Measuring Chain Wear

 

New and improved Dirt Tricks Chain Wear tool! This simple tool will let you know when your chain has reached its wear limit.

You want to keep the chain as tight as possible to measure. The easiest way to do this is to put your bike in gear and roll it backward. This should create tension on the top chain and allow you to take a measurement. Hook a roller with the curved end of this tool and drop the straight end onto the chain. If the straight end of the tool fits nicely between the two rollers, you still have life in you chain. If the straight end hits does not fit down between the rollers and gets stuck on one, it has worn or “stretched” to its wear limit. Made from stainless steel and laser engraved with a functional illustration (see in the images bellow).

520 Chain Wear Gage

chain_wear_gage1

Measuring Chain Wear:

 

How do you determine when your chain is beyond the manufacturer’s wear limit? First of all let’s correct the myth that chains stretch. Chains don’t stretch. The outside measurement of an individual link plate does not get longer with wear. Your bike is not “so powerful” that is stretches the chain. Chains are constructed of essentially link plates, pins, bushings and rollers. In order for a chain to roll around a sprocket the pins must have clearance through the bushing holes, allowing them to pivot. That clearance begins at about .0005″, or 1/6 of a human hair. The pins and bushings are subjected to continual pivoting, and as they pass a sprocket, steel against steel wear occurs. This causes the pins and their mating holes to wear in an eccentric manner as the diagram below shows. In abrasive dirt conditions and especially mud, grains of sand are introduced between these mating surfaces and wear is accelerated many times over. A sealed chain (O-ring, X-ring, Z-ring …) acts to prevent abrasives from entering this pivoting joint.

For all full sized dirt bikes, the standard chain pitch is 5/8″. Chain code numbers indicate the pitch. a 4xx chain has a 4/8 or 1/2″ pitch. A 5XX chain has a 5/8″ pitch. Sorry to those fond of metric units. Similar to the way pipe is measured worldwide, chain is measured by the “king’s thumb”. 5/8″ is the center-to-center distance between pins. Most chain manufacturers limit chain wear to approximately .006″ per link. So if you take that number and multiply it by 100 links, the accumulated clearance that some refer to as “stretch”, is close to a full pitch or 5/8″. So if 99 spaces fit in the distance that 100 spaces were suppose to measure, your chain is shot. So here are two ways to inspect your chain for wear:

Break the master link and stretch your chain out on a work bench in a straight line. Now count out 100 spaces and mark the first and last pins. Now take a tape measurer and measure the distance, center-to-center between pin 1 and pin 101 (It takes 101 pins to create 100 spaces. Just like it takes two pins to create one space). If the distance is greater than 63-1/8″, then it’s time to replace your chain. A brand new chain will be 62.5″. Don’t get confused by the “tape measure” in the diagram. I like to “shave an inch” on the starting end and measure starting at 1″, rather than trust the accuracy of the clip on the end of the tape.

The second method is not as precise, but will save you time in breaking your master link. Suck a wrench between your chain and rear sprocket by rotating your rear wheel by hand, until the chain along the top of your swing arm is tight. Using the method above, count out 24 intervals, and measure the distance center-to-center between the first and last pin. A new chain will be 15″ dead nuts. If you measure more than 15-3/32″ it’s time to get a new chain.

 

Worn-link-3

 

chain wear

O-ring or sealed chains verses non-sealed chains:

 

What is the difference in weight between the two?

 

A Regina 520-RX3, non-sealed premium racing chain, weighs 4.05 pounds. A Regina 520-ORN weighs 4.24 pounds. The difference is 3 ounces. That’s the equivalent of three first-class letters,  1-1/4″ of Coke in the bottom of a soda can, or one pair of “tighty-whitey” underwear. Insignificant! What about rotating inertia? A single knob on a rear tire has a larger rotating inertia (polar moment) than 3-ounces of chain weight. Contrast that with the 3-pound difference between various brands of equal-sized rear tires. Insignificant! Anyone who claims that they can feel the difference between the two chains while riding, needs to loose their underwear.

 

How much additional horsepower does an O-ring chain consume?

 

Well, you can take all the anecdotal remarks about how “I can feel the power difference”, or ” you should never use an O-ring chain on small bike”, or we can measure this objectively. Let’s look at the science.

 

Here is my method of measurement:

 

  • Determine the torque at a rear wheel necessary to maintain free spinning. Measure this value with both styles of chain.
  • Calculate the HP difference between those torque values using speeds of 20, 40, and 60 MPH.

 

Data:

Chain Type Load (oz) Lever arm (inches) Torque (oz-in)
520 ORN 37.5 12.5 468
520 RX3 31.7 12.5 396

The load was determined by hanging weights on a rope wrapped around the rear tire. Small weights were added until the tire would remain rotating but not accelerate. The idea was to measure rolling friction as opposed to static or break-away friction.

 

Calculations:

 

HP=T x RPM/1,008,000   (T in oz-inches)    HP=T x RPM/5252   (T in foot-pounds)

19″ Rear tire diameter =  25″ actual diameter

Tire RPM at 20mph = 265 RPM

Tire RPM at 40mph = 530 RPM

Tire RPM at 60mph = 795 RPM

 

Chain Type Speed (mph) Torque RPM HP HP Diff
520 ORN 20 468 265 0.12
520 RX3 20 396 265 0.104 .016
520 ORN 40 468 530 0.24
520 RX3 40 396 530 0.208 .032
520 ORN 60 468 795 0.36
520 RX3 60 396 795 0.312 .048

 

Summary:

 

What can we conclude from the calculations above? Considering that the average speed around a stadium motocross track is about 30 MPH, we can say that the average horsepower loss between a sealed and unsealed chain is approximately 1/50 of one horsepower. Considering that modern 250F motorcycles being raced, generates about 42 horsepower at sea level. 1/50 of a horsepower equals 1/2000 or a 0.05% change. To put that in perspective, engines loose about 3.2% of their power for every 1000-feet of altitude gain. A change of 0.05% would occur with an altitude change of 15-feet. Here is another comparison. Horsepower is lost at a rate of approximately 0.4% for each degree of temperature (F) rise. Therefore a 0.05% power change would result from a temperature rise of 1/10 of one degree Fahrenheit. My opinion is that no one is capable of differentiating the power difference with a 15-foot altitude change or a one-tenth degree temperature change. Likewise no one is capable of feeling the power change between a sealed and an unsealed chain.

 

Which Chain should be on your bike?

 

Based upon the evidence above, that the weight and claimed power losses are of no consequence, you need to make your chain choice solely upon economics, since performance is not an issue. Two factors determine how much you will spend per year on chains:

1 – Riding conditions.

2 – Hours of riding per year.

If you ride primarily on the street, a sealed chain will not last much longer than an unsealed. For a 450cc bike, we are talking in the range of 5000-15000 miles. If you ride in wet muddy conditions off road, a non sealed chain has a life of about 4 hours versus 40 hours on a sealed chain. In dry, dusty conditions I would estimate, based on our experience, the life of an unsealed chain to be from 10-30 hours versus 100-200 hours on a sealed chain.A high quality unsealed chain retails for about $70 and a high quality sealed chain can be bought for about $90.

Summary: If you ride on the road, stay with an unsealed chain. If you ride motocross or off-road for more than 4 hours per year, the $20 additional investment will save you the cost of a new chain in one day of a muddy ride, and if you did not know which chain was installed, you would never have known the difference in performance. I might add that one huge advantage of sealed chains is the rare need to make chain adjustments. It is not uncommon for experienced motocrossers with unsealed chains, to make chain adjustments after every moto. That alone is a testament to chain (and sprocket) wear (not stretch).

 

Author: Greg Burns, Mechanical Engineer, Dirt Tricks Inc.

Last edited: Dec 2, 2014

If you have questions, feel free to email us at:  sales@dirttricks.com