# Honda RC166

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6 cylinder racing motorcycle

Type of motorcycle

Honda RC166 1967 RC166 that was ridden by Mike Hailwood on display at the Honda Museum at Motegi. Manufacturer Honda Racing Service Club Parent company Honda Production 1966-1967 Assembly Asaka, Saitama, Japan Predecessor Honda RC164 Engine Air cooled inline 6 4 stroke Bore / stroke 41 mm × 31 mm (1.6 in × 1.2 in) Compression ratio 11.0:1 Power 60 bhp (45 kW) @ 18,000 rpm Transmission 7 speed gearbox, chain drive Frame type Duplex cradle Suspension Front: telescopic forks Rear: swinging arm Brakes Drum brakes front and rear Wheelbase 1,410 mm (55.5 in) Weight 112 kg (247 lb) (dry) Footnotes / references [1][2][3]

The **Honda RC166**, also known as the *Honda 6*, is a [Grand Prix](/source/Grand_Prix_motorcycle_racing) racing motorcycle produced by [Honda](/source/Honda) which raced in 1966 and 1967. The technological advanced bike was a 250 cc (15 cu in) [DOHC](/source/DOHC) [air-cooled](/source/Air-cooled) [inline 6](/source/Inline_6). On the bike [Mike Hailwood](/source/Mike_Hailwood) took the 250cc riders championship and Honda the constructors championship in both years it raced. It was evolved from the earlier 3RC164 and RC165.

## Background

Honda had first enterered GP racing in 1959 and by 1962 were dominating the 250 cc class. In 1964 the Hondas were no match for the [Yamaha RD56](/source/Yamaha_RD56).[4] The existing [inline 4](/source/Inline_4) [RC164](/source/Honda_RC164) was at the limit of it's development.[5] Honda started working on a new model to restore their dominance in the class.[6] The engineer put in charge of the project was 24 year old [Shoichiro Irimajiri](/source/Shoichiro_Irimajiri).[3][a] Design started in January 1964[10] and the initial sketches were completed in February 1964.[3] A running engine was produced in June.[10]

## Predecessors

### 3RC164

[2 stroke](/source/2_stroke) engines, as used by competitors [Suzuki](/source/Suzuki) and [Yamaha](/source/Yamaha_Motor_Company), have a power stroke every [crankshaft](/source/Crankshaft) rotation, whereas [4 strokes](/source/4_stroke) as used by Honda only produce a power stroke every 2 rotations of the crankshaft. [Soichiro Honda](/source/Soichiro_Honda) had already made a public commitment to make quieter, cleaner running, more efficient 4 strokes. The solution was to make the four stroke rev higher to produce more power strokes. To achieve this while maintaining reliability Irimajiri reduced reciprocating weight by using 6 cylinders and [4 valve](/source/Multi-valve#Four_valves) [heads](/source/Cylinder_head). The engine was an engineering masterpiece, no wider then the four it replaced and narrower than the Yamaha twin.[3]

Although being developed for the 1965 season, the bike was ready[11] for the September 1964 [Nations Grand Prix](/source/Italian_motorcycle_Grand_Prix) at [Monza](/source/Monza_Circuit). It was designated 3RC164, to suggest to competitors that it was an evolution of the existing four cylinder machine. The bike was shipped with only four exhausts to further fool the competition.[3] The bike was sent to Monza in secrecy. Some sources give it accompanying engineer Michihiko Aika and rider [Jim Redman](/source/Jim_Redman) on a [BOAC](/source/BOAC) [VC10](/source/VC10) from [Tokyo](/source/Tokyo) to Monza. The 3RC164 proved to be faster than the Yamahas but suffered a vapour lock in the carburettors.[7] [Phil Read](/source/Phil_Read) won the race on a RD56 clinching the championship, Yamaha's first World Championship.[12] At the following GP, the [Japanese GP](/source/Japanese_motorcycle_Grand_Prix) at Honda's circuit [Suzuka](/source/Suzuka_Circuit), Redman won on the 6.[3]

### RC165

Early in the 1965 season an updated version, the RC165, was introduced. Honda did not attend the 1965 season opener at [Daytona](/source/Daytona_International_Speedway) and in the 2nd round at the [Nürburgring](/source/N%C3%BCrburgring) Redman fell and injured himself in the 350cc race. This prevented him starting the 250 race and also caused him to miss the 3rd round in [Spain](/source/Montju%C3%AFc_Circuit). Fit again for [France](/source/Rouen-Les-Essarts), he suffered gearbox problems whilst in the lead. In [Ulster](/source/Dundrod_Circuit) Redman fell in the 350 race and broke his collarbone. This putting him out the 250 race and the following round. Feeling fit enough to race at Monza he was told his bike had not been sent to the circuit so he stayed at home in Rhodesia.[13][b] Although only competing in 6 rounds of the championship Redman achieved 3 wins, a second and a third, finishing 3rd in the championship.[14] Honda finished 2nd in the constructors championship.[13]

Late in 1965 Mike Hailwood signed a contract to returned to Honda for £40,000. Honda convinced the organisers of the season finale, the [Japanese Grand Prix](/source/Japanese_motorcycle_Grand_Prix), to move the 250 race to the end of the programme so Hailwood could fulfil his [MV Agusta](/source/MV_Agusta) contract racing their 350 and then ride the Honda in the 250 race. After winning the race on the RC165 his opinion of it was *bloody awful*.[15] Hailwood allegedly asked the mechanics to remove the rear suspension units and then threw them in a pond telling the mechanics to fit [Girling](/source/Lucas_Industries#Girling) units. He also asked for a new frame made of stiffer tubing and with the [wheelbase](/source/Wheelbase) lengthened 3.5 in (89 mm),[3] and suggested Dutchman Nico Bakker built the new frame but Honda baulked at an outsider being involved.[16] Redman had also been urging Honda all season to develop the bike further.[15]

## RC166

For 1966 an updated version, the RC166 was introduced.[15] With the stiffer and longer frame Hailwood had requested the handling of the bike improved significantly.[17] Hailwood and the RC166 were dominant in 1966, winning all 10 of the races he entered,[3] although only the best 7 results counted towards the championship.[5] As well as Hailwood's rider's championship Honda won the constructors title.[18]

Redman crashed in the 500 race at [Spa](/source/Circuit_de_Spa-Francorchamps) in torrential rain breaking his wrist. When his wrist was too painful to race at Ulster five weeks later he decided to retire.[14] [Stuart Graham](/source/Stuart_Graham_(motorcyclist)), son of [Leslie Graham](/source/Leslie_Graham), is brought in to replace Redman.[2]

[Ralph Bryans](/source/Ralph_Bryans) partnered Hailwood on the RC166s for 1967.[19] Yamaha had developed a [water cooled](/source/Water_cooled) [250 V4](/source/Yamaha_250_V4) in response to Honda's 6. For 1967 it was re-engineered to reduce size and weight.[20] Hailwood and Yamaha's Read tied for points at the end of the season. Hailwood won the championship as he had five wins as opposed to Read's four. Honda won the constructors title for the second year running.[19]

At the end of 1967 the [FIM](/source/F%C3%A9d%C3%A9ration_Internationale_de_Motocyclisme) introduced new regulations for the 1968 season that levelled the playing field and favoured the European manufacturers, leading to Honda withdrawing from GP racing.[21] Paddock rumours were that the 6 would have been replaced with a new water cooled [V8](/source/V8) in 1968 if Honda hadn't have withdrawn from GP racing.[5] Honda presented Hailwood with a RC166 in recognition of his two world titles on the model.[c][22] They also lent [Ralph Bryans](/source/Ralph_Bryans), who had won the 50cc title for Honda in 1965, three bikes for 1968 including a RC166 to compete in non-championship events. Bryans had to maintain the bikes himself.[7]

## 350cc RC174

Main article: [Honda RC174](/source/Honda_RC174)

In 1966 Hailwood had complained about the handling of the 350cc four cylinder [RC173](https://en.wikipedia.org/w/index.php?title=Honda_RC173&action=edit&redlink=1). For 1967 Honda produced a larger capacity version of the RC166 to race in the 350 category. The stroke had been increased to 37.5 mm (1.48 in) giving a capacity of 297 cc (18.1 cu in). Hailwood won the first 5 races of the season which was enough to secure the championship. Bryans rode the bike for the rest of the season and finished 3rd in the championship.[19]

## Technical details

### Engine

Honda RC165 engine

The compact 6 was no wider than the 4 it replaced. The block was cast as part of the upper crankcase and the heads were cast in two pieces, one for each 3 cylinders.[3] The engine extensively used [titanium](/source/Titanium)[23] and [magnesium](/source/Magnesium) castings and revved to over 18,000 rpm.[17]

The [crankshaft](/source/Crankshaft) was pressed up on precision jigs from 13 separate components.[24] To reduce the effective vibrating length of the crankshaft, drive to the clutch was transmitted through a [jack shaft](/source/Jack_shaft) driven by a gear between cylinders 3 and 4. Because the torsional forces on the built-up crank were greater near the centre of the engine, different sized [crankpins](/source/Crankpin) were used, largest for cylinders 3 and 4, smaller for 2 and 5 and the smallest on 1 and 6.[5] [Conrods](/source/Conrod) were one-piece with roller bearings.[7]

Drive for the [camshafts](/source/Camshaft) was by a train of spur gears between cylinders 2 and 3.[5] The camshafts were barrel shaped with the greater mass at the centre to minimise flexing.[24] 4 valve heads were fitted with each one of the four valves a different shape.[25]

The RC166 had a bore and stroke of 41 mm × 31 mm (1.6 in × 1.2 in) giving 245.6 cc (14.99 cu in).[2] (39 mm × 34.5 mm (1.54 in × 1.36 in) (247.3cc) on the 3RC164[11] and 39 mm × 34.8 mm (1.54 in × 1.37 in) (249.4cc) on the RC165)[13]

Transmission was via a multi-plate [dry clutch](/source/Dry_clutch), 7 speed gearbox (8 on the RC165) and [chain drive](/source/Chain_drive). It produced 60 bhp (45 kW) at 18,000 rpm. (54 bhp (40 kW) at 17,000 rpm for the 3RC164, 56 bhp (42 kW) at 16,500 rpm for the RC165)[2][11][13]

Two oil coolers were fitted on the RC165, one in each side of the fairing.[2]

### Cycle parts

The bike used a [duplex cradle](/source/Motorcycle_frame#Full_duplex_cradle).[3] It was stiffer and had a longer wheelbase than the original frame of the 3RC164 and RC165.[17] Front forks were [telescopic](/source/Telescopic_fork) and the [swinging arm](/source/Swinging_arm) was controlled by 2 Girling [shock absorbers](/source/Shock_absorber) (Honda shocks on the 3RC164 and RC165). The brakes were [drums](/source/Drum_brake), a 230 mm (9 in) 4ls on the front and 200 mm (8 in) [2ls](/source/Twin-leading-shoe_drum_brake) on the rear, both brakes were fitted with cooling rings. Wheels were 18 inch shod with [Dunlop](/source/Dunlop_Tyres) K124 tyres.[3]

## Racing results

Points were awarded to the top six finishers in each race. Only the best six races were counted in 1964 and 1966, 7 in 1965 and 1967

Position 1st 2nd 3rd 4th 5th 6th Points 8 6 4 3 2 1

Year Rider 1 2 3 4 5 6 7 8 9 10 11 12 13 Points Rank Wins 1964 Jim Redman USA ESP FRA IOM NED BEL GER DDR ULS FIN NAT 3 JPN 1 42 2nd 3 1965 Jim Redman USA GER ESP FRA NC IOM 1 NED 2 BEL 1 DDR 1 CZE 3 ULS FIN NAT JPN 34 3rd 3 Ralph Bryans USA GER ESP FRA IOM NED BEL DDR CZE ULS 5 FIN 3 NAT JPN 6 13th 0 Mike Hailwood USA GER ESP FRA IOM NED DDR TCH ULS FIN NAT JPN 1 8 10th 1 1966 Jim Redman ESP NC GER 2 FRA 2 NED 3 BEL 3 DDR CZE FIN ULS IOM NAT JPN 20 3rd 0 Mike Hailwood ESP 1 GER 1 FRA 1 NED 1 BEL 1 DDR 1 TCH 1 FIN 1 ULS IOM 1 NAT 1 JPN 56 1st 10 Stuart Graham ESP GER FRA NED BEL DDR 4 TCH Ret FIN 2 ULS Ret IOM 2 NAT Ret JPN 15 6th 0 1967 Mike Hailwood ESP Ret GER FRA 3 IOM 1 NED 1 BEL 2 DDR Ret TCH 3 FIN 1 ULS 1 NAT Ret CAN 1 JPN Ret 50 1st 5 Ralph Bryans ESP 2 GER 1 FRA 4 IOM 3 NED 3 BEL 3 DDR 3 CZE 4 FIN NC ULS 2 NAT 3 CAN 3 JPN 1 40 4th 2 Sources: [26][27][28][29] Colour Result Gold Winner Silver Second place Bronze Third place Green Points classification Blue Non-points classification Non-classified finish (NC) Purple Retired, not classified (Ret) Red Did not qualify (DNQ) Did not pre-qualify (DNPQ) Black Disqualified (DSQ) White Did not start (DNS) Withdrew (WD) Race cancelled (C) Blank Did not practice (DNP) Did not arrive (DNA) Excluded (EX) Bold – Pole Italics – Fastest Lap

## Notes

1. **[^](#cite_ref-10)** Irimajiri also designed the twin cylinder 50 cc [RC115](https://en.wikipedia.org/w/index.php?title=Honda_RC115&action=edit&redlink=1), five cylinder [RC148](/source/Honda_RC148) and worked on the [RA270](/source/Honda_RA270) [Formula 1](/source/Formula_1) engine.[7] Irimajiri later led the design teams for the [Gold Wing](/source/Honda_Gold_Wing)[8] and [CBX](/source/Honda_CBX).[9]

1. **[^](#cite_ref-15)** This was due to miscommunication within Honda and the bike actually had been sent to Monza[13]

1. **[^](#cite_ref-25)** The bike was displayed in the [Birmingham](/source/Birmingham) motorcycle showroom that Hailwood owned with [Rod Gould](/source/Rodney_Gould_(motorcyclist)). After Hailwood's death Gould sold the bike to a Dutch collector. Hailwood’s widow, Pauline, put the matter in the hands of the police when she realised the bike was missing. Although Gould was convicted of theft the bike was never returned.[22]

## References

1. **[^](#cite_ref-1)** ["Honda RC166: A Legendary Racing Motorcycle"](https://pyramidmoto.co.uk/blogs/news/honda-rc166-a-legendary-racing-motorcycle?srsltid=AfmBOopFQH1lG8qBbjoNuzbWP1cS9LozZScEmXbYoO0J8i-c9_frwtQD). *Pyramid Motorcycle Accessories*. 27 February 2023. Retrieved 8 May 2026.

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1. **[^](#cite_ref-seminuevos_4-0)** ["Honda RC166: reviviendo una vieja gloria de seis cilindros y un cuarto de litro"](https://www.seminuevos.com/blog/honda-rc166-reviviendo-historia/) [Honda RC166: Reviving an old glory of a quarter-liter six-cylinder]. *Blog de Seminuevos.com* (in Spanish). 18 March 2015. Retrieved 8 May 2026.

1. ^ [***a***](#cite_ref-Cycle_World_5-0) [***b***](#cite_ref-Cycle_World_5-1) [***c***](#cite_ref-Cycle_World_5-2) [***d***](#cite_ref-Cycle_World_5-3) [***e***](#cite_ref-Cycle_World_5-4) Cameron, Kevin (19 December 2017). ["Calming The Crankshaft Of Honda's Six-Cylinder Racer"](https://www.cycleworld.com/calming-crankshaft-hondas-six-cylinder-racer/). *[Cycle World](/source/Cycle_World)*. Retrieved 10 May 2026.

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1. ^ [***a***](#cite_ref-Martin_11-0) [***b***](#cite_ref-Martin_11-1) [Martin, Guy](/source/Guy_Martin) (18 October 2018). [*We Need to Weaken the Mixture*](https://books.google.com/books?id=BJ9HDwAAQBAJ). Random House. [ISBN](/source/ISBN_(identifier)) [978-0-7535-4548-5](https://en.wikipedia.org/wiki/Special:BookSources/978-0-7535-4548-5).

1. ^ [***a***](#cite_ref-vf750fd_64_12-0) [***b***](#cite_ref-vf750fd_64_12-1) [***c***](#cite_ref-vf750fd_64_12-2) Kortekaas, Joep. ["Honda's Race History - 1964"](https://www.vf750fd.com/Joep_Kortekaas/1964.html). *www.vf750fd.com*. Retrieved 12 May 2026.

1. **[^](#cite_ref-13)** Dawes, Geoff (15 September 2014). ["Grand Prix motorcycle racing"](https://motovue.net/tag/grand-prix-motorcycle-racing/). *MotoVue*. Retrieved 9 May 2026.

1. ^ [***a***](#cite_ref-vf750fd_65_14-0) [***b***](#cite_ref-vf750fd_65_14-1) [***c***](#cite_ref-vf750fd_65_14-2) [***d***](#cite_ref-vf750fd_65_14-3) [***e***](#cite_ref-vf750fd_65_14-4) Kortekaas, Joel. ["Honda's Race History - 1965"](https://www.vf750fd.com/Joep_Kortekaas/1965.html). *www.vf750fd.com*. Retrieved 12 May 2026.

1. ^ [***a***](#cite_ref-MotoGP_16-0) [***b***](#cite_ref-MotoGP_16-1) ["MotoGP™ Riders | Jim Redman"](https://www.motogp.com/en/riders/jim-redman/7435f9e4-13f7-4053-be64-975735860cc4?tab=overview). *The Official Home of MotoGP*. Retrieved 9 May 2026.

1. ^ [***a***](#cite_ref-SPEEDWEEK_17-0) [***b***](#cite_ref-SPEEDWEEK_17-1) [***c***](#cite_ref-SPEEDWEEK_17-2) ["56 Jahre vor Kalex: Die Honda von Mike Hailwood"](https://www.speedweek.com/a/motogp/56-jahre-vor-kalex-die-honda-von-mike-hailwood) [56 years before Kalex: Mike Hailwood's Honda]. *SPEEDWEEK.com* (in German). 20 May 2023. Retrieved 10 May 2026.

1. **[^](#cite_ref-18)** Bloemendaal, Willem. ["Honda 6 cylinder, Mike Hailwood, wereldkampioen 1971"](https://www.modelmotoren.nl/motoren-overige-race-klasse/honda-6-cylinder) [Honda 6-cylinder, Mike Hailwood, 1971 World Champion]. *www.modelmotoren.nl* (in Dutch).

1. ^ [***a***](#cite_ref-Motorcyclist_2_19-0) [***b***](#cite_ref-Motorcyclist_2_19-1) [***c***](#cite_ref-Motorcyclist_2_19-2) Frank, Aaron (20 May 2011). ["Mike Hailwood and His Bike: Honda RC166 | ICON"](https://www.motorcyclistonline.com/blogs/mike-hailwood-and-his-bike-honda-rc166-icon/). *Motorcyclist*. Retrieved 10 May 2026.

1. **[^](#cite_ref-MaxxMoto_20-0)** Jaspers, Arno (27 March 2025). ["Eregalerij: Honda RC166"](https://www.maxxmoto.be/reportages/eregalerij-honda-rc166/) [Hall of Fame: Honda RC166]. *MaxxMoto* (in Flemish). Retrieved 10 May 2026.

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1. **[^](#cite_ref-22)** ["RD05A - Racing Information | Yamaha Motor Co., Ltd"](https://global.yamaha-motor.com/race/wgp-50th/race_archive/machines/rd05a/). *global.yamaha-motor.com*. Retrieved 10 May 2026.

1. **[^](#cite_ref-23)** Diaz-Valdés, Tomás (17 February 2017). ["Una moto de leyenda: Honda RC 166"](https://www.motorpoint.com/una-moto-de-leyenda:-honda-rc-166) [A legendary motorcycle: Honda RC 166]. *motorpoint.com* (in Spanish). Retrieved 8 May 2026.

1. ^ [***a***](#cite_ref-Cycle_World_2_24-0) [***b***](#cite_ref-Cycle_World_2_24-1) Duckworth, Mick (September 1992). ["Hailwood's Honda In Holland"](https://magazine.cycleworld.com/article/1992/9/1/hailwoods-honda-in-holland). *Cycle World | The Complete Archive*. Retrieved 10 May 2026.

1. **[^](#cite_ref-26)** Macauley, Iain (21 March 2021). ["Mike Hailwood's Honda RC174 replica is motorcycling perfection reborn"](https://www.gq-magazine.co.uk/cars/article/mike-hailwoods-honda-rc174-replica-reborn). *British GQ*. Retrieved 10 May 2026.

1. ^ [***a***](#cite_ref-Petrolicious_27-0) [***b***](#cite_ref-Petrolicious_27-1) Franklin, Alan (5 April 2013). ["Honda's RC166 Had More than Met the Eye"](https://petrolicious.com/blogs/articles/honda-rc166?srsltid=AfmBOop3KkA46SWQlyz-ITOsePADeHwyWOG693_8-5LVqqQynSl5O1Ux). *Petrolicious*. Retrieved 10 May 2026.

1. **[^](#cite_ref-28)** Hancocks, Simon (24 June 2019). ["This screaming Honda 'Six' around the IoM TT course is awesome!!"](https://www.visordown.com/news/viral/screaming-honda-%E2%80%98six%E2%80%99-around-iom-tt-course-awesome). *www.visordown.com*. Retrieved 10 May 2026.

1. **[^](#cite_ref-29)** ["motogp.com · 250cc World Standing 1964"](https://web.archive.org/web/20190530114627/http://www.motogp.com/en/Results+Statistics/1964/JPN/250cc/World+Standing). *www.motogp.com*. Archived from [the original](http://www.motogp.com/en/Results+Statistics/1964/JPN/250cc/World+Standing) on 30 May 2019. Retrieved 10 May 2026.

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1. **[^](#cite_ref-31)** ["motogp.com · 250cc World Standing 1966"](https://web.archive.org/web/20191205132420/https://www.motogp.com/en/Results%2BStatistics/1966/JPN/250cc//World%2BStanding). *www.motogp.com*. Archived from [the original](https://www.motogp.com/en/Results%2BStatistics/1966/JPN/250cc//World%2BStanding) on 5 December 2019. Retrieved 10 May 2026.

1. **[^](#cite_ref-32)** ["motogp.com · 250cc World Standing 1967"](https://web.archive.org/web/20190616093810/http://www.motogp.com/en/Results+Statistics/1967/JPN/250cc/World+Standing). *www.motogp.com*. Archived from [the original](http://www.motogp.com/en/Results+Statistics/1967/JPN/250cc/World+Standing) on 16 June 2019. Retrieved 10 May 2026.

v t e Honda Grand Prix motorcycles MotoGP RC211V RC212V RC213V 500cc RC181 NR500 NS500 RS500 NSR500 NSR500V 350cc RC170 RC171 RC172 2RC172 RC173 RC174 250cc RC160 RC161 RC162 RC163 RC164 2RC164 3RC164 RC165 RC166 NSR250 125cc RC143, 2RC143 RC148 RC149 RS125 50cc RC110, RC111 RC112 RC113 RC114 RC115 RC116

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Adapted from the Wikipedia article [Honda RC166](https://en.wikipedia.org/wiki/Honda_RC166) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Honda_RC166?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.