gear box rebuild cost

[jeffbock]

Have a friend interested in purchasing an Aeroteck (?) with Rotax that has 900 hours on it and wondering what the Gearbox rebuild cost would be in round figures. I understand it's a good idea to do it at 1,000hours.
Thanks, Jeff

[WWhunter]

I sent mine to Mississippi Light Sport (?) And if I remember correctly it was around $230-250 with return shipping.

[Av8r3400]

Gearbox maintenance should be done more frequently than 1000 hours.

3-400 hours is a better schedule.

[jiott]

If you are running Mogas the Line Maint manual says 800 hours. I run mogas and have 700 hours on my gearbox with no indication of problems yet. Friction torque in spec, no funny noises or kickbacks, smooth idle, etc. I will go "on condition" but I agree that after 400-600 hours you need to start paying close attention to the gearbox.

FWIW I also am going "on condition" for my carburetors. The book says to disassemble and inspect every 200 hours; mine are now at 700 hours and have never been disassembled. Engine is smooth at idle and up, and I have checked sync every 100 hours, but have not needed to readjust for 300 hours. Why try to fix what ain't broke. I will be doing the 5 year rubber replacement when that time comes (soon) and will disassemble them then.

[Floog]

I had Hal Stockman R & R mine (for the first time) at 1,300 hours. He replaced the Belview (large spring) washers and re-shimmed as req'd. The only wear was about .010" on the Belview washers which was 'normal'. All for about $200 and quick turn around. Thank you, Hal! In my opinion, some of the Rotax intervals are way conservative with the exception of oil changes. I do 50 hrs. and run 99.9 MOGAS.

[Jeremy MacGregor]

Gearbox Inspection cost depends on parts used and the extent of the inspection. Calendar age and hours along with extent of previous inspections also very price. A gearbox on the bench typically takes 1-2hrs to disassemble clean and inspect. If the bearing and seal are replaced, that will add about 175$ in parts. The 3 disk springs should almost always be replaced with a few exceptions at $75. Gearset, thrust washers, clutch hub and prop shaft can increase cost if fracturing or wear is detected. Your clutch may be due for a cleaning and adjustment and that adds 1-1.5hrs of labor.

[Danzer1]

If you are running Mogas the Line Maint manual says 800 hours.

If you are running a gearbox with an overload clutch and over 30% leaded fuel annually the manual says 600 hrs.

If running strictly mogas with an overload clutch the manual says 1,000 hrs.

If running a gearbox without an overload clutch the manual says 600 hrs. no matter what type of fuel.

If you are running a gearbox with an overload clutch you are also supposed to check the friction torque every 100 hrs or at annual (whichever comes 1st).

Maintenance schedules are preventative. If you are waiting until it's "broke" hopefully you are on the ground. Can't see bearings, seals, springs, washers, pitting or spalling without opening it up - whether it runs "smooth" or not! Actually you could see some of it with an endoscope.

Do what you want, but keep in mind you as the owner are responsible for maintaining an airworthy aircraft.

YMMV, Greg

[Av8r3400]

I've serviced several gearboxes (including my own) that had far less than 1000 hours, one at 200 hours, that needed to be worked on. Heavy props (particularly Warp Drive) are notorious for shortening the life on a gearbox. It's not a difficult job to do and adds considerable life to the engine.

Routine maintenance parts (shims) and sealant can be less than $20.

[Danzer1]

I've serviced several gearboxes (including my own) that had far less than 1000 hours, one at 200 hours, that needed to be worked on. Heavy props (particularly Warp Drive) are notorious for shortening the life on a gearbox. It's not a difficult job to do and adds considerable life to the engine.

Routine maintenance parts (shims) and sealant can be less than $20.

I agree Larry.

The other two most prominent causes of gearbox wear are:

1. Poorly balanced prop - Rotax recommends dynamic balance, but it should be mandatory!

2. Improper oil type, infrequent oil changes and operating oil temperatures out of spec for extended periods.

Less prominent is, frequent overloading the prop at improper rpm.

YMMV, Greg

[jiott]

As further clarification of my "on condition" statements:
First, Greg is correct in that the manual states 1000 hours (not the 800 I was recalling) for 912ul/uls with overload clutch and less than 30% use of 100LL.

My use of "on condition" maintenance comes from closely following Mike Busch's excellent webinars on the EAA website. This guy is a nationally recognized and awarded AP/IA mechanic and owner of a large maintenance company for mostly certified aircraft. He is a strong proponent of "on condition" maintenance where appropriate. First of all it doesn't apply to ac in commercial use, and doesn't apply to items likely to catastrophically fail like rubber and hose and belt replacement. The items it does apply to are things that rarely fail catastrophically, but start giving warnings well ahead of complete failure, like cyl heads, piston rings, carbs, many bearings, etc. Don't take my word for this but watch his webinars in the EAA webinar archives. "On condition" is not for everyone, but requires either a knowledgeable hired mechanic watching things, and/or an owner that is very comfortable mechanically and knows the tests and warning signs to watch for.

In my own case I feel the gearbox is one of those items that will give warning (sure there is a small risk of sudden failure as is true of most items) if you pay attention and know what to look for; this also true of carburetors in my opinion. That said, I will definitely replace rubber parts near the 5 year recommendation, tear down the carbs, maybe even overhaul the gearbox during this convenient downtime since it will be near the 1000 hours. Everything has to be done with common sense rather than blindly following a book, although following the book is never bad. I believe following Mike Busch's philosophy gives the best combination; after all, going "on condition" may cause you to repair some item far sooner than the book says.

[Danzer1]

As further clarification of my "on condition" statements:
First, Greg is correct in that the manual states 1000 hours (not the 800 I was recalling) for 912ul/uls with overload clutch and less than 30% use of 100LL.

My use of "on condition" maintenance comes from closely following Mike Busch's excellent webinars on the EAA website. This guy is a nationally recognized and awarded AP/IA mechanic and owner of a large maintenance company for mostly certified aircraft. He is a strong proponent of "on condition" maintenance where appropriate. First of all it doesn't apply to ac in commercial use, and doesn't apply to items likely to catastrophically fail like rubber and hose and belt replacement. The items it does apply to are things that rarely fail catastrophically, but start giving warnings well ahead of complete failure, like cyl heads, piston rings, carbs, many bearings, etc. Don't take my word for this but watch his webinars in the EAA webinar archives. "On condition" is not for everyone, but requires either a knowledgeable hired mechanic watching things, and/or an owner that is very comfortable mechanically and knows the tests and warning signs to watch for.

In my own case I feel the gearbox is one of those items that will give warning (sure there is a small risk of sudden failure as is true of most items) if you pay attention and know what to look for; this also true of carburetors in my opinion. That said, I will definitely replace rubber parts near the 5 year recommendation, tear down the carbs, maybe even overhaul the gearbox during this convenient downtime since it will be near the 1000 hours. Everything has to be done with common sense rather than blindly following a book, although following the book is never bad. I believe following Mike Busch's philosophy gives the best combination; after all, going "on condition" may cause you to repair some item far sooner than the book says.

Jim, I am familiar with Mikes webinars. My recollection is that he recommends "on condition" overhaul or repair when there is a reliable method of inspection, test and or data analysis to determine if a non critical componeent can likely go longer than manufacturers recommendation for overhaul or repair.

Personally (read - my opinion), I don't think "smoothness" qualifies as an inspection or test. Further the Rotax requirements for both the gearbox and carbs are to "check" i.e. inspection. It does not require replacing parts unless out of spec. It is an inspection - which Mike promotes.

Additionally, if any of you have an SLSA, Mikes opinion is that nothing applies except what the manufacturer states. Go here: https://www.savvyaviation.com/home/resources/mikes-webinars/ and search for the webinar "TBOs and other maintenance intervals" at 45:23 he discusses this topic.

To be clear, these are my opinions of what works for me, I am simply encouraging other readers to do their own due diligence as to what works for them and not me or Jim or even Mike.

Each of us has their own tolerance for risk and how we approach risk management. Do what works for you, you are ultimately responsible for your decisions!

YMMV, Greg

[jiott]

It is interesting that SLSA's are required by the FAA to follow manufacturer's recommendations for maintenance intervals. It is a weird anomaly in the FAA rules that Mike Busch thinks is strange and not reasonable. Certified ac are not restricted like that. Also, I don't believe Mike promotes "inspections" that require total disassembly if there is no reasonable indication to do it, even if maintenance manuals recommend it.

Regarding Rotax gearboxes with overload clutch, I do faithfully do the clutch friction torque test/measurement every 100 hours. In addition I disagree with Greg and strongly believe smoothness during starts and shutdowns and at low idle, as well as sounds and any kickbacks can tell a lot about the health of the gearbox. My own 700 hours and discussions with Rotax trained mechanics as well as posts on this forum seem to all indicate that the gearbox nearly always gives some of the above indications well ahead of total failure. I would welcome anyone correcting my thinking on this who has had actual experience otherwise. In all respect, Greg I am not aware that you have ever flown behind a Rotax 912 or ever built or maintained a Kitfox; If I am wrong about this I apologize.