When does a 8 cylinder Recip become an Oil Pump?

[Grizzly]

When, as I discovered today. All 8 pistons had their piston ring gaps in-line!
Yep!
I was asked a couple of days ago, to investigate a Compressor that had been observed literally pumping itself dry of oil.
A full service kit including a new set of piston rings were ordered.
With parts in hand, I set about stripping and rebuilding the recip.
Having honed all the liners to remove any glazing and scoring.

I started to remove the piston rings from each piston replacing with new as I went. when I finished I realized that all the worn rings had turned in their liners and were all in-line.
Hence the super efficient oil pump!

I know that the original rings had not been installed in-line, because I do the annual overhauls of these compressors.
And whilst doing so I always remove the liner to check the orientation of the piston ring gaps.

So here is my question.
I am assuming that when a set of piston rings become so worn they can rotate within the bore.
In doing so they become self aligning?

I have seen several in-line sets of rings in a comp before but never the complete set.

Has anyone an alternative theory?
Grizzly

[monkey spanners]

I don't know! Most of the stuff i work on is too small to have rings, old prestcold stuff just has grooves machined in the cast pistons.

Thats some interesting stuff you get to work on Grizzly, you should get yourself a camera and put some vids on youtube!

Jon

[RANGER1]

Grizzly,
It;s not the answer you want but I think you may of overlooked staggering rings on this one.

You can never rule out anything , but what are the chances of rings lining themselves up!

Its like a lot of mysteries I seem to work on, sometimes you have to put it together the best you can & see what happens.

Of course I'm not telling you anything you don't know.

[Grizzly]

MS.
You do yourself an injustice, you regularly captivate us with you descriptions of various equipment issues on your posts.
The largest was last year or was it 2 years ago, anyway a piston con-rod and liner was just 0.7kg under 50kg. What a mother that was.
Ranger.
Good point and one i would of likely come up with myself, if someone else had posted similar.
Only it is almost a year since this comp was serviced by me, but it has only recently been throwing it's oil!

Up until recently it was running fine, surely if I had done as you suggest it would of had issues from the outset?

Anyway it's mended now (Well almost!)
But has anyone had similar or can suggest another cause?

[mikeref]

Grizzly, It's been a long time since i've worked on 8, 12 or 16 cylinder compressors, but never had your situation happen. Disturbing to think that it may happen again with this overhaul. Guess you used internal micrometer to check for bore defects? Still, that doesn't account for all 8 being the same, so somehow, there is common problem to all and i'm guessing 4 pots are fixed so they can't unload, which brings possibilities back to only gas and oil movement with pressure to force alignment.... Nope, beats me.. Mike.

[Magoo]

Hi Grizzly

Similar problem with a cheap re-build by others, the actual oil ring groves in piston slug were warn /larger than standard, plus the ring gap clearances were out of spec., could not really point a finger at any particular thing, but replace all 8 pistons and rings etc., honed the hell out of bores that were marginally within tolerances. The end result was a definite reduction in oil carryover. Plus I had the heads / water cooling circuits chemically cleaned.
When removed the alignment of oil rings and compression rings were fairly close to each other, not sure if installed like that or all rattled around to be like that.

[RANGER1]

When, as I discovered today. All 8 pistons had their piston ring gaps in-line!
Yep!
I was asked a couple of days ago, to investigate a Compressor that had been observed literally pumping itself dry of oil.
A full service kit including a new set of piston rings were ordered.
With parts in hand, I set about stripping and rebuilding the recip.
Having honed all the liners to remove any glazing and scoring.

I started to remove the piston rings from each piston replacing with new as I went. when I finished I realized that all the worn rings had turned in their liners and were all in-line.
Hence the super efficient oil pump!

I know that the original rings had not been installed in-line, because I do the annual overhauls of these compressors.
And whilst doing so I always remove the liner to check the orientation of the piston ring gaps.

So here is my question.
I am assuming that when a set of piston rings become so worn they can rotate within the bore.
In doing so they become self aligning?

I have seen several in-line sets of rings in a comp before but never the complete set.

Has anyone an alternative theory?
Grizzly

So Grizzly what wear did you find on old piston rings ie ring gap etc.
You mention that if pistons rings get so worn that they "may" rotate!

If they are flapping in the breeze it could be a secondary problem,
as if they are worn significantly then there must be other issues as well
if only run for 1 year.
Were valve plates & seats in good condition on disassembly?

Was it a Sabroe or something else ?

[RANGER1]

Grizzly,
Out of interest I asked a very experienced man in automotive engine reconditioning.
He said he had never heard of it.
As it did happen , it must be 1 in a million & you were very unlucky.

[Grizzly]

Hi Ranger.
My original post must of mislead slightly the rings are not changed every year just checked.
Hence my original comment about "and piston rings included ".
In fact it is not recorded when the piston rings on this machine was last changed if ever?
Which is why I requested them originally having been told how "you can see the oil level dropping"!

I also spoke to a rebuild specialist he also had never heard of the problem.
Although he did say that in his opinion the rings being in-line should not be an issue. as the ring gap at around 10 thou was to small to make a difference.

I will let you know how it runs when I run it up on Tuesday (Bank Holiday on Monday in UK).
The Valve plates were quite worn but no more than usual for this machine, as it supplies chilled glycol for a production line.
As a consequence it is hammered day in day out and a miracle it continues to run with some of the abuse it gets.
There are signs of excessive heat on parts of the comp body (blistered paint), who knows when that occurred.
This particular pack has a real history and I could fill the forum with "stories".

It's one of those where as you dig deeper you find out more and more.

I will let you know more later.

Cheers Grizzly

[RANGER1]

Grizzly,
We would agree that its good practice to stagger piston rings.
If rings are not staggered it can lead to a clear path from top of piston to sump.
The oil scraper ring would not be 100% effective.

Automotive is alot more precise as we think engine is a lemon if it uses oil.

Refrigeration is different ,machines use oil but also run a lot longer.

If it was a Sabroe & rings were very old they may have been cast iron only unlike the new hardchrome replacement.

[NH3LVR]

Now I make myself unpopular.
I cannot imagine why sometimes rings sometimes seen to align in a bore, but I have seen a few pistons that way in a machine. Years ago I read a scientific article about why the staggering of ring gaps makes no difference. Since the rings will turn in their grooves anyway I do not think it makes any difference what so ever. I know this is contrary to common sense. I had this discussion with someone I once worked with who was adamant about staggering the rings. I suggested that he call a engine manufacturer and apply for the job of staggering rings. I do not believe any such position exists.
I found a interesting word document a few minutes ago. http://www.google.com/url?sa=t&sourc...bh4PzQ&cad=rja

[mikeref]

Now I make myself unpopular.
I cannot imagine why sometimes rings sometimes seen to align in a bore, but I have seen a few pistons that way in a machine. Years ago I read a scientific article about why the staggering of ring gaps makes no difference. Since the rings will turn in their grooves anyway I do not think it makes any difference what so ever. I know this is contrary to common sense. I had this discussion with someone I once worked with who was adamant about staggering the rings. I suggested that he call a engine manufacturer and apply for the job of staggering rings. I do not believe any such position exists.
I found a interesting word document a few minutes ago. http://www.google.com/url?sa=t&sourc...bh4PzQ&cad=rja

Interesting reading. Thanks for posting. So now we wait for Grizzly's return.

[RANGER1]

NH3LVR very interesting article , also a lot agree on no ring staggering if you google it.

I think I would still stagger rings as its not hard.

If I put it together without staggering rings & it used oil everyone would be unhappy +
could,nt eliminate it unless I did.

[Grizzly]

Thanks for the interesting info NH3LVR.
Well worth reading
Spoke at length with a chartered engineer today about to stagger or not to stagger?
Basically in simple terms.
You are correct to argue that not staggering the rings makes little effect on the compression and oil carry over.
And as pointed out when new the gap has little difference.
However as was explained to me:-
As the piston reaches top dead centre and stalls before being driven back down.
The rings are at their least lubricated (Gas flow past them which contains oil has stopped).
Add at the point the forces push down and the crank draws the piston down.
The forces around the rings change from an upward motion to a downward motion.

This in effect distorts the ring shape into a oval shape with the widest part of the oval at 90 degrees left and right to the ring gap.

With this in mind his argument in favour of staggering was that if this action and the subsequent wear it causes.
Would be concentrated in the same portion of the liner for every ring that is in-line.
Therefore as you and others (thanks for the input Ranger, mikeref and Magoo.) have pointed out my original oil carry over has nothing to do with ring gap.
But the excessive wear of rings and or liner does which is made worse when the rings are in line.

I was hoping to be able to give you all a update on the rebuilt compressor as it and the second on the pack were finished today.
But due to production timings I was not in a position to run it.
My colleague is due back there tomorrow and if practicable it will be ran up and proved.

As soon as it is back on-line I will post an update.

[NH3LVR]

Very good technical information. I will digest that a bit. Whether or not and how much the rings turn in operation is the key issue.
I have to get away from the computer. A friends son is on the Deadliest Catch TV show and I need to get the recorder going.