TBO Decision

[N1424D]

I have a very nice, highly polished '51 170A which is almost to TBO [1,700 hours on the engine now]. It has excellent avionics and interior; a real 'keeper' airplane. Although it is running very well [annual just completed with compressions all in the 70's and about 1 qt. of oil per 5 hours] I recognize that I must eventually do 'something' about the engine. I am wide open for suggestions as this is the first 170 I have ever owned [previously owned 180's and other things]. I would like to hear pros and cons for overhauling my engine [C145], or changing to O300, or even changing to O-360A with or without a CS prop. A friend has an 0-300D which he has offered to rebuild for me, but I don't know if that is a legal engine in my airplane or even if it's a good idea. You folks have all the experience in the world and I'd really like to hear your suggestions - maybe one of them will be that I'm in the wrong place on the website, in which case I apologize cuz I'm new at this, too! Thanks for any and all suggestions. Don Lindholm; N1424D; SDL.

[N1478D]

Unless you are doing alot of flying over unforgiving areas, I would fly another 100 or 200 hours and then start looking at your options. The C145 and 0300's are basically the same engine. You can search and find out all of the differences here on this site. I sure am happy with the C145 in my A, have put over 800 hours on it and hope to run it at least to 1800 hours. The plane is flown often which helps the engine last longer, but the hours pile up faster. Like they say, the worst thing you can do to your airplane is not fly it, the second worst thing you can do to it is fly it.

[zero.one.victor]

According to my copy of the TCDS, the C-1452 (& 2H) along with the O-300A are approved. An O-300D would require a field approval or STC. That said, they are plenty of 170's flying with the D engines. Check with 170 Assn HQ for copies of field approval 337's &/or STC's for this swap, or in the back of The 170 Book for STC listings.
You'll need a 6 bolt prop ( & spinner stuff), and a new starter/starter drive if the D engine you're considering doesn't come with them. Also need to wire in a starter button. I think most everything else off the 145 should work.
Personally, I'd just stick with the C145. Except for being able to overhaul the other engine ahead of time & avoid downtimem, the only advantage I can see is the D engine's vacuum pump if you feel you need one of those instead of the trusty "deer horns".

Eric

[Bruce Fenstermacher]

It sounds like you feel you engine is safe to operate. I would continue to do that till you don't feel safe regardless of the total time whether it's 50 hours or 500 hours from now.

Don't fix something that's not broke. I'm not saying through caution to the wind either. New engines fail to. A friend has a 6 month, 75 hour Mattituck (a well respected East Coast Rebiuld shop owned by TCM) engine back to Mattituck for tear down for excessive metal. Their old engine was operating just fine but one day it hit the magic 2000hr TBO (Lycoming) and out it came.

Joe hit the points about the difference between the c-145 and the 0-300. There is a STC from an association member to association members that is very very resonably priced to install the 0-300D if you go that route.

If and when the time comes if I where you I'd rebuild your C-145 like I just did. The only benefit I see to the 300D is the possibility of the vacuum pump and that isn't a real big plus in my mind.

There are plenty of discussions here about bigger engines. Most of us would like to have the power of one but most of us don't want to pay the high price involved. Do a search for these posts. I'm sure you'll find hours of reading.

[blueldr]

Why not gve some thought to what you would do with your engine if it had only 900 hours, but it used a quart of oil every 1 1/2 hours, the oil pressure was at or below minimum, oil temperature was real high, compression was terrible and the valves all were leaking. Sounds like time for a major overhaul, doesn't it? You need an overhaul because of the "CONDITION" of the engine.
Right?
Now consider your engines present "CONDITION". Sounds to me like it's pretty good. If it was mine, I'd fly it until its "CONDITION" indicated thet it needed something. That being either a "Top" or a "Major". I've seen a good many 300 cu. in. Continental engines go to 2400 hours without any problems at all. Admittedly, these were generally engines that were flown regularly and frequently and had the proper care in the manner of preventative maintenance.
It really boils down to "Don't fix something that isn't broke!"

[N2218B]

While I don't necessarily recommend it, I ran my last engine to slightly over 2400 hours. When I bought the plane it was approaching TBO but the engine appeared to be in great shape. It had been topped at 1200 hrs and compression and oil consumption were all good. I just continued to monitor everything and flew the heck out of it. At 2400+ I decided I had pushed it enough even though it seemed to still be running well. I now have about 650 hours on the new engine and I have to admit the last 600 hours flown with a new engine were more comfortable than the last 200 or so hours I flew the old engine. It comes down to a matter of trust.

Now for the downside. On teardown we found the engine to still be in good shape with one exception. The crankshaft was cracked in two places! Could that have something to do with the notation in the logbooks about a freshly overhauled prop that I saw but ignored when I bought the plane? Bottom line? The 0300 is a good engine and will hold up well if flown often but the previous history of the engine must be considered.