How Lycoming (and Rotax, and Continental) build engines

compare 3:38 in the rotax video
with 2:26 in the Lycoming

pmh wrote:

compare 3:38 in the rotax video

Juuuust prior to that, the video quickly mentions that Rotax 912/914 crankshafts are pressed up from multiple pieces like their two-stroke cranks. Funnily enough they didn’t show that particular operation in the video… Anybody here have any experience in that area, and the subsequent alignment process? (says he ) Here’s a video by a guy who thinks he has a clever way to do it with a simple single throw crank, much simpler than a 912 crankshaft

You’ll notice there’s a lot of screwing around, its a classic tool room style job. I don’t how Rotax approaches crank assembly and alignment, but when it was still common practice for four cyliinder engines produced in high volume motorcycle engine factories (up untl the early 80s), they utilized lead hammers or alternately a lead faced bench top onto which the crank could be repetitively dropped by hand to laboriously knock all the throws into aligment with each other. Its not exactly a robotic process

Videos aside, most of the work in making anything is in making the parts and subassemblies.

It’s interesting to look at the scale of things. Lycoming makes 1500 new engines each year. Rotax makes 14000 (7% of 200k). Rotax makes almost ten times as many aircraft engines as Lycoming, or almost twice as many today as Lycoming did in their prime.

ULPower is also interesting. It’s basically one milling machine producing the parts (most of the parts)

Peter wrote:

I think pressed cranks are a horrible approach. But they do allow the use of a one-piece conrod.

Yes, and a few other things. In the old days when people didn’t trust oil pumps and/or built two-strokes, built up crankshaft and needle rod bearings (which are relatively tolerant of poor oil supply) were much more common. One four stroke aircraft example would be pre-war Hirths, German engines. Another advantage is that the crankshaft is slightly shorter because the individual pieces can be machined in a way that machining of a one piece crank prevents. You can’t grind the rod journal for a Rotax 912 crank if it were made in one piece. There are always specific advantages to any technology, even after they fall out of favor for very good reasons.

@LeSving, I’m certain that l’ll never buy an aircraft engine new, only parts.

Silvaire wrote:

I’ll never buy an aircraft engine new, only parts

So do I

Peter wrote:

How many of the 14k go into go-karts, etc?

I think Rotax makes 3000 or so aircraft engines per year. The rest are mostly snowmobile and motorcycle engines for Ski-Doo and Can-Am. They used to have a substantial business with BMW and Aprilia motorcycles (once the exclusive supplier for the latter) but that has dropped off a lot. BMW moved to China and Piaggio, an engine manufacturer, took over Aprilia.

I seem to remember reading / hearing that the default way to overhaul a Rotax was to replace the whole thing. I take that is not true and overhauling them is cost effective?

A few people do advertise Rotax overhauls, but the parts bill appears expensive. Without any personal experience it appears to me that for a major overhaul you’d reuse Rotax crankcases and cylinder heads, and not much else. My engines are a 65 HP A65 Continental and a 150 HP O-320 Lycoming. Both can be overhauled quite a few times, in my useage effectively forever. I picked the planes and specifically their engine models with stuff like that in mind.