Cessna 180

slowmover said:

Help me understand... why would I top the engine or do a full overhaul for one exhaust valve?

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Just based on my experience with the IO-520 in my 185. Granted mine was on floats which tends to run hotter temperatures than a straight wheel plane due to less ram cooling air passing through the engine. I found that in a short period of time after working on one cylinder, another one would need some work and then something else would crop up. Then also I often flew into the remote sections of Canada where it would have been a long walk home. Perhaps my comfort level is a bit different than yours. When my engines began talking to me I majored them. Perhaps they would have gone another 2 or 300 hours, maybe they would have left me in the bush. I wasn't willing to find out.

There has been a lot of discussion on this forum about breaking in engines after having cylinder or more work done. In none of those discussions do I recall running peak EGT for break in. Run em hard, keep em cool!

As Pete implied the term “TBO” is kind of a suggestion, not a fact. I’ve had similar experiences to Pete with big continentals. I’ve seen guys wind up replacing six cylinders with “200 to go” till tbo.

So, maybe one cylinder, but when do you stop? When the sixth goes south?

MTV

The vibration is related to this repair. What makes a newly repaired cylinder vibrate? Push rods incorrect? Rockers incorrect? Bad hydraulic lifter? Maybe the bad valve was a symptom, not the problem?

I appreciate all the advice. I'm not looking to postpone the overhaul decision any more than I need to. But, I have an engine that has been running well with zero issues other than routine maintenance. If I can another year or two out of it for minimal additional investment, then I will try to do that. If it becomes a money pit or if I lose confidence in it then off it comes. I'm not operating over remote parts of Alaska or Canada but still I value my life and my comfort more than my checkbook balance.

Went back to the IA today. He insists that all the parts are correct. Then he ran it and agreed that the vibration was abnormal. He wanted me to fly it a few more hours to see if it smooths out but understood when I told him I wasn't comfortable flying it. So, back into his shop it went. I assume the vibration is related to the cylinder change, but I recognize that there could be something else. They're going to go back through it all to see if they can figure it out.

So, you do have the correct rings for the cylinder? Long ago a local cylinder change made a bunch of vibration. They had put chrome rings in a chrome cylinder... or cast rings in a steel cylinder.. I don't remember.. but that is one way to make it go wrong. (of course cast rings go with chrome, and chrome rings go with steel) A peek inside the cylinder might be warranted. As I remember the cylinder with the wrong rings had developed quite a "washboard" wear pattern in short order. Probably not it, (especially since your mechanic says all correct parts used!) but one more thought.. So here's another one... was the valve dry lash checked? Maybe wrong pushrod length for that particular new cylinder? I've seen that happen too, but it resulted in more of a misfire than a vibration. And I hate to say it, but is the rest of the engine so tired that one enthusiastic new cylinder might just be putting out enough more power to make it vibrate? I doubt that last one though..I'm in that camp that most operators couldn't tell the difference on takeoff between high compression numbers at 100hr and low numbers, unless they were told...

slowmover said:

Thanks for the tips... keep em coming.

Reference piston weight, it's the same piston that was there before. Vibration started right after the new cylinder was installed so I think it must be related. My other 5 E valves were good on the annual, and I've flown a .5 since then.

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Did he remove all the carbon from the piston top when he reinstalled it? If he did it doesn't weigh the same as the other 5 carbon top pistons left untouched

Glenn

He didn't move the mag to torque the cylinders and forget to re-time right? Sorry if too basic but it's gotta be something...

slowmover said:

I appreciate all the advice. I'm not looking to postpone the overhaul decision any more than I need to. But, I have an engine that has been running well with zero issues other than routine maintenance. If I can another year or two out of it for minimal additional investment, then I will try to do that. If it becomes a money pit or if I lose confidence in it then off it comes. I'm not operating over remote parts of Alaska or Canada but still I value my life and my comfort more than my checkbook balance.

Went back to the IA today. He insists that all the parts are correct. Then he ran it and agreed that the vibration was abnormal. He wanted me to fly it a few more hours to see if it smooths out but understood when I told him I wasn't comfortable flying it. So, back into his shop it went. I assume the vibration is related to the cylinder change, but I recognize that there could be something else. They're going to go back through it all to see if they can figure it out.

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Read the links which DENNY posted in #31
http://www.supercub.org/forum/showt...avgas-and-premium-uleaded&p=720272#post720272
Once upon a time I had a roughness as you have described when I was a long long long way from home. It was very nerve racking in that it was necessary to keep flying back to civilization. I nursed it home. fortunately it had a turbo charger so that I was able to boost the lost power. The compressions remained in the safe zone. When I got home and started looking into the trouble, pulled the rocker covers and found in one of them a BIG pile of aluminum chips. The valve guide was stuck to the valve and the cylinder head had become the guide. The valve had remained seated thus the good compression. I overhauled and/or replaced all 6 cylinders and rod bearings with good result and many more flying hours. If you only knew where I had been flying and had experienced the anxiety you would understand why I recommended topping all six.

Problem resolved. My IA forgot to plug the primer hole of the new cylinder. This caused the roughness. It also made the engine idle higher (800 instead of the 500 that had been normal) and reduced the carb heat drop from about 150 to 50. Now that the plug is installed, the engine runs smooth and acts like it used to.

That was the second issue I had with that shop on this annual. The first one was that they missed the bad exhaust valve on the first borescope. After the first low compression, I flew it for 45 minutes IAW the service bulletin and redid the compression check. Only when they pulled the cylinder after the second failed compression test did they find the valve problem shown in the above picture. I think I need to find another shop.

Skywagon8a, I appreciate your perspective but I don't think I would top this engine given that it's 1850 SMOH. I would just do a full overhaul at that point. Plus, I've read too many Mike Busch articles about risks associated with major engine work while the engine is attached to the plane.

No probs, I always suspect the worst but am delighted when it turns out to be something simple as it was in your case.

Joe, I have had all the cylinders off several cylinders without issues. Mike Busch is a Chicken Little in my opinion. You install torque plates and retorque everything while cylinders are removed and then teat it like you are building the engine up when you are installing the new ones. Not rocket science but scary stories sell subscriptions to Savvy Aviator Services. Granted there are bad mechanics just like there are bad pilots etc. but over the years I feel like Busch exploits the extremes that benefit his cause. I told him that and he said I was to thin skinned. Oh well. Sorry for the soap box just one of my pet peeves.