![]() |
Strange looking cylinder wall
The IO-360-A1B6 engine in our RV-8 has been making some metal. I first noted it when inspecting the oil filter after an oil change in August - I found roughly 50 shiny, ferrous flakes. I consulted Lycoming SI1492D, which describes various types and amounts of metal one might find in an oil filter, and recommends action. Based on that recommendation, and after consulting with three Aircraft Maintenance Engineers (an AME is the Canadian equivalent to an FAA A&P), I flew the aircraft for two hours and checked the filter again. I counted 7 flakes, so I flew 10 more hours (I was away for most of the rest of the year, so this took until January). This time I found the rate of making metal had gone up quite a bit, and now I was seeing what looked like alumimum along with the steel, so I grounded the aircraft.
When I first found the engine was making metal, I feared it could be the cam. After finding aluminum too, I did some research, which lead me to wonder if it could be a broken piston ring. I acquired a Vividia VA-400 borescope, and today I took a look in the cylinders. Three cylinder looked pretty good, but #4 has a very strange, wide area where the cross hatching is not visible. This area goes all the way up the cylinder. At first I thought it might be a piston pin issue, but I'm pretty sure it is no where near the front or back of the cylinder (you can see the top plug hole, with borescope shaft through it, in the second photo). The next step is to find an AME to help me pull that cylinder to investigate. ![]() ![]() Has anyone seen anything like this before? |
It goes beyond the top of the ring travel. I think you're going to find a piston problem at least.
|
Looking again I see I was fooled by the ring step, so something in the top ring.
|
I had the same issue. It turned out to be the cap that covers the wristpin was rubbing in the side of the cylinder. This caused scoring on the cylinder wall and the. On the rings. My best guess was it was caused by oil sludge that baked into a hard ring and kept the cap from floating like it should. This pushed the cap into the side wall if the cylinder.
What is odd about yours is that is in the wrong position to be the cap. My compressions were below acceptable and I had to change the cylinder and piston assembly. |
I have seen similar in auto engines. Cause was ingestion of debris, but they were narrower than yours. I believe something is amiss in the top ring area. Hard to say if it is a broken ring, maybe ring land damage, maybe debris. It likely first wore the cylinder wall smooth, but the appearance of aluminum in the oil would point to the piston now wearing. the clocking of the wear pattern excludes a piston pin issue.
You definately need to pull the cylinder and investigate. You might still be able to hone it depending upon how much metal it has removed. You can also bore it out, as you will likely need a new piston given the appearance of AL material in the oil. I am curious to see what the cause is. Larry |
Borescope?
Quote:
Can you give us more input about it? How do like it? I'm about to order one. Thanks! |
Quote:
|
Picture purfect
It is hard to tell from a couple of pictures, but you are doing the right thing here by removing the jug and looking at the rings and wrist pin ends. If it were a wrist pin plug the wear would be in line with the front or back of the cylinder just like the line between the spinner to the tail and would be the diameter of the pin. I think this scarring is a little wider than the pin cap would be, but it is hard to tell from the JPG. Looking at the wear on the cylinder up from the bottom it looks like the top compression ring is going up a little higher than the scar goes. this would lead me to think it would be at the second ring or the oil wiper ring. Again it is hard to tell from the picture, but you will find it when you pull the jug. Just a guess in the dark, but I would suspect a broken or wedged ring or ring grove, it does happen. You will be fine with a jug transplant. Good luck, Yours, R.E.A. III #80888
|
Finger strainer check
Hi Kevin,
Just curious if you checked the oil sump finger strainer and if so what you found there. Depending on the size of the metal flakes you might find more material there. Joe |
Quote:
|
Quote:
|
Well, the failure is interesting, but only one thing to do - remove and repair.
The area seems much too well defined to be carbon polishing. And too high to be anything but a piston ring. No material transfer for a FOD compression of the top land, and no associated head damage. A guess, is it is likely a broken ring that has finally banged around and turned to scrape the wall. in a most unpleasant way. |
Is that a pool of oil?
|
Quote:
|
Oil
Sure looks like oil to me. I had broken rings in a Pitts and it looked exactly like that. It was burning a quart of oil in less than 2 hours.
|
Issue
Scoring looks to be to high up the cylinder wall to be a wrist pin cap. My guess would be a ring or possibly a FOD. :(
|
So where is all the aluminum coming from if it is not the wrist pin (which I agree it is not)? The rings are steel as is the cylinder liner. Is the piston coming apart. I guess I could wait for Kevin to pull the jug, but I am just curious and impatient.
|
Quote:
Larry |
KennyM
This is my first post. I own a Cessna 152 & have dreams of building an
RV 8. The post about Lycoming making metal got my attention. I bought a zero time LC235 got 700 hrs. before it starting making metal. Was Piston wrist caps ( bad design in my opinion) Can be checked without Removing cylinder pass rings. Good luck |
Quote:
Pretty sure we will see a large distorted ring groove worn in the piston. So - it makes ferrous metal from the wall and aluminum from the piston. It may be causing some skirt erosion as well from debris trapped in between. |
Ok I just reread the OP so it all fits. It will be an education to see the insides. Sorry that it is at Kevin's expense but I am happy that this was all found on the ground and we will learn from it. Thanks Bill.
I watched Mike Busch's webinar called "the perils of cylinder work". It was an eye opener for sure. Highly recommend it. |
Quote:
When my engine's plugs were oily with I pulled the cylinders. Once the cases were open I found a dying camshaft, so that was that anyway! I hope yours is just the one dead cylinder and piston and the flakes haven't done any damage to the oil pump/accessory case: the contaminated oil will have gone through that on its way from the sump to the filter! |
Bottom line... Once an engine starts producing ferrous material in the filters/screens no amount of hoping or praying is going to fix it.
|
Kevin, wonder if this is in any way related to the overspeed event you experienced a few years ago. IIRC you had the engine disassembled and inspected and no damage was found. Two unusual events in the same engine may just be coincidence............
|
Quote:
I hope to pull the jug on Saturday, assuming one of my potential helpers is available, and the weather isn't too terrible. |
Did I miss this or have you commented on what the top of the piston looks like? Any signs of detonation hence a melted piston top at the affected area? Can happen quick...and..... it can detonate and have nothing happen to the piston. Just curious.
|
Lee, a coworker, helped me remove the #4 cylinder on Sunday afternoon. The strange cylinder wall seen during the borescope inspection was quite visible. There is definitely some wear all the way up the cylinder wall, but it isn't very keep at all. I'm guessing it is perhaps 0.001", which isn't nearly enough missing metal to explain what I found in the filter. Drat.
![]() The piston has a stuck lower compression ring, and signs of significant blow by. The cylinder and piston would obviously need sorting out before the aircraft goes back into service, but the bigger issue is the ferrous metal in the oil filter. ![]() Now that the cylinders have been ruled out as a source, there aren't any good options left. If it is cam or crank, then the engine needs to come off and head to an overhaul shop. If it is the oil pump, or in the accessory gear box, that could probably be sorted out here, but the engine would need to come off the mount. I'll use a mirror and borescope to inspect what I can see of the cam from the #4 cylinder area whenever we get a break in the weather, and work allows me to get to the hangar. Does anyone has any bright ideas on possible wear sites that could be corrected with the engine on the mount? If not, it looks like the next step is to remove a front cylinder, to get a look at that part of the cam. If that checks out, I'll have an AME (Canadian equivalent of an FAA A&P) help me inspect inside the accessory case. If nothing is seen in there, I'll ship it to an overhaul shop. |
Metal
Kevin you'll most likely find the lifters going south. They fail ahead of the cam usually, so run your finger across the face of each one and check for pits, you may have to remove the rocker arms so you can run your finger under the lifter face of any cylinders still installed. So while on the way look close for broken valve springs, etc. Unfortunately you'll have to pull another cylinder to inspect the other end of the cam shaft and those lifters unless of course you find something where your at now.
You could have a look at the gears as best you can through the mag holes, or even pull the sump and look up into that area, especially the crank gear, idler gear shafts and retaining bolts. Be sure to look over the impulse coupler also. If you have only ferrous metal, no brass, copper, al., etc its most likely going to be the cam and lifters. A bad crank bearing will throw several different metals. Good luck Tim Andres |
Darn, that's unfortunate. Do you have any pics of the flakes you found in the filter?
|
Kevin, You might be able to look at the cam with your scope. Note there are some particles embedded in the skirt, and the top ring face looks rough. It is hard to tell in that photo. If the ring face disintegrated (root cause), it could cause the flakes, and then the blow-by overheated the ring (and top land) and froze the ring. Skirt FOD elevated the aluminum.
It seems too much a coincidence that you shed cam flakes at the same time as a ring failure. |
Quote:
Given the wide area of .001 area, clearly there is a lot of pressure here. Remember, each time you bring the engine up to full temp, that AL piston is growing faster in size than the barrel and this is likely when the wear is occurring. I would examine the ring closely. If the Chrome is worn off, I would speculate that the ring has been making metal in your filter. Be sure to mark the area of the ring adjacent to the wear area before removiing. You can then mic the ring in that area and compare to others to see how much wear there has been. Crank issues highly unlikely. You'll see bronze material long before steel. Lifters are certainly a possibility, but seems a big coincidence if the cylinder wear is new. If you recently saw a rise in oil consumption that would indicate the cylinder wear is new. However, what you have here shouldn't create a significant reduction in power and may have been there for a while. Good luck and let us know what you find. Larry |
Thanks for the advice guys. I'll get back out to the hangar this weekend to take a closer look at the valve train and pull the piston pin so I can bring it home for a closer inspection.
|
Today was warmer than the past few days, and I had a slow afternoon at work, so I took some time off and headed to the hangar. I warmed the wrist pin bosses in the piston with a heat gun, then managed to push out the wrist pin with a piece of wooden dowel. Then I stuck my borescope inside and took a look.
The #4 intake tappet looks pretty ugly. Drat. I managed to get the tip of a finger on the tappet by rotating the crank a bit, and it feels slightly rough, which confirms the borescope image. ![]() I won't print what I said. I've been resigned to finding valve train issues since I first found metal in the oil, but I had been holding out hope that there was a cheaper explanation. At least now I know what the issue is, and what I need to do to get it sorted out. I'll start pulling the engine on Sunday, and then figure out where I will send it. This is the second time in 3 years with cam or tappet issues, so I'll get the roller lifter mod done this time. Time to get drink wine. Lots of wine. |
Question /educate me...
When this sort of trouble starts, does the erosion start in the center and make a "dent or low spot" which then causes more erosion of the surface toward the outer perimeter!
My first thought when looking at the photo was "that seems really close to the edges, how does that erosion of the surface get that close to the edge?" Kevin, thanks for the thread, sorry for your trouble. Jim |
Kevin, any theories on the underlying cause of the valvetrain issues? Do you think the overspeed incident caused the followers to hammer on the cam, or is something else at work here?
|
Quote:
|
As much as this sucks, it was found on the ground before it became a safety problem. If anyone ever needed a reason to cut open their filter here it is.
|
two separate issues?
so at this point, do we think that the piston ring/cylinder wall issue and the cam follower spawling issue are completely separate and unrelated? Did debris from one source precipitate the other problem?
I have a hard time imagining that this traces back to the overspeed. Folks run these engines at much higher revs than you saw continuously in racing. |
Wow Kevein - ugly isn't a strong enough word for that tappet face! Even the "ridiculously beat up" examples at Lycoming school didn't look that bad.
Is this a first-run engine, or was it built up as an overhaul? If its first run, there has been something going on in there that wasn't right in the first place. Paul |
The image makes one wonder if it is a lubrication problem. Sure looks awful. Glad it did not fail in flight and wreck your airplane.
I am a wimp when it comes to engines...and needlessly spend money to offset the wimpiness by calling Barrett Precision in Tulsa and order a new one. Done it twice and never looked back. That's one reason I am slowly going broke but the motor up front sure runs well. |
| All times are GMT -6. The time now is 01:25 AM. |