Gearbox Service Instruction

by MARK JACKSON in General Tech Discussion 7 years ago

So according to the latest service instruction, EVERY 912 gearbox bearing has been fitted the wrong way around at the Rotax factory. Is this the case or is the service bulletin wrong. Surely they have not been fitting them the wrong way for 30 years and only just realised, or have they?

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Re: Gearbox Service Instruction

by Roger Lee » 7 years ago

Roger Lee

125 5.11k 4.52k

Hi Mark,

It says this was done during gearbox maint. in the field.

Quote:
Information from the field has shown that in the course of repair or maintenance, the installation of
the ball bearing was not carried out properly and also has not been instructed accordingly. Specifically,
the ball bearing cage (plastic ball retainer) should be facing towards the propeller. This
document should eliminate uncertainties of the corresponding installation position.
NOTE: Obey this information at the next gearbox removal event. It is not necessary
to inspect for, or replace a incorrectly positioned bearing until the next gearbox
removal.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Gearbox Service Instruction

by MARK JACKSON » 7 years ago

MARK JACKSON

12 332 11

Hi Roger

I know it does. How bad is that. Rotax have been fitting them this way forever, and then are blaming it on people fitting them the wrong way around during maintenance.

As far as I know, there has never been a lubrication problem fitting the bearings the old way. Are we now going to start seeing problems fitting them the other way. Only time will tell.

It seems a bit silly to me.

Mark

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Re: Gearbox Service Instruction

by Bill Hertzel » 7 years ago

Bill Hertzel

13 1.95k 7.96k

Mark,

You are reading too much from the instructions.
Bear in mind that Rotax has German as its primary language and that some of the intent may have been lost in translation.
Nowhere does it say that the were installed backward from the factory.

[quote]Information from the field has shown that in the course of repair or maintenance, the installation of the ball bearing was not carried out properly ...[/quote]

Let me rephrase that as...
"Anecdotal evidence indicates that in the course of field repairs or maintenance, some mechanics may have installed the bearing improperly..."

[quote]... and also has not been instructed accordingly.[/quote]

And Rotax admits that their instructions for the proper installation are lacking in clarity.

Therefor, Rotax has issued the Service Instruction to clear up any misunderstanding as to the proper installation of the bearing.

They also admit that installation with the race facing the inside of the Gearcase and lubricating Oil is such a minor problem that it does not warrant immediate correction.

If your gearbox has never been repaired, there is no reason to suspect a bearing problem.
If your gearbox has been repaired, Just check it the next time you're in there and flip it around if needed.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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Re: Gearbox Service Instruction

by MARK JACKSON » 7 years ago

MARK JACKSON

12 332 11

This is a copy of the heavy maintenance manual for rebuilding the gearbox. Please don't blame this on bad translation from German to English.

The ball bearing has always been fitted the old way with the open balls facing the propellor shaft to improve lubrication. Every single 912 engine that has come out of the factory has the bearing fitted this way.

I presume the intension was that the balls are running in an oil bath between the bearing and the oil seal. Why after 35 years of trouble free operation and probably millions of operating hours would they want to change something like this, and if it is not a problem which way it is fitted, why produce a service instruction.

It is even drawn with the balls facing the prop flange in the illustrated parts catalogue.

Also Bill, if your gearbox has never been repaired, then you do have a problem because your bearing will be fitted the wrong way around. If this isn't a problem, then why bother changing it.

Heat gearbox housing (1) with hot air (or in an oven) to approx 100 °C (212 °F). Press shaft seal (2) into the gearbox housing from the inside, using insertion jig, part no. 876518, and grease sealing lips (3). Add radius ring (4) 36/50/ 5.5 with rounded side towards shaft seal. The weight of the ball bearing (5) must cause it to fall into the bearing point of the heated gearbox housing. Fix ball bearing with LOCTITE 221 in position, using 4 hardened washers (6) 7.2/18.8/3 and hex. screws (7) M7x16. Tighten to 15 Nm (130 in.lb).

◆ NOTE: For optimum lubrication of the bearing this has to show with the open side to the propeller flange.

If it is fitted this way for optimum lubrication, I think I will be leaving it this way.

Mark

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Re: Gearbox Service Instruction

by Bill Hertzel » 7 years ago

Bill Hertzel

13 1.95k 7.96k

Mark,
I stand corrected and join you in the confusion.
Rotax works in mysterious ways. :unsure:

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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