Oil Leak at Prop Hub

[hnorber]

Hi All.   Wondering if I might get some enlightened opinions on the attached pictures of my prop/hub.  This oil streaking is from about 1.75 hours of flight time.   My prop was overhauled about 9 months (75 hours) ago.    My mechanic is suggesting that this may be normal (I recently switched from Phillips 66 X-C to Areoshell W100 Plus - but I don't think that would have contributed to this - if anything, I would imagine that the Aeroshell  W100 Plus is less likely to leak since it's a higher viscosity).

I'm specifically wondering whether there's a danger that this leak could be something that becomes a rupture or otherwise could cause a catastrophic oil loss in flight?  

Thanks,

-Howard

 

[thinwing]

Pull the spinner ,can't tell the source

[Bryan]

McCauley or Hartzell?

Is it grease or oil?  Color?

I had an M20F with a Hartzell that had a slight leak like this. I contacted my local prop shop and said the seals would need to be replaced to stop this but it was not a big deal with the streaking like you have. I asked when is too much and the answer i got was “you’ll know” or when you are tired of cleaning it off the cowl and windscreen. I think the seals have a calendar expiration and an hour lifetime; if yours was 9m and 75h ago neither would be close.

[FloridaMan]

I think that's probably grease and not oil. Oil tends to come out over the cowling and not around the blades. 

Someone could have overgreased your prop too. Happened to me once (on a Hartzell, not sure if it's the same); IA removed bottom grease fitting and pumped grease in until it came out the other side. I didn't know any different and ended up with grease streaks like that. The good news is that a prop R&R and reseal isn't all that bad. 

Also, if you decide to pull the spinner and especially if it has the bulkhead that attaches to the flywheel (as opposed to the back of the hub), make damn sure the spinner fits tightly on the hub or you'll find yourself with a nasty crack and needing a new spinner assembly. 

[jaylw314]

51 minutes ago, hnorber said:

Hi All.   Wondering if I might get some enlightened opinions on the attached pictures of my prop/hub.  This oil streaking is from about 1.75 hours of flight time.   My prop was overhauled about 9 months (75 hours) ago.    My mechanic is suggesting that this may be normal (I recently switched from Phillips 66 X-C to Areoshell W100 Plus - but I don't think that would have contributed to this - if anything, I would imagine that the Aeroshell  W100 Plus is less likely to leak since it's a higher viscosity).

I'm specifically wondering whether there's a danger that this leak could be something that becomes a rupture or otherwise could cause a catastrophic oil loss in flight?  

Thanks,

-Howard

It's tough to tell from your photo if it's oil or grease.  The prop hub is filled with red-dyed oil, so if it was just black when you wiped it off it's probably grease (although my hub leak with bad enough all the red dyed oil had gone).

If I understand correctly:

• If it's a McCauley prop, it could still be leaking a little grease and be normal.  If it continues to leak grease, it will eventually run out and cannot be replaced.  When it stops, you may be in trouble
• If it's a Hartzell prop, the hub is re-greased at annual, so leaking grease is not a huge issue, and you might expect to see more every year

Neither leaking grease or oil (if mild) are safety-of-flight issues, but they are safety-of-wallet issues so shouldn't be ignored.  But if your mechanic tells you to fly it until you can't stand the leaking, fly it and be prepared for some repairs at your next prop IRAN.

Also, Hartzell suggests deep-cycling the prop during run up a few times to see if that reseats the blade seals, and then reassess after a few more hours of flight.  I'm not sure how that's supposed to work, but that's what they suggest (I read it but couldn't find the reference).

[jaylw314]

4 minutes ago, Antares said:

I think that's probably grease and not oil. Oil tends to come out over the cowling and not around the blades. 

My oil leak started out looking like that, I wonder if oil leaks carry out some of the grease onto the blades?  It only started misting the windshield and cowl about 3-6 months later.

[N201MKTurbo]

The McCauley prop hub will fill with oil if the seal on the pitch change piston starts to leak. After it fills with oil it will start to force the grease/oil mixture out the blade seals. The prop shop told me that is the usual cause of grease being slung out.  

[hnorber]

Thanks.  This is all helpful information.  

BTW - it's a McCauley prop.  I just looked at my logs and was reminded that it was a  reseal (not an overhaul) that was done in August (although the bill seemed to be more in line with an overhaul!)

 

[N201MKTurbo]

5 minutes ago, hnorber said:

Thanks.  This is all helpful information.  

BTW - it's a McCauley prop.  I just looked at my logs and was reminded that it was a  reseal (not an overhaul) that was done in August (although the bill seemed to be more in line with an overhaul!)

 

If it has been that recient, I would call the prop shop for their opinion.

[N201MKTurbo]

If the above sceanario is correct it will not catastrophically fail. It will gradually get worse. You can fly it until you can’t stand the mess it is making.

[skydvrboy]

My prop looked exactly like that and I was worried about how much that repair would cost.  Did some searching on MS and found that it wasn't a big deal and could be from a number of things.  I cleaned it up, started monitoring it, and haven't seen any since. 

One of the possible culprits mentioned was oil spilled during an oil change.  I think that was my problem as I had dumped a lot of oil on the engine before that flight trying my own oil change for the first time.

[hnorber]

Thanks.  I'm in touch with the prop shop that did the work last year and so far they're  being very helpful and seem to be stepping up (together with my mechanic who directed me to them). 

I suppose that it's possible that this is grease -but I would have thought that grease is a bit too thick to streak out that far in thin, well defined lines.  I sent the pics to the prop shop and will also try to wipe some off with a white rag to verify whether it's black or red.

BTW - I generally cycle my prop 3 times during my runnup - each time starting at about 1450 RPM, pulling the prop all the way back and watching for the RPM to drop, Manifold Pressure to increase and oil pressure to return to within the the green after each cycle.   Wondering if anyone sees anything wrong with this method or has any better suggestion?

 

Thnx

-Howard

 

[jaylw314]

12 minutes ago, skydvrboy said:

One of the possible culprits mentioned was oil spilled during an oil change.  I think that was my problem as I had dumped a lot of oil on the engine before that flight trying my own oil change for the first time.

I think that idea comes from the fact the doghouse cowling actually blows air forwards from the upper deck in some places, so if you spill oil, it can get blown forwards onto the prop hub.  That should not happen in the M20J cowling, though.

[jaylw314]

1 minute ago, hnorber said:

Thanks.  I'm in touch with the prop shop that did the work last year and so far they're  being very helpful and seem to be stepping up (together with my mechanic who directed me to them). 

I suppose that it's possible that this is grease -but I would have thought that grease is a bit too thick to streak out that far in thin, well defined lines.  I sent the pics to the prop shop and will also try to wipe some off with a white rag to verify whether it's black or red.

BTW - I generally cycle my prop 3 times during my runnup - each time starting at about 1450 RPM, pulling the prop all the way back and watching for the RPM to drop, Manifold Pressure to increase and oil pressure to return to within the the green after each cycle.   Wondering if anyone sees anything wrong with this method or has any better suggestion?

 

Thnx

-Howard

 

Starting at 1450 RPM??  Do you mean you only run up to 1450 RPM, or that you start from 1900 RPM and pull it back to 1450 RPM?

Cycling the prop on the runup is only necessary to determine if it works.  See other threads, but the single-engine hubs we have don't cycle a lot of volume and will not get warmed up, so there's no point doing a deep cycle.

IDK for sure, but at prop runup speeds, I'm guessing the RPM only drops once the blades become as coarse as they ever will during normal flight, so I'd go with the idea of just letting the RPM's drop only a couple hundred RPM before pushing the knob forward, and I just do it twice now.

[Bryan]

I do it twice, once to watch the oil pressure drop and the second to observe the rise in MAP. I don’t do it deep cycle either (or to a specified RPM drop) as once thought to cycle the ‘cold’ oil in the prop. I, too, learned that the hub cycles very little oil. I think my POH states runup to 1700 or 1800 RPM.

[hnorber]

Thanks.  Yes - I used to do it at 1700 RPM, but was told that it was better to use 1450 RPM (meaning that I start at 1450, pull the prop control full out, let the RPM drop, MP rise and then check that oil pressure returns to green after I push the RPM control back in).  Sounds like it might be better to do it twice rather than 3 times, and to start at 1700 RPM and push the RPM control full forward right after the RPMs start to drop (rather than waiting for them to drop as low as possible).

 

 

[jaylw314]

2 hours ago, hnorber said:

Thanks.  Yes - I used to do it at 1700 RPM, but was told that it was better to use 1450 RPM (meaning that I start at 1450, pull the prop control full out, let the RPM drop, MP rise and then check that oil pressure returns to green after I push the RPM control back in).  Sounds like it might be better to do it twice rather than 3 times, and to start at 1700 RPM and push the RPM control full forward right after the RPMs start to drop (rather than waiting for them to drop as low as possible).

I think the M20J POH says 1900 RPM.  Not sure what the rationale of 1450 RPM would be.  That's not even close to anything like a realistic power setting for a runup.  It does mean you're cycling the prop to pretty much its fullest coarse angle every runup.

There's no rationale for me choosing to cycle the prop twice.  Once should be enough in theory, I just do it twice to convince myself  

[Ned Gravel]

On 6/18/2018 at 6:55 PM, Bryan said:

I do it twice, once to watch the oil pressure drop and the second to observe the rise in MAP. I don’t do it deep cycle either (or to a specified RPM drop) as once thought to cycle the ‘cold’ oil in the prop. I, too, learned that the hub cycles very little oil. I think my POH states runup to 1700 or 1800 RPM.

+1 

[Guest]

On 6/18/2018 at 6:14 PM, jaylw314 said:

I think that idea comes from the fact the doghouse cowling actually blows air forwards from the upper deck in some places, so if you spill oil, it can get blown forwards onto the prop hub.  That should not happen in the M20J cowling, though.

Not all pre J models have a doghouse.

Clarence

[RobertE]

I too had streaks like that after my prop overhaul.  It proved to be nothing.  

[Cody Stallings]

It’s not uncommon for a McCauley Propeller to Poop a little grease out sometimes.

That is a very small amount.

If that Doesn’t dry up pretty soon an/or gets worse,  may wanna have it looked at.

I would just fly it an keep an eye on it.