Gearbox upgrade on older 912

[WWhunter]

Being a novice at anything to do with the Rotax 912 I have read comments about an upgraded gearbox that is possibly needed on the older pre-95 912's. What does this entail? Anyone done it and what would I be looking at cost wise.

Questions are due to my current dilema...I am very close to making a final decission on purchasing a plane that is not yet finished and it is a '92 model IV with an 80HP 912. I am trying to figure out if the costs involved to get it flying are worth the added expense and work verses buying an already flying plane. I've been down the 'just needs a little to get it flying' road and it usually costs more to get a project flying than one can buy an already flying plane. I am actually in this conundrum right now with a RANS S7. I have spent over $10K on a 'flying plane that needs just a couple of things' and should have spent the money on a better plane. Trying to save a dollar never seems to work that way for me.
Needs a windshield, fuel tanks, etc. etc. that all add up to considerable expense and lots of labor.

[68niou1]

Your post hits home with me in a lot of ways.

I have a 94 UL 80hp that had been sitting for most of its life. From what I can gather there are quite a few of these out there- for some reason or another got built, and never really got flown. Initial setup on these engines is critical, and back then nothing was really known on how to do that. I think a lot of it might be the early gearbox- and also remember that the Rotax was a new quantity back then. As far as a update is concerned I don't know if you can bolt on the later wide gear set on a early engine or not(hopefully someone will chime in and answer this) but I do know that if you need any kind of update concerning the dog gear, or gears in general its not going to be cheap. Pretty sure that if you can retro a newer gearset you would have to do it as a entire assembly(new case,gears,clutches,shims etc.)- so hang on to your wallet. Also there is a rocker arm update as well- and that is not inexpensive either.

Don't get me wrong, I love my plane- but if I was to do it over knowing what I know now unless you are saving a significant amount of money on the non flying example it could be a real money pit. I would spend a little more and get a model 7 with a 912S. FWIW

[kmach]

You might consider asking this question on a rotax engine forum.

I subscribe to rotaxowner dot com, it has helped me with learning the 912 uls.

An older engine that has sat not run for years , I personally would want it totally inspected by a rotax service center, they would let you know if it needs upgrades or maybe even rebuild.

[Av8r3400]

Owning one of these "early" engines and putting a bunch of time on it, I don't consider "updating" the gearbox a mandatory thing.

I would say that this a perfectly run-able motor as it. Maintenance is key, however. I was told that the earlier motors need to have the gearbox serviced every 300 hours (I've never been able to confirm this, but it sounds reasonable). Servicing consists of checking the belview (spring) washers for proper preload and inspection of the drive dogs and gear faces for wear. This is easily a owner performed inspection for even the slightly skilled owner-mechanic.

I did not do (or know about) this maintenance and paid the price. I did have to replace the gear set and drive dog due to erosion and spauling damage. An expensive ($1500) repair.

IMO the early motors are far less tolerant of a heavy prop. I have a 68" nickel inlaid Warp Drive (extremely heavy) prop. If I had a GSC or IVO, I doubt that I would have had the issues.

[WWhunter]

Av8r3400,
This doesn't concern my question for this thread but in my current plane I am wondering if that may be the issue I am having also. Darn thing is giving me fits trying to get it to run smoothly and in my search for answer I found a few guys that had gear box issues that caused the engine to run rough.

My current issues with the engine I have is the reason for my concern with buying this other plane. Darn thing has become a major money pit. For supposedly modern engine design it sure has issues, and VERY expensive ones at that!

[Av8r3400]

Speaking from experience, most vibration issues are carburetor related. Even rebuilds from Rotax service facilities are not infallible.

The gearbox upgrade replaces the 22mm wide gears for 27mm wide units with an updated hub design that promotes better oil distribution.

[Peteohms]

I have a very early 912 (1990) with nearly 1100 hours. At the 600 hour mark I went to SOUTH MS LIGHT AIRCRAFT and took the service and maintenance courses from Ronnie Smith. At that time Ronnie helped me do the 600 hour inspection on my gear box. It was in great shape but many of the parts were considered obsolete. Ronnie had everything I needed to change out in his second hand parts drawer. I saved a bunch and learned something. Maybe you could send your gear box to Ronnie or better yet take his courses and work on yours there.

PS: Another benifit to taking the course is the help I've had from Ronnie when I've need some guidance.

[WWhunter]

That sounds like great advice. Only problem for me is the additional cost involved for all the travel. I am in Northern MN and it is quite a drive to Ronni Smiths place in Mississippi. I would like to eventually take his class though, just not in the budget right now.

[Peteohms]

That sounds like great advice. Only problem for me is the additional cost involved for all the travel. I am in Northern MN and it is quite a drive to Ronni Smiths place in Mississippi. I would like to eventually take his class though, just not in the budget right now.

You can still get what you need from him and advice too. Or just send what you have and have them do it.

[WWhunter]

Pete,
Thanks for the advice and it is exactly what I was thinking of doing. I had actually forgotten about Mr. Smith and your post reminded me.
I have another engine here I have but the Zipper kit in and I am having the darnest time trying to get it to run correctly and in my search some people have said that gearbox issues can cause rough running conditions. May have to tear it off and send it in also.

The question though was in reference to a Kitfox I am looking at to purchase. The negatives are starting to outweigh the positives so I may pass on this project.