Finishing a MiniMax 1100 project, performing break-in on the Rotax 447 with a B gearbox. The engine is new, but has been sitting for a number of years (no oil in gearbox until now). Added gear oil to the gearbox until started running out bottom side hole per instructions. While doing the break-in run, oil runs out the vent plug on the gearbox. Several teaspoons leaked, so I stopped the engine. Swapped the vent plug with another one, same result. Replenished oil to proper level. Leaking oil is frothy, which I would expect since there must be air in the gearbox as well. The tailwheel is on the ground, so the engine has about a 10-12 degree tilt, which I assume should not matter. Question: is it normal for it to vent the oil in that amount? Rough running at low RPMs, still dialing that in, does that exacerbate the situation? Any suggestions welcome.
My MZ202 engine had a similar gearbox arrangement, with the same instructions for filling. But the engine manufacturer told me to make sure the engine was level (i.e. tail chocked up so engine base horizontal) before filling, as tail down would lead to overfill.
Yes, I had propped up the tail so it was level when filling. I seem to remember the leak tapered off some during one session after a few minutes, but it's unnerving to see it happen at all. Put more in after that and it leaked again. I know the gearbox doesn't hold much oil, but am I safe to run it until it stops leaking, then leave it at that level? Runups are done with the tail down, of course.
Rough running at low RPM and gearbox oil frothing and leaking suggests to me that there might be a problem of engine crank-case being linked to the gearbox casing because of a poor power take-off crankshaft seal. Pulses of pressure from the engine crankcase being added to agitated oil in the gearbox.
I don't think it matters if you fill as you described and of course it should make no difference what the attitude of the aircraft is when running - after all it's normal to taxi in that attitude for some distance.
Is the gearbox oil of the correct specification? It should pour very slowly like treacle. Oil should be at the correct level - don't alow it to 'find its own level'.
Using Valvoline 80W-90 gear oil which I happened to have on hand, labeled as meeting the API-GL5 spec. The breather plug is the gold-domed type labeled Mintor. I assume it is operating as designed as two of them I have tried yield the same result. Going to try once more with oil at proper level and try to keep the rough-running at low RPM to a minimum. Again, this engine was new, but sat for a number of years before being installed and this is the initial break-in. Any comments on crankshaft or other seals which may need to be replaced due to age, rather than wear?
Serial number is 5161528 Not sure how to determine the mfg date. This is a new engine that has been stored dry until now. Just to confirm, the only leak is from the breather plug. Seems to run okay (other than rough at low RPM) but don't like seeing that leak. Maybe it was one or two degrees tail low when I filled it, and the leak will stop after a few teaspoons? Going to try again when I get time. How easy a job is it to pull the front of the gearbox off and check for obvious issues? Don't want to do anything that requires special alignment or tools.
no special alignment tools that I remember. However, more of a concern is whether or not the engine seals are leaking front and rear. They are only good for 5 years, unless I'm told they are the newer Viton stuff. Watch your EGT's and gauge accordingly. If you don't have EGT and CHT gauges, install them now.
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