Rotax C-gearbox shim failure

[Abe]

Hi fliers!
As with many things mechanical, one can fly for months just putting in fuel, but if you hit one snag, it seems lots of other problems raise their ugly heads and then you seem to spanner forever!
Has anyone here heard of or seen a failure of the shims on the pinion shaft in a Rotax gearbox model C, and could you perhaps hazard an opinion on what may be the cause? (Part #427021 Shim 26.5/34/.2, item 16 on my exploded view.) Aviation Engines could not help.
Symptoms are coarse metal shavings sticking on the magnetic plug. Dismantling the gearbox I was relieved to see no damage to the gears, but the single shim badly mangled. Allen key was torqued to spec 40NM on assembly and Loctite was holding on dismantling. My first thought was that the ball bearing it pressed against was seizing, but it seems smooth. I think I should replace it in any case.
FlySafe!
Worried Abe.

[andreb]

Abe
What a coincidence. On Sat morning whilst holding short on 03 at Microland I smelt burning oil smell and wrote it off to ZS-NEL who had just taken off.
We took off uneventfully and flew for 15 minutes or so before turing back to Microland (Marius pax was terrified). Before landing I did q low level in the GF and toauch and go at Lieb Grabe's airstrip. Just after the touch and go I heard I rattling noise. I thought it was something loose from the touch and go. However as I was on downwing leg at Lieb Grabe I discovered the noise increased with revs. Without knowing what it was I joined on long final to 03 and landed OK.
On inspection on the ground I saw gearbox oil coming out of the gearbox casing and dripping onto exhaust.
I will have to get Hanes to take a look on Monday, and hopefully there is noe serious damage. Could it be a similar problem?
I will post if it is...

Andre

[Abe]

Hi André and other C-box users.
I found my gearbox problem, happily not as expensive to fix as I suspect André's will turn out...
First, correction of two errors in my original post:
The Allen key involved is torqued 24NM. (It is the rubber dougnuts's bolts that take 40NM)
There were two .2mm shims, it transpired that two more were needed.
Accurate dial micrometer shows end play of .8mm, which under stuttering engine can explain the bashed shims. (A lot of experimenting was done with this gearbox, and it had earlier even suffered a dougnut damper failure.)
I today made up a single .8mm shim from spring steel, should hold up better.
Reading the litterature, I see several mods over the years to this gearbox, which my old one still does without, so there are always more to worry about.
FlySafe!
Abe.

[vernon11]

When I rebuilt a Rans S12 with a 618 and C box. I found shavings When draining the box. I found the bolt loose and shim completely destroyed. All I could do was replace the bearings with a new shim. lock tite and torque.
I am not sure if this is a problem with the c box.
cheers,
vernon.

[Dobbs]

Hi Guys,

Coincidentally, a friend of mine recently found a lot of play in the horozontal plane, of the output shaft - the one which attaches to the prop when pushing his plane into the hangar (C box on a 503). Some time later, after the box had cooled down, the play was gone.

On further investigation, he found out that this is something which, although rare, only occurs with the C boxes, and although not expensive to fix, it does require the dis assembly of the box.

The concerning thing is that with a cold box, the play is not apparent, and only manifests itself as the box warns up - not sure if these are the same symptoms which you are reffering to?

Cheers

Dobbs

[Bubble Guts]

??????

[Graham Mac]

Hi Guys,

Coincidentally, a friend of mine recently found a lot of play in the horozontal plane, of the output shaft - the one which attaches to the prop when pushing his plane into the hangar (C box on a 503). Some time later, after the box had cooled down, the play was gone.

On further investigation, he found out that this is something which, although rare, only occurs with the C boxes, and although not expensive to fix, it does require the dis assembly of the box.

The concerning thing is that with a cold box, the play is not apparent, and only manifests itself as the box warns up - not sure if these are the same symptoms which you are reffering to?

Cheers

Dobbs

Hi Dobbs
This sounds exactly like i am experiencing at the moment.
Do you know what the final outcome was and what was the problem within the box.
I need the same repair to be done.

Graham