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Thread: Cylinder conversion from R60 to R75?

  1. #1
    Smoooooth at 430 gch71's Avatar
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    Question Cylinder conversion from R60 to R75?

    Gentlemen....and ladies, since I'm currently unemployed (1st time ever since my teenage years) lots o time on my hands.....an idea popped into my head...always at the wrong time when i don't have any real money hehe, change my 1974 R60/6 to a 750. So I need some input and some great advice, so far i know need a set of cylinders/pistons, heads, carbs and a camshaft....it's a 74 model so is it a 97 or 99 mm base? What else would I need? Thank you fellow airheads...
    Glenn
    ...driving to work on my airhead
    '74 R60/6, '75 R60/6(boxes)

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    Administrator 20774's Avatar
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    Should be 97mm...they went to 99 at the beginning of the '76 model. On this page it says engine housing up to 9/75:

    http://www.realoem.com/bmw/showparts...25&hg=11&fg=11

    You might want to step back and think about this. The R60/5 /6 series had a very tight cam profile in order to make the smaller engine work well...the bike had 9.5:1 compression ratio. The R75/5 /6 engines had a different, wider cam profile. I can't say what will happen, but the mixing of an R75 topend with a R60 cam might not work so well. It would probably run, but you might have a pretty anemic bike.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Smoooooth at 430 gch71's Avatar
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    Quote Originally Posted by 20774 View Post
    Should be 97mm...they went to 99 at the beginning of the '76 model. On this page it says engine housing up to 9/75:

    http://www.realoem.com/bmw/showparts...25&hg=11&fg=11

    You might want to step back and think about this. The R60/5 /6 series had a very tight cam profile in order to make the smaller engine work well...the bike had 9.5:1 compression ratio. The R75/5 /6 engines had a different, wider cam profile. I can't say what will happen, but the mixing of an R75 topend with a R60 cam might not work so well. It would probably run, but you might have a pretty anemic bike.
    That's what I was thinking, however even if I replaced the cylinders/pistons, heads (the whole top) cam and carbs with R75 parts that should do it correct? Basically keep the bottom end the same just change the top end and cam.
    Glenn
    ...driving to work on my airhead
    '74 R60/6, '75 R60/6(boxes)

  4. #4
    Administrator 20774's Avatar
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    Well, yes, it you were willing to go that far. Top end replacement is pretty straightforward...getting into the bottom end takes a bit more knowledge, skills, and tools. In my grading system, a top end might be like 3 out of 5 wrenches. A bottom end overhaul is like a 4.5 out of 5 wrenches.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Joel Rappoport has a book "Hopeless Class" about his 2009 Iron Butt exploits on a R60/6. By the time he was done, it was basically a R75. I think the frame and engine case were original. He eventually added a Hannigan fairing. I stumbled upon his information while looking for new rear view mirrors for my Hannigan fairing.

    His site is rappoport.ws but is in disarray due to a move and a lot seems missing. It reminds me of the airheads.org site that everyone seems to reference, but none of the information is there due to site reconstruction. Anyway, if he is ever able to rebuild his site then there should be some good information about all the conversion details. At least, he used to have all that written down - maybe it is in his book? Good luck!
    Last edited by Stan_R80/7; 09-22-2012 at 06:20 PM. Reason: spelling
    Stan

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    Registered User f14rio's Avatar
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    what about drive train gearing?

    you might wind up with a buzzer that revs higher than it should.
    i dunno.

    i always thought r-65's were kind of buzzers
    "Enemy fighters at 2 o'clock!...Roger, What should i do until then?"

    2010 r1200r, 2009 harley crossbones, 2008 triumph/sidecar, 1970 norton commando 750

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    Smoooooth at 430 gch71's Avatar
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    Quote Originally Posted by f14rio View Post
    you might wind up with a buzzer that revs higher than it should.
    i dunno.

    i always thought r-65's were kind of buzzers
    Originally, I was planning on changing the rear drive to a 32/11 but then I realized that going on a cruise at 70-80 mph with bags for a long time is really a strain for that size engine. Maybe I'm wrong , I'll try with new rear drive first and see what she does. You see what happens when an airhead freak has to much time on his hands and runs out of whiskey
    Glenn
    ...driving to work on my airhead
    '74 R60/6, '75 R60/6(boxes)

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