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Skippydiesel

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Dec 15, 2021
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If you look at a 912 or any other Rotax 4 stroke, you can not help but notice all of the crap hung off of the engine with precariously high mass at long moment arms. No wonder they are maintenance hogs! I use them as a worst case example on how NOT to build an A/C engine.
Ha ha ha!
Not sure what world you inhabit BUT Rotax 912 's have much lower servicing requirements - 3Loil/filter/plugs (if you feel like it) change every 100 hrs. There is also a "rubber" replacement every 5 years - any half decent, well prepared, home mechanic can do the lot in a morning, with all, but a few, parts coming from your local automotive store.. Most will make TBO & well beyond without any intervention at all (there is a mid life gear box check). Personally I find them easy & intuitive to work on. Big plus in my book is they are all metric & just like any automotive boxer engine - simple as.
I have heard LAIM's winging about them but that's because they are brainwashed on LyComs, to work on anything else puts a strain on their comfort zone - no logic in it whosever.
You can argue with me to your hearts content but the sales figures for Rotax 80-114 hp engines, world wide, eclipse the LyCon equivalents (I would speculate Jabs as well).
If you want smooth, low noise, comparatively high power to weight, low fuel burn, reduced air pollution, astonishing reliability - GO ROTAX!!!
 

PMD

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Martensville SK
Ha ha ha!
Not sure what world you inhabit BUT Rotax 912 's have much lower servicing requirements - 3Loil/filter/plugs (if you feel like it) change every 100 hrs. There is also a "rubber" replacement every 5 years - any half decent, well prepared, home mechanic can do the lot in a morning, with all, but a few, parts coming from your local automotive store.. Most will make TBO & well beyond without any intervention at all (there is a mid life gear box check). Personally I find them easy & intuitive to work on. Big plus in my book is they are all metric & just like any automotive boxer engine - simple as.
I have heard LAIM's winging about them but that's because they are brainwashed on LyComs, to work on anything else puts a strain on their comfort zone - no logic in it whosever.
You can argue with me to your hearts content but the sales figures for Rotax 80-114 hp engines, world wide, eclipse the LyCon equivalents (I would speculate Jabs as well).
If you want smooth, low noise, comparatively high power to weight, low fuel burn, reduced air pollution, astonishing reliability - GO ROTAX!!!
As someone who has built race and commercial working engines for a half century, I am truly offended by all of the stuff tacked on instead of being incorporated into the block and head castings.

As someone interested in seeing aviation being sustainable and practical, the dependence upon such a dangerous fuel as gasoline and use of such a highly polluting and unavailable fuel as avgas also offends my sense of what is right.

But, at well over 50k aviation engines in 30 years, I think that they have clearly identified a segment of the market that simply won't tolerate O-200 and O-235 prices and weights. I don't think Lycoming sells quite as many, but bear in mind some of those are 3x the power and 5x the price of a 912. I do somewhat respect what Rotax has done (and have been looking over their shoulder as an OEM customer when they went from start of 2 strokes to start of 4 strokes) but if I am going to cross bush in the dead of winter or vast expanses of open water, I would vastly prefer to do so with a pair of IO-320s that any other recip power supply. I might consider doing that with a pair of Austros today, but sure as heck NOT Rotax.
 

TFF

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912s and 235s, the question is European or US? It makes a big difference.

First, no one buys overhauled 235s from Lycoming. In fact when my friend bought his O-320 to replace his 235, Lycoming took it in on a trade because they had none as cores. It was a surprise. Overhauled 235s are almost all field in the US. The value of the airplanes they are on don’t allow expensive overhauls. When all the 235s were manufactured they were $5000 engines new. Because they cost a lot more now doesn’t mean they actually sell any. Lycoming just hast to have the option available. No one uses it.

912s are a mixed bag, in my experience. I have had to do more engine work on them overall than Lycomings. They might be great if flying day in and out, but for a lot of how they are used in the US, they might get three months of summer run time in a specialty airplane and sit the rest of the year. While sitting isn’t good, the same sitting for a Lycoming is less trouble. And an American owner wants it when he wants it and forgets about it the rest of the time. The Rotaxs are always a fight to wake up. Lycomings will just run. Wear in these situations is measured in tens of years so TBO is usually a non issue.

Europe has to maintain their aircraft differently. It doesn’t rain airplanes any worse here or their, and we have at least double the number of private planes to the whole world. They are different places and different uses.
 

Pops

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Hard to beat a Lyc 0-320 and parallel valve 360. Have about 1700 + hrs flying behind the Lyc- 320- H2AD and never trusted it. We had a factory rep here one time right after the H2AD came out. Trying to tell how great an engine it was. Local flight school owner spoke up and said he had 2 and both didn't last 100 hrs. The rep just said we are still working on the problems and changed the subject and talked about he is the third generation working for Lyc.

BTW-- When I was at the Lyc factory and museum the only Lyc engine not there is the H2AD. I ask why. The tour guide said " we never made that engine".
 

Dan Thomas

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First, no one buys overhauled 235s from Lycoming. In fact when my friend bought his O-320 to replace his 235, Lycoming took it in on a trade because they had none as cores. It was a surprise. Overhauled 235s are almost all field in the US. The value of the airplanes they are on don’t allow expensive overhauls. When all the 235s were manufactured they were $5000 engines new. Because they cost a lot more now doesn’t mean they actually sell any. Lycoming just hast to have the option available. No one uses it.
I bought Lycoming factory overhauled engines, including the O-235s, and they cost little more than field overhauls (and cost less in some cases) and were of far better build since almost everything was new. Lycoming doesn't waste time trying to save worn or corroded stuff. Once in a while I'd get a brand-new engine at the overhaul price because they were short of cores.

American Champion still uses the O-235 in its base Citabrias.
 

TFF

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I got a few new engines over the years for the helicopters. Odd model got what they could give out.

The IO-233 is the saving grace for the 235. Same engine. So I guess they do make new ones. Lycoming makes about 1500 new engines a year now. Overhauls about the same number. Champion makes about 40 planes a year of all models together. They aren’t buying many. 5 years ago when I did the engine swap, Lycoming sounded like it was rare to hear the name 235 from the tech guys.
 

proppastie

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what impressed me about Rotax just listening to them.....starts like a car and sounds like a sewing machine or Japanese Motorcycle. ....what impressed me about the 0235 was the solid non hydraulic lifters and the big manual adjustments on the rockers.....adjustment of the valve lash with a screwdriver and feeler gauge.....
 

Pops

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Adjusting rockers with solid lifters is so simple that 6 year old could do it. The hardest job is getting the valve cover off and on.
 
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Dan Thomas

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what impressed me about Rotax just listening to them.....starts like a car and sounds like a sewing machine or Japanese Motorcycle. ....what impressed me about the 0235 was the solid non hydraulic lifters and the big manual adjustments on the rockers.....adjustment of the valve lash with a screwdriver and feeler gauge.....
The O-235 is the only current Lyc with solid lifters. I don't know why. Setting those lashes has to be done in accordance with the Lyc manual, or you get goofy results. The crank has to be rotated to get certain valves closed and others opened, to force the camshaft over to one side before setting the lash. There's enough clearance in the cam bearings to make a difference. Doing it wrong could result in too little clearance and a burned valve.

We had to do the lash checks every 100 hours.

My 1946 Continental had hydraulic lifters.
 
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proppastie

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My 1946 Continental had hydraulic lifters.
My first Aircraft overhaul 1943 A65....I was very impressed with the new limits tolerances for what was to me a very old engine....I would guess the valve guides were manufactured on a cam operated Brown and Sharp belt driven screw machine with an overhead line shaft the length of the screw machine bay. I recently looked at a firearm built in 1912 and it is a work of art manufacturing wise.
 

Bob H

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Jun 9, 2022
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The 912 uses flat tappets as did American muscle cars in 1960s. Oil companies added ZDDP to oil to keep cam and tappets from wearing and all worked well until the cars began to show bad cam wear in 1980, right after cars had to install catalytic converters. Turns out the ZDDP in oils poisoned the converters so the oil companies reduced the concentration of the ZDDP and that caused the cam issues. Auto manufacturers switched to roller tappets which did not need the ZDDP and auto owners were happy...except for Harley motorcycles which had the flat tappets.
To keep the Harleys going, oil suppliers formulated oil with the ZDDP back in it and could legally sell it for the Harleys because they did not have the converters. And the same oil for Harleys works great for 912 tappets. Mobil 1 V-Twin oil is full-synthetic and has ZDDP in it. Walmart sells an equivalent Quicksilver motorcycle oil with ZDDP. But full-syn oils don't hold lead particulates in suspension like mineral base oils do so using av fuel 100LL caused lead to deposit in the cooler running 912 engines. Then Rotax contracted with Shell Oil to produce the Aero Shell brand which is 70% mineral and 30% syn and has ZDDP in it. This blend has most of the beneficial properties required for good operation for the 912.
I use the Quicksilver in my 912 engines with good results and try to use unleaded mogas exclusively. On long cross country trips where I have to use 100 LL, I add TCP to fuel to minimize lead deposits.
 

Skippydiesel

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Dec 15, 2021
Messages
66
The 912 uses flat tappets as did American muscle cars in 1960s. Oil companies added ZDDP to oil to keep cam and tappets from wearing and all worked well until the cars began to show bad cam wear in 1980, right after cars had to install catalytic converters. Turns out the ZDDP in oils poisoned the converters so the oil companies reduced the concentration of the ZDDP and that caused the cam issues. Auto manufacturers switched to roller tappets which did not need the ZDDP and auto owners were happy...except for Harley motorcycles which had the flat tappets.
To keep the Harleys going, oil suppliers formulated oil with the ZDDP back in it and could legally sell it for the Harleys because they did not have the converters. And the same oil for Harleys works great for 912 tappets. Mobil 1 V-Twin oil is full-synthetic and has ZDDP in it. Walmart sells an equivalent Quicksilver motorcycle oil with ZDDP. But full-syn oils don't hold lead particulates in suspension like mineral base oils do so using av fuel 100LL caused lead to deposit in the cooler running 912 engines. Then Rotax contracted with Shell Oil to produce the Aero Shell brand which is 70% mineral and 30% syn and has ZDDP in it. This blend has most of the beneficial properties required for good operation for the 912.
I use the Quicksilver in my 912 engines with good results and try to use unleaded mogas exclusively. On long cross country trips where I have to use 100 LL, I add TCP to fuel to minimize lead deposits.
Terrific information Bob - I have been flying Rotax 912ULS for about 12 years - so far great reliability, economy, smooth, quiet (relatively) and performance.
To minimise any need to use AvGas, on an away trip, I carry two 20L collapsible fuel bladders, so that I can get ULP off field - system works well and there is usually a friendly business/private individual who will lend or transport me to the nearest reliable source of 95-98 RON.
For personal piece of mind, I do a 50 hr oil change (no filter) using AiroShell Sport plus 4 - no science behind this but I do hope I am enhancing my engines longevity.
 

Skippydiesel

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Dec 15, 2021
Messages
66
That is not correct. The by-pass valve prevents oil starvation when cold, thick oil is clogging the cooler. It also prevents oil starvation if the cooler becomes clogged with debris/sludge. Dependant on the susceptibility of the cooler to these issues, the latter functions can be vastly more important than a fast warm-up. The by-pass does need to be checked, including for correct orientation. Removal for test purposes is reasonable. However, the first priority in this instance is check and calibration of the instrumentation - replacing the instrument does not in itself assure that the temperature data is correct.
Paul - your concept of oil performance when cold, is somewhere back in the mid 1900's (or earlier) when all that was available was single weight (viscosity) oils. We now have multi grade oils that change viscosity as its temperature increases. Some synthetics start as low a 0 (scary ) and pour just like water when cold. Aviation oils may not have such a low cold viscosity but certainly down to 20 is common.
So the use of an oil thermostat/valve to bypass oil "prevents oil starvation when cold" is of questionable value, if in fact this was ever its purpose, which I doubt.
Thermostats are primarily about speeding engine warm up and in some applications to assist in maintaining engine temperature within optimal operating conditions (say on decent) - they do this by automatically bypassing the external cooling system ie oil/coolant radiators.
 

rv7charlie

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You can be a doubter, but doubt has little influence on the aviation world's reality. Lycoming and Continental aviation oils, are mostly single-weight, and even the multiweight oils are being run in engines that were designed to run single-weight. Lyc oils are typically 50 weight. Consider a positive displacement oil pump (they all are) trying to push 100% of the oil through a cooler with the temp of the oil somewhere below freezing temps. Stuff can break.

Try googling 'vernatherm for Lycoming' for more info.
 

TFF

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You might get 95 RON gas but around me only 91 RON non ethanol. The Aeroshell Sport seems to be their Ducati oil in 10-40. Motorcycle oil was recommended before they got their Custom oil. The Aeroshell was probably invented to keep Americans from dumping 50 wt in like they want to.
 

Skippydiesel

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Dec 15, 2021
Messages
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You might get 95 RON gas but around me only 91 RON non ethanol. The Aeroshell Sport seems to be their Ducati oil in 10-40. Motorcycle oil was recommended before they got their Custom oil. The Aeroshell was probably invented to keep Americans from dumping 50 wt in like they want to.
91 RON! - so how do you comply with the Rotax recommendation for minimum 95 RON?
We in the "Lucky Country" (Australia) used to be able to get 91, 95 ,98 RON in unadulterated (no ethanol) ULP. Unfortunately a lot of fuel stations have rationalised their service to 91 & 98 RON, despite a lot of vehicles specifying 95 RON. So these days, I mostly use 98 RON (always from a high turn over/popular supplier of a known brand).

When I started with Rotax they had just brought in the AeroShell - the manual was still listing approved motorcycle oils, many of which were not available in Australia). They had tp be of the correct multigrade viscosity, & be compatible with an integrated (shared oil supply) gear box that had a slip/dog clutch.
 
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