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Cylinder conversion from R60 to R75?

gch71

Smoooooth at 430
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...:bow
 
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.do?model=0267&mospid=51887&btnr=11_1725&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.
 
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.do?model=0267&mospid=51887&btnr=11_1725&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.
 
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.
 
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!
 
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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
 
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 :dunno, 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:bolt:drink
 
More info about converting 60/5 to 75/5

Good evening gents,

One of my cylinders was damaged beyond repair and I'm having difficulty finding a decent replacement. I saw this video in youtube about this guy restoration and conversion to R75/5. The upgrade included bigger carbs as well.

Then I found this shop in Germany selling it. Have any of you heard about this? Not very experienced in this matter.

https://www.bmwbayer.de/en/conversion-kit-800cc-bmw-r60-5-r60-6-09-75

Cheers,

Ivicenzo
 
Conversion?

Lots to think about here. First changing the cam is a good bit of work and not for the do a few things in the garage. If you have done a timing chain then you understand some but not all that is involved. I never liked and rarely have done a used cam and lifters as just too much that can go wrong.
Best money to success route would be find an r75 or r90 motor and do a whole swap. This has the problem of numbers not matching but that may be a none issue.
I have a 73/5 750 top end that I removed completely working and replace with an r90 top end. I would get rid of this pretty cheaply if your interested. I will say this I have not locked at this except to remove. I never checked the piston to cylinder clearance and I would not recommend putting any used head on without a valve job and associated check of springs keepers valves and guides. This can run a good bit of money. If your think your might be interested I will do a piston to cylinder clearance check before we talk money as if it needs bored and new pistons I would recommend you look elsewhere.
Gator
 
R60 Conversion

Lots to think about here. First changing the cam is a good bit of work and not for the do a few things in the garage. If you have done a timing chain then you understand some but not all that is involved. I never liked and rarely have done a used cam and lifters as just too much that can go wrong.
Best money to success route would be find an r75 or r90 motor and do a whole swap. This has the problem of numbers not matching but that may be a none issue.
I have a 73/5 750 top end that I removed completely working and replace with an r90 top end. I would get rid of this pretty cheaply if your interested. I will say this I have not locked at this except to remove. I never checked the piston to cylinder clearance and I would not recommend putting any used head on without a valve job and associated check of springs keepers valves and guides. This can run a good bit of money. If your think your might be interested I will do a piston to cylinder clearance check before we talk money as if it needs bored and new pistons I would recommend you look elsewhere.
Gator

Gator,

I converted a close friends 76 R60/6 to a 750cc by installing R75/6 cylinders and pistons removed from my R75/6. The ONLY modifications we had to make was: (1) a base gasket to keep the compression down, (2) larger jets in the carbs (this R60 had the Bing slide carbs), (3) retarded the timing a couple of degrees, (4) changed the rear drive ration to a slightly higher one. My friend has several thousand miles on the bike and is VERY happy with the increase in power.

IF I read your post correctly you have the 97mm bore so you will have to use the 97mm cylinders or have them turned down.

Hope this helps.
 
Power corrupts!

Depends on your riding mode. If you haul a lot of "stuff" then a bigger engine may be an advantage. To get the best out of a bigger engine you'll want to change the rear drive. The R75/5 (except for the earliest models) came with a 3.20 ratio. Bigger engine=taller gears.
On the other hand if you ride solo with minimal gear then the R60 is certainly adequate. One of my best /5s was an R60 that I rode solo for a few years. Wish I still had it! If you want to go fast, buy a faster bike.
 
Cam of R60 is different from that of an R75/R90. Ignition timing is the same according to technical specifications. CR differs too. Carb specs and all of this stock info found in great 1973 owner's manual. That blue book under the seat. Valve sizes and lift also differ; this with almost all data is in BMW blue covered Reparaturanleitung.
 
As a rule of thumb, I generally tell 'want to be bike builders', it's much easier to just move up to a bike that already has the power and torque you want by buying a bike that has it from the get go. That said hopping up a bike to gain more performance can be a fun and satisfying experience. But, more times than not, I generally see the project fail to meet expectations. Usually along with build not meeting the target, is the expenditure of a lot of cash the builder really couldn't afford. Good luck with your project build.
 
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