The International Cessna^® 170 Association

1954B, 0-300D. Have had this strange oil leak that manifests itself with a film of oil on the bottom of the firewall, runs down the fuselage and drips off the drain hole at the bottom middle of the fuselage. I've noticed there is a small amount of oil at the bean-shaped hole at the bottom of the alternator front end, just aft of the connection to the accessory case.

I had the cowling off and decided to de-grease the engine and wash it off. When the hose hit the alternator, oil started pouring out of the alternator (and I really do mean pouring).

My mechanic said it was probably the drive shaft seal in the alternator. I contacted an ex Jasco repair station and he said there's no oil seal in the front of the alternator. So then, what the heck keeps the oil from filling the thing up in the first place, since a previous post made the observation the drive mounting is below the dipstick oil level??? An alternator shop is now looking at the alternator and he says there's no shaft seal in the front of it, just sealed bearings. He'll know more tomorrow as to the soundness of the alternator.

Engine compression is good. Can the accessory case vent get clogged? Any other ideas?

JohnSunday
N2786C, Ratty ole Alaska Bush Plane

Do you have a proper connection on the oil pressure line at the drain hole on the center bottom of the fuselage?

I tried to post a picture of the alternator breakdown in the Continental service parts catalog, but it was too big. (3.01MB). If you have the book, it is on page 30 and it shows an alternator shaft seal (-14), an "O" ring seal (-13) and a gasket (-9) between the case and alternator face. We had our alternator rebuilt last year and there definitely was a seal, "O" ring, and gasket. We have a Ford 60 amp alternator on an 0300D, but I would assume the principle is the same. As long as you have it out, check the coupling. SB95-3B, attached.

Here is a pic of the PN 352068 oil seal (14) and AN-123864 O-ring (13) depicted in the TCM Parts Catalog:

Kirk and George, thanks so much! No wonder all the Jasco folks denied there was a seal in the alternator; the drive is part of the engine...not the alternator, duh.... Parts are on order!

How is the access to the seal and o-ring once the alternator has been removed? It sounds like this should be a pretty easy job to replace those, but I would like to confirm that with those whom have been down this road before. Any tricks to removing/replacing these items?

Happy Thanksgiving to All

Jughead

You must remove the gear assembly from the front of the alternator drive shaft. My alternator repair guy, a personal friend, did me a huge favor and cleaned my alternator, then tested it to make sure it worked. But, since he wasn't charging me anything, he told me he wouldn't remove the drive coupling since it would expose him to the liability of having to replace it.

My mechanic, on the other hand, quite nonchalantly, took a pair of dykes, removed the cotter pin, took it off and replaced the O ring. Been working great since. Good Luck! Johnsunday

Part # AN-123864 has been superseded by AS3570-111. It's dimensions are 7/16 ID x 5/8 OD x 3/32. Available both on-line and at various supply houses.

counsellj wrote:Part # AN-123864 has been superseded by AS3570-111. It's dimensions are 7/16 ID x 5/8 OD x 3/32. Available both on-line and at various supply houses.

Including O'Reillys.

(It's one of the most common sizes of O-rings.)

BTW, the O-ring performs differently than one might imagine. The oil seal does most of the work, but the O-ring prevents the migration of oil thru the inside-diameter of the rubber bushing housing and drive-gear (along the armature shaft.) The bushing housing O.D. is sealed by the oil-seal, but it's inner surface can, by capillary action, wick oil along the armature shaft. The aft-end of the housing fits against the O-ring, effectively preventing that migration.

.....and when it migrates, it's an impressive migration...

JohnSunday

gahorn

I thought all you RED airplane guys bought your parts at Pep Boys, The Green parts come from O'Reilly's, NAPA carries a good supply of Blue airplane parts I hear.

Jughead

If you want to SLOW down an oil leak.... then go GREEN!

Seriously, I recently re-sealed my own generator immediately prior to launching for this last summer convention. (I thought it was leaking but the actual source was something entirely different....it was the cyl base o-ring on number 2 cyl which flowed back onto the generator.)

Anyway... neither Spruce, nor any other supplier I could find had that official part number in-stock, nor did any of the accy repair stations in the DFW area, nor did Aviall. Time was running short to launch for convention, so I gave up and got the specs from TCM who confirmed it to be a common Buna-N composition O-ring, (sized as already mentioned) same as used in automotive O-rings. O'Reilly sells a complete assortment including the correct one for less than $6. It's got 40 hours on it now and doing just fine.

Van Bortel Aircraft, Cessna Dealer at Arlington, Tx doesn't have the o-rings in stock, but they can get them within a few days. They quote approx $4. I forget the exact number.

Aircraft Spruce & Speciality has them at .51 cents ( AS3570-111)

The FIRST attempt I made was Spruce. They don't actually have them "in stock" and must order them.
The SECOND attempt I made was locally here in Arlington (near where I work all week) they also did not have them, must order them, but will drop-ship and I could have had it in 4 days unless I was willing to pay $25 overnight shipping for a $4 part that really costs about 25 cents at any auto supply.

I wanted to get job done in the next 24 hours so I obtained one locally. As already mentioned, it's a standard part and legal for installation.