TBO etc et al

[n86121]

Good Morning Fellow Thrasherists!

I've had my T337 for fifteen years, with a nearly new engine out front (TCM new), and about 1,200 hrs on the rear. I do not expect to sell the airplane for many moons, if ever, so 'TBO' as a market value consideration is nil to me.

My strategy has been to replace any cylinders on the rear as they get weak with NEW TCM cylinders (no metallurgical cycles), and have replaced all of the fuel lines, injector lines, etc. I've done four out of five, and am about to replace yet another. Except for the one about to go, 66/80, the rest all show 74+/80.

Is 66/80 worth worrying about?

I run 50 hour oil samples, and have for years.

My belief is that I can keep the top end of the engine fresh this way, and oil analysis will pick out anything starting to wear on the bottom end.

Years ago I spoke with a TCM guy, who felt this was a reasonable strategy.

I also know a fellow who states that he used to fly for a check carrier that used a bunch of T senecas, (same engines) and they just kept swapping cylinders, and had better than 4,000 on the bottoms ends.

Am I crazy, or does this make sense?

(Perhaps two unrelated questions...)

David Wartofsky - Potomac Airfield
www.potomac-airfield.com

[WebMaster]

David,
Your approach seems reasonable, especially with, what I suspect the VAR issues will be if you crack the case.

As long as the engine isn't producing metal, you will be fine. When we bought mine, the front was at 1750, and was producing metal. It was also non-VAR crank, so we did a reman. As long as I don't have to crack the case, I'm replacing cylinders. I have one on the rear engine that will get replaced this year, as well.

Will we see you at PWA??
Larry

[WebMaster]

Oh, and I heard a new term for our plane, recently, an Engine Sandwich!!

[kevin]

David,

I don't agree with Larry's comment that "as long as you are not making metal, you will be fine." (Sorry Larry.) You can have failures, including catastrophic failures, with no unusual amount of metal in the oil prior to the failure.

I will let others who are mechanics comment on the rest of your message, they are more qualified than I. I will say that I have followed approximately your strategy on both my 337s (and other airplanes I have owned). The difference is that I would not have run my engines beyond about 1800 hours. As the time gets higher, the chances of a catastrophic failure get higher, and if it happens, other than the obvious safety implications, your core is worth less by a good chunk when you replace the engine. Also, I would consider very carefully the wisdom of doing more cylinder work on an engine past TBO. If it is just one cylinder, I would likely do it. But more than one, the chances are that you have to do more at the next 100 hour or annual, or you have to overhaul the engine, and then you don't get much value out of the cost of that cylinder repair (because you are replacing it at overhaul anyway).

As I say, I hope we hear from some of the mechanics on the board on this issue, and on your compression question. My previous mechanic told me that the compression question is more complicated that just a reading of 60/80 or better, or whatever. There is a Continental bulletin on this I believe, and I think it matters whether the leakage is intake or exhaust, etc. etc. But I can't remember the details...

Kevin

[Richard]

I'd say the compression looks fine. More importantly is where the leak is coming from. Exhaust leak.... won't be long till you spit a valve. If you have a good seal on the exhaust side, I'd run it.

I've heard of outraggious bottom end times too, but these engines seem to know when they need an overhaul.... They tell you by leaving messages all over the floor everytime you park it. I've noticed thay when they get tired they just weeze all over from every joint imaginable. If it leaks more than it burns, thats when I'd seriously consider major work.