The International Cessna 170 Association

Hello guys having some cylinder problems and looking for opinions...

Engine is a mixmaster Top Overhaul: 4 superior steel cylinders, 3 are new out of the box, one is older with new valves, all standard. Two cylinders are continentals chromed to standard. oldest cylinder has 250 hours, newest about 50. the 3 brand new superior millenniums are the newest cylinders. Flew it to Oshkosh and engine used less than 1/4 quart in 5 hours which is normal for this engine. On way home over a quart so that was interesting. Oil consumption stayed higher past few weekends since, but we have had warm weather. Over weekend airplane seemed to be underperforming. On the way back to the airport oil temp spiked to 230, always ran below 220 in hottest weather here in Ohio. Belly is covered with oil, obviously from breather. So we performed a compression check expecting to find a low cylinder. Here is what we found:

1(Chromed) - 77/80
3 - 10/80
5 - 66/80
2 - 25/80
4 - 35/80
6(Chromed) -76/80

Obviously these numbers are alarming and seemed to happen very fast. At last annual 8 months ago numbers were all 74+/80. So what happened? The airplane exhibited no symptoms of this before and even traveling to Oshkosh. We do lean the engine as most with an 0-300 do, but we have not modified that procedure the past four years. We do not have cylinder head temperature gauge. Do I have one bad cylinder and the heat of the blow by caused the other rings to stick so maybe they just need rehoned and perhaps reringed? Found it interesting that whatever happened the chrome survived and the steel did not. We will pull the cylinders this weekend, mike them, and I'm sure get more answers but my big concern is how did four new cylinders go bad this fast? Thanks for any thoughts or advice.

Ryan

Firstly what oil were you using for the run in ? At what RPM were you running the engine initially? You should have run the engine flat out as it sounds like that you have glazed bores. When you,were doing the compression checks did you check where the air was escaping . If the air can be heard escaping from the crank case breather or the oil filler port it’s the rings are not sealing. If the air is escaping from the exhaust outlets it’s the exhaust valves and if the air can be heard escaping from the intake it’s the intake valves . It sounds like it’s glazed bores and they will have to be rehoned . However another question has to be raised is did you see the rings being gapped and fitted and were the correct rings fitted to the correct cylinders ? Chrome bores demand a different ring to a steel bore . I have seen people mix up the pistons and rings when fitting many different types of cylinders to a engine .

Oil was changed to Aeroshell W100 this past summer after running Aeroshell mineral oil for the last 50 hours to seat the rings on the last replaced cylinder. Pretty sure we are not mixing rings as the cylinders were not all changed at the same time and three of the four cylinders that went bad were brand new superior mill. kits straight out of the box. The engine was run at basically redline for the first 10+ hours of a cylinder replacement. It was around that time we noticed oil consumption go down. Oil consumption the last 40 hours or so has been around 1 quart for 10 hours. We normally cruise at 2450 RPM. Air was definitely escaping past the rings as air was blowing when removing the oil filler cap.

I had to ask some strange questions as there wasn’t enough info in the first blog.if you have air passing the rings there are possibly only 2 issues. The bores are glazed or the rings were not correctly gapped. Superior products are very good quality normally. In the past I have found new engines from Lycoming having under size pistons fitted but with correctly sized rings fitted but all within book tolerances. Engines ran fine until shut down and then would pump oil into the cylinders and into the intake tubes where it would run into the fuel injector unit. It had me guessing for about 3 weeks and Lycoming keep saying it was due to the aircraft being flown incorrectly. Then it was noted only American champion decathlon new aircraft in the last 9 months of delivery had this issue . Thank god for the internet.
I am also assuming that the rings were fitted correctly also [not up side down ] . But superior rings are a little softer than the Lycoming rings also . That’s some thing I have been told but no proof. Have a talk to the guys at superior ,they are very helpful .

Sounds like sticking exhaust valves due to lead build up on the exhaust valve stems. The new cylinders have the tightest tolerances between the valve stem and valve guides and are more prone to problems. The normal fix is to ream the valve guides and clean the valve stems. This can be done without removing the cylinder.

FredL wrote:Sounds like sticking exhaust valves due to lead build up on the exhaust valve stems. The new cylinders have the tightest tolerances between the valve stem and valve guides and are more prone to problems. The normal fix is to ream the valve guides and clean the valve stems. This can be done without removing the cylinder.

He said the compresson checks demonstrated air leaking into/out-of the crankcase...not the exhaust.

Thanks for responses so far guys. Going to start taking it apart tonight and see what we find. Would one cylinder going bad and its associated blow by cause the others to glaze like that? If thats not the case we have something different. I'll update on what we find.

Up date to our cylinder problem. The piston in No. 2 cylinder failed. There was a chunk out missing between the top two compression rings. This was a piston with about 150 hours. Purchased from Fresno. Now trying to determine why it failed, whether from heat or if it was a freak thing that the piston was defective []

tcraftpilot wrote:Up date to our cylinder problem. The piston in No. 2 cylinder failed. There was a chunk out missing between the top two compression rings. This was a piston with about 150 hours. Purchased from Fresno. Now trying to determine why it failed, whether from heat or if it was a freak thing that the piston was defective []

In the early ‘70s I was forced to land on a levee in the Mississippi Delta while flying pipeline patrol due to a rough engine. One piston had failed similarly, it was believed to be from a spark-plug-tip which had seperated and fallen into the combustion chamber damaging the piston, which in-turn began to disintegrate and broke down thru the ring lands.

The fix was a cylinder assy and oil change/screen cleaning and the engine cont’d in service. Got lucky on that one.

tcraftpilot wrote:Thanks for responses so far guys. Going to start taking it apart tonight and see what we find. Would one cylinder going bad and its associated blow by cause the others to glaze like that? If thats not the case we have something different. I'll update on what we find.

Blow-by alone from one cylinder alone should not cause the other cylinders to glaze. Glazing usually occurs during break-in of new cylinders when the rings don't seat against the cylinder wall and the oil cokes up on the cylinder wall. That cylinder will continue to use oil.

A broken part from one cylinder could possibly find its way to other cylinders but I think you would have all sorts of other indications of sound and roughness if that happens. Your discovery of a broken piston would make me in the least, do a thorough bore scope inspection of the other cylinders. If it was mine, I would pull and inspect all of the other cylinders.

Also, with the problems you are seeing, it might be a cost-effective solution/good insurance to buy a complete set of new cylinders. Fixing cylinders one at a time as they fail is very expensive and you chance losing the plane if a catastrophic failure happens somewhere you can't make a safe landing. You have no idea about the history of those cylinders except the 3 Superiors, that is not required, the rest could be ancient.

You need to check all of your cylinder baffles and baffle seals and make sure they all are in place and correctly installed with no holes bigger than a dime. Without CHT info you don't know what is happening.

Your earlier post mentioned 3 low-compression cyls but did not identify which ones (for example) were they the 3 new Superiors? Or were they older...? If those were the 3 new Superiors then I”d wonder if their assembly process was improperly performed. (Upside-down rings, etc.). I’m not surprised the chromed cyls are doing well because I’ve always had good fortune with channel-chromed cylinders and have run many many engines using them with good results.

Which cyls were the failing cyls?

The cylinder that exhibited the failing piston was an O/H superior with a new piston and ring set from Fresno. History of the cylinder before the O/H was unknown to me. The cylinder was standard so the O/H was limited to the valves. That cylinder not only had the failing piston, but also showed some scoring on the cylinder walls. It will be replaced with a new Millenium cylinder kit this time around. The other three that failed were brand new Milleniums out of the box. They show no scoring but each has stuck rings to varying degrees from a partially stuck top compression ring to all compression rings stuck on one. The further away from the failed cylinder/piston you get, the number of stuck rings was reduced. I am having the Millenium cylinders and pistons gauged. If they are in limits they will be rehoned and the rings replaced as the cylinders are low time. This all assumes that nothing else is found. We are sending an oil sample out. Both screens were clean (no metal) when pulled. We are going through the induction system now looking for cracks/leaks.
We will replace all gaskets and intake boots while it is apart. We are also going to install a CHT gauge. [img]IMG_1807.jpg/img]

I had problems with my ECI's that also had seized rings that couldn't be removed from the piston. Out of 6 ECI cylinders I replaced 3 - 2 ECI's and 1 with a Millenium. I never had problems with the Milleniums so I went back to them. I am sure the ring grooves were cut too close for no clearing movement.

John

While it’s nearly impossible to see the writing on the actual ring after it’s been seized on the piston but it sounds like the rings were either incorrectly gapped or put in upside down . If honing was incorrectly done this usually appears in the first hour of running the engine . The first hour of running a engine with new rings fitted is very important also. Another issue that comes to mind was the correct part numbered rings fitted . I would be looking at the work sheets /log books to see the part numbers correspond to the parts book.