Mike Grage, Customer and Technical Support at The Bonneville Shop and British Iron.
As any seasoned rider knows the easiest modifications a person can make to their motorcycle to increase acceleration or top speed is changing the tooth count on your sprockets. They also wear out and have the potential to cause damage when they fail. So, in this blog I’m going to go over what to check and maintain. And how to get the most life out of your chain and sprockets.
Motorcycle Chains and Sprockets
Damping/Shock Absorption
I get it, that is not what anybody expected to be the first part in this blog. A lot of people, including professional technicians tend to overlook these parts. Without some form of shock absorption, the chain and sprockets will wear out in a very short period of time. The rollers in the chain will be beating the sprocket teeth like they owe them money. On vintage Triumphs the clutch hub shock absorber rubbers do all the work. Vintage Nortons have the additional assistance of the rear cush drive rubbers.
Nobody enjoys the pain of changing out their clutch rubbers, and I’m sure that is the reason why the engineers who designed the Hinckley Triumph models put damping springs on the clutch baskets and used rubber dampers rear sprockets. If your chain last less than 10,000 miles, check your clutch dampers and rear sprocket dampers. Chances are they are hard as a rock or went bad in another way. The natural shock absorption in a primary drive belt will also help extend the life of the final drive chain.
Chains
Motorcycle chain sizing is determined by the distance between the pins and distance between the inside plates, not the overall width. This is why o-ring and x-ring chains have a tendency to be wide enough to rub the cases of vintage Triumph, BSA, Norton and some other makes.
Chains come in a variety of sizes (ex: 530, 525, 520, 420, 415 etc.) and they must be fitted with the sprockets. The first digit the pitch, or distance between the pins measure in an 1/8 inch. 5xx is 5/8” between the pins, and 4xx is 4/8 or 1/2″ inch between the pins.
The second and third number is the distance between plates, originally in 1/8’s of an inch (x30 is 3/8”, x20 is 1/4”, x25 is 5/16”). People good with math will notice the missing decimal point for the width, the 525 chain is 2.5/8 or 5/16 wide. I have no idea who came up with that sizing system, but I know a few people who would like to talk to him about the missing decimal point. Especially the Japanese bike techs that occasionally deal with 428 chains, which are 2.8/8 or .35” between the plates.
The majority of vintage motorcycles that The Bonneville Shop supplies parts for use 530 chains, which is the standard size for just about all of the vintage British twins and triples. Some single cylinder bikes like the 1966 Triumph T20 Cub lists 1/2” x 3/16” for the rear chain, that translates to a 415 chain. The 1971 Triumph T25 lists 5/8” x 1/4″ which is a 520 chain.
The chain needs to be kept clean, lubricated, and properly adjusted. Breaking a chain can be devastating. A broken chain can cause injuries, property damage, and put big holes in engine cases.
One of the easiest ways to tell if your chain is worn out is to see if you can lift one of the rollers off of the very back of the rear sprocket, if you can see light between the sprocket/chain it is worn out. You should also check for axial (left/right) play in the chain. There should be a small amount of axial play in any chain, if the chain can twist or contact the tire it is dangerous and needs to be replaced. An o-ring or x-ring chain will feel spongy, traditional chains will not. All of the links should move smoothly, the chain should be replaced if there are any stiff or tight links.
Sprockets
Sprockets determine the final drive ratio, changing the tooth count can increase or decrease this ratio. A higher ratio will increase acceleration and lower fuel mileage. A lower ratio will increase top speed and fuel mileage. Needless to say, sprockets must match the chain. The teeth on a 530 sprocket will never fit inside a 415 chain.
Changing the tooth count on the gearbox sprocket will make a bigger difference than making those same changes to the rear sprocket. To calculate the final drive ratio, you divide the rear sprocket tooth count by the gearbox sprocket tooth count. The 79 T140E parts manual list 20T gearbox sprocket and 47T rear as standard, that provides for 2.35 final drive ratio. Same parts book has two more option for gearbox sprockets, 19T (2.47 w/47T) and a 18T (2.61 w/47T) option. There is also a 45T rear sprocket option that will give you a 2.25 ratio with a 20T gearbox sprocket.
Lowering the final drive ratio for the highest top speed sounds like it can be fun, but there are some serious downsides to doing so. Going too low increases the stress on the entire drivetrain. This will increase your potential to cause detonation from lugging the motor. Make the primary chain and clutch work harder. And increases the pressure on the dog/slots in the transmission.
When a sprocket is worn out it begins to take the shape of a circular saw blade. They will also have some burrs build up around the teeth. If the teeth start taking a hook shape they can hang up on the chain, and this increases the risk of chain failure.
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Frequently Asked Questions
What size chain does a vintage Triumph, BSA or Norton use?
Most vintage British twins and triples use a 530 chain, the standard size on nearly all classic Triumph, BSA and Norton twins and triples. Some smaller models are different: the 1966 Triumph T20 Cub uses a 415 rear chain, and the 1971 Triumph T25 uses a 520. For a 5-speed T140 or TR7, a DID 530 x 120-link final drive chain is a common replacement. You can also browse by model in Shop by Vehicle.
What do motorcycle chain size numbers like 530, 525 and 520 mean?
The first digit is the pitch, meaning the distance between the pins, in eighths of an inch. A 5xx chain has 5/8″ pitch and a 4xx chain has 1/2″ pitch. The last two digits give the inside width between the plates, also in eighths of an inch but without the decimal point: x30 is 3/8″, x25 is 5/16″ (2.5/8) and x20 is 1/4″. So, a 530 chain has 5/8″ pitch and 3/8″ inside width. The chain and sprockets must match. Shop the BikeMaster 530 drive chain or the BikeMaster 525 drive chain.
Can I put an O-ring or X-ring chain on my vintage British motorcycle?
Sometimes, but check the clearance first. Chain size is set by pin spacing and inside plate width, not overall width. O-ring and X-ring chains are wider on the outside, so they can rub the cases on vintage Triumph, BSA and Norton motorcycles. Renthal’s chain fitting guidance says to check case clearance near the gearbox sprocket and to switch to a narrower non-O-ring chain if the chain touches any metal. Shop Renthal and BikeMaster chains and sprockets at British Iron.
How do I know if my motorcycle chain is worn out?
Try to pull a roller away from the very back of the rear sprocket. If you can see light between the chain and the sprocket, the chain is worn out. Also check side-to-side (axial) play: a little is normal, but if the chain can twist or touch the tire, replace it right away. Every link should move smoothly, so stiff or tight links also mean it’s time for a new chain. For a measurement-based check, Renthal explains how to measure chain stretch over 16 links.
Why do O-ring chains feel spongy compared to standard chains?
The rubber O-rings or X-rings between the plates hold grease in the pins and keep dirt out, so the chain feels slightly cushioned when you flex it. That is normal. A traditional non-sealed chain won’t feel spongy. On either type, stiff or binding links mean the chain should be replaced.
Why is my motorcycle chain wearing out so fast?
On British motorcycles, the usual cause is worn shock absorption in the drivetrain. Without damping, the rollers pound the sprocket teeth and the chain and sprockets wear out quickly. If your chain lasts less than 10,000 miles, check your dampers. On vintage Triumphs, the clutch hub shock absorber rubbers do this job. Vintage Nortons also use rear wheel cush drive rubbers. Hinckley Triumphs use damping springs in the clutch basket and rubber dampers in the rear sprocket. Find replacement parts in Clutch, Drivetrain and Transmissions.
What are the signs of a worn motorcycle sprocket?
As a sprocket wears, it starts to look like a circular saw blade, with burrs building up around the teeth. Teeth that have worn into a hook shape can catch on the chain and raise the risk of chain failure. Renthal recommends replacing the chain and sprockets together, since an old chain on new sprockets (or the other way around) wears quickly. A Triumph 750 5-speed chain and sprocket set covers everything in one order. You can also browse all chains and sprockets.
How do I calculate my motorcycle’s final drive ratio?
Divide the number of teeth on the rear sprocket by the number on the gearbox (front) sprocket. Using the 1979 Triumph T140 Bonneville and TR7 Tiger parts book as an example, the stock 20-tooth gearbox sprocket and 47-tooth rear sprocket give a ratio of 47 ÷ 20 = 2.35.
What sprocket options are available for a Triumph T140 Bonneville?
The 1979 T140E parts book lists a 20-tooth gearbox sprocket and a 47-tooth rear sprocket as standard (2.35 ratio). Other listed options:
19-tooth gearbox sprocket with the 47T rear: 2.47 ratio
18-tooth gearbox sprocket with the 47T rear: 2.61 ratio
45-tooth rear sprocket with the 20T gearbox sprocket: 2.25 ratio
Should I change the front or rear sprocket to improve acceleration or top speed?
A one-tooth change on the gearbox sprocket makes a bigger difference than the same change on the rear sprocket. A higher (numerically larger) ratio, from a smaller front sprocket or a bigger rear, improves acceleration but lowers fuel mileage. A lower ratio, from a bigger front sprocket or a smaller rear, raises top speed and fuel mileage. Shop sprockets by tooth count in Chains and Sprockets.
Is gearing a motorcycle too tall bad for the engine?
Yes, it can be. Gearing too low, for maximum top speed, adds stress to the whole drivetrain. It makes it easier to lug the engine and cause detonation, makes the primary chain and clutch work harder, and puts more pressure on the gearbox dogs and slots. If you’re working on the drivetrain, see the primary and transmission tools and transmission and gearbox parts.
How often should I check and maintain my motorcycle chain?
Keep the chain clean, lubricated and properly adjusted, and check it as part of every pre-ride inspection. The Motorcycle Safety Foundation’s T-CLOCS checklist includes the chain. A broken chain can cause injuries, damage property and punch holes in the engine cases. For slack specs and service intervals on modern Hinckley models, check your Triumph owner’s handbook. For help choosing the right chain, contact British Iron.
