budyerly(at)msn.com
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 Posted: Fri Jul 20, 2018 5:31 pm Post subject: On your greasing / oil leak. |
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Bill and all early or used Airmaster Owners with the 308 or circa 2000 and early AP332s.
I’ll see Martin at Oshkosh this week (if I don’t get WX CNX again by the airlines) and discuss the messy greasing procedure.
For now, this is what I will bring up with him:
Reference SB14 for the Airmaster AP308.
Airmaster and we builders were worried about water incursion in our seaplanes. SB 14 covered what to do to fill the void in the blade ferrule and the cam follower hole that allowed water or moisture to enter the blade ferrule bearings and ferrule support causing expensive repairs.
One side effect of the SB14 sealing was now old oily grease (grease does separate from the thickening agent) could not go up into the blade ferrule either and come running out the blades. Which was nice.
The new 332s and 332Ss are sealed pretty well from water incursion, and are also sealed at the outside of the blade ferrule right at the blade exit, which is so nice (and clean). These sealing improvements have really improved that old grease all over the plane slinging common of the old 308. To seal the prop using SB 14 please do not use off the shelf sealant to do this SB or to seal around your blades like the new props, as the acid added to the sealant will corrode your aluminum. Use the Dow 737 non acid clear sealant. Bottom Line: These improved sealing methods used by Airmaster pretty much eliminated the massive grease slinging and water incursion, unless….
Reference SL 1 Greasing Procedure.
In the greasing instruction paragraph e, with its photo, if followed exactly with that much grease, the new grease will ooze out of around the O ring on the retention nut, and during operations one will get a spray of grease for quite some time all over your aircraft. The prop will never corrode, and it will be well lubricated, which is good for Airmaster, but may make a mess of your aircraft.
My suggestion to successfully lube the prop and still keep the aircraft relatively clean is to grease the bearings as shown, but use a clean towel to wipe the excess grease off of the ferrule threads, and the O-ring seat area of the hub to a thin film, not the pasting of globs of grease as shown on the threads and O ring area on the ferrule as shown in Service Letter 1. (The bearing seat area still must be greased well and fully packed as any bearing should be.) In my opinion, and from 15 years of practice, one should not see an opaque layer of grease on the threads, it should just be just a shiny film on the threads of the bore. If the threads of both the blade ferrule and the hub are full of thick grease, during assembly, it will ooze inside the gap on the underside of the nut, and after tightening the blade, the grease will be pushed up and out around the O-ring and along the blade assembly retention nut to the ferrule base and will take quite a few hours to fling out.
Education comment:
Grease is actually oil (synthetic or blend) with a thickening agent (Mineral, soap, plastic) that allows the oil under pressure and or temperature to release the oil and lube the area of contact while the excess thick grease squeezed out around the bearing surface to continue to transfer the oil to the contact surfaces of the bearing or friction plate over time. Some greases appear to dry out (become wax like) in the presence of air, others are highly water resistant, others still are designed for specific temperature ranges and pressures. Every application has a grease that is just right (the Goldilocks grease).
Back to the Prop:
If a significant oily trace is coming out from the ferrule nut (refer to figure 2 Page 9 of the operators/install manual for the 332), the careful observer can see how the oil from the excess grease can run out from around the seals all around certain areas. It is obvious centrifugal force is forcing the grease up the ferrule wall and the ferrule gaps in and around the retention nut threading, O ring and eventually out of the prop where the blade exits the Ferrule nut and all over the aircraft. Study this figure well and see those areas which allow oil to fling out of the blade. In my opinion, the main culprits are the Retention Nut Seal O-ring under the flange where the #10 Allen screws are, the blade ferrule seal to the body.
Consider this:
One must clean out the old grease well, , but, look also at your old grease that has slid along the outside of the retention nut and clean it up well before adding new... that old oil is now freely running and with new grease added compounds the problem and will add to your mess. Slide the retention nut up and down and see just how greasy/oily that area is and wipe clean… It should be clean of fluid, or solid grease, but a film should remain. Note that any runny oily fluid or caked grease may be a sign of previous over-greasing. Once cleaned up, apply new grease to the blade retention, alignment and preload bearings ensuring the bearings are packed, and the valley around them is also filled as you would any bearing. Again, carefully wipe excess off your outside areas or non bearing areas.
Finally, make sure the threads of the blade nut are covered with only a thin film of grease (virtually transparent and shiny) as is the O ring area prior to assembly. Install the blade and start cranking down on the nut by hand and to clean up any ooze, use a lint free towel to wipe as you go. I fold a Scott lint free paper towel (those blue mechanics ones) and while turning the blade nut, I wipe all around the underside of the flange on the ferrule retention nut until the O-ring starts to nearly grab the towel and then back off, wipe some more until the cloth is clean and finish tightening the nut and wipe some more... The towel will be wet with the oil film but should not have any thick grease remaining.
Finally on leaks on a tractor engine,
Possible other oil leaks seen on the cowl should be investigated also:
On the airframe, keep your spinner to cowl gap distance to an 1/8 to 3/32 inch as a larger gap will interfere with air pressure in the cowl. Normally the gap pulls air out of the pressurized cowl and over the cowl face. Any engine oil leak will be pulled from the engine and exit around the prop shaft and out around the spinner backplate. Since the Airmaster standard slip ring is attached to the spinner backplate, the rings get covered with engine oil as well as the cowl.
If the prop was severely over greased, with the grease coming out of the blade ferrules and collecting on the inside of the spinner, it will travel out through the holes in the spinner backplate then on to the cowl and out. If the inside of the spinner is clean, and oil is on your slip rings, look hard at the engine because you may have an oil leak. In this case engine oil is normally brown ish, and so one must lube the prop with a red grease such as Mobile 28 to tell the difference. If the grease or oil for that matter are the same color, you don’t know where it is coming from. Look hard.
Sorry for the tome,
Bud Yerly
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