O-340-A1A review & comments

[anejohn]

Any comments on the Lycoming O-340 A1A 170 Hp engine. Every thing from durability, performance, available parts etc. are welcome. I understand the A1A model is the only version of the O-340 series that supports a hydraulic adaptor for the constant speed prop option. Comments about the constant speed prop performance and maintenance would also be helpful.
Thx all

[Bill_Green]

My 1952 170B had the O-340 installed in accordance with the original Doyn STC in 1957. The specific Hartzell propeller that is part of the conversion is subject to a recurring inspection. As I understand the history, the O-340 was an evolution of the original Lycoming O-320 series engines. The development of the O-360 series soon left the interim O-340 engines as the unsupported step-children at Lycoming. Being that the O-340 was not produced in the large numbers that the other four cylinder engines have been, combined with the limited propeller options, seems to have relegated us Doyn converted 170 owners to a shrinking minority. All that being said, my experience is that this is a good combination. The engine is quite smooth, delivers cruise speeds comparable to a C-145 powered 170, but with somewhat better takeoff and climb performance. It should come as no surprise to anyone in this group that flying this 170 still puts a smile on my face. What more could I ask for?

[anejohn]

Just came across this post in 2010 from Scott who was answering a forum post & thought I would repost it here. The original question was from a member rebuilding a C170B with this STC and he was asking for help in finding the exact STC version.
Very interesting response.

“by ‪Blue4‬ » Wed Jun 02, 2010 1:34 pm
I looked at purchasing a 170B with a 170 hp O-340 engine, so I did a little homework on it. It is my understanding that there are several versions of the Doyn / Doyne conversion. (I've seen it spelled both ways so many times I haven't a clue which is correct -- much less the proper pronunciation!)

If the airplane I was looking at had the sole sin of an O-340 engine, I would have bought it. Money well-spent on a prebuy, however, had me pass. 2 airplanes later, I'm very happy with the one I bought (with an O-360).

The prop is a major headache. The number I've heard quoted for new propeller is $19,000. Yes, $19k. Its my understanding that there is not another prop available with the STCd engine. Parts such as cylinders are available, but they are rare. Neither of these are a show stopper, but its not going to be easy.

My final and important point is this: once you locate the exact STC your airplane was converted under, look hard at the paperwork. _SOME_ of the Doyn conversions allowed for EITHER an O-340 or an O-360. Well, wouldn't that be nice? O-360s aren't cheap, but they're ubiquitous. In pilot-speak, that means you can find a lot of 'em easy. An O-360 would solve your propeller problem as well. I wish you the best of luck, we're curious as to your results!
-Scott”

[n2582d]

D’Shannon now holds STC SA3-13, the old Doyn Lycoming O-340 STC. For those looking for missing paperwork, it might be worth trying to contact them.

[Bill_Green]

In the Engine sectIon of the MX Library there are a couple of entries on the subject of the O-340 Lycoming conversion. One member has even sent in an electronic copy of the installation drawings, which I was not able to obtain anywhere else. So, as is most often the case, this organization proves to be the best resource for information on operating and maintaining 170's.

[anejohn]

I think it’s time tie up this tread and thank everyone you who put in their two cents in on this topic. Especially Bill who reached out to tell me about his great experiences with his C170B & the O-340 STC. This gave me hope. I did find a lot of information on this topic by searching through Google, most coming from this Forum group. I also reached out to three engine repair stations and two propeller repair stations for their input. The general consistence is Lycoming and Hartzell no longer supports these components. Serviceable parts maybe hard to impossible to find. Some operators with this STC have already accumulated an inventory of parts but new comers would need to start from scratch.
One engine repair station commented that cylinders are not a problem since the O-320 cylinders can be modified but the rods or crankshaft are unique to the engine because of the longer stroke. For parts acquisition the TwinNavion aircraft also used the O-340. Though I’m not sure about the TwinNavion engine series. There are four versions of this engine but only the A1A has the hydraulic propellor control used by Hartzell and its constant speed propellor components.
As for the Hartzell propeller and hub assembly, that’s a completely different story. Again because parts supply. Besides a repetitive AD inspection every 250 hours or 5 years. (A.D. 97-18-02 R1) This repetitive inspection calls for a fluorescent dye penetrant and the eddy current process of the blade and retention area of the blade. In addition to a magnetic partial inspection of the blade clamps.
A neat back story about Hartzell. When I brought up the forum comment about a prop hub costing $19k, the prop shop guy commented that was probably when the “Browns” owned Hartzell and they would do custom projects like that for customers. But the ownership has changed since then and custom work like that is no longer an option.
So as much as I liked the idea of a 170 hp O-340 A1A in a Cessna 170, I’m going to pass on this one.
Too bad Sensenich never invested in a STC for a fixed pitch propellor option for the O-340 and the remaining Cessna 170B operators.
Hope I got all this right, thanks for reading.