HarleyTechTalk

I came across this video this AM. It speaks to the myth of piston rings don't rotate, as they commonly do in all motors where the rings aren't pinned.

As well taking a cylinder off the piston and rings and then putting the cylinder back on poses no problems to the motor. The rings will rotate anyway. The crosshatch is what drives the rotation.

https://www.motortrend.com/how-to/1803-the-science-behind-piston-rings-and-grooves-explained/

Cool quick video. My first thought before watching was: "Then why does it matter that the ring gaps are oriented they way they are when being assembled". They addressed that.

Zach

I had a phone conversation with one of the techs at Total Seal last summer. He confirmed that rings do rotate by design. He said if for no other reason to keep from having a score mark in the cylinder if the gap of the ring never moved. I do remember that two cycle dirt bike motors that I owned as a kid were pinned to not rotate. But I always assumed that was to keep the ring end from grabbing a port in the cylinder.

This was just the first video I've ever seen that just spells it out. Like the link to the Motortrend article, they speak to ring rotation if you read down to about halfway.

This video may help understand the physics or ring rotation too.  One good takeaway is the description of how the common 45 degree crosshatch angle is calculated.  the other is what deviation from the prescribed angle does. 

I picked up several of these gauges at their SEMA booth about 10 years age.  They have a thin pad on the back to stabilize then while you inspect the angle.

Well I've never actually measured it but I always thought cross hatching was supposed to 60 degrees. I have never honed a cylinder myself. I have had it done at shops and I have also bought fresh cylinders. Just eyeballing it's always looked to me to about 60 degrees. I'm talking about the horizontal section of the "X". That'd be 30 on that plastic gauge? Whatever, I knew cross hatching was associated with ring seal but I did not know/never thought about cross hatch angle affecting ring rotation speed. Makes perfect sense. Thanks for exercising my grey matter!