Rotax engines (3) waterless coolant

Rotax 2013 cylinder headsIn 2013, Rotax introduced (without much of a fanfare) a new design of cylinder head for their 912 carburettor series engines. These cylinder heads have been fitted to all new engines since then and may be retrofitted to earlier engines.

Having received a couple of queries from owners whose engines incorporate the new heads, it is important to understand that you cannot use waterless coolant in conjunction with these heads.

In addition it’s worth noting the following:
– the new heads are similar to but not the same as those fitted to the 912iS fuel injection engine. If you have to replace cylinder heads, make sure you get the right ones.
– the CHT sensor is in a new location
– what was the CHT sensor now measures coolant temperature not cylinder head temperature. You therefore have to use a new coloured-arc temperature gauge to reflect the correct coolant (not CHT) temperature limits.
– the sensor screw must be sealed with Loctite as the sensor is now immersed in coolant; the earlier CHT probe fitted into a dry void in the cylinder head.
– the cylinder head bolts must be torqued to a different value from the old ones, and also in a different order.

You can access detailed information about these cylinder heads in at least three places:
(a) Rotax Service instruction SI-912-020
(b) Rotax Line Maintenance Manual temporary update
(c) ‘Rotax Minute’ video, which briefly describes to differences between old and new design cylinder heads (may be Rotax can change that awful voice over??)


Rotax engines (2) carburettor floats

Rotax carby floatsAt last Rotax has issued a final service bulletin covering replacement carburettor floats. For those not fully up to speed on this, Rotax has had a problem with ‘permeable’ carburettor floats on most recent 912 series engines. Basically any faulty floats absorb fuel and sink to the bottom of the float chamber, causing rough running and potentially overflowing fuel. Floats on affected engines had to be checked every 25 hours and if needed, replaced.

The latest service bulletins (click on the numbers to see & download): SB-912-067 and SB-912-067UL list the affected engine numbers and necessary actions.

In addition, Rotax has posted information on their blog about how to get your replacement floats.

In Australia, contact Bert Flood Imports – phone 03 9735 5655 – near Melbourne, give/send them your engine number, and they will send you replacement floats and an invoice for them. Returning the old floats quickly together with the invoice will result in a refund/credit or cancellation of the invoice.

Hopefully this will see a conclusion to the concerns over faulty floats.

Rotax engines (1) scheduled service intervals

Rotax serviceOn what basis do you record your times for scheduled services on your Rotax engine? Engine running hours – start to stop? Starting to taxi to stopping – wheels turning to wheels stopping? Flight time via an air switch – wheels off to wheels on the runway?

At bigger and/or busier airfields there could easily be a big cumulative difference between engine start/stop and wheels off to wheels on the runway – as much a 25% or more by some LAME accounts. So what is the correct procedure for recording times to determine scheduled maintenance on your Rotax engine? The answer, it seems, has been about as clear as year-old engine oil!

The initial response from the Rotax service department to my query was that maintenance must be carried out based on engine running time as recorded by ‘an electronic engine hours timer’ – ie start-up to shut-down. This is different to some of the statements in their maintenance manuals and certainly not the way most flight schools and clubs record time for engine servicing; they usually use take-off to landing times for overhaul.

Please note:
What follows has now been superseded by the following: all Rotax engine scheduled maintenance times are currently based on engine running times – ie from start up to shut down. Therefore, for maintenance purposes, record engine running times accordingly. Also check to ensure that the airframe manufacturer aligns their mandatory maintenance schedules with the engine maintenance requirements. Most of them do – including Aeroprakt.

Please also see my updated blog post on scheduled maintenance times:

When questioned a little more, Rotax finally clarified that their engine scheduled maintenance times comply with standard FAA (and CASA) practice – that is, take-off to landing time, ideally measured with an air-switch hours meter. I now have this in writing (by email) from them, so if you or your engineer need written confirmation, let me know.

So, repeating, for the sake of avoiding all doubt – record your engine scheduled maintenance times from take-off to landing. Maybe even fit an air-switch-operated hours counter if you need to. In the long run, this can save you quite a lot when it comes to servicing, likely well more than the cost of fitting an air-switch.

PS – Don’t forget: if you are late with a service – eg 55 hours instead of 50, the next service is still due at 100 hours, not 105. Read the Rotax manuals!

Measuring the LSA market

Rotax 912 ULS engineI found an interesting article in General Aviation News about the growth of the Light Sport Aircraft (LSA) market, both in the USA and worldwide. Click HERE to read the article.

Written by Dan Johnson (see his aviation blog at it concludes that Rotax is by far the world’s biggest aviation engine manufacturer, with well over 50,000 four-stroke and over 120,000 two-stroke aircraft engines delivered to date. As a result, their annual engine sales can be used as a barometer for the recreational/LSA market as a whole, as other manufacturers like Lycoming and Continental are not really players in this market.

Dan makes some interesting remarks around the different proportions of LSA versus GA registrations in the USA in comparison with the rest of the world. In the USA, the GA-LSA ratio is 80-20, while in the rest of the world the ratio is reversed: 20-80 in favour of LSAs. He comments that this is probably because GA is relatively cheap in the USA and perceived to be very expensive elsewhere. (Tell me about it!). Although USA is the biggest single LSA market, nearly twice as many LSAs are actually sold outside the USA.

Other influencing factors in the USA may be that many aircraft service centres are unfamiliar with Rotax engines and some don’t even have access to the metric tools needed on the engine. Contrast that with Europe – and even Australia – where the Rotax is now a familiar engine.