R

rookie1255

Member
Cylinders can be rechromed, then replaced when they can be rechromed no more. Crankshafts can be ground, crankcases repaired. Will IRAN forever always be cheaper/a better value than overhauling? Even if something expensive needs to be purchased it would be cheaper than mandatory replacement of cylinders, etc...

Granted the engine would have an absurd total time and TSMOH, and while it may not ever be "overhauled," a disassembly and inspection of component service limits might be advisable around overhaul time for safety's sake.

Part 2 of my question is value. Would the above method be the best way to get the most bang for your buck, or would you actually lose money due to decreased engine value? How does this compare with the following methods:
1)Field overhaul to service limits
2)Field overhaul to new limits
3)Overhaul to service limits
4)Overhaul to new limits
5)Factory overhaul
6)Factory new

Which method provides the highest ratio of value:cost?
 
With modern day engine monitoring systems, I think many engines will run longer than they used to thanks to avoid excessive CHTs, at least for cylinders.

Cranks may last longer since we are able to avoid detonation and cams should last as long as the engine does not sit for too long without oil to stop corrosion.

So, the value might really be in a good engine monitor versus the method of bringing the engine back to life after it requires repair.
 
While theoretically one can go forever on IRAN type maintenance, but the question soon becomes reliability and how much interim maintenance you find acceptable as things become a problem and demand down time for repair.

The other principle that drove Lycoming to eliminate chroming cylinders and to drive replacement cylinder assemblies into the marketplace, was fatigue. The engine vibrates, and everything metal have fatigue limits when're cracking and possibly catastrophic failure can occur. This typically is seen in cylinder head cracking for cylinders overhauled several times and more, crankshafts that go long lives, even crank cases crack. The longer they are in service the higher the fatigue risk. I have operated 320's into the 4000+ hr range without overhaul, and I suspect the fatigue issues really don't show up until several thousand hours more. However if you bought an engine with overhauled, especially chromed cylinders, you have no idea how many hours in service they have seen from a fatigue standpoint. One operation I worked with kept chroming cylinders and were replacing them due to cracked heads a couple of times per year for each airplane. I stopped that practice, put all new cylinders on as replacements and the cracking problems weren't away. This was for a small fleet of airplanes flying anything from 320's to 540's.

On a new engine I suspect not replacing parts is ok if you can be sure you keep your known hour parts on the engine. Often cylinder chroming or rework are exchanges, you don't the time on the cylinders you get back.

Anyhow, a cost analysis can be done to determine best value, but if you get the last penny out of the engine and it quits with much excitement was it really worth it?
 
An overhaul to service limits is not much better than a whack with a hammer. Since you have to split an opposed engine to do any lower end work there isnt much savings in either labor or parts. I'm not seeing the IRAN value so much because these engines are simple and clearances etc grow at a fairly well known rate. When you have a bunch of time on the bottom end you usually also have a bunch of years. Rip it down, make it new and pretty inside with quality parts and new limits. Everybody feels better. Cylinders are catch as catch can. If you get a set that actually goes the distance they're gonna be ready to go. Even the terminology of overhaul doesn't apply to experimentals. You don't have the luxury of "shutting down number one", so don't wait until it breaks.
 
reminds me....

Reminds me of a great cartoon under the glass at the Volvo parts dept counter.

The parts guy has just asked a customer what year his car is, and the customer replies, "well, it was originally a '64, but if you account for all the replaced parts, it averages out to about a '75."
 
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