Exhaust Sound Emissions from Classic and Vintage Motorcycles By Allan Johnson, B.S.A., M.Sc. 51 Market St., Georgetown, ON, L7G 3C4 Tel. 1(905) 877-1565 Email: afjohnson@sympatico.ca
Introduction Proposals have been made by the Canadian motorcycle industry association (MMIC) that a recently developed Society of Automotive Engineers (SAE) on-road motorcycle sound emission test, known as SAE J2825, be adopted by Canadian municipalities and their police forces in order to control motorcycle noise. Promotion of this roadside stop and test program raised questions amongst Canadian Vintage Motorcycle Group (CVMG) members as to whether their Vintage and Classic motorcycles would be able to pass such a test, since most of their motorcycles were manufactured before there were any required Canadian national numerical standards for allowable sound emission levels. A preliminary sound testing program on 52 Vintage and Classic motorcycles was conducted at the CVMG Annual Rally held at Paris, Ontario from June 18 – 20, 2010. The following is a report of the testing undertaken, the results obtained and some observations on the findings.
Materials and Methods The test instruments were those of the type used by the Canadian Motorcycle Association (CMA) and its member clubs for official testing of CMA and FIM sanctioned competition events requiring testing to the SAE J1287 protocol – a sound measurement testing protocol and standard for off-road motorcycles. The Digital Sound Level Meter used was an Extech model 407740, an Extech model 407744 Sound Level Calibrator was used as a 94 dBA calibration standard and where the motorcycle being tested did not have a tachometer, a Treysit sirometer placed on the bike’s saddle or rear fender was used to adjust the bike’s engine to 2000 or 5000 rpm. A small, marked wooden plate was used to gauge the correct 45 degree angle of measurement from the end of each silencer tip. It was removed before testing was done to eliminate any sound reflection from the plate, the 45 degree angle being then indicated by an appropriately placed narrow stick of soft wood radiating from below each exhaust outlet. A distance gauge to accurately place the sound meter 50 cm from the silencer tip on the 45 degree axis and at a height above ground equal to the silencer tip distance from the ground was constructed of soft wood so as to hold the sound meter in the correct position and alignment for each exhaust tip. This gauge also allowed the calibration unit to be rapidly deployed to check the sound meter calibration. The sound meter was used with the foam diffuser ball in place, except when calibrating the meter. Before the sound meter was placed in the testing position it was pointed away from the test bike to check that the background noise level was sufficiently low for a valid bike test to be conducted. The sound meter was steadied in place by hand while readings were being taken. If a motorcycle had two separate exhausts on opposite sides of the motorcycle the sound 1
levels at each silencer outlet were separately measured and recorded, then averaged for statistical purposes. Where a silencer outlet was a circular pipe, the 50 cm distance was measured from the center of the pipe orifice. If the silencer outlet was a slot as was usual with the “fishtail” form of silencer exit port, then the 50 cm distance was measured from the mid-point between the two lobes of the tail. All tests were done on motorcycles placed on their center or rear stands or held in a vertical position to ensure consistency. Side, prop or “jiffy” stands were not used. If the bike was being held vertically and/or the operator was operating the throttle, they stood on the side of the motorcycle away from the sound meter. The motorcycle was at least 10 feet away from any other motorcycle or other object. Only the person holding and reading the sound meter was near the meter. The ground under all the test bikes was a mowed, compacted grass field. Weather conditions on all three test days was in the 25 – 30 degrees C range and sunny. Emphasis on selection of motorcycles tested was on motorcycles manufactured prior to the silencer noise limit standards brought in by the Canadian federal government for 1983 model year and subsequent year manufactured and imported motorcycles. 48 of the tested motorcycles were 1982 or earlier models whose exhausts systems were not subject to any numerical sound limit regulation at the time of manufacture. Of the four remaining motorcycles, one was a 1988 motorcycle with stock exhaust system and three were post1982 models with aftermarket or home-made exhaust systems.
Results The individual results for each of the 52 motorcycles tested with details of the tested vehicle, the exhaust system used and other details are presented in Appendix A. Twentynine different makes of motorcycle were tested and these ranged in model year from 1913 to 2000. All 52 of the motorcycles tested at idle speed were found to emit less than the 92 dBA idle speed limit proposed by SAE test J2825. The quietest motorcycle at idle, a 1978 BMW 980cc opposed 4stroke twin, registered under 69 dBA. 2 elderly (1914 and 1928) twin cylinder motorcycles with stock exhaust systems were found to emit greater sound levels than the 96 dBA SAE J2825 proposed limit at 2000 rpm. 2 further motorcycles (a 1942 twin and a 1984 4 cylinder), each with a non-standard exhaust system, were found to exceed their respective 96 dBA and 100 dBA SAE J2825 proposed limit. The remaining 48 motorcycles (43 with stock exhaust systems and 5 with “aftermarket” or non-stock exhaust systems) recorded less than the 96 dBA at 2000 rpm or 100 dBA SAE J2825 proposed limits for their respective engine cylinder class. The motorcycles tested were grouped by engine cylinder number, and in some cases engine type and size in order to provide the summary statistics presented in Table 1.
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Table 1. Summarized results of Vintage and Classic motorcycle sound testing at the CVMG Paris Rally, June 18-20, 2010. dBA values in Mean and range. (NA – not applicable. < equals “less than”. Stock ex. = Stock, original type exhaust system) Motorcycle Class ------------------------------1 cylinder, 4 stroke 500cc (1913- 1979) Stock ex.
# Idle dBA 2000 rpm dBA 5000 rpm dBA ----------------------------------------------------------9 83.1 (80.2 – 86.5) 93.7 (88.1 – 96.0) NA
1 cylinder, 4 stroke <250 cc (1968-1971) Stock ex.
3
78.4 (71.0 – 84.1)
90.5 (86.1- 94.7)
NA
1 cylinder, 2 stroke <250 cc (1922 – 1975) Stock ex.
6
80.6 (72.0 – 89.0)
92.6 (86.5 – 96.0)
NA
2 cylinder, 4 stroke, Stock ex. 18 83.0 (68.7-92.7) (1914 -1988) 250 –1,000 cc
89.8 (79.4 – 98.0)
NA
2 cylinder, 4 stroke, Non-stock 5 86.7 (79.0 –91.9) ex. (1940-2000) 650-1,700cc
94.3 (90.2 – 106.0)
NA
2 cylinder, 2 stroke, Stock ex. (1928) 500 cc
1
91.8
100.0
NA
3 cylinder, 4 stroke, Stock ex. (1971) 750 cc
1
83.8
90.1
94.2
3 cylinder, 4 stroke, Non-stock 1 ex. (2000) 900 cc
77.0
86.0
98.6
4 cylinder, 4 stroke, Stock ex. 6 (1925 – 1977) 400 –1200cc
82.6 (76.1-89.3)
4 cylinder,4 stroke, Non-stock ex. (1984) 750 cc
1
79.0
Wankel rotary engine, Stock ex. (1976)
1
84.0
NA
97.0 (95.8-100.0) (note 1) 101.4
86.4
97.0
(Note 1: four of the six motorcycles in this group were 1925 to 1947 models not designed to be operated at levels as high as 5,000 rpm so their dBA readings above idle rpm were taken as a “flash” reading at momentary wide open throttle.) The Vintage and Classic motorcycles tested consisted of a variety of original and unrestored, original and maintained, and restored to original specification vehicles. It is therefore no surprise that the sound level values vary considerably from motorcycle to motorcycle. It must also be realized that prior to the 1983 model year, motorcycles sold new in Canada were not subject to any numerical sound standards criteria. There were no such Federal regulations until that year and sound emissions from motor vehicles were generally regulated by provincial highway traffic laws or local nuisance control by-laws. 3
It was, therefore, the role of the motorcycle manufacturers prior to the era of government regulation to fit what they considered adequate silencing equipment to their motorcycles. To-day’s motorcycles use modern sound attenuation technology such as double-walled pipes, sound-absorbent packing and computer-designed chamber and pipe dimensions. The makers of early motorcycles were without such advantages. As well, most motorcycle manufacture was carried on by relatively small factories without the research and development resources to design and test sound control systems. It was not until the 1960’s, with the rise of large motorcycle manufacturers making hundreds of thousands of motorcycles per year that research and development on motorcycle sound levels became common. That is not to say that the problem of excessive sound from motorcycle exhaust systems was not recognized much earlier than the 1960’s and motorcycling literature from the late 1920’s onwards indicates that in Britain, then the world’s largest motorcycle manufacturing country, quiet motorcycles were a design and manufacturing objective. Much media attention and advertising was centered on motorcycle maker’s efforts to produce motorcycles with low sound emissions. It is therefore refreshing to find that in nearly all the cases of the antique and classic motorcycles tested in this study that those with stock (standard) types of exhaust system as originally fitted were able to control sound levels to at or below the criteria proposed in the SAE J2825 test. Both single and twin cylinder four stroke stock exhaust motorcycles produced average idle values about 9 dBA below the J2825 allowed criterion. For the J2825 2000rpm 96 dBA criterion the 500 cc 4 stroke singles averaged just over 2 dBA below that criterion, while the 4 stroke twin cylinder bikes, although generally larger in engine size, averaged 6 dBA below the allowed 96 dBA criterion. The small two-stroke singles averaged 11 dBA below the 92 dBA idle allowed criterion and just over 3 dBA below the 96 dBA at 2000 rpm allowed criterion. Small 4 stroke singles, even though two of the three motorcycles tested were competition types, averaged 13 dBA below the J2825 idle criterion and 5 dBA below the 2000 rpm (96 dBA) criterion. Twin cylinder motorcycles with non-stock exhaust systems averaged 5 dBA below the idle criterion and 1 dBA below the 2000 rpm criterion of 96 dBA. The 5 motorcycles in this group included the motorcycle which had the highest recorded 2000 rpm sound test in this study at 106 dBA. This modified 1942 Indian Scout 800 cc side valve v-twin was equipped with a 2 into 1 exhaust pipe and a “Brooklands Can” pattern of silencer originally designed in 1907 to attenuate racing car and motorcycle exhaust sound from the Brooklands race track at Weybridge, Surry, England. It appeared to be sized for a smaller engine than the one it was fitted on and this may be the reason for its ineffectiveness. Another motorcycle, a 650 cc twin “Chopper” without any silencers at all was only 2 dBA below the idle criterion but was 5 dBA below the 2000 rpm criterion, an unusual situation. This anomaly appears to result from the builder welding a “half washer” inside 4
each exhaust pipe to act as a silencer. This resulted in such restriction to gas flow that the engine could not properly run at higher revolutions – but it did limit the sound level significantly. Only two 3 cylinder motorcycles were tested, one 1971 motorcycle of 750 cc with a stock exhaust system and it was 8 dBA below the idle criterion and over 5 dBA below the 5000 rpm test criterion. The 900 cc 3 cylinder motorcycle with a “factory off-road” exhaust system was 15 dBA below the idle criterion and 1 dBA below the 5000 rpm test criterion. Of the six four cylinder motorcycles tested in this study four of them were designs which originated 70 or more years ago. As such, they were not capable of reaching the 5000 rpm test level required by the SAE J2825. As a result, the “high rpm test” was done as a “flash” full throttle reading of the highest dBA reading obtained. Since none of these four motorcycles were equipped with their own tachometers and the sirometer must be preset to a known rpm value in order to operate properly, accurate rpm measurement was not attainable. Nevertheless, the idle dBA of the six motorcycles averaged 9 dBA below the SAE J2825 idle criterion and the maximum throttle average value was 3 dBA below the 5000 rpm criterion. Since these elderly engines were intended to operate at much lower revolutions than 5000 (generally in the 3500 rpm range or less) it would be more appropriate for them to be tested at the 2000 rpm criterion level. Two of these motorcycles had attached hard-bodied sidecars on the same side of the motorcycle as their single exhaust pipes. It was noticed that some sound reflection from the sidecars was affecting the dBA readings from the exhaust. The single 1928 twin two-stroke tested met the 92 dBA idle criterion but exceeded the 2000 rpm criterion of 96 dBA by 4 dBA. The simple expansion box and narrow tailpipe exhaust system traditional on this make and model are usually more effective and it may be that the expansion box attenuation wire packing was missing. The single Wankel-type rotary engined motorcycle was tested at all three criteria and was well below the proposed allowable dBA levels.
Observations and Conclusions
1. The preliminary study reported here generally indicates that Vintage and Classic motorcycles of 1, 2, 3 and 4 engine cylinders and Wankel rotary engines with stock (standard pattern for year, make and model) exhaust systems in good (as designed and manufactured originally) condition will test at lower decibel (dBA) levels than permitted by the proposed SAE J2825 stationary on-road motorcycle sound test. 2. The report does indicate that some old design (1930s and earlier) four cylinder motorcycles cannot reach the 5000 rpm test level for 4 cylinder motorcycles and should either be allowed to test at the lower (2000 rpm) level, although they do meet the 100dBA criterion at momentary maximum revolutions, or be exempted from testing altogether.
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3. On certain Vintage and Classic motorcycles which are equipped with sidecars on the same side of the motorcycle as the exhaust system, there is some effect on sound readings from reflection off the hard body of the sidecar. 4. With some motorcycles with hard saddle cases there may be significant measurable reflection of sound towards the sound test meter from those cases, especially if the motorcycle is not tested in an vertical position but tested when leaned over to one side on the side, prop or jiffy stand and the measurement taken on the silencer on the side opposite to the side stand. (Usually the right side of the motorcycle, the side stand being normally on the motorcycle’s left side.) 5. Engine noise from valve gear and other exposed components on very early motorcycles can be a significant sound contributor, although the exhaust sound itself may be of limited volume, particularly at idle. 6. While the SAE J2825 proposed stationary on-road motorcycle sound test addresses the issue of whether a single motorcycle may be “too noisy”, it does not address the real problem of particular community disturbance from numbers of motorcycles, and other vehicles, operating along public roads. The inverse square law of acoustics states that Sound Pressure Level varies inversely as the square of the distance from the source. In regard to a point source, such as a single motorcycle exhaust, where there are no reflecting surfaces, background sounds or interference, a sound level drops 6 dB for every doubling of the distance from the source. However, in traffic sound studies along a linear corridor or road, the traffic sound of a number of vehicles is considered a “line source” which produces cylindrical spreading of the sound to the roadsides. This results in a sound level reduction of only 3 dB per doubling of reception distance. This is half of the attenuation which would occur from a point source such as a single motorcycle exhaust. A long parade of motorcycles on a group ride – even if each individual motorcycle in the parade met the SAE J2825 test for allowed sound emission – would result in a higher level of noise reaching the roadside community.
7. Although a motorcycle may be able to pass the SAE J2825 test, it is well understood by many motorcyclists that inappropriate use of large throttle openings in lower gears, racing the engine in neutral, violent acceleration, ignition switching, and such tactics can cause objectionable noise with almost any motorcycle. It would seem unlikely that a program of roadside motorcycle sound testing would be conducted at such times and places as to deter such sporadic antisocial behaviour. Thus, while SAE J2825 may measure the motorcycle’s capability to be operated within certain sound level guidelines, it cannot affect the motorcycle operator’s use and behaviour without significant and expensive police enforcement effort. 8. It is well recognized in the motorcycling community that although Federal government standards for sound level control in motorcycle exhaust systems have been in force since 1983, it is still possible to purchase new motorcycles from franchised dealers in this country and have non-road legal, noisy, exhaust systems (some provided by the motorcycle manufacturer) fitted to these motorcycles. Comments by CVMG members who volunteered their motorcycles for this sound testing project invariably mentioned 6
that in their experience, the real motorcycle noise problem is with purchasers of new motorcycles who are enamoured of the “biker image” and feel that the installation of an noise-producing “factory off-road racing” or “aftermarket performance” exhaust system somehow “enhances their self-image.”
Figure 1. Sound Level meter, Calibration source and sirometer used in testing. (See attached figure IMG_1504.jpg)
Figure 2: Alignment method and gauge for Sound Level measuring. (See attached figure IMG_1500.jpg)
Sound Test Individual Results for “Exhaust Sound Emissions from Classic and Vintage Motorcycles” Report. Appendix 1 : Results of individual motorcycle sound emission testing at the CVMG National Vintage Motorcycle Rally, Paris, Ontario, June 18-20, 2010 ( m/c = rpm measured by the motorcycle tachometer, S = rpm measured by sirometer, R = right silencer value, L = left silencer value, K = 1000 rpm) Motorcycle Year, Make model Engine size/type -----------------------------
dBA values obtained Idle 2K 5K other --------------------------------------
1978 BMW R100/7
68.7R 79.9R
(4K)92.8R
Comments
--------------------------Stock pattern old 7
980 cc 4str opp.twin low compression, small carb version
68.7L 78.9L (4K)93.4L silencers, unrestored, 68.6R (without Craven pannier bags) m/c 68.5L ( “ “ “ “
1938 Brough Superior SS80 82.0 990 cc, v-twin, side valve 79.0
93.0 (silencer only) Stock pattern silencer 90.0 (silencer plus (carbjector type) and stock “fishtail”) cast alloy fishtail. S. 92.5 at 50% power (2200 rpm)
1926 Nimbus “Stovepipe” 750 cc Ioe inline 4 cyl.
86.0
100 at max.rpm 4 into 1 short ex. (standard system) no expansion box or silencer body. S.
1922 Neracar 2 stroke 220 cc single TS
84.0
1947 Nimbus “Bumblebee” 750 cc ohc inline 4
84.2
1975 Batavus moped 2 stroke 1 cyl. 50 cc
78.8
94.1
stock original ex. pipe. S.
1968 Norton Atlas 750 cc ohv 4 stroke twin
84.1R 84.2L
91.4R 92.1L
Reproduction ex. to original pattern Restored. m/c.
1955 Ariel VH 500 cc ohv 1 cyl
81.0
94.7
Reproduction ex. to original type. Restored. S.
1976 Suzuki RE5 Wankel-type rotary
84.0R 84.0L
86.1R 86.7L
1967 Triumph T20SM “Tiger Cub” 200 cc 4 stroke single
84.1
94.7
Stock off-road exhaust. S.
1950 AJS 18S 500 cc ohv 1 cyl.
80.2
88.1
Stock “Burgess” style silencer. S.
1980 BMW R100RS 980 cc ohv 2 cyl full fairing, Krauser cases
78.0R 78.0 L
85.0R 86.0L
Stock original m/c.
93.2
expansion box and ex.pipe outlet under floor pan. S. 95.1 (max rpm)
97.0R 97.0L
4 into 1 short stock ex.pipe oval small outlet close to right hand metal Steib sidecar. Restored. S.
Stock original exhaust. m/c.
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1948 Vincent Meteor 500 cc ohv 1 cyl.
86.0
94.0
pattern silencer engine“Comet” spec. S.
1988 BMW R100GS 980cc ohv 2 cyl
78.0
83.0
standard ex. Dual sport model. m/c.
2000 Triumph Thunderbird 900 cc 3 cyl, ohv w/c
77.0R 77.1L
85.9R 86.0L
98.6R 99.0L
Triumph “offroad” ex. m/c.
1982 BMW R100R 980 cc 2 cyl ohv
79.0
94.5
(3K) 97.0
2-into-1 with “Super Trapp” silencer. m/c.
1977 Yamaha XS650 650cc ohv 2 cyl
74.1R 74.1L
86.5L 86.5L
Stock ex. m/c.
1968 Honda 65 65cc 4 stroke single
71.0
86.1
Stock silencer S.
1975 Kawasaki Z1 900cc 4 cyl 4stroke
83.0R 86.0R 83.0L 86.0L
1980 BMW R100T 980 cc 2 cyl 4 stroke
74.2R 74.6L
85.9R 86.2L
1977 Honda Super Sport 400 cc 4 cyl ohc
76.1
83.2
1975 Ducati 750GT 750cc ohc 2 cyl.
86.0R 85.5L
94.3R 94.2L
1937 Indian Dispatch-Tow 750 cc v-twin side valve 3 – wheeler
82.1
90.6
Stock Ex. fishtail exit under body.S.
1942 Indian Scout 800 cc from 500cc v-twin side valve
91.9
106.0
“Brooklands” “Can” with fishtail. S.
1940 Indian Scout 800 cc from 750 cc v-twin side valve
86.1
95.5
Standard Indian “Chief” ex. system. S.
1940 Indian Scout 750 cc v-twin side valve
80.2
93.1
Standard Indian “Scout” ex. system. S.
100.1R 99.1L
Restored stock m/c. Stock ex. m/c
96.0
Original ex. 4-into-1 m/c. Stock ex. m/c
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1971 BSA Rocket 3 750 cc ohv 3 cyl 4 stroke
83.8R 83.8L
90.1R 90.1L
94.3R 94.0L
1968 BSA 650 “Chopper” 650 cc 2 cyl 4 stroke
89.3R 89.1L
90.9R 90.6L
Straight pipes no silencers “half washer welded inside each pipe.” S.
2000 Harley-Davidson “Classic Special” 1700 cc v-twin 4 stroke
87.0R 87.1L
90.1R 90.2L
Vance & Hines “Monster Oval” 49 state legal aftermarket m/c.
1913 Rudge “Multi” 500 cc single Ioe 4 stroke
84.0
95.6
expansion box with straight short, small dia. Outlet original pattern Restored. S.
1925 Henderson DeLuxe 1200 cc 4 cylinder 4 stroke
89.3
98.4 (max. rpm)
Stock ex. sys. m/c
baffle on expansion box closed. Short tail pipe. R/H sidecar reflecting sound. S.
1924 Sunbeam Model 6 TT Replica 86.5 500 cc side valve 1 cyl.
95.2
Stock TT ex. pipe racing type length can be adjusted for tuning. S.
1914 Douglas 4 hp flat twin 600 cc 4 stroke
92.7
98.0
Expansion box short, small dia. Ex. pipe. S.
1927 Zenith 680 sv JAP engine 680 cc 2 cyl. 4 stroke
88.6
95.2
short silencer. S.
1970 Hodaka Ace 100 cc 2 stroke single cyl.
72.0
86.5
Stock exhaust. S.
1936 Francis-Barnett Power Byke 98 cc 2 stroke single cyl.
79.4
94.8
Stock exhaust. S.
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1946 Mobylette Moped 50 cc 2 stroke single cyl.
80.4
91.2
Stock exhaust. S.
1934 Francis-Barnett Cruiser 45 250 cc Villiers 2 str, 2 port,1 cyl
89.0
96.0
Cast expansion chamber single ex. pipe no silencer & fishtail. S.
1961 Honda C77 Dream 305 cc ohc 2 cyl 4str.
72.2R 72.1L
86.1R 85.9L
Stock ex. sys. reproduction. S.
1967 BSA Royal Star 500 cc ohv 2 cyl 4str.
82.4R 82.5L
93.0R 93.1L
Stock ex. sys. Restored. m/c.
1972 Norton Commando 750 cc 2 cyl 4 str.
80.1R 79.9L
91.8R 91.7L
Stock pattern ex. sys. m/c.
1971 Triumph 250 TRW 250 cc 1 cyl. 4 stroke Trials
80.0
90.7
Sammy Miller trials type mini silencer. S.
1926 Scott Super Squirrel 500 cc 2 cyl. 2 stroke w/c
91.8
100.0
expansion box and short small dia. pipe. S.
1951 Moto Guzzi Falcone 500 cc 1 cyl 4 str.
82.8
96.0
1984 Yamaha XJ750 750 cc 4 cyl 4str.
79.0
92.0
Stock Guzzi Silencer. S. 101.4 Home made can Silencer. m/c
1940 Indian 4 1300 cc 4 cylinder, 4 str.
77.0
93.0 (max rpm) Stock Indian 4-into-1 ex. pipe S.
1967 Triumph Bonneville 650 cc 2 cyl 4 str.
80.2R 80.3L
93.5R 93.5L
Stock ex. sys. restored. m/c
1979 Yamaha SR500 500 cc 1 cyl 4 str
80.5
94.5
baffled “café racer” style exh. m/c.
1937 Rudge Sports Special 500 cc 4 valve 2 port 1 cyl 4 str
84.0R 84.1L
92.9R 92.9L
2 high level pipes. 2 silencers 4 valve engine.S.
1982 Kawasaki LTD 250
76.0
84.0
Stock ex. sys. m/c. 11
250 cc 2 cyl 4 str. 1968 Velocette Venom Clubman 500 cc ohv 1 cyl 4 str
83.0
92.6
Stock Velo ex. pipe & silencer built-in fishtail. m/c.
1970 Norton Commando Roadster 750 cc 2 cyl 4 str.
83.0R 82.9L
94.1R 94.5L
“Daytona” pattern silencers, not std. Replicas. m/c.
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