I tried searching and reading the FSM and the rebuild book. They touch on it but I am pretty dim witted so....

piston 12 o clock is the front of the piston as if it was installed in the engine. So example the piston pin is front 12 o'clock and back 6 o'clock

Gaps at o'clock please

1) bottom oil control ring at "  " o'clock

2) oil ring expander ring at "  " o'clock

3) top oil control ring at "  " o'clock

4) bottom compression ring at "  " o'clock

5) top compression ring at "  " o'clock

 

 

 

Edited May 24, 20204 yr by Dave WM

It's been awhile but 12 oclock from what I remember was the windshield then 3 would be driver's side, 6 radiator and 9 passenger's side. There is that little nick showing the front of the cup which would be the radiator.

Good timing. I'm messing with the same thing right now.

I didn't find "clear cut positions" anywhere either, but I believe the overarching gap position rules go like this:

1) All the gaps should be at a 45 degree angle away from the piston pin center
2) The 4th (bottom) ring and second ring gaps should both be in the same as position
3) The 3rd ring and top ring gaps should be 180 degrees away from bottom and 2nd
4) oil wavy ring gap (expander) should be 90 degrees from all the other rings

Some additional rules, not specifically related to gaps, but since we're talking about rings, it's probably appropriate to mention them here:

5) Put the wavy expander in first and make sure the split portion is titts down, like an "M".
6) The thin 3rd and 4th rings do not have a top/bottom. Doesn't matter.
7) 2nd and top rings DO have a top and bottom and make sure you have identified that and get them on correctly.

So, interpreting those rules... Put the waver scraper ring on first. Pick a position for the gap. The rule is "45 degrees from piston pin", so you have four choices - 1:30, 4:30, 7:30, or 10:30. And then once you have picked a position for the expander, the rest of the positions should fall into place.

An example:

Put your wavy expander at 4:30. This mean that all your other gaps must be at 1:30 and 7:30. Fourth and second being the same at either 1:30 or 7:30, but third and first must be opposite.

I looked closely at my block and tried to figure out where the rings originally were from the factory and then when I put the new rings in, I tried to put them somewhere ELSE this time. Figuring I would "even things out". Not sure it makes much difference, but that's my plan.

Before I put the rings on, I marked the piston tops with sharpie to make it easier for my little brain to keep things straight while moving the gaps around. I'll clean the sharpie off after the pistons are installed. Looks like this:

However, all that said, please note that I'm no expert in such matters and give a little time for other people to throw their bodies in front of advice before you put all your pistons in. I'd like to give other people some time to tell me just how wrong I am before you go and repeat mistakes that I've made.

It would be interesting to see where they are on an engine being disassembled.  I think that they "walk" over time anyway.  I thought that the starting offset was more just to improve the odds of not grooving a cylinder wall or getting poor sealing.  I don't know though.

My understanding is that the starting offset was to maximize the length of the path between compression and non-compression. The longer the labyrinth, the less leakage. And staggering the gaps +180,  -180,  +180,  -180  is the best you can do.

And while some things are designed to "walk", I don't think the rings are one of them. I believe the gaps are intended to stay where you put them.

But all of this is why I'm hoping some of the engine builder experts will chime in. I have all my rings on pistons but haven't put the pistons back in the block yet. I still have time to completely change all my gap locations if someone throws their body in front of what I'm planning.

I’m no expert but play one on TV.

I did mine per the FSM. The 77 FSM doesn’t mention the oil ring but the 82 FMS does.


You need to be careful when using the ring compressor when installing them as it will cause the rings to migrate. I had to redo a couple. You’ll need to verify them afterwards. You can either use a d flashlight or rotate to crank and look for oil witness marks. See attached pics.






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I find the pictures from all the FSM's a little confusion because they don't put the FRONT notch up top. All those FSM manual pics have the piston pin running side-to-side instead of top-to-bottom, and I just find it confusing because I want the notch at the top. To get the FRONT notch at the 12:00 position, you have to rotate that sketch. And also interesting to note that they do not specify "FRONT" at all. Just the piston pin direction. Seems it really doesn't matter which is FRONT. You could rotate that sketch either direction and it would still be right.

I rotated it and put on the two possible FRONT notch locations:

Either of those FRONT locations would follow the "rules".

The FSM shows the pressure rings all at 4:30 and 10:30, but I don't see any reason why 1:30 or 7:30 would be any different.

2 hours ago, Captain Obvious said:

And while some things are designed to "walk", I don't think the rings are one of them. I believe the gaps are intended to stay where you put them.

My point was about what happens, not what was designed to happen.

Many two-stroke engine pistons have a peg in the groove and the ring ends are shaped to fit the peg.  that's a design meant not to walk.

http://m.2strokeengine.net/gordonjennings/twostroketunershandbook.php

My thoroughness is letting my coffee get cold...

https://fpsdistribution.com/articles/piston-ring-gaps-preventing-engine-damage/

"

Aligning Ring Gaps

Unless pegged, all piston rings slowly rotate round in their grooves while the engine is running. For this reason, it isn’t important to make sure the ring gaps are aligned – though you may find it easier for fitting if you stagger the ring gaps before you apply a ring clamp. However, no harm will be done if the gaps temporarily align in service.

3 hours ago, Captain Obvious said:

I find the pictures from all the FSM's a little confusion because they don't put the FRONT notch up top. All those FSM manual pics have the piston pin running side-to-side instead of top-to-bottom, and I just find it confusing because I want the notch at the top. To get the FRONT notch at the 12:00 position, you have to rotate that sketch. And also interesting to note that they do not specify "FRONT" at all. Just the piston pin direction. Seems it really doesn't matter which is FRONT. You could rotate that sketch either direction and it would still be right.

I rotated it and put on the two possible FRONT notch locations:

Either of those FRONT locations would follow the "rules".

The FSM shows the pressure rings all at 4:30 and 10:30, but I don't see any reason why 1:30 or 7:30 would be any different.

Isn't it notch towards the front, # to the left of the notch and oil squirt hole on the passenger's side? 

Monroe's book page 125.

 

I'd guess that the fact they never specified front or back, only thrust direction, means that it doesn't matter.  Looks like they're just saying "don't line your gaps up with the thrust direction, make sure top and bottom ring gaps are opposing, and put the spacer gap between the two."

They used the same picture all the way through 1983, even with the turbo engine.

p.s. I see that I confused the oil ring discussion with the overall ring gap discussion.  Sorry about that.  Still, it's looking like it doesn't matter much.  Space the gaps out and expect them to move during usage.

p.s. #2 - it would still be neat to see where the rings are in a high mileage engine.  The dynamics might cause them all to end up in a similar position.  A "resting" place after their walks.

Edited May 25, 20204 yr by Zed Head

This is the instructions that came with my Nissan OEM rings.




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