Thread: Oil Leak at Gearbox?

I think I have developed an oil leak between my gearbox and engine. See photo below.

I had started to notice a little oil showing up in the bottom cowling, but it wasn't what I'd call a quantity, more like oil had been misted by the incoming air / across the coolers. I wasn't really missing any oil from the tank. It would show up on the bottom of the cylinder cooling fins and rocker covers too - just a drop hanging from some of the surfaces.

I flew 2.5 hr last week in nice temps (70-75F) about a week ago. Yesterday, I go in to wash the plane and notice a small spot of oil on the concrete - looks like it was about 15 drops or so. Removing the cowling, there was oil film on the cowling. It looks like the oil was coming from somewhere in / near the radiators, since it was obviously blowing back (you could see where it had been entrained in the air blowing past the radiators).

Closer inspection yielded the photo you see. Oil seems to be leaking out of the bottom of the gearbox/engine flange, and it appears that some of the gasket material (this is a formed gasket, right?) has come loose - see screwdriver on left pointing at blown out gasket material. My gearbox was overhauled in 2007/8 as part of the recall by a local A&P.

#1 - Is this likely where the oil is coming from?

#2 - How critical is the problem? Am I going to be able to ferry the aircraft to get it to a shop? Is it something to take care of at annual? I don't mind loosing a little oil and cleaning it off the belly, but I don't want to have an in-flight failure.

Thanks,
Doug

Hi Doug

I dont think the gearbox joint has a gasket (sure Roger will correct me ) its Loctite 574 joint/sealing compound and if its leaking the only way to cure it will be to remove gearbox de grease it and reseal ..i have seen a few leaking in this area

Mike

Originally Posted by micromike

I dont think the gearbox joint has a gasket (sure Roger will correct me ) its Loctite 574 joint/sealing compound and if its leaking the only way to cure it will be to remove gearbox de grease it and reseal ..i have seen a few leaking in this area

You're right, that's what I meant by "gasket". I suspect they didn't want a real gasket to keep the rigidity up?

Hi Doug,

First a leak in this area can be misleading. The high speed air coming in to cool the engine can make a leak look like it is coming from some place it is not. Check these places first.

Make sure the oil filter is on snug and no oozing oil is coming out the bottom.

Clean out the radiator of old oil by using a degreaser down through the radiator fins.

Put a wrench (even if you think they are tight) on the two big oil fitting nuts on top of the oil radiator. I have seen this one a couple of times and it's hard to detect because the air blows any oil of the nuts.

Look up under the cyl. heads and make sure the push rod tubes aren't leaking where they insert. (not real likely)

Clean the entire area of oil film with a bio-degradable degreaser so all the metal is clean.

The gearbox could leak, but not as probable as other places. The sealant for the gearbox is Loctite 5910 or 574. I will tell you 5910 works better and easier to get a good seal. There is no gasket for the gearbox. It is a metal to metal seal. Of all the leaks I have seen in this area none have been the gearbox, but that doesn't mean yours can't be. That is why I say eliminate other possibilities before you want to pull the gearbox.

Oil filter or oil radiator nuts are my bet at this time.
If it turns out to really be your gearbox then let me know and re-sealing is fairly easy. Looking at the sealing compound in your picture it doesn't look like the right sealant. 5910 is black and 574 is red. I have seen the wrong sealant come out of the old FD West several times now. Some kind of clear sealant which is not Rotax approved.

Your not in a big hurry here so do the other checks first. If you have any questions you can call me.

Roger -

Thanks. Oil filter is hand tight. Oil pressure sensor is tight. Haven't checked the oil cooler fittings, will do so. Need to clean out the radiator, but since I haven't changed the oil in the last 20 hours, I wouldn't suspect it to be coming from there.

Not sure if the photo shows, but the material that is coming out of the flange is redish and in the shape of the flange (look at right side of the photo, between the two bolts). Oil can be found on the top of the oil pump, in between the pump and the bottom of the gearbox. That and the missing "gasket" material is what makes me think that's the culprit.

So far, the leak isn't noticable in the tank, i.e., not needing to add oil. However, I sure don't want to find out the hard way that it's going to get worse in a hurry, like when it all leaks out in flight (bad).

Doug

Hi Doug,

Run your finger under the lip of the oil filter. If you get oil on your finger tighten the filter just a tad more. If it is a red sealant on the gearbox then it might be 574. Just because you see some squished out of the edges doesn't mean it is not sealed. The excess on the outside edges is just that excess. You may have to re-seal it, but let's do the easy stuff first. Oil leaks in this area can really fool you.

Hey guys just wanted to keep everything straight. First of all on older engines (pre-2004) they had used an ORANGE colored Gasket sealant from Germany which has the code number 574. This is very similar to the American formula from Loctite number 518 which is RED. Both sealants are from the same Loctite family and both are considered non-hardening liquid gaskets or Gasket Eliminators for the trade name. Since around 2004 Rotax has switched over to an industrial strength sealant thats more like a glue then a Sealant and this is a Loctite Code 5910, which indicated by the number is in a different group of flange sealants. During the last 3yrs since the start of the Rotax Gear Set Recall there have been a number of gearboxes removed and installed with the 518 as it is the only one readily available. The 518 will work but its not very forgiving and much attention is need when using it. The 574 is only available thru Rotax and is like $75 for a very small tube of it (got to love Rotax prices) the stuff you want to use is the 5910 but here in the USA its only available in a 32oz.Caulking Tube which is way more then you will ever need but its really the only way to ensure you wont have a leak anymore. The price is about 34.95 for the entire tube so its not extremely expensive.

As far as fixing your leak, once you get your hands on the right sealant, I have a trick of the trade I have learned from removing and installing over 40+ gearboxes. When installing the 4 lower bolts on the gearbox, take a bit of your sealant and apply it to the shank of your bolts, this then gets forced inside of the bore of the mounting holes on the flange and helps ensure no leaks occur in those 4 very critical area where the sealing surface is only about 0.5mm wide. Also pay very close attention and make sure no oil from the gearbox drains down over your sealant when you tilt the box into position, this will inevitable cause a leak.

You gotto love this forum with this kind of advice!

Priceless!

Hi Jeremy,

There aren't any 2004 CTSW's. I believe they started in 2005. I haven't seen any orange on any of the CT's.
I also got my numbers mixed up. It is 5910. I'll correct my last post. I haven't had any leaks using 5910. Most people tend to apply too much. A little sure goes along ways. I have never bothered with the 574. The 5910 works so well and easy to use.

I agree there is no comparison to the 574 to the 5910. With the amount of time it takes to remove a prop a gearbox, the 5910 ends up being good insurance.