1974 R90S VERSUS '75 & '76, DIFFERENCES

Post Reply
kirkpatrick3890
Posts: 57
Joined: Fri Oct 27, 2006 3:00 am

1974 R90S VERSUS '75 & '76, DIFFERENCES

Post by kirkpatrick3890 »

THE R90S MODEL
Introduced on the 50th Anniversary of BMW Motorrad


It has been said the R90S is to BMW Motorrad as the Mercedes 300SL Gull Wing is to Mercedes Benz. They are both iconic.



“FIRSTS” FOR BMW With the Introduction of the R90S:

Designed by a designer, Hans Muth, not engineers
900 cc engine (up from 750 cc)
5 speed trans, was 4
Dual front disc brakes
No fork gaiters, the fork tubes were exposed for visual appeal
No stays on the front fender, again for visual appeal
Steering damper
Separate tachometer and speedometer in same housing
Polished float bowls
Seat cowl
Smoked paint (referred to as "Silver Smoke" only in ’74, "Tourist Trophy Silver Smoke" & "Daytona Orange" in ’75 & ’76). Daytona Orange was meant to mimic the sunrise at Daytona Beach.
Factory fairing
First Superbike win, at Daytona in 1976, then won “Superbike Championship” for the full year
Only model with Del’Orto carburetors


Visual Differences For the 1974 R90S Compared to Later Model Year R90Ss:

The ’74 had many nice features compared to later R90Ss, the main driver being to keep down costs. This was never stated but note the differences from ’74 to later, many are cheaper alternatives. But these changes are not easy to note, one really must look hard to notice the differences.

/5 handlebar controls, in looks only; the wiring was unique for this year and different from the previous /5 models
Aluminum gas cap, later chrome casting
Smaller diameter front axle (14mm, then became 17mm"
Aluminum turn signal bodies
Hand levers curved with finger detents, anodized, they naturally turn purple with age
Seat was “smooth”, fewer indentations compared to later
Chromed right rear lower shock mount, an acorn nut
Speedo/tach read “0” for neutral, later “NEUTRAL”
Five position ignition switch versus three later
Carb to airbox clamps had dull finish, later were chromed
Smooth swingarm black plastic covers, later crinkle finished
Brake master cylinder diameter went from 16 to 17 mm for ‘76
Brake caliper went from 38 to 40 mm for ’76
Tape stripes (wallpaper), painted stripes came in ’75 & ‘76
Mirror stalks smaller diameter and curved (more elegant)
White line around the speedo and tach glass diameter, inside the glass
Solid discs, later drilled in a 3/2 pattern then 2/2 pattern
More chrome fasteners than later
Last year for kick starter being standard
Some early fairings had two holes in the bottom as access for removing the headlight bezel
Early throttle tubes were bent, later were straight
Later transmission cases had exterior “lines” added for strength, getting ready for the 1,000 cc engine
Early front axles had one pinch bolt versus 2 later
Horns had a chrome center, later flat black

Not all these “visuals” were strictly for the ’74 model as “running changes” were the norm.
As parts were used up newer style parts were installed. Sometimes…

NOTES:
There is no such thing as “always” or “never” in the R90S world. As soon as you say that, it always seems an exception pops up.

Even when an original owner says, “I picked up my R90S from the dealer, so I know mine is how it came from the factory.” What about transit damage? Did the dealer alter the bike or fix a problem before turning it over to the original owner? Did the dealer swap parts to please another customer? Is your memory that good after 45 years? How many owners has your bike had?

After the Superbike win at Daytona in 1976 on Daytona Orange bikes, it is documented that some customers had dealers take off their TT Silver Smoke parts and install Daytona Orange parts. So maybe your Daytona Orange bike was originally TT Silver Smoke? BMW “might” be able to verify that as some records were lost.

And because the current "O-fish-ul" BMW parts fiche says so (say at Max BMW), that is NOT necessarily how BMW assembled R90Ss originally.

And BMW made numerous other running changes to the starter, alternator, trans, front end, really everywhere. The ’76 model is thought of as the best example since it had all the upgrades.

The transmission in the ’74 model: Oak Okelson’s frank advice was to swap it out for the trans from a later year as it was not a good transmission, however many are fixed and soldier on. I have one and once repaired, it is fine. Some trans parts for '74 are no longer available.

When BMW employees first saw the Daytona Orange color they referred to it derisively as “egg yoke”.

Which color is the best? TT Silver Smoke is Elegant, and Daytona Orange is Stunning, per Rob & Mac.
SO: Daytona Orange is for going to the beach, TT Silver Smoke for going to the opera.

Some R90Ss had cloisonné (enamel) emblems, some did not; there is no pattern.

Early fairings had two holes in the bottom for access to remove the headlight bezel.

R90Ss came with 3 keys; metal, with large black round fob, folding gray plastic.

The very last of the R90Ss had flush gas caps like the /7 models, and for years replacement gas tanks had flush caps, which upset owners.

Upgrades to consider:
R75 rear drive w/matching R75 speedo & tach (better acceleration), 14 mm brake master cylinder with 40 mm calipers (optimal braking ratio), 1,000 cc kit from Siebenrock, Nikasil coating of cylinders from Powerseal USA, trans “shift kit”, “cush drive” driveshaft, chrome plated stainless spokes for longevity as well as originality, higher output alternator (up to 600 watts), kick starter, Nippondenso starter motor (stronger, less draw), Kat Dash instrument lights, but of course the sky is the limit for $$.

The R90S almost did not see the light of day; Bob Lutz is considered the Father of the R90S, see the book “BMW R90S” by Ian Falloon, page 33.

Interesting R90S article below (previously sent via email)
https://www.rideapart.com/articles/2486 ... o-edition/



Mac Kirkpatrick
drbeemer73@gmail.com
Presented at the PA Airhead SuperTech, Boyertown, PA
Feb 2019
Mac Kirkpatrick
President, VBMWO

pwfix
Posts: 2
Joined: Fri Oct 12, 2018 8:21 am

Re: 1974 R90S VERSUS '75 & '76, DIFFERENCES

Post by pwfix »

Mac
Could you clarify something for me in regards to the changes to the mirrors from the 74’s to the 75’s?
I am aware that 74’s were thin stem and curved. Where 75’s typically also thin stem but straight?
When I ordered a set from Motobins that we’re supposedly correct to my 75 they came with thicker stems than the ones I was replacing, which had slight damage to them. When I questioned Motobins on the discrepancy they responded that it was news to them.
Also if I’m correct in my opinion that they should be thinner stemmed do you know of a vendor that might have them?
Thanks for your time.

Patrick

User avatar
RickR90s
Posts: 87
Joined: Mon Nov 28, 2016 4:54 pm

Re: 1974 R90S VERSUS '75 & '76, DIFFERENCES

Post by RickR90s »

The original mirrors on my early '74 (built 10/73) are thin but appear to have a shallower angle to the end of the bars compared to other, later models I've seen.

Rick Griffith
RickR90s

kirkpatrick3890
Posts: 57
Joined: Fri Oct 27, 2006 3:00 am

Re: 1974 R90S VERSUS '75 & '76, DIFFERENCES

Post by kirkpatrick3890 »

Patrick, I think it is impossible to know when exactly BMW changed mirrors on the R90S. I just don't think they thought it was a huge deal to make such a small change plus without computers it would have been so difficult to document these small, to them, changes.
After all, in their eyes this was an improvement since the first mirrors did not stay in place.

That is why MotoBins told you what they did, no one has any idea when this change occurred.

On my restored R90S, I bought new mirrors and gently bent a curve into the mirror stalks, which I think helps a lot.
Mac Kirkpatrick
President, VBMWO

kimmsinger
Posts: 16
Joined: Thu Aug 06, 2015 2:39 pm

Re: 1974 R90S VERSUS '75 & '76, DIFFERENCES

Post by kimmsinger »

Anyone heard of twin plug heads?
bwboulder

User avatar
schrader7032
Posts: 7624
Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX

Re: 1974 R90S VERSUS '75 & '76, DIFFERENCES

Post by schrader7032 »

Twin plug heads? Sure, that's a modification that some have done to their bikes. It involves adding carefully drilled/tapped holes on the other side of the heads along with special consideration to coils and wiring. I forget what specifically the advantages are but I believe one is that it will run better on lower octane fuel...maybe improves cold starting. Because of the second plug, the flame front burns from two directions and does a better job at combustion.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

MikeL46
Posts: 130
Joined: Fri Jan 01, 2016 1:58 pm

Re: 1974 R90S VERSUS '75 & '76, DIFFERENCES

Post by MikeL46 »

Dual plug heads were popular in the late 70s/80's when it was hard to find quality gas. Frequently, the valve seats were replaced at the same time to be able to use unleaded fuel. My R90S has been dual plugged. Since high octane gas is readily available the 2nd plug is not really needed and mine is not used. The bottom plug is left in place and the upper plug is used the same as a normal bike.

Mike
67 R50/2 w/R100 engine/trans and Ural Sidecar
69 R60/2 76 R90S 78 R100RS
70 Triumph w/Spirit Eagle Sidecar

jjwithers
Posts: 2
Joined: Sat Dec 26, 2015 3:46 pm

Re: 1974 R90S VERSUS '75 & '76, DIFFERENCES

Post by jjwithers »

Nobody made mention of the elusive handlebar clamps...
I have a '74 with a hodge podge of upgrades and parts. Missing those handlebar clamps. Flat gascap. Orange. Dual Plugged.
Previous owner wasn't concerned about originality but since it is a R90s, I kinda wish he was.

Gpol
Posts: 1
Joined: Thu May 20, 2021 12:38 pm

Re: 1974 R90S VERSUS '75 & '76, DIFFERENCES

Post by Gpol »

Patrick, My name is Greg Polzin. I have had a R90S since it was new in 1975. My mirrors had thin curved stems. I needed to replace one of the mirrors and my dealer ordered a replacement for me. It was obviously different when it arrived. This was in the spring of 1976. I was not happy with the mismatched mirrors and was told that the mirror that they ordered was the same part number and was the new improved style. So I ordered a replacement for the other side and that is what is on the bike now. This last year I ordered a set of mirrors from S. Meyer that had the long thin curved stems as had originally come on the bike and they are elegant. The upgrade mirrors from BMW had thicker straight stems and were supposed to offer a better more vibration free view of the traffic behind. They probably are better but the curved thin stems look better to me. I hope this helps and the old style are available but probably not from BMW NA or your dealer.

Post Reply