Motorcycle Primary and Secondary Drive Chains Explained

Motorcycle Chains Explained

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Indian Larry: Chopper Shaman
The World's Fastest Indian

    There is much confusion over exactly what size, type etc. chain has been used on the primary sprockets of older British and American motorcycles. There are several “standards” for roller chain, including ANSI, ISO, BS, etc. Don’t trust a quick visual inspection, or comparison of only a few points of reference when buying a chain or sprockets. Some types that appear very similar are not compatible, typically due to differences in the roller diameter. Others will work acceptably with only slight additional wear.
    Chain dimensions are usually given in the following order: 1st = pitch, 2nd = roller width, 3rd = roller diameter. This is not all the useful data, and cannot be used reliably to determine whether chain repair parts (master link, connecting link, offset link, roller, repair link, etc.) can be interchanged. For pitch, roller width and roller diameter dimensions are given in fractional inches, decimal inches, and millimeters where practical.
ANSI (U.S. and commercial)
    These give pitch in 1/8” increments as the 1st number.
    The 2nd number refers to the chain being a roller chain, 0 = roller chain, 5 = bushing. E.g., #50 is a 5/8” pitch roller chain; #35 is a 3/8” pitch bushing chain.
    The suffix is the number of strands: -2 = duplex. E.g., 35-2 is 3/8” pitch dual row bushing chain.
ISO (Metric, British)
    These give pitch in 1/16” increments as the 1st number. E.g., 3/8” pitch =#06.
    The letter “B” means “European Standard”.
    The suffix is the number of strands in the chain: -2 = duplex chain. E.g., 06B-3 is a triple row 3/8” pitch European Standard.

Roller Chain Types

ASA Type
Alternate
Number
Pitch
Roller
Width
Roller
Diameter
Rows
Use
25
 
1/4”
.250”
6.35mm
.130”
3.30mm
1/8”
.125”
3.18mm
1
Commercial size, used on electric bicycles, not motorcycles
219
 
.306”
7.75mm
.200”
5.08mm
.183”
4.65mm
1
Commercial size, used on karts, not motorcycles
35
 
3/8”
.375”
9.53mm
3/16”
.1875”
4.76mm
.200
5.08mm
1
H-D Hummer 125, 165, Super 10 primary
35-2
 
2
H-D 45 primary
35-3
 
3
H-D K/KH, Sportster; Indian Scout primaries
35-4
 
4
Indian Chief 74 & 80 primary
ISO 06B-2
Renolds
114038
7/32”
.225
9.53mm
1/4”
.250”
6.35mm
2
BSA 1947-58 A7 & A10 early rigid & plunger frame; Triumph; Royal Enfield primaries
ISO 06B-3
Renolds
116038
3
Norton P11, Ranger, Commando; BSA A75; Triumph T140, T150, X75 primaries
ISO 07B-2
Renolds
114513
7/16”
.4375”
11.11mm
?
?  
2
Triumph T160
410
 
1/2”
.500”
12.70mm
1/8”
.125”
3.18mm
.306”
7.75mm
1
 
415
 
3/16”
.1875”
4.76mm
1
 
41
 
1/4”
.250”
6.35mm
1
Commercial size, not used on motorcycles
420
 
1
 
ISO 08B-1
Renolds
110046
.306”
7.75mm
.335”
8.51mm
1
BSA Gold Star, 1954-62 swing-arm pre-unit; Matchless; Norton Atlas; Triumph pre-unit primaries. Note: very similar to #428
40
 
5/16”
.3125”
7.94mm
5/16”
.3125”
7.94mm
1
Commercial size, not used on motorcycles
428
126
.335”
8.51mm
1
Note: very similar to ISO 08B-1
428-2
 
2
H-D Big Twin primary 1930-*
520
170, 135
Renolds
110054
5/8”
.625”
15.88mm
1/4”
.250”
6.35mm
.400
10.16mm
1
BSA M20, M21; other singles rear
525
Renolds
110055
5/16”
.3125”
7.94mm
Moto-X rear
530
50, 171
Renolds
110056
3/8”
.375”
9.53mm
Common H-D, other big bike rear
630
60
3/4
.750”
19.05mm
Kawasaki Z1 rear
ISO 12B-1
 
.460”
11.68mm
.475”
12.07mm
Morgan trike

    British transmissions do not use the same primary chain type as the Harley-Davidson 45 or Sportster. Although they may appear similar, they will not work.
    There is one useful similarity: the single-row British primary chain types are frequently ISO 08B-1 (” pitch, .306” width, .335” roller diameter), including some 1954-62 BSA twin swing-arm models. This is almost the same as ASA #428, used on Harley-Davidson big twin (not 45) primary chains since 1930.
    In my opinion, since they are not an exact match (the #428 roller is .0075” wider than the British 08B-1 dimension), a H-D big twin sprocket (#428-2 dual-row) will fit the British chain a bit too tightly. It may be possible to remove the extra material from both sides of the sprocket tooth row and use the British chain, but this may effect hardness, and I have not tried this method. However, the #428 chain will fit the H-D big twin sprocket exactly, and will be only slightly loose (.0075” extra side-play between the sprocket tooth and the chain’s side-plates) on the British clutch drum, which will cause slight additional wear but nothing serious.
    Almost all British transmissions use the same rear drive chain as the H-D twins, so no adapting or fabricating is required here. A common exception* the BSA M20 & M21 WD (military), and some other later singles which use #520; a sprocket from a similar BSA box in #530 may fit.
    Chain must be sized to meet several different requirements for proper application, which normally begins by selecting the smallest pitch distance that will suit the power delivery needed, using dual or triple row as needed.
    The reason for small pitch is its higher maximum speed in feet per second, which is one reason why primary chains have smaller pitch than drive chains: the drive chain’s larger pitch is safe at the lower speed, typically 50-67% of the primary speed.

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