBrowedNeandereer

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    If you expect to be in situations that only low octane is available, I would lower the compression. Rather than shims, I would install the 9:1 90/6 pistons. You can still do the ton all day long. I would put in a 32/10 rear drive as well to make better use of the modified torque.

    With my 9.5 RS, fine tuning is essential to reduce pinging with current premium. I set the mixture at the high end of spec and drop the timing back 2 degrees. Keep the rpms up for highway work and easy on the throttle around town at lower rpms. That works well with current premium, which is at least 2 points lower octane than the premium spec they were designed for and available 30 years ago.

    And you cannot compare an 11.5cr jap combustion chamber design to the airhead. Current Porsches have higher cr than the airhead but are designed for lower octane used today.

    It is like comparing a wedge head to a hemi head. Apples and oranges.

    Make a photo copy of the factory maintenance schedule. Address everything as time allows and cross them off as you go.

    Do sign up for the Airheads list. Daily answers to specific question from million mile airheads. Best, find an experienced airhead by joining the ABC group. Some one who has owned several with 30 or more years experience, to help you with hands on inspection and procedures.

    Get yourself to an Airheads Barley Therapy. Even if you can't bring the bike, go and watch and ask questions. Sharpest way to kick the learning curve in the butt. If you feed the kitty with 10% of the value received, there will be plenty for Barley water for everyone.
    #25
  6. _cy_

    _cy_ Long timer

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    nah .. R90S oxidized condition jives with what a machine would look like after 30 years of being stored in an non air conditioned environment. Summers and winters in Tulsa both can be harsh. there's an old saying in Tulsa... don't like the weather? wait a minute, it'll change...

    being in the geographic center of USA. Tulsa gets it on both ends of extremes in temps. there's other details of purchase that I cannot post, that verifies this bike provenance.
    #26
  7. DoktorT

    DoktorT BigBrowedNeandereer

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    Please do see if you can find any ommissions whatsoever not covered by what I said. "the factory maintenance schedule. Address everything "

    All lubes and fluids IS covered by that, and EVERYTHING ELSE. No need to repeat the minutae of that which is already given by the best source available.
    #27
  8. _cy_

    _cy_ Long timer

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    thanks... that's exactly what I will do... making a copy of factory maintenance schedule. then using it as a check off list.

    under no illusions here ... there is NO way I can hope to be in the same league with folks with 25+ years of Airhead experience. finding out there's tons of technical resources available with a bit of digging. someone made a comments about going blind looking for something on Snowbum's site. I'm going blind after reading some of the voluminous articles on Snowbum's list.
    #28
  9. _cy_

    _cy_ Long timer

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    that is amazing..a BIG congrats!!! almost identical bikes. except yours is ready to go and the mystery of the black engine on mine. finding out Butler and Smith from time to time offered un-advertised bikes set up a special way. they would take a base machine, tear down. then add features. http://www.omnilex.com/public/bmw78/

    seems actual spec's for USA bikes matched USA ads closer than models destined to go elsewhere.
    found this Butler & Smith advertisement from early 1974 claiming 77hp for early R90S
    http://www.beemergarage.com/documents/74r90s.pdf

    finding out according to serial numbers for USA spec bike starting in 495xxxx. there were a total of about 5,000 USA spec's R90S bikes made. about 1650 per year made it into USA for 3 years.

    does your serial numbers match on engine and frame?
    noticed you went with modern tires instead of Metzler.

    what tire/tube combo did you have installed?
    #29
  10. Wirespokes

    Wirespokes Beemerholics Anonymous

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    One piece of advice I'd like to share: don't assume anything!

    It's easy to figure one part looks like another and assume they're the same, when some minor difference makes them totally different. And don't assume that the specs for one year are the same for the next. These airheads were an evolutionary process - constantly upgraded and improved since their creation in 1923. The problem is that BMW would initiate these changes at any time, midyear or whenever, so you pretty much need to know what you're looking at.

    Just a word of caution (there are some pretty deep pits we can fall into making the wrong assumption with these things).
    #30
  11. supershaft

    supershaft because I can

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    That was my point spoken differently. Lube all the bearings? I would first find out if you don't need new cylinders and a valve job for corrosion. That and the transmission rebuilt.
    #31
  12. DoktorT

    DoktorT BigBrowedNeandereer

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    SnoBum's site is a learning experience in itself. Keep paper and pencil available and take notes specific to your year and model. It takes a coupla months to get familiar with use of the site, but worth it for time/money saving details. He is right up there with Oak for deep experience. And recently he updated his on-site search engine and it works very well to speed up finding of specific info.

    And speaking of Oak, how would you like to get info from the technical services director for Butler and Smith back in the days of US Airheads imports. AskOak@aol.com with get you that. If anyone knows about black 90S engines, he would know.
    #32
  13. _cy_

    _cy_ Long timer

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    WOW!!! been digging... digging... digging about my black engine with no luck. if he was around when Butler and Smith was going. this would be the best lead so far. will be sending a connect msg to Oak.

    thank YOU!
    #33
  14. _cy_

    _cy_ Long timer

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    test polishing a few parts ... it's going to be slow. mechanicals take first priority.

    purchased a new gel cell battery, it's a bit smaller in size. but that's OK.
    the Yusa battery that came out was so tight, had to break drain tube on side to get out.

    some rust on battery tray, so that's got to come out for sand blasting and new paint.

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    #34
  15. supershaft

    supershaft because I can

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    Well, since no else is doing it I guess I will warn you about snowbum's site. Yes, even I go there for some info sometimes but by no means take everything on that site for gospel. He is off base sometimes and other times just wrong. I don't hear this take on the net much but I hear it ALL the time off the net. Read him with your waders on.

    I have mentioned this popular sentiment off the net here before and doc has insisted that I point out one for instance almost as if the bum is infallible. :lol3 I said then that they come up in this forum ALL the time and have many times over since doc last made that nonsensical ruse. Some websites go on and on about all the errors in the manuals as if their websites don't have tons of them! They do!
    #35
  16. bringenufgun

    bringenufgun Been here awhile

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    #36
  17. Renner

    Renner combustophile Supporter

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    regarding da 'bum: if one finds an error on his site, one can send an email to him regarding it.
    He is generally responsive and is not opposed to making corrections or clarification as is warranted.

    as with anything from the 'net, it's best to gather infomation from several sources while continuing to use one's own head.
    #37
  18. Bato

    Bato Been here awhile

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    beautiful... this is something that i would like to do i rod one in the 70's
    Subscribed!
    #38
  19. squish

    squish Out of the office.

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    One of the great things about airheads is that there are a zillion people who are willing and free to give you advice about the bike and issues with it.

    One of the worst things about airheads is that there are a zillion people who are willing and free to give you advice about the bike and issues with it.

    As an owner you have to wade through the crap and figure out who has the answer that's closest to the truth.
    Or failing that who's idea fits in with your own ideas best.

    Remember there are hundreds of riders who've put thousands of miles on these bikes never having to fix the "issues" that the internet experts claim there are, with the same token there are hundreds of riders who have had to do exactly what the "experts" say needs to be done.

    Do what you think is best, getting as much information for as many different sources as you can.
    #39
  20. _cy_

    _cy_ Long timer

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    back on topic :D

    check out this before and after a bit of elbow grease, all sitting in my living room.
    looks much better in person. that darn flash shows every little imperfection.

    been reading all the tails of fab adventure in remote parts of the world on Adv.
    sure glad I found this site. can't wait until it's my turn to post about adventures to parts unknown.

    dry weight is suppose to be 452lb or within a desired range. been scheming on how to mount one hard aluminum box and two soft paniers.

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    #40