EA81: oil control piston rings alignment

[torpedo51]

I'm rebuilding this EA81, and see two things that I've never seen before. 

I have an ITM piston kit, and it came with no instructions.

How do I align the expansion ring on the pin located in the groove?  The break in the ring straddles the pin?

What am I supposed to do with the tab on the ring?  Is this the bottom or top ring?

See pictures

 

[Steptoe's photos]

I think you are correct in the break/ butted join is intended to be at the pin. Firstly though, have you fitted the ring to the bores to measure your gaps? I bought some AE branded British made pistons that frustratingly came with the rings already fitted up. Now, I need to hold my breath and remove them, size them up in the bores then refit.

Have you got any Subaru instructions at all ? The expansion ring, the wriggly thing needs to NOT overlap at the join, just to butt up to each other. Well,  that tab has to at least point towards it's brother rail .

If the piston groove has a pin in it, that is a help, but not having done this in a while cannot say how and where it should be in relation to things. The gaps of the rails are supposed to be far apart from each alignment and the gudgeon pin location gets a say as to where your compression rings need to be. I have some ring info, just not handy. Please tell us how you go. Just looking at my piston mentioned above, it has a flat point in the lower groove low side to locate the lower rail. None for the other. I found some instructions that mention that the gaps for each groove need to be 120 degrees apart from each other. I have some recollect that the gaps of both rails align with each other. Could be wrong , I do recall generic ring instructions may conflict with Subaru specific instructions.

 

I just looked at my EA81 series FSM and surprised no mention of what you ask at all !! Nothing on where the gaps are to be, not even a starting point .

 

I don't know how many others do what I did on one dismantle...used tape to stick rings to a sheet of paper, marking which ring was top or lower, next to the top compression ring is the top rail with tab on it. That tab has to point inwards (but I taped it tab up, just to confuse myself years later

My Australian Gregories manual describe that ring with your tab as "the upper rail tang"

Draw yourself a clock or compass  Looking from the top , put piston so locating pin in piston at 9 or West. 30 degrees down at 8 o'clock is where oil ring lower side rail gap and lower compression ring gaps are. 30 degrees below 3 o'clock , so 4 o'clock is top comp ring gap

 

Tang faces down on top oil rail ring about one hump to your left

 

That locating pin should be dead centre above gudgeon pin centre ?

 

Edited July 13, 2022 by Steptoe's photos

[torpedo51]

Yep - thanks for that.  I read in some half believable posting elsewhere that the pin and tabbed rail ring prevent spinning such that the gaps become accidentally aligned. The rationale was that the piston/rings are sideways in a horizontally opposed engine and gravity would take affect: the gaps on the oil control rails would eventually float to the top (towards the sky)

If there's any truth to this, my best guess is that the UNtabbed ring is expected to float such that the gap faces the sky, the tabbed ring's gap should be spaced somewhere away from that.  To force that spacing, the expansion ring seam needs to straddle the pin, and the tabbed oil control rail is offset from the pin and from the untabbed ring.  That sucks, because the pin and floating rail gap have to be 180 deg... which violates the "120/120/120" rule of spacing the gaps.

Of course this all seems bunky because the upper two main compression rings require no such "tab" to stay in position, even though they are also suspended "sideways"

My piston kit is from ITM... can't find any info or diagrams for this.  Ugh.

[Steptoe's photos]

From memory - I tossed instructions that came with one set of rings as they conflicted the non Subaru workshop manual that went to more effort than Subaru to describe gap placement and tangs and tabs. Whoever assembled rings to my pistons I have sitting ready for EA82 assembly - set the gaps of the oil control rings 180 degrees apart. I have followed that description I gave you above on countless EA81 and EA82 with no troubles. Did you check gap positions of all the rings when you pulled last EA apart ??

 

[Rupart]

On 7/12/2022 at 8:37 PM, torpedo51 said:

I'm rebuilding this EA81, and see two things that I've never seen before. 

I have an ITM piston kit, and it came with no instructions.

How do I align the expansion ring on the pin located in the groove?  The break in the ring straddles the pin?

What am I supposed to do with the tab on the ring?  Is this the bottom or top ring?

See pictures

 

Hi, i found the information you asked about. 84 fsm pg 3-80 fig 3-169. the rings are refered to as Riken , it shows the tab as upper rail and the tab points down inside the expander in one of the lo gaps in it. Also stopper pins, point toward each other on each bank. so 1&3 pins face each other and 2&4 face each other. the two compression rings should have a letter mark both to be facing toward top of piston. hope this helps some.

 

[Steptoe's photos]

sorted? How is this build going ? I recently pulled rings from my new EA71 oversize slugs in order to measure up the ring gaps up and down the intended bores. The scraper rings are identical, no tabs/tangs at all. And just a short 4? mm step on the lower land to stop the scraper ring ever rotating. That is as far as I got ! Luckily I remembered/worked out how to remove the lower comp ring without breaking it

 

[torpedo51]

Hi - build going good.  Shortblock complete.

I found an EA81 build on YouTube that was pretty thorough, and contained the exact pistons and rings (with the tab) that I've got.  I don't have a FSM, but another member suggested that it was in the FSM on a specific page.

Here's what was recommended by the video builder and what I did (see picture):

This is piston 1.  
The arrow points towards the front of the engine (for the benefit of novices: the front of engine has the pulleys, the timing gears are on the back of the engine)
The pins on the pistons point towards each other as someone else noted above (e.g. pins on pistons 1 & 3 point to each other)
The tang on the upper oil control rail ring faces down towards the corrugated oil control ring

KEY:
TOP = top ring
MID = middle ring
TOP OIL = top oil rail ring
OIL CTRL = corrugated oil control ring
LOWER OIL = lower oil rail ring

Note - my pistons were NOT marked to indicate upwards or forwards.  They were all punched "STD" (standard size) on the piston face, with the ring pin extruding to the left.
In other words, if you look at this picture of piston #1, you can see "STD" punched "upside down", and when piston #3 is installed adjacently, it's punch is "right side up".

 

Thank you!

Edited August 14, 2022 by torpedo51

[Steptoe's photos]

nice. Not sure if the con rods can actually go in the wrong way, think it is all boomerang logo to the front. The ring locator pins facing their paired mate is new to me, thanks for sharing and updating.

[torpedo51]

According to the Non-Factory service manual that I have and the build video that I used, the boomerang on each and every rod must face the engine front.  

Worth noting - each connecting rod was hand etched with an arbitrary (?) number that spanned the seam where the rod and its mate came together.

In other words, I was trivial to match each rod with its own cap.  (see photo)

Here are the four hand etched numbrers from each of my pistons 45, 2, 34, 14

I weighed them on a scale (metric and imperial) and didn't find any matches to these numbers, e.g. 30.45g

 

[Steptoe's photos]

nice. I must also be trivial matching the "signature" across the two pieces.

Now, you have tested the rings in the bores to measure gaps up and down the bore ?

If so, what gap did you find or need to adjust to ?

I have only this week found my engine building guide on ring gaps through various performance stages.

They used 3" and 4" as examples so lazy me who forgot to write up what 92mm bores gaps need at each level, is gonna have to work it out again

The pistons I bought came rings fitted. I hate removing rings, scratch, break    

Got them off one so far. I like how you used marker pen to save brain space on assembly. Must do myself