HarleyTechTalk

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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.

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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.

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

Quote from: FSG on April 16, 2024, 09:25:32 PMa good pic is worth a 1000 words   

Speaking of pictures...I measured the old vs. new rotor and found the below numbers.
When I installed the new rotor a couple weeks ago, I left the shim in and therefore the sprocket would have been 0.020" more outboard than the previous rotor..... Would that have been enough to cause the knocking I was hearing? or is it still more likely tied to the comp either being too little torque or the nut bottoming out?

Regardless, I'm going to shorten the comp nut today. Then I'll reinstall, torque properly, and make doubly sure the sprocket alignments is correct.

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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 possess 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/

I've been trying to remember what I did with my '75 but it's been over 40 years.
Give it a shot & see what happens. If you run into any problems maybe it will jog my memory.