NSR-WORLD.COM
NSR-WORLD.COM
The all-new NSR250R MC21 was released on 13th of February 1990, and took the marque to the next level!
Styled after the works NSR250 NV1G racer, updates and upgrades could be seen across the entire machine, and even included technology yet to find its way onto the GP bikes.
1990 NSR250R [MC21]
Starting with the motor, the Honda engineers had gone right through it, with changes to the crankshaft, crankcases, barrels, and heads.
The OD of the crankshaft counterweights was increased over the 1989 R5/6K model, necessitating a redesign of the crankcases, which now also featured a housing for a GPS [Gear postion sensor.]
The cooling efficiency of the barrels was increased by making the water jacket wider. The newer barrels (and higher compression heads) are easily identified by their “round” appearance, as opposed to the hexagonal barrels and heads of the previous years. Stronger M8 head studs replaced the previous M7 items.
The cases were now fed by new 32mm Keihin TA22 flat slide carburettors, that looked virtually identical to those used on the MC18s, but differed internally.
As a consequence of the updates, the MC21 motor was a approximately 500g heavier than the MC18 R5/6K model.
Click to enlarge
Starting with the motor, the Honda engineers had gone right through it, with changes to the crankshaft, crankcases, barrels, and heads.
The OD of the crankshaft counterweights was increased over the 1989 R5/6K model, necessitating a redesign of the crankcases, which now also featured a housing for a GPS [Gear postion sensor.]
The cooling efficiency of the barrels was increased by making the water jacket wider. The newer barrels (and higher compression heads) are easily identified by their “round” appearance, as opposed to the hexagonal barrels and heads of the previous years. Stronger M8 head studs replaced the previous M7 items.
The cases were now fed by new 32mm Keihin TA22 flat slide carburettors, that looked virtually identical to those used on the MC18s, but differed internally.
As a consequence of the updates, the MC21 motor was a approximately 500g heavier than the MC18 R5/6K model.
Click to enlarge
The 1990 NSR250R MC21 introduced the PGM-III, the most sophisticated 2-stroke engine management by Honda seen to date.
In fact, so capable was the new ECU, that a variant was used from 1997 on the customer NSR500V NX6 and RS250R A-kit, and from ’99 the factory NSR250 NV3 & RS250RW NJB GP bikes!
The new generation of PGM now took inputs from the TPS [Throttle Position Sensor], RPM, countershaft speed, and now a GPS [Gear Position Sensor].
The PGM-III not only detected the postition of the throttle, but also the speed at which it was opened at any given time, in any given gear, under any given load, and adjusted the air correction, via two solenoids, ignition timing for each cylinder [independently], and the RC Valve timing.
The NSR250R MC21 with PGM-III achieved a unique level of tractability and responsiveness in the 2-stroke 250cc class.
The NSR250R MC21 chassis and bodywork received a massive overhaul in 1990, taking on the appearance of the works NSR250 NV1G Grand Prix machines.
The MC21 frame was substantially upgraded, with deeper stiffer extrusions, and larger castings around both the headstock and swingarm pivot/shock mount, just as the NSR250 NV1G had received the previous year.
The steering angle remained the same as the previous MC18 R5/6K model, however the wheelbase was shortened yet further to 1340mm courtesy if the infamous “Gull-Arm” swingarm, which again was a cross-over from the works Grand Prix bike.
A 17″ real wheel was utilised on the MC21 for the first time in 1990, with a 150/60R17 Bridgestone Cyrox tyre.
Suspension remained similar to that of the MC18 R5K, with the 41mm front forks adjustable for preload only, and a non-adjustable rear shock. The damping and Pro-Link geometry was revised though, leading to a superior ride and more stable handling. The MC21 was deceptively compliant, compared to the sometimes nervous MC18, leading some to believe the MC18 was the “sportier” chassis, but the reality is it’s simply easier to go faster on the MC21.
The 1990 NSR250R MC21 "R" model launched with three colour schemes available. Each livery was based on Tadayuki Okada's All-Japan NSR250, just with varying colour combinations.
On April 2nd 1990, the first NSR250R MC21 SP model was released in a Cabin Racing livery. Once again it was simply a variation on Okada's NSR250.
As with the R6K model the year before, the MC21 SP featured preload and rebound damping on the front forks, and preload, rebound, & compression damping on the rear shock.
Once again Magteks featured, now with a 17″ rear, but the SP’s wheels were shod in sportier Bridgestone Battlax tyres as opposed to the Cyrox of the R models.
Contrary to popular belief, the dry clutch SP transmission featured the same ratios as the R model.
While the compression ratio of the SP motor was the same 7.4:1 as the R model, different barrels and heads were installed, an engineering foresight in readiness for various race classes.
SPEC: 1990
NSR250R [MC21]
Engine type: 90-degree V-type 2-cylinder
Capacity: 249cc
Bore x Stroke: 54.0 x 54.5mm
Power: 45PS @9,500rpm
Torque: 3.7kg-m @8,500rpm
Weight (Dry): 132kg/133kg [SP]
Price (1990): ¥609,000/¥719,000 [SP]
SPEC: 1990
NSR250R [MC21]
Engine type: 90-degree V-type 2-cylinder
Capacity: 249cc
Bore x Stroke: 54.0 x 54.5mm
Power: 45PS @9,500rpm
Torque: 3.7kg-m @8,500rpm
Weight (Dry): 132kg/133kg [SP]
Price (1990): ¥609,000/¥719,000 [SP]
SPEC: 1990
NSR250R [MC21]
Engine type: 90° V-type 2-cyl
Capacity: 249cc
Bore x Stroke: 54.0 x 54.5mm
Power: 45PS @9,500rpm
Torque: 3.7kg-m @8,500rpm
Weight (Dry): 132kg/133kg [SP]
Price:
¥609,000 [R]
¥719,000 [SP]
The MC21 was the first incarnation of NSR250R that wasn't updated to a new model after its first year. However, a new variant, the MC21SE [Super Edition], was introduced in 1991.
The 1990 MC21R range of colour schemes were carried over to 1991, and was enhanced with a new black & gunmetal colour.
An SE model was introduced, which was effectively an SP but with the R model’s Enkie alloy wheels. The SE bridged the price gap between the R and SP, appealing to buyers who wanted the desirable dry clutch and adjustable suspension, but without the premium price tag of the SP and its Magteks.
The MC21SE colour scheme again replicated Okada’s All-Japan NSR250, while the MC21SP was released in a replica of Shinichi Itoh’s NSR500 Pentax livery.
SPEC: 1991
NSR250R [MC21]
Engine type: 90-degree V-type 2-cylinder
Capacity: 249cc
Bore x Stroke: 54.0 x 54.5mm
Power: 45PS @9,500rpm
Torque: 3.7kg-m @8,500rpm
Weight (Dry): 132kg/134kg/133kg [R/SE/SP]
Price: ¥620,000/¥660,000/¥730,000 [R/SE/SP]
SPEC: 1991
NSR250R [MC21]
Engine type: 90° V-type 2-cyl
Capacity: 249cc
Bore x Stroke: 54.0 x 54.5mm
Power: 45PS @9,500rpm
Torque: 3.7kg-m @8,500rpm
Weight:
132kg [R]
134kg [SE]
133kg [SP]
Price:
¥620,000 [R]
¥660,000 [SE]
¥730,000 [SP]
There were two significant changes in 1992, both related to engine reliability.
The crankcases and 2-stroke oil pump were revised for the 1992 models, with a gallery drilled into the RHS main bearing seat, and a new oil pump installed with an additional feed in the bottom of the pump body.
Minor changes were made to the PGM-III year-on-year, but nothing more signifcant than minor software tweaks, further refining ignition and air correction. TA22B carburettors and new needles were also introduced, but everything [aside from the oil pumps, which needed to match the correct crankcases] remained interchangeable.
A white and blue, with red accents R model joined the lineup in 1992, and two SEs were available in either white and red, or black and red, all based on the All-Japan 250.
The 1992 SP was inspired by the works NSR500 Rothmans machines of Mick Doohan and Wayne Gardner.
A limited edition of the NSR250R MC21 SP was announced on July 24th, & released as a 1993 model.
The rarest of all NSR250Rs, the “Flash Colour Special” MC21-SP was limited to just 900 units.
The design was based on the 1992 works All-Japan Road Race Championship NSR250 NV2B, and used the high-saturation red paint developed for the “HONDA NR” [NR750] production bike.
Thep secifications of the 1993 NSR250R MC21SP were unchanged from the previous year. The sale price in 1993 was ¥730,000.
2 Comments
Cool, one of the best Honda Racing street bikes
Arguably the best, Paulus!