76 R90/6 - ideal RPM's & engine braking

hey guys--

just picked up a 1976 R90/6 with 27k on the ODO. so far i'm loving it, but this is my first BMW, and i can definitely feel some differences in riding versus my other japanese motorcycles i've owned in the past.

what is the ideal RPM's to be riding at on these? i've found i'm in the 3K - 4K range a lot, but should i be looking to push further than this? i've really only done residential riding so far, haven't really gotten her up and going over 60 yet.

also, engine braking feels like it's less of an option on a shaft driven opposed twin versus a chain driven machine. definitely can feel the torque on the down shift and i'm a little worried about trying it at higher speeds. is it there a trick to downshifting, with increasing RPM perhaps? any insight would be greatly appreciated. thx! here she is!

Welcome to the forum! Nice Havana Gold! '76 R90/6 is a very nice bike to have.

I pretty much cruise most of the time at 4K and I also spend time between 3 and 4K. My /7 has a tallish rear end so 70 mph is around 4K...your bike might be slightly higher than that at highway speeds. Some like to keep the RPMs higher as you get more into the peak power and torque range of the motor. But I'm more conservative and don't spend much time above 4.5K.

Personally, I'm not a fan of engine braking...I find it easier to replace brakes than engines!! I certainly downshift when slowing down but I only bring the engine up to match the road speed, not to slow the bike down.

Pretty bike, ride and enjoy.

Welcome, CP!

Haven't had an airhead for a while (had two R75's, two R100's, and friends with R90's), but as I recall, 4K RPM is the sweet spot. Below 3500 is lugging it - don't...

Shifting - AND acceleration & deceleration - is directly affected by the flywheel + clutch assembly. With your stock setup, let it spin up a little before you shift, and synchronization between your wrist and your foot is more important than with Japanese bikes. If/when you ever take the clutch apart, that would be good time to investigate having the flywheel lightened. Especially note during the clutch dis- and re-assembly, that there are balance marks to pay attention to, to keep things smooth.

If those are the stock shocks and fork innards, you may want to consider modern upgrades in there, too.

Enjoy!

Pauls1150 said:

Welcome, CP!

Haven't had an airhead for a while (had two R75's, two R100's, and friends with R90's), but as I recall, 4K RPM is the sweet spot. Below 3500 is lugging it - don't...

Shifting - AND acceleration & deceleration - is directly affected by the flywheel + clutch assembly. With your stock setup, let it spin up a little before you shift, and synchronization between your wrist and your foot is more important than with Japanese bikes. If/when you ever take the clutch apart, that would be good time to investigate having the flywheel lightened. Especially note during the clutch dis- and re-assembly, that there are balance marks to pay attention to, to keep things smooth.

If those are the stock shocks and fork innards, you may want to consider modern upgrades in there, too.

Enjoy!

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thanks for the input, much appreciated! PO installed progressives for the front shocks, rear shocks are stock. looking into upgrading after another paycheck or two rolls in...

Consider joining the national Airheads Beemer Club (www.airheads.org) offering lots of support, technical assistance, information and social activities regarding a range of BMW motorcycles that many current dealers are no longer familiar with. The ABC is organized by states and has a fairly strong presence in the Northeast. It will be the best $30 you ever spend on your new bike.

Friedle

PS: If you have not yet found MAX BMW shop in Brookfield. CT I would highly recommend them for Airhead work, parts and service over the rest of the NYC area dealers.

For me, normal cruising along in urban traffic is in the 4 to 5K range. Running up through the gears is as mentioned above, syncing the speed of the flywheel to when your foot actually does it's thing. I try to wind up to 5k or so when going away from a light. No, not running it up fast; but just giving it to go up to speed as it feels natural to do...…...Later, out on the 55mph roads, cruising along as mentioned at 70 is in the 4k to 5k range. It just feels so good at that RPM.....smooooooth …...5K IS PERFECT FOR PASSING AND JUST LET IT RUNNN

Downshifting is NOT an art form and is perfect for slowing down and getting ready to hit the apex of a curve and accelerate out of it. YES, your butt will feel a bit of a blip when you actually let out the clutch at 5k or above. IT ISNT GONNA TWIST OUT FROM UNDER YOU. Just a little horizontal piston engine/crankshaft/flywheel action when the clutch meets the flywheel...……...You are hurting nothing!!!


Cruise along ABOVE 3000 RPM...…...NEVER BELOW.....Your timing chain will love you for that...…..RIDE

'76 /6 Upgrades

Just a little aside. From a tech point of view the '76 has quite a few upgrades over the earlier /6's. In fact a lot of those upgrades were added to the /7. Most are almost invisible to the majority of owners. Much improved tranny. This is seen on the tranny with a pronounced seam that runs front to rear about the middle of the tranny. The very complex cluster gear much upgraded on this model. Much more frame bracing. There's more but I'll have to think about.

I believe the '76 got the larger engine case openings, going from 97mm to 99. This was in preparation for the 1000cc motors coming out in 1977. The significance of this is that some post 1976 engine items can be directly substituted easily...and aftermarket options are a little more wide open when considering engine upgrades.

The two Airheads I ride that are in stock tune are happiest at 5000rpm.

https://forums.bmwmoa.org/showthrea...n-on-a-R75-5&p=1145297&highlight=#post1145297

I don't know how to answer the engine braking question other than to put some miles on it.

Bill

concernedparent said:

..any insight would be greatly appreciated. thx! here she is!..]

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Hi CP:

Welcome to the Forum and congrats on your purchase.

The Airheads I have ridden like 4 to 5 thousand in top gear, or 4th, (if you have 5).

You can go lower in the lower gears but I would stay above 3,500 as an arbitrary limit, until you get a feel for where the bike is lugging.

For engine braking, just roll off the throttle, but avoid doing this abruptly, especially at high rpm.

Have fun.

Nice choice. I think engine braking is an art on these compared to a chain drive Japanese bike, particularly a four cylinder (some fellow named Pridmore told me that). That said, it's just a matter of practice -- get that in a straight line before you try it leaned over. Also depends on how hard you're pushing. And note how the engine twists to the right when you rev it at idle; kinda fun but if you roll off suddenly in an off camber left turn something will touch down. DAMHIK

There is a time and place for engine braking, primarily in matching road speed to engine speed while shifting and also in maintaining a fairly constant forward momentum while riding (the "pace") BUT if attempting to come to a stop the brakes are far more effective than downshifting. An added benefit is that brake pads are far less costly than a transmission rebuild.

Compare the technique of engine braking to slow for corners vs. trail braking in corners. We teach beginners to brake before the corners making sure to match engine speed to the road speed. We teach more experienced riders seeking better technique and a smoother ride the concept and execution of trail braking. Both will work, many riders never try level two.

Friedle

+ 1 on MAX BMW & the ABC.
Irv Seaver BMW is my local source for bike parts.
Bill

concernedparent said:

hey guys--

just picked up a 1976 R90/6 with 27k on the ODO. so far i'm loving it, but this is my first BMW, and i can definitely feel some differences in riding versus my other japanese motorcycles i've owned in the past.

what is the ideal RPM's to be riding at on these? i've found i'm in the 3K - 4K range a lot, but should i be looking to push further than this? i've really only done residential riding so far, haven't really gotten her up and going over 60 yet.

also, engine braking feels like it's less of an option on a shaft driven opposed twin versus a chain driven machine. definitely can feel the torque on the down shift and i'm a little worried about trying it at higher speeds. is it there a trick to downshifting, with increasing RPM perhaps? any insight would be greatly appreciated. thx! here she is!

Click to expand...

Welcome!

My first BMW was a '76 R90/6.... I bought it new, put about 200K on it and regret ever parting with it. In retrospect it was probably the best bike I've ever owned.

As noted in one of the responses below the '76 has several good features not found on the earlier /6's. One of these features (also on the '75 /6's I believe) is that the cylinders have an extra longitudinal boss in the cooling fins which enables the cylinder to accept a bore out to 1000cc. I did this to my bike at about 60K to take out the slight high end buzz that most of the 900cc bikes experienced. I had the new pistons teflon coated before installing and never had any trouble with the conversion. I stayed with the stock Bing carb's but added a set of slightly less restrictive megaphones from D&D in Haltom City, TX., which was like putting a slightly higher duration cam in..... greatly increased the throttle response. The only other thing I would consider would be a /7 front end to get the twin disc brake setup.

Congratulations.... you've got one of the best!

VIEJO said:

Welcome!

My first BMW was a '76 R90/6.... I bought it new, put about 200K on it and regret ever parting with it. In retrospect it was probably the best bike I've ever owned.

As noted in one of the responses below the '76 has several good features not found on the earlier /6's. One of these features (also on the '75 /6's I believe) is that the cylinders have an extra longitudinal boss in the cooling fins which enables the cylinder to accept a bore out to 1000cc. I did this to my bike at about 60K to take out the slight high end buzz that most of the 900cc bikes experienced. I had the new pistons teflon coated before installing and never had any trouble with the conversion. I stayed with the stock Bing carb's but added a set of slightly less restrictive megaphones from D&D in Haltom City, TX., which was like putting a slightly higher duration cam in..... greatly increased the throttle response. The only other thing I would consider would be a /7 front end to get the twin disc brake setup.

Congratulations.... you've got one of the best!

Click to expand...

A couple of additions to the above......

I second the motion that you link up with the Airheads Beemer Club ASAP.... incredible resource for information/guidance/folly on all things Airhead related. In all probability every question you may have about Airheads has been answered there.

With regards to your question(s) about shifting in general. Airheads are characterized by a rather clunky shifting feel.... nothing amiss, just the result of fairly heavy flywheels (I do not subscribe to the "lighten the flywheels" school of thought). Most Airhead riders I know will "pre-load" the shifter slightly just prior to shifting, up or down. Not a great deal of pressure, only enough to take the slack out of the shifter. If you decide to do this it will become second nature quickly..... I do it on my K bike also.

There is a plethora of aftermarket gear available to bring your Airhead into the 21st Century and most of it is quite good. However, your low milage '76 is quite capable of running for many miles/years with the gear originally fitted. Don't be in a headlong rush to start "modernizing" unless you have deep pockets and the money's burning a hole in them. If the R90 series had a weak spot it was the ignition/charging system; good for the time but still room for improvement. Consider a modern solid state ignition/charging system for an initial upgrade. EME [www.euromotoelectrics.com] is a great resource for all things electric.

4K and blip it on downshifts

On my stock 1975/6 4K is the sweet spot.

On 1->2 shifts I preload the shifter to avoid the massive 'clunk'. I get it right 7 times out of ten, all occasions for rejoicing. The other 3 times I check the rear view mirrors to see if my gearbox has shed parts. After almost 30 years with the bike this is the best I can manage, having long resigned myself to the belief that the clunk is a feature, not a problem.

And on all downshifts I rev match by blipping the throttle when the clutch is disengaged. This makes for smooth shifts. Otherwise the heavy stock flywheel slows things down too much and you are looking at earlier clutch plate replacement.

Enjoy your bike - it’s a beauty.

THOMASPIN said:

On my stock 1975/6 4K is the sweet spot.

On 1->2 shifts I preload the shifter to avoid the massive 'clunk'. I get it right 7 times out of ten, all occasions for rejoicing. The other 3 times I check the rear view mirrors to see if my gearbox has shed parts. After almost 30 years with the bike this is the best I can manage, having long resigned myself to the belief that the clunk is a feature, not a problem.

And on all downshifts I rev match by blipping the throttle when the clutch is disengaged. This makes for smooth shifts. Otherwise the heavy stock flywheel slows things down too much and you are looking at earlier clutch plate replacement.

Enjoy your bike - it’s a beauty.

Click to expand...

Some further thoughts about downshifting.... if you are downshifting for braking purposes then I would think you would want to make the gear change as quickly as possible in which case the two essentials are knowing the bite point of your clutch and the relative throttle grip rotation required to achieve the desired RPM. IN MOST CASES it isn't really necessary to pull the clutch lever in to full stop or close/open the throttle completely when shifting... up or down. Fine tuning your shift points is just a matter of consistent riding.

Personally, I do not favor downshifting for braking on a /6. If done properly it's a perfectly safe maneuver... but hard on tires, clutch assembly, u-joint/rear spline assemblies, and ultimately the wallet. Downshifting to match engine rpm with road speed is another matter and is generally done in a more "leisurely" manner than a braking downshift.

YMMV,

Viejo

From what I've learned, in stock tune 4000 RPM on an Airhead is a sweet spot for carbon buildup.*
It was tough for me to do at first, with most of the torque being on the low side of 5000 RPM, but the Airheads I have/owned run cleaner at 5000 RPM and above.
Max torque on /5&6 bikes is at 5,000 RPM, on my '92 R100GSPD max torque is at 3,750 RPM.

The PD had a top end reseal at 30,000 mi.
The mechanic had to decarbonize the piston etc.
He recommended to run at 5,000 RPM after I told him that I usually run at around 4,000 RPM.
Recently when the heads were off at 80,000 miles, there wasn't any carbon build up. The same was true on my '76 R90/6 at 70,000 mi.

Bill

*Oil getting past rings & valve guides will also cause carbon to buildup on valves, heads & pistons.


Photo is near Sherman Pass Ca. (9,200') 9/7/17

I have a 75 R90/6. I just ride it like every other bike I've owned of the same age. Upshift/ downshift very much like Honda Goldwing from 1975 till 1987.
Have enjoyed the performance of my stock model. To be honest, I don't baby mine when I ride it, or give it special attention during the ride.

Great find, have fun.