HarleyTechTalk

I'm not going to have a big argument about piston rings and rotation.  But I will say this.  In my experience, limited as it is, they do not normally rotate.  The basis for that is having worked for Chrysler when certain disgruntled union members were lining up ring gaps as they built engines.  Chrysler and their ring supplier did some real extensive investigations on that.  And at no time did they find rings had moved away from their set up locations.

Then later on I was having ring failures in a motor setup and worked with Seal Power to try and run it down.  Turned out to be another issue and not the rings.  But during that process one of the things that was done was to dimple the pistons where the gaps were located.  None of the rings moved in the three engines that this was done on. 

Now, that does not mean that rings can't move.  Just that they are not expected to rotate around the piston in service.  We know that failing to cross hatch cylinder walls will cause them to rotate.  And there are some issues with side port cylinders.   

A two stroke was mentioned above.  That's a whole nother creature.  The shape of the port in the cylinder wall can drive the rings and cause them to rotate.  And with some designs, the end of the ring can get caught by the port edge.  It's a port shape issue, not a ring issue.  Yamahas come to mind, they will sometimes break the locator pins and come to a bad end.  The fix is to either pin the rings or taper the port edges.  By far, most use tapered ports.

So what about the issue the op has?

Installing the expander so that it is resistant to dropping out of expansion might be all that is needed to prevent the rings from coming into gap alignment.  And is certainly one of those best practices sort of thing.  Or not. 

Although the MoCo makes no mention of it in the installation instructions.  it is probably a good thing to do.   It is a known an issue that is seen on pistons with wide oil drain slots.  But most MoCo pistons use very small drain slots.  Or none at all as is the case with the new Mahle 110 high compression slugs.

How did the lower ring get pushed out of alignment and bent as the photo shows.  And with the OPs issue, how did it happen on both jugs in an almost identical way?

The one piston looks as if the ring caught a drain slot.  On the other the end is obviously bent, but not in a oil drain.  I'm pretty sure that both are bent, just in different areas of the ring.  And the misalignment of the lower ring caused the other rings to rotate into alignment.  First the expander and top oil ring moved as a unit, until the expander gap met the lower ring gap and misaligned.  Then the upper ring continued to rotate until its gap met the expander gap and locked into place.  The bent lower ring drives the rotation, and acts like a sprag to keep it going.  So how did this happen?  The bent ring is the tell. 

I'll offer explanation.  The lower oil ring is escaping the ring compressor before it enters the jug, and is damaged in the process.  The bent lower ring being the issue that causes the problem.  And this is on the person who did the assembly.  Again, think about it.  If just having a oil ring gaps rotate randomly into alignment would creat a real big issue.  Most of them would eventually end up in alignment.

And, anyone who has bottom loaded pistons into jugs should know how easy it is to have that last oil ring escape the ring compressor before fully entering the jug.  The proof on this would be to carefully remove that oil ring, so as to not damage it further.  Then see if there is a bend or radial rotation of the ring.

Now back to that most of the explanation thing.  Why did they both end up at the rear of the piston?  I thought on this a while and ended up with the mechanic again.  But it's just an opinion.  I'm thinking that when the lower ring gets bent on assembly, it's fixed in place.  The other rings are driven into rotation until they line up with it.  And the person loading the rings on the pistons repeated the process the same way on both pistons. 

A couple of observations.  the one photo shows the bent lower ring aligned with an oil drain slot.  In the other it is not.  That leads me to believe that it is not an issue caused by the slot.   What I see them having in common is some twist in the lower ring. 

   

More data for perusing.


https://www.highpowermedia.com/blog/3954/rotation-of-piston-rings


https://inis.iaea.org/search/search.aspx?orig_q=RN:30059348

This link contains a lot of very useful info regarding piston rings, their design, pistons, and lubrication.


Piston Rings for Combustion Engines

Quote from: Nutoy on March 04, 2018, 07:27:26 AM
FDT what brand piston are those I have not seen piston with oil return holes in the bottom of oil ring land?

OEM 96/103 pistons have the drain slots just like those in the photos.

SE 110 drop on kit pistons are like that.  Bob

Wiseco is like that.

http://blog.wiseco.com/show-your-harley-some-love-with-wiseco-black-edition-pistons-featuring-armorx-and-armorfit


My CP's are also, but, by design they have a lower ring support rail due to the cutaway in the wrist pin area. The rail supports the oil control ring pack and gives it a solid base to ride against.

[attach=0]

The new Mahle pistons for the steel lined 110 jugs don't have the drain slots.

Quote from: Nutoy on March 04, 2018, 07:27:26 AM
FDT what brand piston are those I have not seen piston with oil return holes in the bottom of oil ring land?

I guess they came with the S&S 106 kit, i didnt install this kit.

Quote from: Thermodyne on March 04, 2018, 12:59:07 PM
The new Mahle pistons for the steel lined 110 jugs don't have the drain slots.

Look at my picture  they are from that exact kit. Over both skirts are drain slots.  Bob

Quote from: FXDBI on March 04, 2018, 04:25:23 PM

Quote from: Thermodyne on March 04, 2018, 12:59:07 PM
The new Mahle pistons for the steel lined 110 jugs don't have the drain slots.

Look at my picture  they are from that exact kit. Over both skirts are drain slots.  Bob

Because this is a fresh kit, you must have the instruction sheet. Does S&S indicate the proper orientation (according to them) for the expansion ring?  Does it say M or W?

Quote from: kd on March 04, 2018, 04:56:12 PM

Quote from: FXDBI on March 04, 2018, 04:25:23 PM

Quote from: Thermodyne on March 04, 2018, 12:59:07 PM
The new Mahle pistons for the steel lined 110 jugs don't have the drain slots.

Look at my picture  they are from that exact kit. Over both skirts are drain slots.  Bob

Because this is a fresh kit, you must have the instruction sheet. Does S&S indicate the proper orientation (according to them) for the expansion ring?  Does it say M or W?

W

I'll offer explanation.  The lower oil ring is escaping the ring compressor before it enters the jug, and is damaged in the process.  The bent lower ring being the issue that causes the problem.  And this is on the person who did the assembly.  Again, think about it.  If just having a oil ring gaps rotate randomly into alignment would creat a real big issue.  Most of them would eventually end up in alignment.
If it wasn't for the 10k kms already on the top end i would say highly possible, but i guess we will never know for sure.

In the first picture of the piston on page 1, it looks to me like one of the valves was making contact with the head. Is that just an illusion?                       


Joel 2001 FLHT

Quote from: joelp34252 on March 05, 2018, 07:40:44 AM
In the first picture of the piston on page 1, it looks to me like one of the valves was making contact with the head. Is that just an illusion?                       


Joel 2001 FLHT

If you enlarge it and look real close you'll see it is the light reflecting off of the wet oil pooling on the piston.

Quote from: FXDBI on March 04, 2018, 04:25:23 PM

Quote from: Thermodyne on March 04, 2018, 12:59:07 PM
The new Mahle pistons for the steel lined 110 jugs don't have the drain slots.

Look at my picture  they are from that exact kit. Over both skirts are drain slots.  Bob

I just installed a 110 kit, no exterior drain slots in the Mahle pistons.  10.2:1 pistons.  Part number on the piston is MoCo 2190050

Quote from: Thermodyne on March 05, 2018, 08:47:39 AM

Quote from: FXDBI on March 04, 2018, 04:25:23 PM

Quote from: Thermodyne on March 04, 2018, 12:59:07 PM
The new Mahle pistons for the steel lined 110 jugs don't have the drain slots.

Look at my picture  they are from that exact kit. Over both skirts are drain slots.  Bob

I just installed a 110 kit, no exterior drain slots in the Mahle pistons.  10.2:1 pistons.  Part number on the piston is MoCo 2190050

I have the SE 110 drop on kit piston part number is 21900051, has you can see in the picture I posted it has 2 oil returns on each thrust face side. The kit the pistons were included with are #92500039.  Pistons have a manufacture date on them 15/05/20  Bob

Thrust side.      Pistons are coated as well.  Bob

Quote from: FXDBI on March 05, 2018, 10:02:15 AM

Quote from: Thermodyne on March 05, 2018, 08:47:39 AM

Quote from: FXDBI on March 04, 2018, 04:25:23 PM

Quote from: Thermodyne on March 04, 2018, 12:59:07 PM
The new Mahle pistons for the steel lined 110 jugs don't have the drain slots.

Look at my picture  they are from that exact kit. Over both skirts are drain slots.  Bob

I just installed a 110 kit, no exterior drain slots in the Mahle pistons.  10.2:1 pistons.  Part number on the piston is MoCo 2190050

I have the SE 110 drop on kit piston part number is 21900051, has you can see in the picture I posted it has 2 oil returns on each thrust face side. The kit the pistons were included with are #92500039.  Pistons have a manufacture date on them 15/05/20  Bob

Mine are a different kit, with different compression, no idea as to what changes in the pistons with the PN change.



Here the instructions that came with them as far as rings.

Quote from: kd on March 03, 2018, 03:42:21 PM
The reason I asked for a more accurate description of the cam was I had noticed that the overlap on mine caused carry-over of the oil into the front intake port of the manifold and head.

When you look at the finish in the cylinders, can you see a shadowy linear figure up the length along where the studs are?

Now i have had time to have a decent look i do see a shadow line both where all the studs are, and also where the dowels.
I have checked the cylinder with torque plates on ( didnt really see a lot of difference in the measurements) but funny enough the cylinders were tighter from front to rear, they have about .002 extra width to them.

Quote from: FDT on March 08, 2018, 12:59:28 AM

Quote from: kd on March 03, 2018, 03:42:21 PM
The reason I asked for a more accurate description of the cam was I had noticed that the overlap on mine caused carry-over of the oil into the front intake port of the manifold and head.

When you look at the finish in the cylinders, can you see a shadowy linear figure up the length along where the studs are?

Now i have had time to have a decent look i do see a shadow line both where all the studs are, and also where the dowels.
I have checked the cylinder with torque plates on ( didnt really see a lot of difference in the measurements) but funny enough the cylinders were tighter from front to rear, they have about .002 extra width to them.

Common distortion on HD cylinders due to the cylinder design.

Quote from: 1FSTRK on March 08, 2018, 03:40:57 AM

Quote from: FDT on March 08, 2018, 12:59:28 AM

Quote from: kd on March 03, 2018, 03:42:21 PM
The reason I asked for a more accurate description of the cam was I had noticed that the overlap on mine caused carry-over of the oil into the front intake port of the manifold and head.

When you look at the finish in the cylinders, can you see a shadowy linear figure up the length along where the studs are?

Now i have had time to have a decent look i do see a shadow line both where all the studs are, and also where the dowels.
I have checked the cylinder with torque plates on ( didnt really see a lot of difference in the measurements) but funny enough the cylinders were tighter from front to rear, they have about .002 extra width to them.

Common distortion on HD cylinders due to the cylinder design.

Are you saying .002 on the outside spigot dimension, or bore?

I would bet the bore.

Quote from: 1FSTRK on March 08, 2018, 06:39:08 AM
I would bet the bore.

yes the bore.
so the rings lined up o the narrowest part of the bore, not the widest as you have seen before.