Topic: keeping ring grooves where they were or restaggering them 120'

[Redline it]

something strange happened that answered a lot of questions or doubt about rings wearing into a specific "set" of cylinder ovals and tapers. a carbon cleaning project on a 400f with worn but within specs pistons and rings and bores. scraped a lot of carbon from under the rings, that restricted ring travel. and some on this site believe that keeping the ring gaps where they were during disassembly is important because of a set pattern of wear on the rings due to bore/piston oval or tapers. so after cleaning the rings were  a lot more free to move around the pistons.

assembly they were set according to honda at 120' apart. that was followed well by using ring compressor that kept the rings in position while inserting them into the bores. the bike then ran for no more 4 or 5 minutes max, and for other reasons the cylinders were then removed to find that 3 pistons had number 2 rings that migrated at least 120' to almost match perfectly the gaps in the top rings. and the pistons after the first disassembly had obvious wear marks of where the ring gaps were, by a little dark trail of where gasses had passed through the gaps, the marks were below the gaps, so they were staying in place long enough to get that mark.

[bryanj]

A marine engine i worked on as an apprentice eons ago was proved that the rings rotated 6 times per hour when flat out at 110rpm--------bore 1meter stroke 2 meter piston weight 1.5 tonne and rings 2inch square cross section.

[robvangulik]

And so do these rings, you wrote that they only ran for a few minutes, what do you think will happen when riding at 8000 rpm for an hour?

[maxheadflow]

Rings do rotate in the bore when operating correctly.   A big issue with getting this to happen is using the correct angle of the cross hatch when honing.  If they stop spinning you can have issues.

[Tracksnblades1]

A marine engine i worked on as an apprentice eons ago was proved that the rings rotated 6 times per hour when flat out at 110rpm--------bore 1meter stroke 2 meter piston weight 1.5 tonne and rings 2inch square cross section.

+1

While I don't know any thing about those little bitty 😳marine pistons BrainJ mentioned.

I do know the late great Smokey Yunick wrote extensively about ring rotation and the need for torque plates primarily because of it. Since his favorite Chevrolet cylinder pulls in, at the upper most part of the bore adjacent to the head bolts/studs by several thousands. He wrote in his books that if the rings were not made to rotate they may eventually seal after the wore in.

Revisiting a Chevrolet engine manual, it is interesting where they recommended the top ring end gap to be positioned on each bank. Considering major and minor thrust, it makes since. Until you read the rings are engineered to rotate. My question would be " Does the rings maintain there original stagger to each other on the individual piston"...?  I say not.

I saw a little piston like Brain mentioned. I think it was on a FairBanks Morse engine. A man was standing on it, scraping carbon off of the top of it with a shovel.....

[jgger]

All this is interesting,  so 2 strokes are different?  I remember the 2 strokes I used to ride having a pin in the ring groove to keep them from rotating. What's the theory on that?

[bryanj]

The main reason 2 strokes are pinned is to stop the ends catching on the port edges.

If you guys would like to google Doxford marine diesel you will see some biggish stuff, always an odd number of cylinders and there used to be a video of a running one.

[jgger]

Now that makes sense, thanks. Somehow I vaguely remember that, I might be getting part timers.

[dave500]

rings may or may not rotate,one may go clockwise the others counterclockwise,they may go part way then back again over and over.

[Redline it]

A marine engine i worked on as an apprentice eons ago was proved that the rings rotated 6 times per hour when flat out at 110rpm--------bore 1meter stroke 2 meter piston weight 1.5 tonne and rings 2inch square cross section.

6 times? they're moving.

that's a big piston, be nice to have one and a sleeve or liner. build a combustion/expansion chamber under the piston, like a large cannon, or spud launcher.

[dave500]

lifters in older pushrod car motors had the geometry offset to force a rotation of the lifter and or valve,if the rings rotate its a good fluke with no control or design.

[Redline it]

lifters in older pushrod car motors had the geometry offset to force a rotation of the lifter and or valve,if the rings rotate its a good fluke with no control or design.

i couldn't count how many hours i festered on putting them just right, and trying to piece together the 2 dimensional drawings honda uses to illustrate that perfect arrangement is pretty difficult not to mention offsetting 3 gaps 120' apart and staying away from inline with the pin or right angles to it. that doesn't leave any margin of error except a few degrees. maybe in a new bore and rings it's more critical. it's like putting the moly disulfide grease on the valve stems, i did that once, and had to take it apart again but this time because  head and cylinders got some dust/carbon particles stuck to it the oily areas, i washed them in a air pressured kerosene bath, then blew it dry, i aint gonna take the valves out again for that grease, or should i? it's killing me.  i can't figure out if anything more than 2 dowel pins set the base gasket. the front studs have dirt in gaps around the studs, picking that out is a night mare trying keep dirt out of the crank case.