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Analisi tecnica RUMI RM701 di Alan Cathcart da RCM (EN)

Revival Racer

rm701 rumi supermono

rm701 rumi supermono

Forty years on from Rumi’s 125 race track debut thè Italian manufacturer returns with an SoS racer. Alan Cathcart tested it
Almost forty years after thè last Rumi racer took part in top level competìtion, a 125 two-stroke twin with distinctive horizontal cylin-ders, thè famous Italian marque returned to thè racetrack last sea-son in thè Supermono/SoS class for four-stroke singles.
Rising British roads circuit star Simon Beck debuted thè Rumi RM701 in thè Isle of Man TT and Ulster GP, putting in impressive performances which augur well for thè new model’s future. Though in both races he was forced to drop out within sight of thè cheq-uered flag, Beck showed that throwing an all-new bike in at thè deep end of rating made sense. Far from sinking under thè weight of expectations, thè new Rumi single swam with thè SoS sharks. Beck held a firm third piace in thè TT and lapped at over 110 mph to piace ahead of many better developed bikes - includìng the Daytona-winning Ducati, usually raced by ex-GP star Alan Carter, and ridden on this occasion by IoM singles
Manx GP winner Bill Swallow - before beìng forced to retire with a broken camchain tensioner halfway round thè final lap.
Then in thè Ulster GP on thè 7.4 nule Dundrod circuit - now Britain’s fastest track, with a Superbike lap record of more than 126 mph - Beck and his dad Stan struggled to repair a host of minor teething troubles in practice, thè sort you fìnd in any prototype race bike, before running a solid second to Kiwi Robert Holden on another Ducati.
When Holden’s engine exploded on thè last lap, Beck looked set to give thè Rumi a fairytale victory in ìts second major race -only to coast to a halt just three corners from thè end with a broken electrical connection. Heartbreaking stuff - only partly compen-sated for by thè fact that thè Rumi had been fastest through thè speed traps, more than five mph quìcker than Holden’s Ducati at 144 mph.
The bike’s creator, Oscar Rumi, nephew of Donino who founded thè Rumi marque almost half a century ago and presided over it
until thè last bike rolled out of thè Bergamo factory in 1962, must be well pleased with thè promising showing of his new baby.
A baby that’s taken quite a while to be born, given that thè RM701 was launched to thè world’s press at thè Monza round of thè World Superbike Championship back in October 1992!
Development hasn’t exactly been desultory since then, but it has had to play second fiddle to getting thè Team Rumi Honda RC45 Superbikes up, running, raceworthy and competitive for last season - a process that can be saìd to have been achieved, with Rumi’s Simon Crafar a regular top-six fin-isher in WSC rounds and vying with Andy Meklau for thè honour of top privateer in thè points table.
Hopefully, then, thè resources will now be available within thè Team Rumi operation to complete the development programme on thè RM710 Supermono and get it into limited production as a potent rivai to Ducati’s supreme single - as Oscar Rumi intended ali along it should be.
“I like four-stroke singles,” he says, “and I could see more than three years ago thatthe Supermono class would become popular ali over thè world as a valid support category to Superbike and Supersport, both of which we are heavily involved in and commìtted to.”
That’s an understatement. Apart from his Superbike operation, which this season in-cluded running a bike for thè Argentinian Superbike champion in recognition of thè South American business interests of the Rumi family’s huge, high-tech foundry com-pany. Team Rumi also built more than 30 CBR600 Supersport engines for customers last season, as well as running their own SS600 team.
Thaf s how Rumi and thè Beck team, father and son, got together. Already a rostrum finisher in thè 600 Supersport TT, Simon Beck was just thè kind of rider Oscar was looking for to gain IoM success with his bikes, as well as to take over thè languishing RM701 singles project and sort it out. The promising showing of thè bike since thè Becks took it over confirms this was a smart move.
It’s one that frankly doesn’t augur well for those of us in thè Supermono class riding Ducatis, as I found for myself when Simon and Stan Beck brought thè solitary Rumi RM701 built so far to Mallory Park for me to sample a few days before last year’s Ulster GP. Having seen thè bike in half-built form when I’d visited Team Rumi’s Bergamo base a year before, talked to Kiwi project engineer Norris Farrow (Fred Merkel’s race mediarne when he won both World Superbike titles on Rumi Hondas, now working with Castrol Honda’s Aaron Slight in thè Castrol Honda
team) about it, then watched Rumi’s ‘93   into a purpose-built racing World Superbike rider Tripp Nobles making thè bike’s debut at Monza in testìng, riding    success in this class, and thè finished article squared thè circle. And though my ride confirmed that there’s stilL Wait fair bit of development needed to refine thè  RM701 into thè bike it was intended to be, thè fact is that thè Rumi is already a very impressive package - certaìnly far and away thè most competitive Honda Dominator-based SoS racer ever built.
Perhaps thè reason for this is that there’s not a lot of thè basic Honda motor left anymore, apart from thè crankeases, crank-shaft and gearbox. “Because of Oscar’s dose ties with Honda, thè originai idea was to build a Dominator-based racer with some modified engine parts we’d designed ourselves, to try to overcome some of thè ùibuilt handicaps thè air-cooled Honda motor has in top-level Supermono racing,” said Norris Farrow as he showed me thè prototype Rumi soon after its preliminary dyno tests.
“But gradually it’s become less Honda and more Rumi, and I can see thè smart thing is going to be to replace thè Honda bottoni end with a proper Rumi design that will turn it  into a purpose-built racing have shown that’s what you  success in this class, and we probably need  to follow suit. But in spite of its trail bike roots, this engine has a lot of potential. Wait till you ride it!”

To modìfy thè air-cooled NX650 sohc four-valve engine, measur-ing 644cc in stock form with its 110 x 82 mm dimensions, Rumi en-listed thè services of Carlo Facetti. He’s one of Italy’s top development engineers and a noted name in FI racing car circles after his work designing FI race engines for Alfa Romeo      and,     just     recently, Lamborghini.
Facetti already works on thè Rumi Honda Superbike motors alongside another freelance engineer from thè racing car world Ernesto Degan - formerly a designer for Alfa’s Autodelta racing subsidiary who’s used to adapting produetion engines for racing.
Facetti completely revamped thè top end of thè NX650 motor, retaining thè crank-cases, wet clutch and five-speed gearbox from thè stock Dommie engine, but convert-ing thè air-cooled engine to water-cooling and replacing thè radial-valye sohe top end with Degan’s dohc design with paired valves. The originai chain drive to thè cylinder head is retained, but instead of turnìng thè originai Honda camshaft, it now drives a half-tìme pin-ion, outboard of which is thè waterpump and inboard a gear wheel meshing directly with thè twin overhead Rumi camshafts. Twin 43mm inlet valves and 35mm exhausts are fitted, with a fiat included l-just 26.5 degrees. At present, though . gìne was designed to run on fuel ir and has already been dyno tested guise (using twin Weber injectors ar. ‘ software on a TDD engine managen.-. tem similar to that used by Bimota : own BMW-powered BB1 Superino: prototype racer is running on twir. Keihin flatslides, in which form it deli” bhp at 9,000 rpm on thè Rumi dyno  already have 77bhp with EFI, accoro: Norris Farrow.
All thè hardware, including a batte-pump and air duets for a pressurisec needed for EFI are already in piace.  the switchover from carbs and th-: Honda CDI presently employed quitt
As well as water-cooling thè engine has also bumped it out to 697cc with ir of a 104mm three-ring Mondìal forge: delivering 10.3:1 compression, and th-gives thè sort of jump out of slow corot thè Mallory liairpin or chicane that thas-riding 550cc ‘Ducatinas’ can only dreac
The engine is unbelieyably punchy when you crack thè throttle wide open, especially at high rpm. Out of a fourth gear corner like thè Mallory Esses you can feel thè front wheel rise lazily in thè air as you get hard on thè gas, confirraed by thè way thè bars jiggle gently in your hands as you monowheel to-wards thè Hairpin cranked hard over.
Exiting a slower turn like thè chicane or hairpin causes quite a bit more excitement if you try to do it in either of thè bottoni two gears. First is actually way too low for racing use, but great for improving your wheelie credit rating with spectators. But get thè Rumi motoring out of a slow turn and it’ll get
a jump on a Ducati that takes a while to peg back, as I discovered for myself riding briefly with Simon in Dundrod qualìfying - untìl an-other minor glitch sent him coasting up thè slip road with a dead engine. Then, at thè other end of thè performance scale, thè Rumi is very fast in a straight line on outright top-end speed, certainly quicker than thè five-valve Yamaha XTZ engine of equivalent capacity, as thè Ulster GP speed trap showed. The Stephens Yamaha that Jim Moodie used to win thè TT was no match for thè Rumi on absolute performance.
So what’s thè problem? Why isn’t this bike winning every Supermono race it bothers to enter? Ah, well - all is not what it seems. The RM701 has huge poten-tìal as an SoS contender - but it’s not there yet and there are two related problems which need to be ad-dressed before it can hope to see off thè competition regularly. Though thè engine is very responsive and tractable low down - just like any Honda-powered SoS racer l’ve ever sampled (and thanks to thè retention of thè gear-driven balance shaft from thè stock NX750 motor is almost as smooth and vibe-free as a Ducati ) it only achieves what other Hondas lack - an appetite for revs and serious top-end power - at thè expense of an extremely cammy power clelivery that thè lack of a proper six-speed racing gearbox only underlines.
There’s a huge hole in thè power curve between 7,000-7,500rpm which especially shows up round a long, sweeping turn like Mallory’s Gerards, which you round on part throttle. Just as you want to gas it wide open for thè exit, thè engine starts to splutter and run raggedly, forcing a quick look at thè tacho. Yup - right in thè seven grand fiat spot. Solution? Either kick it down a gear -in which case be prepared for thè back wheel to take a hike, thanks to thè huge l,200rpm gap between ra-tios in thè evenly-spaced, wide-ratio, enduro-derìved cluster - or else per-severe with thè right hand, and even-tually it’ll come on song again.
Very hard, actually - just as thè rev counter needle hits 7,800rpm, a good number of those 79 horses line up for inspection and thè rear wheel does get unhooked for a moment. Then suddenly thè Rumi is straìghtened up and flying right. FAST! From there up to max revs of 9,200rpm thè engine picks up revs very fast, indicat-ìng that Facettì has certainly lightened and rebalanced thè crank, and delìvers really competitive power by thè standards of thè Supermono class, which shows that thè dohc cyunder head is breathing very well. This is a refined and potent engine - but thè problem is that you have just l,400rpm to play with. It’s not enough.
Well - it would he if you had a Ducati-type six-speed racing gearbox with a high bottoni gear and correctly matched ratios, but thè Rumì’s enduro-based five-speed Street cluster is a big handicap. In practical terms if s a four-speeder because bottom is so low, but it’s even hard to keep thè engine on thè boil swapping between thè higher ratios, because of thè big gaps between them.
The fact that even thè smallest rear sprocket thè Becks had made thè bike way overgeared for Mallory, so I couldn’t even pulì a proper top gear, made things stili worse, but there’s no doubt that thè single most vital thing Oscar Rumi needs to do to turn his Supermono into a Ducati-beater is to source a six-speed gearbox for thè bike, to allow you to take full advantage of that im-pressive power delivery. If that means junking thè Honda crankcases in favour of a Rumi bottom end with a dry clutch to release a couple of extra bhp, so be it, After ali, Honda repaid Rumi’s loyalty to thè Japanese marque — for whom they won two World Superbike titles, then laboured for four more seasons with an increasingly uncompetitive RC30 while awaiting thè delayed arrivai of thè RC45 - by giving thè job of running thè works team in World Superbike to someone else, thè British-based Castrol Honda set-up
who had no experience ofWSC competition.
Oscar Rumi and bis team were understand-ably crushed by this disappointment, so I don’t tìiink anyone would blame them if thè Honda narae carne off thè side of thè RM701 erigine, and it became a 100% Rumi effort by thè time it starts winning top level Supermono races - do you?
If thè Rumi erigine feels punchy at thè top end, ìt also gìves thè impression of being very robust and solid as well as smooth ali through thè rev band. Apart from thè chain tensioner in thè Isle of Man, none of thè teething problems thè Becks have encoun-tered have related to thè mechanical package, only minor things like broken connectors or lìnkages that show what thè bike really needs is a serious development programme with an intensive series of track tests to refìne thè package into reliable, race-winning guise.
“Carlo Facetti told us they’d run thè engine on a dyno at 9,200rpm for 24 hours,” says Sìmon Beck. “And it suryìved! I know thè Rumi has so much potential as a customer bike as well as a works racer, because it’s strong as well as powerful - you don’t have to worry about cracking crankcases or break-ing thè rod like on so many other engines. And it’s got thè extra capacity that thè Ducati lacks, so once we get it sorted, I know we can be serious contenders for top SoS honours anywhere. But there’s a lot of work stili to be done.”
Also on thè must-do list is to refine thè han-dling of thè Rumi chassis, a beautifully triade GP-style aluminium twin-spar chassis built in Verona by VRP, which with just a 1345mm wheelbase - less than a Honda NSR250 -gives thè RM701 a very small stature. The water header-tank is incorporated in thè chassis headstock (which has a stock 24 de-gree head angle, but can be changed with ec-centric inserts), with thè oil tank for thè dry sump engine located above thè upper mount-ìng point for thè rear Ohlins shock, behind and beneath thè carbs. Twin water radiators bracket thè front of thè bike, without adding notably to thè overall width, and with Simon slightly taller than I ani, thè riding position feels uncannily spacious for such a small bike, with some body weight on your fore-arms thanks to thè semì-GP style stance.
The bike feels very manoeuvrable, steer-ing from side to side in thè Mallory chicane as quickly as an RS125 Honda GP racer that I followed through there several times that afternoon - (well, I kept powering past him. but he’d outbrake me into thè hairpin every time). The problem is that thè Rumi is basi-cally underbraked. The twin 260mm Brembo front discs aren’t big enough to stop a bike that presently weighs thè wrong side of 130 kg, thanks to some heavy fibreglass body-work and not much attention at this proto-type stage to weight-saving.
Norris Farrow told me he thought 124 kg - thè sanie as a less powerful Ducati Supermono - was a realistic target for thè Rumi to be slimmed down to, but even at that weight it’d need thè same 280mm front Brembo stoppers we have on thè Ducatinas -which also have thè benefit of allowing you to max out on engìne brakìng, runniiig to 13,500rpm safely on thè overrun thanks to
desmo Vi.-■;/-;: _.-.- _-_:–._ :..esn’t have that benefii. ^ :_–:? :–”-_: :rakes - a twin 300mm tron: BredDo shouid do thè job for such a fast. heaw bike, even if it is ‘jusf a single.
One thar, for ali its manoeuvrability, doesn’t feel as precise in turns as l’d ex-pected. especìa&y after riding its RMS650 sis-ter heftwiphanri, but fitted with thè stock Honda NX650 motor io produce a sweet Street szngle. Thcmgh thè RM701 racer feels stable and reassorìog round a fast sweeper like Gerards or Derib Elbow, where thè pro-gresswe fiok rat» of thè rear suspension soaked no road shock and bumps like they dìdn]t oòst. tfae front end felt vague and imprecise nnder hard traking for thè Esses or hairpin, as ìf thè 40nwn Ceriani forks were bendn^» or ttrihlàig in theìr triple clamps.
Obvkwsly, «idi upskic down forks that’s impossìble, but whfle I do think thè forks need to be betfter set np with different choice of springs - espeòalh if they fit bigger brakes - die ariprit this time seemed to be thè front Dobp tfre, which I could feel squirmmg rader hard braking for thè Hairpin. Apparenti^ Donlops softest, thè con-structioQ vas defio^elv not stiff enough for such a beavy bike - Okay for a 250 GP racer weighing 30 kg fess, perhaps - underlining how cruciai trre chwce is for thè Singles class these days.
You need qnfee a stiff carcase and a softish compound to cany thè aD4mportant corner speed that is thè difiereoce between being on thè pace m SoSiacngand making up thè num-bers- The Rana chassis has thè potential to do h. provided it’s shod witìi thè right front tyre -though I must say I prefer thè Ducati’s Ohlins forks. Oh yes - and you do need a speed shifter on a bike with such a nar-row power band: Rumi already use KLS imipì on their RC45s.
Oirt of thè many Supermono/ SoS racers I’ve ridden ali over thè worid m thè past couple of years, thè one that most im-presses me in terms of its potential is thè Rumi. Our Ducati wins races because it’s thè best all-rounder. With a little serious development work thè Rumi has ali thè ingredients to out-Ducati thè resi of us: it’s already one of thè fastest Supermonos, even without thè fuel injectìon package that is bound to offer even more performance. When Ìt gets a six-speed gearbox and refìned han-dling. we’re in trouble! ■
Alan Cathcart

specs:

Engine: Water-cooled dohc four-valve
Stngle-cy li rider four-stroke with gear-
driven balance shaft, Dimensions: 104×82mm Capacity: 697cc
Output: 79bhp at 9000rpm (at gearbox) Compression ratio: 10.3:1 Carburation: 2 x 41 mm Keihin flatslides Ignition; Nippondenso electronic CDI Gearbox: 5-speed Clutch: Multiplate oilbath Chassis: Aluminium twinspar Suspension: Front: 40mm Ceriani/Forcella
Italia inverted telescopio forks Rear: Fabricated atuminium swingarm with
single Ohlins shock and risìng rate
linkage.
Head angle: 24 degrees Wheelbase: 1345mm Weight: 134kg. with oil/water, no fuel Weight distribution: 53/47% Brakes: Front: 2 x 26Qmm Brembo cast
iron discs with four-piston Brembo
calipers
Rear: 1 x 220mm Brembo steel disc with
two-piston Brembo caliper Wheels/tyres:
Front: 3.10/4,80-17 Dunlop KR106 radiai
on 3.50 in. Tecnomagnesio wheel
Rear: 155/60-17 Dunlop KR108 radiai on
5.50 in. Tecnomagnesio wheei. Top spoeti: Over 145mph (Dundrod -
Ulster GP)
Year of construction: 1993 Owner: Team Rumi, Bergamo, Italy.

Posted 23 years, 4 months ago at 4:41 pm.

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