Oil ring ?

Can an oil ring be broken yet there be NO cylinder barrel scoring, NO high oil consumption and NO prematurely blackened oil ?

Compression is fine, oil analysis showed a spike in Iron and Chromium and most notably, the bottom plug keeps oil fouling. In flight parameters are fine, in flight mag check is fine.

Anyone ever seen this before?

Darren

Yeah, an oily bore will show undeserved good compression. If your dead sure that plug is firing normally, then my guess would have to be the ring/bore interface. Maybe you've got 3 real good jugs masking a little oil consumption on the dud. It doesn't have to have a broken ring, and the problem very well may be part way down the bore. They don't have to be very far out of round to lose the seal. Sac Sky ranch has some pretty good pictures/discussion about cylinder bores. Picture's worth a thousand. You still haven't said what kind of cylinders you've got. Steel and nitrided will have chrome plated comp rings. Chrome & cermichrome, of course have chrome bores. I've seen rings go right through cermichrome into the steel with only a couple hundred hours. On 4 ringers you can have a scraper upside down.

The problem isn't in your rings, its your cylinder walls....specifically the roughness of the hone crosshatch.

So, is it possible to simply rehone the cylinders (assuming nitrided barrels) and reassemble with the same components? Is it worthwhile installing new rings at the same time?

Yes, go with new rings. Examine the bore carefully after removal, before honing. Look for bore flaws, scores, skips, etc. If you see skips indicating the bore is not true, I wouldn't use a dingle ball hone. It'll just make it worse. Like Bob was saying, if its just the hone finish, that's easy. If your chrome spike in the oil is coming from this area with a steel jug, it may be the top ring(s) coming apart. If you re-ring and hone be sure to check end gap on the rings. Todays rings are so consistent they almost acts like a bore gage. Big gaps means you've got a big bore. On an 8.5:1 360 the top of the top ring stops at just about 6 3/8" from the bottom of the jug. If you use ECI rings the gap will be near minimum there with a normal choke.

Thank you for the thoughts. It's a Superior engine put on the plane in 2006. Sorry I don't know what type of cylinders I have. I assume I have steel barrels, but I'm not sure. It's a garden variety IO-360 with 775 hours on it.

The consensus sounds like the jug needs to come off. I'm not one for pulling bolts unnecessarily but I'd rather take care of a problem sooner than later. I would put new rings and honing if that is indicated. Then I would have to break-in that jug again I figure.

Now for possible causes. The engine runs regularly, CHT's never over 400 degrees, I add Camguard to the oil to help decrease wear. The dang engine is babied and yet this still occured!! Is this just how these Lycoming are? No matter what you do a jug is going to have to come off before 1000 hours?

I usually keep the oil at 5 quarts and lean out any chance I get. This wouldn't have anything to do with a cause?


Thanks again for the clarification

Darren

Oil fouling of bottom plugs is not unusual, in fact its normal.

rocketbob said:

Oil fouling of bottom plugs is not unusual, in fact its normal.

Click to expand...

Do you mean to say its normal or it’s common?

There is a difference. I would not say it’s normal, or maybe I got a good one, 1100 hours or so on the first run of a set of Lycoming angle valve cylinders, no oil ever shows on any of the plugs. AutoLite fine wire plugs.

If the plug is good I would fix the cylinder.

In 33 years of owning airplanes, I have never had an oil fouled plug. But then, I have never had a broken ring or a guide that was that bad.

I have also never had a plug foul from lead deposits...... maybe it's just luck.

You guys must not have ever owned an engine with chrome cylinders. Seeing oil pooled at the bottom of the cylinder after sitting a couple of days is the norm. Even if the cylinder is not chrome oil will accumulate at the bottom and will work its way to the lowest point which is the spark plug hole, especially if the crosshatch doesn't provide for enough surface tension to retain oil on the cylinder walls.

Darren you really don't have a problem that warrants disassembly.

The oil ring is there to effectively meter the amount of oil on the cylinder wall. Oil rings don't typically break because they're never exposed to the same amount of heat and pressure that the top two rings are.

Hey Bob, and others, thanks for the replies. It's easy to get wrapped up in a problem and in trying to do the right thing, get a little out of sorts.

I just came back last night from San Fran. My little girl and I had a great time and the plane ran fine. All parameters were in the green and the oil is still clear looking and down about a half quart.

I will pull another sample and get it checked as it's been 20 hours since the last one that sent me reeling. I will consider the fine wire plugs if the botom #4 keeps getting wet and not firing while on the ground. I am not one for pulling something apart unnecessarily and if this is the "new normal" I'm cool to keep on trucking.

I'll report back what the new oil analysis finds.

Thanks again ,

Darren

Meh on fine wire. REM37BY's or convert to automotive plugs. They're far less prone to getting fouled.

Follow up

I've read lots and lots of threads and there are times when a thread contains the same issue I'm dealing with. I read and read only to find there was no conclusion to the saga, or none posted. So since I started this thread and another similar one, I will give the conclusion to the saga in the hopes that it will help someone....someday.

To backtrack. My original issue is this. Engine is an IO-360, Superior, 750 hours, regular use. It was oil fouling the bottom plug of #4 cylinder. Not huge amounts but more than the other bottom plugs. I did a mag check one day and the plug wasn't firing. I pulled it and it was oil fouled. Then my most recent oil analysis report came back and it showed 12 times higher Chromium (normally 5 ppm and it was something like 70 ppm) and elevated Iron (normally 25 ppm and it was 62 ppm).

I freaked out and started reading and posting questions. The plane ran fine, compression was fine, started fine, no metal in the filter, no excessive oil burn (burns about a quart in 30 hours).

I came back from my San Fran trip and pulled another oil sample. Still elevated Chromium and Iron after 16 hours.

I decided to pull jug #4. Not a simple task !!! The baffles have to come off, a bunch of stuff to disconnect and special wrenches required to pull the base nuts at the bottom of the jug. Much easier said than done !! Also, we had to get the piston off by pushing the piston plug out. EASIER SAID THAN DONE. I'll spare you the gory details of how we did this, but suffice to say we damaged the piston and the copper bushing on the connecting rod. Those had to be replaced.

I was looking for a broken ring, scored cylinder something. Nothing was obvious. There was some wear at the top of the jug where the top compression ring stops and changes direction, and a little wear from the piston skirt touching (perhaps from a cold start). But no smoking gun.

I was disappointed and glad at the same time. They honed the cylinder, put new rings, new piston, new bushing on the connecting rod, checked the valves and gave it back to me.

I hired and AME to help me put the jug back on. I wrecked enough stuff taking it off and didn't want anything to go wrong with the re-install. He brought by his fancy tools and his digital torque wrench and helped me. Then i spent the next two days putting the baffles back together and cleaning up stuff under the cowl.

So....... was it worth it?? NO!!! or at least I don't think so. I did learn how to take a jug off and put it back on, I did see the guts of my engine, learn how to use some new tools. I got to see what my finger looks like with safety wire run right through it !! and how to make a bandaid out of blue shop cloth and masking tape

Here's what I should have done. Not panic first of all. With elevated numbers in the oil analysis, watch the trend. The trend can only be developed with more time and oil samples. With good compression (all cylinders were 76/80 and above), no metal in the oil filter, no excessive oil burn.......leave it and fly the darn thing.

Sample every 25 hours if need be. Oil is cheap compared to what I did. If the numbers rise and then stay the same for several hundred more hours.....so be it. As long as the compression is good, no metal in the filter etc.... just go fly.

These are parts per million we are talking about, don't freak out.

If however the trend is that a particular wear metal goes from 5 ppm to 70 ppm to 250 ppm to 600 ppm in subsequent 25 hour oil changes, well then you need to start checking into what the cause is.

Finally, possible causes. From what I can gather. The rings are suppose to turn through out their life. Sometimes they can align. This could cause oil to escape and foul a plug, this could also cause some extra wear if they get stuck. The solution, you guessed it, keep flying, observe and see if the problem resolves itself.

I have only flown 3 hours since the new jug was put on. I was told to run regular oil and fly WOT for 5 hours. I take off and keep the power at 80%. I burn more gas but it's fun flying fast

Hope this helps someone someday.

Darren

Well at least you learned a few things, and that's worth something.

FWIW I have absolutely no faith in oil analysis as a diagnostic tool. If there aren't shavings in the filter you have nothing to worry about.

As far as pressing the wrist pin out, I have a tool I made which is a large ring with a bolt hole tapped into it, with a large hole in the opposite side for the wrist pin to pass thru. An aluminum plug fits onto the end of the bolt so the pin plug doesn't get damaged.