How to choose the right wear ring for your application

Author admin When it comes to choosing the right wear ring, the devil is in the details. Slot design, fixing groove depth and width, and material all play an important role in the performance and lifetime of the component. In this blog post, we'll fill you in on what you should consider when selecting the right wear ring for your application.

Mechanical requirements for wear rings: pressure, speed and lubrication

The most important factor in the selection of wear rings is the pressure (force per area), which acts on the rings in the application. But frequency and speed of movement also play a major role. The type of lubrication and the coefficient of friction should be taken into account too. But why are these values so important? Wear rings that are exposed to high pressure should be made of the most resistant material possible. Self-lubricating fiber-reinforced plastics or steels are commonly used here; however, they have the disadvantage of being heavier and requiring constant lubrication. Speed of movement also plays a role. Depending on the material used, if the product of speed and pressure is too great, the resulting frictional heat cannot be sufficiently dissipated without additional lubrication. The type of lubrication depends on application requirements and the technical characteristics of the wear rings in question. Wear rings made of plastic or plastic fabric are often self-lubricating. Solid lubricants such as PTFE or molybdenum sulphide (MoS2) minimize coefficients of friction and protect the rod or cylinder from wear.

Wear ring shape and dimensions

Wear rings can be mounted in two ways. They can either be fitted on shafts or rods or installed as guides in cylinders. This is why guide rings are slotted -- to provide the necessary clamping force and flexibility. Wear rings also serve as a sealing function or are designed to let lubricating or hydraulic oil through (depending on the shape of the slot). There are also angled and straight slots or form-fitting variants with a Z or tooth profile. Wear rings made of plastic offer the advantage of less complex shaping since plastics can be processed and machined relatively easily and cost-effectively.

Material variety for wear rings

The world of plastics has an especially wide range of materials. Not all of them are suitable for wear rings though. Additives are also required to specifically optimize the material properties for use in wear rings. In addition to improved properties such as elasticity, coefficients of friction, and mechanical stability, the materials differ primarily in their temperature resistance, thermal expansion, and chemical resistance. The properties mentioned above, mechanical strength and elasticity, maximum PV values, and thermal properties can be compared especially well by means of data sheets. But what do they say about component durability and service life? Here the comparison is often difficult. Design programs and formulas, like our plastic bearing service life calculator, can help here. For assistance choosing the right high-performance plastic wear ring for your application, contact us here or call us at (800) 521-. You can also learn more about our maintenance-free iglide bearing materials here. 

Had a persistent oil leak from the head gasket, and rather high oil consumption, so I dismantled the top end of my Commando and noticed signs of piston blow by as you can see in the pics,there is some carbon build up below the scraper rings. I measured the bores, and noticed minimal wear in all directions (less than 0.015mm) although the cilinder walls do show glazing.
My question is : what causes this . Bent conrods seem unlikely since the bottom end has never been apart. The pistons are sill STD size. bike has run approx 90.000km from new., and oil changes and filter replacements were always done after 2-km.
Both pistons show this pattern, could this be caused by crankshaft flex ?
Opinions please.


Measurements were done with a dial type bore gauge and inside micrometer, The RH piston shows the same pattern, although hidden from view on the pics. It could be that the ring lands have worn out as Jim suggests, could it also be that the cilinder bores are out of parallel ?, although this is not easy to check. (inaccuracy in the manufacturing process ? )
Small chance that the rods are bent, although I will do the check with the straight edge.
Thanks for the suggestions so far.
btw, I have good quality measuring equipment,(dial bore gauge and inside micrometers) and do know how to use it. Peter R, I think your assessment is pretty much on the mark. Out of alignment bores is really an obscure one but thought it worth mentioning. Get a feeler gauge and check clearance between the rings and ring lands. Take care not to nacker up the soft aluminum ring lands while doing this. From recollection acceptable clearance is 0." to 0.002". I pulled some race pistons once with 0.004" after many races and seem to recall my homework telling me that 0.004" is too much and my recollection is they started at 0.002". Get with a manufacture or maybe the manual to confirm acceptable clearances.

As for bores, if you do not have access to quality measuring equipment, strip the the pistons and use a feeler gauge between the bore and piston skirt throughout the bore to check for clearances.

You may be able to install new rings, glaze bust or light hone the barrels and go. If the pistons fit are too loose, look to see if new standard pistons make the grade with proper clearance.

Yes, I would also thoroughly check and service the head.

As stated above, unless you are set up for all of this, it is best to get the barrels and pistons to a reputable and preferably Norton experienced shop to sort things out. The pistons and barrel owe you nothing at this point. You had a decent run with them. That is great life from your engine Peter. I am totally impressed with the even wear on the cylinders as you stated:
"I measured the bores, and noticed minimal wear in all directions (less than 0.015mm) although the cilinder walls do show glazing".

I am surprised at the 1/2 thou wear, I believe that is the typical tolerance for a freshly honed cylinder;
0.015mm = 0.". We know that 1mm = .", or as we are more familiar; 1 mil is 40 thou.
Have you compared your cylinder micrometer measurement to the standard bore size? You didn't mention the piston to cylinder clearance; how much is that? I am also wondering if you did a compression test or a leak down test before pulling the head - if so, what was the result? Good luck with your rebuild, and share your progress.

Some more observations: I did the check as suggested by Jim C, cleaned the tops of the pistons, and checked with an accurate straigh edge, this check showed that the conrods are absolutely straight.
I also measured the amount of play of the piston rings in their grooves, I found 7-8 thou of play (or 0.2mm for the metric world). this seems out of spec to me.

I think you found the problem. Not unusual for the mileage. Jim Mr splatt, I have owned this bike since , and although old age and alcohol may have caused some kind of lapse in my memory, (LOL) I do know for certain that the barrel has never been off before. The cylider head has been off a couple of times due to a stripped thread of the exhaust port (around ). And once again due to a leaking head gasket, approx. 8years ago.
The barrels have never been re-sleeved. Thermal distortion between the bores sounds plausible, although this did not concur with my measurements. Time to shop for new pistons. As stated in my earlier post, I got rid of my pistons with around 0.004" ring land clearance. When you think about it, the scraper and compression rings act like an integral pump/check valve. With minor factory recommended ring land clearances, just enough lubrication passes, too much clearance then too much migrates up past the rings.

Hopefully the barrels allow you to drop in new standard OEM pistons with a glaze bust or light hone; be mindful of any ridge at the ends of the ring travel in the barrel. A good shop can sort this out for you and make recommendations on overbore or not. Well there you go , that's what an engine looks like that hasn't been molested by 25 different owners. As has been recommended, new piston and rings and carry on, and hopfully it will be another 50k before you ever see those marks again
Unfortunately new pistons will probably be on minimum size so clearance may not be perfect but it seems a shame to wear it out quicker by reboring