Backcountry Pilot • O-320 vs Rotax 915is

O-320 vs Rotax 915is

Lycoming, Continental, Hartzell, McCauley, or any broad spectrum drive system component used on multiple type.
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Re: O-320 vs Rotax 915is

Bathman wrote:I haven't got any experience of the 915 but I have plenty of experience of the 912.

I'm also not sure comparing the O-320 (160hp in most versions) to the 915 at 140 is really fair.

I've put over 5200 hours on my 912. Its never had a sticking valve, a cylinder off in fact the engine itself has never had any work done to it whatsoever. I know people go on about the high part prices well frankly it doesn't matter as none of the high priced parts have ever failed.

What I have had to replace is consumables and I would include carb rubbers in that. I’ve also had sinking floats , the last time being about 200 hours ago so I got both carbs overhauled and that still worked out cheaper than what previously paid for an overhauled carb for an O-200.

Oil is cheap, spark plugs are cheap and the 600 hour gearbox overhaul is also cheap also. Although I’ve been told my gearbox wont overhaul again. So at 5600 hours I’m simply going to pull the engine and replace it with a second hand engine with about 1000 hours on it.

AVGAS isn’t a major problem you just have to change the oil every 50 hours and the spark plugs every 200 hours. The oil is dirt cheap semi-synthetic and the plugs are only a few dollars each so I just replace them. And as already mentioned when run on AVGAS the sump needs all the lead cleaning out. In fact my airframe and engine is cleared for 10% ethanol which certainly makes things easier.

My experience with conti and lycoming is not very good. In fact my last 6 engines have failed to make TBO. Two of them were factory rebuilds as well. I think they are just junk

In the 915 the fuel consumption is bound to be less than an O320 and I know people keep going on about specific fuel consumption being the same. But in practice its not going to be the Rotax with all its sensors is adjusting the mixture far more accurately than any pilot can with a mixture lever.

The Rotax 915 might have some teething problems but once they get sorted out it will corner the market just like the 912 has for LSA. Anyone for a O-200D? No thanks


My experience also, though only 2700 hours. It's like every Toyota I've ever owned, it just runs! Let's not forget the almost total lack of oil consumption also, we are not adding qts. every few hours
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Re: O-320 vs Rotax 915is

I remember the shiny five gallon oil reservoir on the beautiful Aero buildup of the R-985 on the junky $10,000 Stearman I sprayed one season with. Some really good engines just aren't practical anymore. O-320 still has a ways to go I think.
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Re: O-320 vs Rotax 915is

That’s the most time I’ve heard of on a single 912 yet. I’ve flown too many IO-540s to consider them junk, in my experiences they’ve been rock solid. I’ve had a cam round off, mag issues, oil leak to a cooler but nothing that would make me characterize it as junk. They are however very heavy and very antiquated, as is true of my 320.

Robinson at their factory will also tell you in dyno’ing new 540s, they never get rated power from the brand new engines they receive from Lycoming. They fall well short, even considering they’re not yet broken in. They don’t care as they’re derated in that application anyhow, but I was cautioned my 300hp engine in the Wilga 2000 wouldn’t actually put out 300hp on a well calibrated dyno. The turbines measured to the same test standards routinely exceed, and are expected to surpass their hp ratings in comparison. Reliable, the Lycoming 320/360/540 certainly is however.

On the comparison in my application here, I suspect the 915 with it’s 141hp, much lighter weight, and constant speed will certainly outperform the fixed pitched 320 in my application. This won’t be true of all comparisons. Being able to carry less fuel and having a lighter engine at the same time is a game changer, plus a lightweight constant speed will make a huge difference- can’t slight my 320 for not being CS it’s just a reality in this swap. It certainly will perform better overall where we like to land floatplanes at the tree line though, with the CS, lighter weight, and turbo.
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Re: O-320 vs Rotax 915is

I just thought I would post an update.

I pulled the 912 at 5536 hours. The gearbox was really starting to rattle, I had got my money's worth and I was worried if it did go bang, everyone would be saying how stupid I was.

Well I sold the engine for 1500 dollars to the local Rotax maintenance outfit. I couldn't believe it when he offered me that much but he was confident that he would be able to use parts of it. He had overhauled the carbs 400 hours earlier and the ignition boxes were the updated ones from europe.

After stripping the gearbox was as expected junk. The camshaft was visibly worn but as for the rest of the engine it was perfectly serviceable You could even see the honing on the cylinder walls and they measured well within limits. In fact he said the cylinders would be reused and he knows of examples with 8000 hours on them.

The local experts have always given the Rotax a hard time probably because they aren’t lycoming or conti but also because of the noise they make on shutdown.But they don't fly the hours I do so don't realise how outdated they are.

I’m absolutely sick of Conti as the last factory rebuilt 0-200 engine had to repair work on 3 cylinders within the first 500 hours and the two before that both had main bearing failure at 1200 hours. So if the 915 is half as good as the 912 it will be a winner.
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Re: O-320 vs Rotax 915is

Rebel on ice.jpg


Enjoying the thread on the engine choices. The good old O-320/360 types are hard to improve on. I agree that the Rotax has gained quite a following and is the way of future powerplants are heading. The downside for me is the complexity of these newer engine systems. Living in the woods and no Rotax authorized places anywhere within a couple hundred miles, I will stick with the Lyc/clones for the time being. They're basic engines that most anyone can work on.

My Rebel has an O-320 and the Kitfox belongs to a friend. It has the Yamaha RX-1 motor. It performs nicely and sure seems smooth running. This is a picture from a couple of days ago when we met up on a local lake.

I have been plowing my strip so I can fly on Bushwheels. Time for me to go on skis.
Snow depths south of me are under 6" while at my place it's much more like a foot+.
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Re: O-320 vs Rotax 915is

Just read the entire thread. :)

I have flown 912’s and 915iS’s and both are great. I think the 915 is hands down the best engine around and not 70+ year old technology. I highly recommend NOT burning 100LL, the sludge buildup is significant.

That being said, I am putting a O-360 angle valve Lycoming in my build that is setup for MoGas, so 190hp rather than 200hp. Why? The weight! My Bearhawk is not designed to have a lightweight Rotax on the nose, and I did not want to be the guy that spent an extra 18 months designing the engine mount etc for the W&B.

I wonder how much the Rotax 916 will weigh? Should find out soon I suspect
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