R100RS - any thoughts

(RIP) Perryhill

(RIP) Perryhill

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I've always had a hankering after an R100RS to go with my GSPD and wondered if anyone had any experience of them.

I've often been told to buy the most original and latest bike you can get but was surprised to learn the later, monolevered version, ran 32mm not 40mm Bings and developed 60 not 70BHP. There is not much difference in the torque at 74nm to 76nm so, in the real world, would the missing 10 BHP make much difference or should I aim for the older twin shock version?


I know you can swop barrels, heads, carbs etc but that seems to defeat the objective of buying most original I can find.

Other comments of a kind and helpful nature regarding R100RSs would be appreciated. Anyone know why they went for less power later on?

Neville​
 
I've got a 100RT, 1981 and the 70BHP engine, gearing, power etc as the RS. The only difference between the two is the fairing and handlebars.

The RS bars are very narrow and feel strange until you get used to them. The fairings work very well. You can belt along at silly speeds with no wind impact on yourself at all.

Twin shock bikes feel very sturdy compared to the later monolevers but the mono's do handle batter. The drop in horsepower of the later bikes was to allow for unleaded fuel. I had a monolever RT last year, the 10BHP is noticable as a lot more grunt at lower revs.


Nice bikes and strangely addictive. I really like mine :cool:

It's a pity you don't live closer you could have taken it for a spin.
 
Neville - I've got a '78 R100RS, although it is now fitted with the front brakes and suspension from an '81.

In line with the rest of the /7 range, the '77-'80 bikes have the ATE swinging caliper and under-tank master cylinder arrangement. The later Brembo fitment gave much, much better braking as well as improved front suspension.

As Rob says, the original bars are very low. I've replaced mine with K-RS bars which still fit within the fairing, but act like bar-backs, bringing things up and back a couple of inches.

I'd also go for the 40mm version. Yes, the mono probably handles a tad better, but a well set up twin shock on Konis and with 7.5w oil in the front forks is rather pleasant.
 

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I had one of these as my London commuter for ages and it was just SUPERB. 1980 twin shock. Reliable as a reliable thing, cheap to run and a blast to ride. Even in Feb the wind stayed off and I stayed warm and toasty behind the fairing. The only thing with mine is that it seemed to track every single rut in the road and slide in the wet quite nastily. Anyone else have the same problem?
 
MMC said:
The only thing with mine is that it seemed to track every single rut in the road and slide in the wet quite nastily. Anyone else have the same problem?
Click to expand...

Yep. Even with Koni's, new swinging arm and wheel bearings. I'm running Pirellis at the moment but will swap to Battleaxes over the next few weeks.
 
MMC said:
I had one of these as my London commuter for ages and it was just SUPERB. 1980 twin shock. Reliable as a reliable thing, cheap to run and a blast to ride. Even in Feb the wind stayed off and I stayed warm and toasty behind the fairing. The only thing with mine is that it seemed to track every single rut in the road and slide in the wet quite nastily. Anyone else have the same problem?
Click to expand...


They ALL do that sir :D
/6's and /7's with heavy flywheels [pre 81]
I always use Metzlers, there not perfect but they are the best of the lot,
99 on the back, Lazer on the front :thumb
 
I had a '78 RS and an '86 (IIRC) monoshock - I actually bought the '78 one after I'd sold the monoshock. Granted, the handling of the monoshock was better but other than that the '78 was a far better machine especially in terms of build quality. No end of problems with the monoshock bike - clutch/brakes/forks/electrics/gearbox - a pile of shite. The '78 felt much more solid, never let me down and I even bought it back off the bloke I sold it to after he'd had it a couple of years. Can't say I noticed the performance of the later model was much different despite it's lower HP. Go for a twin shock IMHO. Wish I'd kept mine :tears
 
Owned 3 R100RS's. Two were post 1981 twinshocks and I have very fond memories of both these bikes. Particularly the one I fitted with progressive front springs and heavy duty BMW rear shocks which transformed high speed handling - a delight to ride and quick for 70 horses - apart from the horrendously noisy screen (in the days before I used ear plugs) Fitting a taller screen ruined the look IMHO and didn't really improve things much.

The third was a monoshock bought new. As has already been said - a pile of shite - totally bland, slow, dull, lacking in quality - I could go on. I got rid of it after 6 weeks

I would go for an '81 on bike - These models had electronic ignition and great brakes. The orignal '77 on models were fitted with BMW's own disc brakes and calipers which made them pretty scary to ride.

I think I'm right in saying that there could be problems running them on unleaded - there was a lot of controversy over this. Worth checking if the valves have been modded? Oh, and Metz ME tyres are brilliant.

A classic brilliant bike - go for it!
 
" think I'm right in saying that there could be problems running them on unleaded - there was a lot of controversy over this. Worth checking if the valves have been modded? Oh, and Metz ME tyres are brilliant. "

I keep checking my valves but so far so good. My bikes only done 31K so I'm expecting some valve seat regression. Lovely sweet engine though. No knocking or pinking even with the higher comp motor on unleaded. it picks up cleanly from 1500 rpm in top gear. I fitted it in my 80G/s while I was doing up the RT's frame but it was far too much for the G/s chassis/brakes.
 
RS.........

:)

Had two, below is my first one, 1978 unfourtunitly "writton off" when a french artic on the 303 yeovil decided to turn right - across my lane and i collided with his trailor!

My second was a 1977 Motorsport white, both excellent bikes to ride, and the fairing is amazing - both had prehistoric brakes, and run on **** star. Use unleaded with a shot of leaded stuff now and again, James Sherlocks have all the spares and good prices to keep them on the road.....!

Excellent bikes, ive a spare rs fairing and fittings, if my ex hasnt binned them plus other bits if needed.
 

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Both the twin and mono-shock models will feel at times as though there's a rubber hinge somewhere in the frame (it's only worse on the twin-shock models when there's a disparity between the wear of the shocks IMO).

The /7 model's ATE caliper brakes are good enough as long as they're maintained. Plenty of brake cleaner stops them getting gummed up with brake dust etc. which is what really affects their performance because they need to have the caliper swing freely to work properly.

Don't expect two-finger action though. They need a good pull but they are surprisingly effective.

Rob Farmer said:
" think I'm right in saying that there could be problems running them on unleaded - there was a lot of controversy over this. Worth checking if the valves have been modded? Oh, and Metz ME tyres are brilliant. "

I keep checking my valves but so far so good. My bikes only done 31K so I'm expecting some valve seat regression.
Click to expand...
Just to add to the 'controversy'......

I'm not certain that unleaded conversion is needed. If you send off to Sherlocks or similar for a conversion kit, all you get is valve seat inserts.

Having taken a pair of /7 heads to a local engine tuning specialist for advice, I was told this:

Alloy heads have steel valve seats because the alloy is too soft to cope with the valve closing. Cast-iron heads need steel inserts: the cast iron can cope with leaded but the higher temperatures of unleaded will cause damage eventually.

When the unleaded fuel came onto the forecourts, engine specialists made a killing "supplying" unleaded conversions to those who turned-up on their doorsteps asking for a conversion, often they'd just consult the books to see if the head had steel valve seats and do nothing but charge the punter anyway. :eek

No doubt someone will tell me that what I've been told is bollix. :nenau
 
MikeP said:
Both the twin and mono-shock models will feel at times as though there's a rubber hinge somewhere in the frame (it's only worse on the twin-shock models when there's a disparity between the wear of the shocks IMO).

The /7 model's ATE caliper brakes are good enough as long as they're maintained. Plenty of brake cleaner stops them getting gummed up with brake dust etc. which is what really affects their performance because they need to have the caliper swing freely to work properly.

Don't expect two-finger action though. They need a good pull but they are surprisingly effective.


Just to add to the 'controversy'......

I'm not certain that unleaded conversion is needed. If you send off to Sherlocks or similar for a conversion kit, all you get is valve seat inserts.

Having taken a pair of /7 heads to a local engine tuning specialist for advice, I was told this:

Alloy heads have steel valve seats because the alloy is too soft to cope with the valve closing. Cast-iron heads need steel inserts: the cast iron can cope with leaded but the higher temperatures of unleaded will cause damage eventually.

When the unleaded fuel came onto the forecourts, engine specialists made a killing "supplying" unleaded conversions to those who turned-up on their doorsteps asking for a conversion, often they'd just consult the books to see if the head had steel valve seats and do nothing but charge the punter anyway. :eek

No doubt someone will tell me that what I've been told is bollix. :nenau
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Mike,

I agree with your comments. I've never bothered converting any of my earlier bike and have never had any long term issues. After the first few thousand miles the valves have always settled in and needed no more adjustment than expected. When I refered to regression I was just refering to this settling in period not full on valve seat errosion. A little misleading.
 
Yoda said:
Neville - I've got a '78 R100RS, although it is now fitted with the front brakes and suspension from an '81.

In line with the rest of the /7 range, the '77-'80 bikes have the ATE swinging caliper and under-tank master cylinder arrangement. The later Brembo fitment gave much, much better braking as well as improved front suspension.

As Rob says, the original bars are very low. I've replaced mine with K-RS bars which still fit within the fairing, but act like bar-backs, bringing things up and back a couple of inches.

I'd also go for the 40mm version. Yes, the mono probably handles a tad better, but a well set up twin shock on Konis and with 7.5w oil in the front forks is rather pleasant.
Click to expand...

I do like this particular bike :thumb
 
I regret getting rid of my last RS it was a 1978 Motorsport fitted with a post 81 front end, braided lines and Lucas Rita electronic ignition. The crank and flywheel had been lightened and balanced. Koni dial a rides on the back and progressive springs in the newish front end. When i bought it it had the original brochure and price list. This bike was almost 3K in 1978, no idea how much that is 28 years later! Fairing was designed by a chap whose name I'll never forget Hans Muth, honest! superb protection

Superb easy to live with classic now, top end in the brochure was quoted as 124 mph and power given as 68bhp. Loads of RTs around and they make a good donor for the front end. If you stick with the old front end make sure the cable to the undertank master cylinder is well lubed and free or fit the master cylinder from the later bikes on the handle bars, makes a big difference to the feel although the ATE brakes were never that good and had to be set up absolutely right and kept free of dust. Brembos much better as long as you dont make any comparison with modern bikes and anticipate further ahead. Tyres are skinny by modern standards and I tried various combinations, bike was always a little skittish although predictable.

Everything is available for these motors and there are still specialists doing engine and gearbox mods, Jim Cray in Kent was well known for his work on airheads, no idea if he's still around.

Good luck
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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