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Cylinder #3 unusual wear mark

V

Vlad

Well Known Member
After measuring compression we took a borescope and looked inside of all cylinders. Cylinder #3 has a mark at about 10 o'clock. We are puzzled what could cause it? Compression for the particular cylinder is 74/80 and the engine is nearing 3,000 hours of trouble free time. Take a look at the pictures below.

Looking at the piston. There are some swirls visible on top of the piston and against the most visible one there is a wear mark.





That's where the mark is located. About 10 o'clock if it matters.





Closer look at the wear mark.





What could be the cause? RocketBob are you around? :)
 
Is the mark in picture two the side of the cylinder wall?

I had a piston pin plug failure on my engine but it left two marks like that. The piston pin had dug into the wall of the cylinder because the plug wore completely down. This cylinder only had about 700 hours on it.

If I hadn't bought the cheap borescope that was recommended here on VAF I would never have seen it. The compression test was normal and the engine ran great. My friends warned me not to look:eek:

I wish I could post a photo but that skill seems to be forgotten.
 
arffguy said:
Is the mark in picture two the side of the cylinder wall?

I had a piston pin plug failure on my engine but it left two marks like that. The piston pin had dug into the wall of the cylinder because the plug wore completely down. This cylinder only had about 700 hours on it.

If I hadn't bought the cheap borescope that was recommended here on VAF I would never have seen it. The compression test was normal and the engine ran great. My friends warned me not to look:eek:

I wish I could post a photo but that skill seems to be forgotten.
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Thanks for the comment Mike. The mark is only on one side of the cylinder wall. Just about 10 - 10:30 which is passed pin indentation. Judging from swirls on top of the piston there is a blow by at that mark.
 
Rocketbob left posting a while back..:mad: I liked him.

Let us know what you find on that Vlad. I have a keen interest in high time, well maintained engine practices.
 
What a picture

I guess I could stick my foot in it. It's always hard to tell from a picture.
If this mark was at the 9 or 3 o clock you might suspect a rest pin wearing the wall of the cylinder. If it were at the 12 or 6 o clock you may think it could be a piston skirt wearing on the wall with a high time engine of 3,000 hours. If it is at the 10-2-4-7 o clock locations on the cylinder wall one might suspect a ring brake or blow-by gas jetting would be taking place at those locations. The lines at approx. 1/2 inch to the right of the main mark and about 3/8 inch to the left along with the main marking on the cylinder wall would make me think a ring is stating to fail at that location. Sorry just a thought in the dark of a photo.
Hope this helps, Yours, R.E.A. III #80888
 
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Thoughts

Vlad: Its fairly obvious that something is rubbing that shouldn't be. The only way to know for sure is to pull that cylinder and have a look. Further running will likely put more metal in the oil and cause more problems & expense. In consideration of the total time and the remote places you go it's time to consider what is the prudent next step.


Don Broussard A&P, IA, ATP
RV-9 Rebuild in Progress
1957 Piper Pacer
 
Another great example of why borescoping is a good idea. Always best to find this stuff on the ground!
 
Hard to say for me. It appears to be smearing not scoring, so likely a softer material - bronze or aluminum? You could get some additional clue from its highest point in the cylinder. Maybe blow by is higher, but the swirls on the piston are likely a heavier oil film on that side. Don't we define blow BY as going to the crankcase :D?

3000 hrs - pretty nice! What's your plan now?
 
Steve Melton said:
is there an accepted practice to simply replace rings if everything else looks OK?
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Normal practice, anyvtime the piston comes out if the cylinder, and especially when new rings are used, is to hone the cylinder as well. When you go that far on a 3,000-hr cylinder, it would make more sense to me to either have it overhauled or replace it with new. This would also be a great time to take a good look at the CAM and lifters.

Vlad, do you do oil analysis? I would send in a sample if this oil and see what metal(s) is(are) through the roof, if any.

Also, on the compression stroke, either side of TDC, but where the valves are still closed and that mark is visible, check compression. A major wear or scuff or blow-by issue should appear by much lower than normal compression at this point.
 
Cylinder wall has surface rust from just normal sitting, piston at bottom, intake or exhaust valve open air coming in. Ring and/or ring land busted in that area, so ring isn't touching wall anymore to clean up surface rust and also causing the blow by seen on top of piston.

That my 2 rubles.
 
BillL said:
Hard to say for me. It appears to be smearing not scoring, so likely a softer material - bronze or aluminum? You could get some additional clue from its highest point in the cylinder. Maybe blow by is higher, but the swirls on the piston are likely a heavier oil film on that side. Don't we define blow BY as going to the crankcase :D?

3000 hrs - pretty nice! What's your plan now?
Click to expand...

I agree, this looks more like a deposit than wear or scoring. Given the indication of blowby in this area, my guess is that the ring de-laminated in this area. Steel walled cylinders get chrome plated rings. If the chrome delaminated in this area, you would get light blow-by (not a significant loss of compression) and a very light build up of carbon on the cylinder wall (no scraping action from the ring where the chrome is gone). The build up would be the thickness of the chrome plating, which I would speculate to be in the area of .002" I would not expect your rings are rotating at 3000 hours and even if they are, the buildup will just follow the de-laminated area.
 
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Steve Melton said:
is there an accepted practice to simply replace rings if everything else looks OK?
Click to expand...

I can't see the value in a hone/re-ring at 3000 hours. I don't think you can expect a whole bunch more hours before you start having issues with the valves or guides. You could consider a top; I don't have any experience to speculate how long you can go on the bottom end. I can't imagine another 1000-2000 hours before needing new bearings or lifters (at least cleaning out plungers), not to mention cleaning out the oil galleries and checking for fretting.
 
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lr172 said:
I can't see the value in a hone/re-ring at 3000 hours. I don't think you can expect a whole bunch more hours before you start having issues with the valves or guides. You could consider a top; I don't have any experience to speculate how long you can go on the bottom end. I can't imagine another 1000-2000 hours before needing new bearings or lifters (at least cleaning out plungers), not to mention cleaning out the oil galleries and checking for fretting.
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:eek::eek: Vlad these guys are telling you that it is time to overhaul your engine. I bet you can get another 3000 or even 6000 hrs:D, especially the way you baby that thing . . .

Hmmm time to set up that GoFundMe account!!
 
Vlad said:
Closer look at the wear mark.


Click to expand...

Also looks to me like a material transfer smear. If this is on the front or aft surface of the cyl bore, it is most likely from a bronze style piston pin plug.

The cyl should come off to have a better look.
 
I'll fund him a few bucks. Set up the account. I don't go to the movies anymore because they are ****. The best entertainment I had this year was reading Vlad's Alaska adventures. I had dreams about it. That's real entertainment!
 
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Jesse said:
Normal practice, anyvtime the piston comes out if the cylinder, and especially when new rings are used, is to hone the cylinder as well. When you go that far on a 3,000-hr cylinder, it would make more sense to me to either have it overhauled or replace it with new. This would also be a great time to take a good look at the CAM and lifters.

Vlad, do you do oil analysis? I would send in a sample if this oil and see what metal(s) is(are) through the roof, if any.

Also, on the compression stroke, either side of TDC, but where the valves are still closed and that mark is visible, check compression. A major wear or scuff or blow-by issue should appear by much lower than normal compression at this point.
Click to expand...

You need to first check for damage to the wall, then measure it for diameter and roundness vs the spec (there are specs for both) and measure for the choke. That is the narrowing of the bore at the top of the cylinder by 1 or 2 thou. If there is no choke left I have been told that the jug will burn oil. It is there to compensate for the bore expanding at operating temps.

If these are all within spec then you can hone it and put new rings in. I would be surprised if they were at 3000 hrs, if that's the time on that jug, but the only way to know is to measure it. But after 3000 hrs it a jug doesn't owe you anything!
 
Thank you all who responded here and off line. I wish I had those answers two days ago when I was still in the warm Canadian hangar disassembled with all tools available. It looks like the jug need to be pulled off to figure out what caused the mark. For now the engine is getting its daily exercise. Jesse, any recommendations where to send the oil sample? Never did it for the life of the motor might get scared after results. I will report here about findings and remedies.

burrowing%20out%20-%201%205.jpg
 
I use Blackstone. Put my name and email in it and use one of my prepaid bulk samples. It's on me. I'll forward the email when I get it.
 
sblack said:
If there is no choke left I have been told that the jug will burn oil. It is there to compensate for the bore expanding at operating temps.
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This is not true. The choke, or lack thereof, has no bearing on oil consumption. My older lyc cylinder have no choke (original lyc design) and my oil consumption is around 15 hours / qt.

The choked cylinder is a method to tighten up the upper part of the chamber and reduce leakage at the critical, initial pressure/power area, yet still leave a larger clearance for the bulk of the cylinder. As you mention, air cooled engines need loose piston/wall clearances to avoid wear during warmup, where the piston grows in size faster than the cylinder. Further, the extreme upper area of the cylinder see hotter temps and therefore expands further. The choke balances this out for a cylinder that is uniform once fully heated.

Larry
 
lr172 said:
This is not true. The choke, or lack thereof, has no bearing on oil consumption. My older lyc cylinder have no choke (original lyc design) and my oil consumption is around 15 hours / qt.

The choked cylinder is a method to tighten up the upper part of the chamber and reduce leakage at the critical, initial pressure/power area, yet still leave a larger clearance for the bulk of the cylinder. As you mention, air cooled engines need loose piston/wall clearances to avoid wear during warmup, where the piston grows in size faster than the cylinder. Further, the extreme upper area of the cylinder see hotter temps and therefore expands further. The choke balances this out for a cylinder that is uniform once fully heated.

Larry
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The barrels are made honed as a cylinder and ready to go before installed on the head. The head is heated to 400F and the barrel (with a hand clamp) is chilled in liquid nitrogen. The when the assembly cools it compresses the steel and makes the "choke" at the top. At operating temperatures the choke is minimized. Simply that. If the choke is worn away, then it is like a bell mouth cylinder on any other engine with the same results.

As for the clearances, imagine a cooking hot engine flying into a heavy rain storm. One big contributor to the larger piston/wall clearances. Engines have seized in flight. Also, the other part of the clearance is fundamental to a heavy duty engine that will operate continuously at high BMEP. That results in a hotter (larger) piston than a terrestrial mobile ( and liquid cooled) engines. Again, not tweaky magic, just fundamental design practices.

Vlad, apologies for getting off topic.

Edit: Vlad found a broken top ring that finally punched through the top land. See the Russia trip beginning. It's obvious in hindsight, isn't it.
 
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