? Rotax 912 minimum things that need to be done for specific hours up.????

[RFguy]

Am looking at procuring a 912ULS.

 

There are a few at 2000 hours. 

 

There are a few at 1500 hours from time to time

 

and of course a new one.

 

Assume aircraft is experimental registered and all approvals got. Put aside electricals and  carburettors, starters etc.

 

The 2000 hour ones, if they make great leakdowns and the oil analysis looks good, and they're not too old - Some private, not flying school ones are old old 20+ years and not many hours. 

the gearbox/clutch would have been done at 1000h (most likely) and the clutch may have been done  again since 1000 h. 

I understand the bores are like diamonds and pretty much last forever unless they're been badly treated, same with the heads unless there has been an over temperature incident (is there with one- way temperature paint ????? ) 

 

They seem like good value . I have not heard or read of anything catastropic going on in 2000+ 912 built in the past 12 years.

 

then there is a big dollar step to sub 2k hours, approx $14/hour remaining. 

 

then there is a new one which makes sense if you are going to keep it till TBO and fly at least 150  hours per year.

 

-glen

 

 

 

 

 

 

 

[Kyle Communications]

My engine for the S-21 is a 2015 2000hr ex flying school engine. It cost me 5k to buy

My pistons and cylinders are brand new in the guise of a big bore kit

The engine totally disassembled and measured to make sure all is still within spec and no fretting of the cases.

The crank has been welded and all rotating moving parts have been balanced 

All new inlet and exhaust valves and springs and collets the heads are original but have been cleaned and speced

All new through bolts and studs

All seals and Oring's and bearings replaced

New sprag clutch

The gearbox has new bearings and seals and has been retorqued to spec

All new oil and water pipes and fuel pump as in the 5 year replacement

Most of the major parts are after market but some just can not be bought that way

Total cost to me is around 13k  others will be much higher

Total cost if using genuine Rotax parts would be around 25-27k..new engine being about 34k now

This will give me 114hp as stock power, with a tricked tuned exhaust I am hoping to get close to 120hp

 

[RFguy]

Good answer Mark.

OK, so to get piece of mind, and also since you want / get extra output, so the rebuild was required anyway, and once you start a rebuild, you dont stop until its all just right.  As I discovered on the Jab top end rebuild- no point in 90% doing anything, might as well once you are there, do it all 100%, bring it up to new, or better than new (in my case). When I say 'new' I don't mean wear on parts, I mean reliability /dependability compared to new. like, my valves were all in excellent condition. no need to change them.

 

Edited June 12, 2021 by RFguy

[Kyle Communications]

on rebuilds for Rotax at TT then you are supposed to change the valves and of course springs etc. The biggest issue with any Rotax rebuild is the block and the journals. A mate went through 3 engines before he found a good one to rebuild. There are a lot of blocks out there that you dont know until you strip them what lies beneath. So if you buy a engine you do so on the proviso that when it is pulled apart that it is able to be rebuilt otherwise you get stuck with a 5K or 6k ornament

 

[RFguy]

there are a few around 2- 4 k from time to time.

but as you say, be prepared.

 

 

 

 

[facthunter]

You are usually starting with the 100 HP version and all of them had the drive clutch which is definitely going to be more of an issue with more power through it. I've seen rebuild needed there well before 1,000 hours it's infinitely more easy to install a C/S prop on that set up if that's a possibility but you are into the giant dollars.. There's a mod or inspection on the drive end of the crank too. Nev

[Kyle Communications]

Yes Nev the block, crank and cam have all be crack tested including all in the gearbox The crank has been welded to take the extra hp, the cam has been totally reground to ensire corrent profile so that the lifters rotate and the gearbox is exactly the same that is used on the 914 engine so it will take the power. The lifters not rotating has been a issue for the Rotax and this has been the source of cam failures in Rotax, The big thing for the gearbox is the weight of the prop and extension and spinner. Mine is only 2.4kg total and extremely balanced so gearbox load and wear will only be by the physical hp applied to it. The main bearings in the gearbox are now SKF and not Fagg  the SKF is a better bearing

 

[Kyle Communications]

My rebuilt engine showing the lifters rotaing as they should after the cam profile had been done correctly

 

 

[facthunter]

That's usually achieved by offset of the cam to the lifter centreline. To make things even more interesting the lifter face is slightly convex. Nev

[Kyle Communications]

yes the issue was the grind on the top of the cam lobes..it wasnt profiled enough to make the lifter spin. The wrecked engine Danny and I bought to have spare parts actually had that failure..the cam wore through and that cylinder when bang

 

 

[facthunter]

On Non roller cam followers the most critical lubrication surface in the whole motor is the cam lobes.  A lot of them require friction modifiers that some modern oils don't have as they kill the Cat converter that many later vehicles have. Nev 

[onetrack]

Quote

The main bearings in the gearbox are now SKF and not Fagg  the SKF is a better bearing

KC - I wouldn't bet the house on that. In my experience, SKF is now a global corporation, and they source their bearings from anywhere.

I've had SKF bearings that weren't up to par, they were from an Asian manufacturer (and it wasn't Japan). They failed to provide satisfactory lifespan.

I always look for the stamped information on the bearing that says, "Made in U.S.A.", "Made in Japan", or "Made in Germany". Only then can you be guaranteed that the bearing is top quality.

I've bought thousands of bearings in my 56 years of repairing, and ran the machines they went in, too. You learn a lot about bearings after that length of time - including things such as "proprietary line" bearings - bearings made specifically to a manufacturers specification for a specific position in a specific machine. These bearings do not follow SAE specifications and standards.

And you can have identical-looking bearings with different load capacities and ratings, only suffixes or prefixes on the part number indicate the difference.

 

Edited June 12, 2021 by onetrack

[Kyle Communications]

These are not made in china..from memory they were made in germany..all the ones we got. The specs between the Fagg and SKF are the same..I think Rotax changed because they got a better deal on bearings.

 

 

[walrus]

Be sure that the cases are post 2002? Before then, cases had a habit of cracking near the gearbox at higher powers. There is an SB  about it.

[Kyle Communications]

yes  mine was a 2015 engine...but they will still frett but no where near as bad as the early cases

 

[RFguy]

If I were to operate a 912ULS in a J230, I'd probably be operating the engine at something like 85% maximum power in cruise.

It's rated for 93.8% continuous.

 

Assume an oversized oil cooler, radiator to make sure it all stays nice and chilly on a hot summer. assume the oil is kept squeeky clean 25 hour changes. 

 

WHile the engine is rated for 94% continuous, since the aircraft engine might  intended to be flown at cruise (75%),  is this shown to reduce the life of the gearbox and clutch assembly ? Or should I expect  run to TBO (1000 hours gearbox and clutch ?)  for the gearbox and clutch at 'max continuous power'  ? (and therefore at 85%, I wll be in good shape) ?

I see the max torque, which might be best breathing outcome , occurs soemwhere around 5100 (80% ish) . 

 

I gather the only comments here will be anecdotal / gut feeling, but by all means lets have em. 

 

 

Edited June 13, 2021 by RFguy

[facthunter]

The "nice and chilly" is not wanted . One problem I've encountered is where you traverse a lot of latitude  or go from snow to desert and a big change of ambient during the flight. You need to run the oil at about 85 C and the coolant as hot as you safely can without losing green stuff.. Where are you going to fit all these oversize items? Regarding the clutch and red. gears.The  Noise it makes and metal on a magnetic drainplug  tells you. The "clutch" is actually a friction damper and a camface drive. You notice it most when starting or shutting down. Sounds B..awful. at times. While some owners will like this conversion I wouldn't rush to do it myself. Sixes are smooth. and you are running less revs. Nev

 

[Kyle Communications]

A lot depends on your prop and setup. No one really looks at hp its the RPM.  5800 max for max for 5 mins then you can run 5500 rpm or less all day long.

Most cruise somewhere between 5000 and 5200 rpm. at 5000 rpm I use 15ltr/hr obviously if your going to run the rpm up around 5400 you are going to be using 18 or so ltrs/hr

Most of the yanks I know regularly cruise at 5400 to 5500 they like to push their engines. many guys there have 1000 hrs plus

The gearbox needs to be done every 1000 hrs but the sprag.it can go for the life of the engine. Most issues with the sprag is not a good enough earth direct to the engine which makes the starter not work quite as well and this tends to wear out the sprag. Spin the enine as fast as you can on start and there doesnt seem to be any issues witht he sprag.

 

[Kyle Communications]

You dont want the engine running too cool either..certainly not below 90degC on the oil..you have to burn off the acidic crap from the oil

 

[Thruster88]

If the propeller is set per Rotax recommendation the gearbox will be happy.

 

[RFguy]

Thanks everyone for their input, esp Nev, your notes on the noises they make and exactly WHAT that noise is. OK on ths sprag not liking a slack starter.

 

By nice and chilly I mean 85 to 100 deg C. AND yes needs thermostatic regulation so the giant oil cooler (and water cooler)  doesnt mean it freezes to death on a YSCB sub zero climbout.

 

So I can take off at Condobolin at OAT=38 and not spend the whole climb relying on thermals to climb into cool air.

 

Our club 912ULS could do with some extra cooling. ran up to 120 fairly regularly last summer... I didnt like that too much.

I usually fly it at 18 lph which is about 75%. (5100 RPM ~ 95 indicated).

 

On pitching, the ROTAX book actually says never operate at WOT below 5200 RPM, excessive engine and gearbox load....

 

 

 

 

 

 

Edited June 13, 2021 by RFguy

[RFguy]

Stuart, which book was that from ? this curve from the tech manual ( I have) looks different.

912ULS torque  (attached below)

 

Edited June 13, 2021 by RFguy

[Thruster88]

Not sure just Googled 912 performance curve. 

[skippydiesel]

Stand to be corrected but I was under the impression that the;

 

• G Box inspection - is at 1200 hrs,  for engines run (predominantly) on ULP. Note this is an inspection - if all OK, just oil seals are usually replaced.
• Sprag Clutch - Kyle has part of the story, however the most common cause of  S clutch failure is persisting with a dying battery - An expensive lesson. Replace your battery at the first sign of low cranking speed and/or failure to charge to at least 14.2 volts.
• Oil temperature - to the best of my understanding; oil should reach 100C at least once in the flight and this should be maintained for about 30 minutes, for best removal of volatile contaminants (mainly water). After this economy cruise temps down in the 80c's are okay but low 90's probably better. This is often a problem for training aircraft and is one of the many reasons note to pay big $$$ for one.
• Fuel consumption at RPM -  has much to do with the slipperiness/draggy nature of the aircraft  & prop pitch eg ATEC Zephyr  /Rotax 912 ULS / ground adjustable prop set for static 5200 RPM / single pilot,  will deliver a sortie fuel burn @ cruise 5200 RPM/105 knots or there about,  of 13.5L/hr. Same aircraft etc will deliver 120 knots @ 18-19L/hr (I flight plan @14L/hr to cover all loading/temp variables)
• Rotax 91 series engines - thrive, if operated within  the RPM band 5200-5500. This may not be a comfortable scenario for direct drive aficionado's, who often fail to recognise it is the prop speed which is important, not the engine speed. CS props change natters  to some degree.
• Oil changes - Rotax recommend changing oil & filter @ 100 hrs (or annual). Personally I favour 50 hrs (oil only) - no good reason for this other than it makes me feel good.
• Sizing of coolant/oil radiators - if you make a habit of operating above 30C, you should modify your expectations for TO role (longer) and climb out (shallower). If you happen to be out at Condo,  on a hot day,, there is more than enough unobstructed air space to maintain a shallow climb  out  - on track - to cruising altitude (no need to thermal). Personally I dont mind landing in the high 30's & 40+C but avoid TO's, by starting my trip at first light, when climatic conditions dictate. By managing the timing, I avoid the need to consider expensive, heavy, complex, modifications to my engine cooling. In winter, I employ a home made  fixed "cowl flap" to restrict exit air (shaped aluminium sheet) which is removed when day temps are consistently at/above 25C - this KISS has worked very well for my aircraft.

[facthunter]

The oil does get hotter in some parts of the engine than the gauge shows. My 85C is I believe the desired minimum. With synthetic oil the higher temps are coped with better. All the vented blow-by goes to the remote oil tank and then over board. That's how the oil is returned. It's the only engine that does it this way that I am  aware of. Nev