Technical Articles

Chain Tips

There are several ‘keys’ to trouble free, chain drive, touring. The basics are:

  1. a good set of sprockets;
  2. a chain that has not excessively stretched;
  3. internal, chain lubrication;
  4. proper sprocket alignment,
  5. and not getting the chain too tight.

 On chain driven vehicles, most of the wear occurs on the small sprocket. If this sprocket is worn, you will never have really trouble-free touring.

 As the chain stretches and the sprocket wears, the load gradually shifts to the top tooth only! This increases strain on the single link of chain, accelerating stretch and further aggravating the problem.

 If the small sprocket is worn, the only solution is to replace it: either by machining out the center of an appropriate sprocket and having it pressed onto your machined original (generally easiest and very satisfactory); or by getting a new sprocket with a thick enough center to be machined as a replacement for the worn sprocket.

 When rebuilt, the load is carried on several rollers, and wear and stretch are minimized. Failure to maintain the sprocket can result in potentially damaging and dangerous breakages.

 As the chain travels over the sprockets, the load goes through the roller, to a hardened pin, and then through the pin to the links. As it goes around the sprocket there is motion relative to the pin and roller — these surfaces must be lubricated.

 Most chains are oily on the outside, but this is of little value, and perhaps even a negative as dust and debris get in the oil and it becomes a grinding paste.

 The key is getting the oil inside the rollers. Don’t rely on the spray can spray lubricant used on motorcycle chains (another thing of the past) and bicycle chains. These have a light oil in a carrier that evaporates quickly, leaving the oil in place. Sounds great, but the oil is much too light for the loads in most automobiles, and is soon forced out.

 To successfully oil the chain it needs to be removed from the car (a good time to check for stretch — more on that later!). Clean the chain thoroughly, kerosene or diesel make good cleaners, but any good solvent will do. Be sure to get rid of all debris and dirt. Then find the deepest container practical to hold your favorite chain lubricant (wish there was a best — but lubing chains is like fishing, everyone has a best technique). Some people still claim the best lubricant is from the boiled fat of a hog, but in most parts of the country, ‘Hog Killing Days’ are a thing of the past (so not real practical). I have had good luck with a mixture of a light, synthetic gear lube and diesel, others use diesel or kerosene and 30 or 40 weight motor oil, while others use light steam cylinder oil and kerosene. If you can safely heat the mixture to lower viscosity it is even more effective. Put your favorite in the deep container, the added pressure of the depth, ever so slight, greatly increases the effectiveness, and put the chain in. Leave for several days, rotating occasionally so all links spend some time at the bottom. Be safe and don’t do near open flame.

 When you remove the chain, wipe the exterior off thoroughly, the lubrication you want is on the inside. A well lubed chain should go a season or two without needing further lubrication. Keep the outside wiped off and clean.



 Always replace chain exactly as it came off the car — same side out, same side to sprockets. File a mark on a side plate as a reminder. On dual chain drive, do not switch sides. Deviation from these practices accelerates chain wear.


Is the Chain is too worn?

Chain is too worn, that is too stretched, when the pitch has increased by three percent (3%). Lay the chain on a flat surface and stretch it out (preferably after cleaning so all the ‘gunk’ is out of the gap between pin and roller). Count 20 pitches (20 pins) and measure the length. Multiplying the pitch by 20 gives the original length. For example, in 1″ (one inch) pitch chain the length should be 20 inches. 3% of 20 inches is about 5/8″, so a 1″ pitch chain with a 20 pitch length of 20 and 5/8″ or greater is excessively stretched and should be replaced.


Running chain too tight?

Running chain too tight is a serious fault, and will surely result in failure! Everything, including shaft bearings, is at risk. Too loose does not hurt, the risk is jumping and/or clinging. The correct tension is easy to find. Measure the tangent length (where the chain first contacts the sprockets on the tight side of the chain. Use the following values to determine correct up and down flop on the bottom or sag side: Tangent length 20 inches, minimum flop = 1/2″; tangent length 30″, minimum flop 3/4″; tangent length 40″, minimum flop = 1″; tangent length 60″, minimum flop = 1 and 1/4″. Interpolate to approximate other values.

Unfortunately, engineering was not always the best on early cars, and very few have radius rods that are correct geometrically, and the chain gets tighter at either extreme compression or extreme extension of the springs. You need to check extension by jacking up the frame, and compression by loading or bouncing the rear of the car. If the chain over-tightens you are courting disaster — sooner or later failure is inevitable! Adjust the chain so that flop is within limits at the extremes; if that makes the chain too loose at ‘normal’ position, you may need to put limiting straps on your rear axle.

If you have double chain drive, watch rear axle alignment; tighten or extend radius rods as necessary, and be sure lock nuts are tightened. Because of road camber, the right side (in countries where we drive on the right, obviously opposite in areas where we drive on the left) works harder and has the most wear. Chain and tire wear will be quite uneven. You may rotate tires, but you cannot rotate the chains, as they wear in to fit alignment and sprockets.

Finally, in automotive usage we frequently exceed the design limits of chain, and that makes good chain lubrication and maintenance even more important. Consider the following ‘lubrication speed limits:’ number 50 (pitch 5/8″), feet/minute limit 1,900, tensile strength 6,600 lbs.; number 60 (pitch 3/4″), feet/minute 1,750, tensile strength 8,500 lbs.; number 80 (pitch 1″), feet/minute 1,475, tensile strength 14,500 lbs.; number 100 (pitch 1 and 14″), feet/minute 1,250, tensile strength 24,000 lbs.

Automobiles work at and above these lubrication speed limits. A seven inch sprocket at 1,000 rpm travels at 1,832 feet per minute at the outer edge; a ten inch sprocket travels at 2,618 feet per minute at the outer edge. These rates tend to throw out light lubricants, going back to the start — lube the chains well. Do not be tempted to use ‘self lubricating chain.’ These chains use sintered iron to retain lubrication at the pin and roller interface. Unfortunately, the speed and load on automotive chains are too great for this type of chain.

Any chain break can be destructive to the car and even the occupants.  In the old days there were many serious injuries (and even a few verified decapitations) when chain would break at speed. Keep yourself and our hobby safe, and inspect those chains and lubricate them properly.