To the OP
From a reliability perspective on chain drives there are several things that can be done to increase overall service life but they are usually severely limited in practice because of the effort to benefit ratio in terms of cost, time etc. so even if possible may not be worth the effort.
A little primer on chains here (good information if nothing else)
From my perspective (Mechanical Engineering) a chain is a chain is a chain. They all function identically regardless of the application and have the same failure modes. In my career I have done everything from application engineering, detailed failure analysis, finite element analysis and applicable predictive/NDT techniques to monitor in service. It always boils down to the same failure modes just in different percentages depending on the application and maintenance of the machine in question.
Over the years I have worked with every chain and sprocket manufacturer there is over a multitude of industrial applications. Very little changes and little can be done to extend their life but not because the technology is not there but the cost of the maintenance and tensioning systems often exceeds the cost of replacing the chains so they give minimal maintenance and basically run to fail. (a business decision, not a maintenance decision)
First we have to be on the same page regarding terminology because engineering terms and conversational terms often contradict and confuse.
Chains do not stretch (that is a misnomer), they elongate due to a combination of pin wear and roller wear increasing clearance on critical tolerances. This wear is a result of a combination of factors. (For a baseline purposes, this is assuming new chains/sprockets and not a combination of new and worn items in a proper application. When new and worn components are on the same run, accelerated wear and short lifespan is a guaranteed certainty and not considered a failure mode of the chain or sprocket because that is a human decision outside the functional properties of the components)
They are: (in no particular order)
Load on the chain (not to be confused with tension) [in cases where the application is correctly engineered- the main focus is on shock loading rather than continuous loading]
Tension of the chain (not to be confused with load)
Pin lubrication/contamination (internal to the roller)
Roller lubrication/contamination (relative to the roller/sprocket)
Misalignment of the sprocket/chain (static or dynamic)
Worn components (beyond the scope of this discussion)
Almost universally the major cause of elongation and enabler of overall wear is loss of lubrication of the pin. Even with solid lubricants, o ring chains and a variety of metallurgies- this is going to happen eventually. It would surprise a lot of people that regardless of how much oil/grease you put ON a chain, little to none of it will work into the pin. Only total immersion systems or soaking will accomplish this adequately. The problem with that is that these systems are messy and are loss systems so they add cost. Manual soaking is time and labor intensive (in terms of maintenance hours as well as downtime).
I do virtually nothing on cars or other rolling stock (other than for me personally) but the automotive timing chain is no mechanically or functionally different than any timing chain arrangement on any other machine on Earth so what I am about to say is directly applicable.
The major problem you are going to encounter (just like I encounter) is that most reliability solutions are going to require modifications to the machine that are either too costly or not realistically possible when measured against the replacement cost of the chain group.
Lubrication (sprocket to chain)- oils as a general rule are not EP lubricants and when you are talking the metal to metal contact during tooth integration as experienced on a sprocket, modern tribology doesn’t have a formula (chemistry or application) that will effectively mitigate that effect.
Splashing, pouring or sumping will not withstand the force encountered when the metal contacts the metal. You can slow it but not arrest it to any significant degree. The only known technology that is effective is oil mist but that’s not practical in this type of application.
(It is significantly different on a gear set but that’s because of the tooth geometry, contact area and oil galley formed at the root- sprockets and chains don’t have this)
Lubrication ( pin to roller)- given the tight tolerances of the average roller chain, even emersion systems don’t have the ability to get in there much because of the RPM ( contact and soak time), Clearances of the components (ability to get in there while under dynamic load, i.e. running) and finally centrifugal forces wanting to sling the oil off. (Not to mention the pin opening and closing the clearance creating a pumping effect)
Alignment- depending on the TIR of the crank and cam and their relative alignment, this is rarely correctible even when detected but should be checked.
Tension- “load” (defined as the force of the driven components) is never a factor with a properly specified chain/sprocket set up but “slapping” of the roller/tooth due to uneven tension causes more damage than lubrication ever will. This changes the sprocket geometry and root gap and once created cannot be altered. (Everyone in the business has seen the “wallowed” sprocket)
Sprockets like gears only have load on 3 teeth at any one time at the incoming run. The rest of the chain just rides. As the gaps open and the teeth brads/wears this arrangement changes to the point where there is random tension all over the chain during the engagement.
Once this condition appears, no known technology or lubricant can mitigate it other than full replacement.
In short, every mechanical reliability engineer I know has done everything possible (in the field and under laboratory controlled destructive testing) to reduce this type wear and the answer is always the same. The cost of specialty heat/cold treatment, alloy recipes, lubrication systems, machine modifications et al far exceed the replacement costs of the chains/sprockets.
The best solution (when feasible) is to upgrade to a timing belt/poly chain but depending on the bearing arrangement, shaft diameter and tensioning ability this isn’t always the best answer either.
If anyone ever does come up with an effective cost beneficial method to reduce this type wear, he or she will become the richest person on this planet.
From a reliability perspective on chain drives there are several things that can be done to increase overall service life but they are usually severely limited in practice because of the effort to benefit ratio in terms of cost, time etc. so even if possible may not be worth the effort.
A little primer on chains here (good information if nothing else)
From my perspective (Mechanical Engineering) a chain is a chain is a chain. They all function identically regardless of the application and have the same failure modes. In my career I have done everything from application engineering, detailed failure analysis, finite element analysis and applicable predictive/NDT techniques to monitor in service. It always boils down to the same failure modes just in different percentages depending on the application and maintenance of the machine in question.
Over the years I have worked with every chain and sprocket manufacturer there is over a multitude of industrial applications. Very little changes and little can be done to extend their life but not because the technology is not there but the cost of the maintenance and tensioning systems often exceeds the cost of replacing the chains so they give minimal maintenance and basically run to fail. (a business decision, not a maintenance decision)
First we have to be on the same page regarding terminology because engineering terms and conversational terms often contradict and confuse.
Chains do not stretch (that is a misnomer), they elongate due to a combination of pin wear and roller wear increasing clearance on critical tolerances. This wear is a result of a combination of factors. (For a baseline purposes, this is assuming new chains/sprockets and not a combination of new and worn items in a proper application. When new and worn components are on the same run, accelerated wear and short lifespan is a guaranteed certainty and not considered a failure mode of the chain or sprocket because that is a human decision outside the functional properties of the components)
They are: (in no particular order)
Load on the chain (not to be confused with tension) [in cases where the application is correctly engineered- the main focus is on shock loading rather than continuous loading]
Tension of the chain (not to be confused with load)
Pin lubrication/contamination (internal to the roller)
Roller lubrication/contamination (relative to the roller/sprocket)
Misalignment of the sprocket/chain (static or dynamic)
Worn components (beyond the scope of this discussion)
Almost universally the major cause of elongation and enabler of overall wear is loss of lubrication of the pin. Even with solid lubricants, o ring chains and a variety of metallurgies- this is going to happen eventually. It would surprise a lot of people that regardless of how much oil/grease you put ON a chain, little to none of it will work into the pin. Only total immersion systems or soaking will accomplish this adequately. The problem with that is that these systems are messy and are loss systems so they add cost. Manual soaking is time and labor intensive (in terms of maintenance hours as well as downtime).
I do virtually nothing on cars or other rolling stock (other than for me personally) but the automotive timing chain is no mechanically or functionally different than any timing chain arrangement on any other machine on Earth so what I am about to say is directly applicable.
The major problem you are going to encounter (just like I encounter) is that most reliability solutions are going to require modifications to the machine that are either too costly or not realistically possible when measured against the replacement cost of the chain group.
Lubrication (sprocket to chain)- oils as a general rule are not EP lubricants and when you are talking the metal to metal contact during tooth integration as experienced on a sprocket, modern tribology doesn’t have a formula (chemistry or application) that will effectively mitigate that effect.
Splashing, pouring or sumping will not withstand the force encountered when the metal contacts the metal. You can slow it but not arrest it to any significant degree. The only known technology that is effective is oil mist but that’s not practical in this type of application.
(It is significantly different on a gear set but that’s because of the tooth geometry, contact area and oil galley formed at the root- sprockets and chains don’t have this)
Lubrication ( pin to roller)- given the tight tolerances of the average roller chain, even emersion systems don’t have the ability to get in there much because of the RPM ( contact and soak time), Clearances of the components (ability to get in there while under dynamic load, i.e. running) and finally centrifugal forces wanting to sling the oil off. (Not to mention the pin opening and closing the clearance creating a pumping effect)
Alignment- depending on the TIR of the crank and cam and their relative alignment, this is rarely correctible even when detected but should be checked.
Tension- “load” (defined as the force of the driven components) is never a factor with a properly specified chain/sprocket set up but “slapping” of the roller/tooth due to uneven tension causes more damage than lubrication ever will. This changes the sprocket geometry and root gap and once created cannot be altered. (Everyone in the business has seen the “wallowed” sprocket)
Sprockets like gears only have load on 3 teeth at any one time at the incoming run. The rest of the chain just rides. As the gaps open and the teeth brads/wears this arrangement changes to the point where there is random tension all over the chain during the engagement.
Once this condition appears, no known technology or lubricant can mitigate it other than full replacement.
In short, every mechanical reliability engineer I know has done everything possible (in the field and under laboratory controlled destructive testing) to reduce this type wear and the answer is always the same. The cost of specialty heat/cold treatment, alloy recipes, lubrication systems, machine modifications et al far exceed the replacement costs of the chains/sprockets.
The best solution (when feasible) is to upgrade to a timing belt/poly chain but depending on the bearing arrangement, shaft diameter and tensioning ability this isn’t always the best answer either.
If anyone ever does come up with an effective cost beneficial method to reduce this type wear, he or she will become the richest person on this planet.
