I'm starting to think about making a souped up cafe/custom bike.

[bmwdebesy]

I was at the Sipapu rally in northern New Mexico over the weekend and saw some pretty interesting bikes which made me want to make a cafe racer sometime in the future. I know most people on here would say "Keep the bike original!! you are only going to mess things up if you try to soupe up an airhead." This is probably good advice but I already have a stock /5 and I really want to see how I can push the limits of the boxer engine. I talked to some people at the rally and here are some of their suggestions:
1. Use a R65 engine since it has a shorter stroke and you can bore it out bigger.

2. Put a 34/12 (I think thats correct) final drive on

3. Dual plugging

4. High performance cam

5. I think someone mentioned high compression pistons but I could be wrong

I would like to know if anyone has any other suggestions. I dont want to do anything ridiculously extreme (like turbos etc.) but I would like to to be pretty entertaining. Also, if anyone has and warnings about what NOT to do, I would greatly appreciate those as well.

I dont plan on starting this any time soon as I have too many projects already but someone once said over planning never hurt anyone.

Is there any one website that has a spread sheet of gear ratios and specifications so I can see which parts would maximize the performance?

Thanks

-Vince

 

[mfwren]

You're right Vince, most people will say keep it stock and while I appreciate a nicely restored bike I'm not offended by a hot rodded airhead. Witch is good because I own a modified '78 R100S. Here's a list of mods that are on my bike:

1- balanced crank, rods and pistons. HC big bore pistons

2- ported duel plug heads, 44 mm intake valves, 40mm exhaust valves, duel intake and exhaust springs with titanium retainers. side thrust bearing. exhaust port opened up to 40 mm exhausting into 40mm Keihan exhaust system.

3- 336 cam

4- 38mm Mikuni carbs

5- later model flywheel/ clutch assembly (for weight reduction and better torque handling capacity) which also necessitated a later model transmission or modification to the original stock trans.


7- I lastly modified frame to handle additional power with side braces, front fork brace, and braced rear swing arm. Progressive spring up front, Ohlin shocks behind and later model Brembo brakes/ forks up front with EBC semi floating discs.

Now I'm not sure how many of these mods could be used on a R65 motor. Most of these mods may only work on larger displacement bikes. But a least you"ll have an idea of what can be done. Good luck

Michael

 

[bikerfish1100]

i would tend to stay away from the R65 as a performance platform for a few simple reasons:
1) it's somewhat the red-headed stepchild of airheads; few parts interchange with other models (among which nearly everything is interchangeable), meaning parts availability is considerably less than for others.
2) it was never really considered to be a "performance" model, so there was minimal support for hopup parts when it was in production (especially true when compared to the R80, R90 or R100 machines), and even less are available now.
3) the above considerations fall out the window if you have: unlimited funds, and/or your own machine shop for parts creation/alteration.

 

[criminaldesign]

Do it dude, and I want to see it.

It's a treat to see beemers that don't look and act like they're 'supposed' to, cos they're few and far between.

It's your bike, get creative and most importantly have fun!

h

 

[mymindsok]

Well, Airhead cafe bikes can be built to work very well and since it sounds as if you already have a /5, I'll work from there but if performance is the name of the game, you're probably going to want to swap a lot of parts, in order for the bike to perform safely and to handle your upgraded power plant.

1) Any /6 or /7 front end will swap right on to a /5 and give you dual disk brakes. I wouldn't keep the drum but you might want to.

2) Gusset the frame. The /5 frame is pretty willowy and stiffer is always better, plus you can add a R100 try cross bar, just in case you want to use an oil cooler.

3) Is your bike a SWB? If so, brace the swing-arm. If it's a LWB, swap in a big tube unit from an 80s bike..

4) If you're going to spend the cash to build an engine, get one from an early 80s or later R100. You ll start out with better oiling, a stronger case and maybe more displacement but Hot Rod 750s are pretty cool! Just remember this: It costs the same amount to build a hot 750 as it does to build a hot 1000 and your mileage will be about the same.

5) Whatever you do, you'll probably want a 5 speed tranny and the updated "Basket" clutch assy.

6) 366 long-nose points cams are AFAIK, NLA from BMW. (Or at least they were last year when I bought mine!). This will mean that a once again you'll be pushed towards a later model "bean can" engine.

7) I'm running big Port heads too but for real street performance you might want to consider small port heads with 44MM intake valves. The smaller exhaust valve heads flow better on the street, the big valve ones are better at high speeds and buying a true 40mm exhaust system is expensive.

Now heres something that I've been thinking about and it would be pretty kool to build.

Take either a beefed up /6 or /7 frame, add a hot rod engine but swap in a braced SWB or shortened up Big tube along with a beefed SWB sub frame and some variation of dual disk front end. That would give you a great handling bike, with all of the upgrades that you might want.

Add in a hand made seat, an aluminum tank and fenders, along with a few more custom touches like a dropped triple tree and clip-ons and you're there!

Just remember.... A lot of the stuff that you'll be changing on your /5 are already in place on a later bike and parts are getting expensive! I hope you have a fat wallet!

PS: Don t even think about hot rodding an R65 engine. unless you really know what you're doing and have very deep pockets!

Good luck!

 

[bmwdebesy]

Thanks for the input! Im not going to hot rod my /5, thats the one that I want to keep original. Since a R65 is not a good starting point, what engine/bike would you suggest? Maybe a R80 or R90? I think a later model would have more of the things I want on it (disc brakes, lightened flywheel, better suspension, etc) but I dont know which one. I dont really have deep pockets so I think it would be best if I buy a whole bike instead of gathering different parts and going from there. Also, does anyone know where I can find some of the performance parts listed? Would Bobs or some other big dealer carry them?

 

[bob_m]

Start with an 84 R100. This was a no fairing version. the 84 is the last year of the classic looking twin shock model. As you will be tinkering with the machine, the glaring shortcoming of the bike, valve recession, will be addressed when you get the heads ported and polished.

Fairly stiff frame, nikasil barrels, electronic ignition..... It is a good bike and a good place to start.

 

[typ181r90]

Also, does anyone know where I can find some of the performance parts listed? Would Bobs or some other big dealer carry them?

http://flatracer.com/

 

[toooldtocare]

I was at the Sipapu rally too, but I do not think that I spoke to you. My bike looks pretty much stock (78 R100RS Motorsport), but has many of the mods you speak about. I am sorry it was not at the rally, I had car/trailer problems and had to leave it home. Bummer, bike-less in those mountains with perfect weather with only a Honda Pilot for transportation. I know, I should have ridden, but where would I put my wife with our dog and our other gear.

Anyway, I find my bike handles well, has plenty of power, and stops better than most any other stock older R100. Below is a partial list of things done. Now, I am not saying that you should add everything that my bike has, but it is a place to start. Many people recommend different shocks and handling upgrades than what I have, and they may be right since they probably are better now. And, I hear that the lightened wrist pins may be a mistake too. My bike was modified by San Jose BMW in 1985, plus last year by me.

It has dual plugs, Dyna III, hotter cam, lightened wrist pins, lightened flywheel, stronger aftermarket clutch plate (my addition) balanced con rods, hardened valve seats, Koni shocks, San Jose handling kit (aluminum upper tripple clamp, reinforced swing arm, progressive springs, SS brake lines, fork brace). Also, 40mm exhaust, oil cooler, K75S bars (my addition), floating rotors and ceramic pads (also my addition).

I am probably forgetting something, but you get the idea. Good luck, and hope to meet you next year at Sipapu. I will be there with a NEW TRAILER and my Motorsport, or I won't be there at all.

 

[crazydrummerdude]

I am probably forgetting something, but you get the idea. Good luck, and hope to meet you next year at Sipapu. I will be there with a NEW TRAILER and my Motorsport, or I won't be there at all.

He's the young dude with the blue/purple/something GS and jean jacket.

 

[beemerguru]

This is one way to go


http://airheadreborn.blogspot.com/

 

[punkasskid]

See sig line.

 

[VANZEN]

Caff'd !

GO 4 IT !

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