National Aeronca Association Bulletin Board

I have been experiencing spatter like oil deposits on my windshield lately after only a 20 minute flight. It looked like it was coming from the area around the front main crank seal so I replaced it last week but the leak is still present.

The oil accumulates (2.3 oz/hr) on the underside of the cowl above the Number 3 cylinder close to the oil breather fitting. The oil appears to migrate up through the hinge slot in the cowling and accumulates on the top of the cowl and
then the airstream or the prop wash throws it onto my windshield, it also appears to accumulate on the top surface of the left horizontal stabalizer.

I would like some suggestions from fellow members of this forum as to how I should proceed. I plan on removing the cowl tomorrow and making a close inspection of the engine then I plan on checking the breather hose for any blockage. Other
areas on my mind are valve cover gaskets and push rod tube seals. I have also ordered a black light and some IR dye.

Any input would be appreciated.

Regards,
Sam Burke N6404C L16A (7BCM)

Your oil leak might be coming from the welch plug in the front of the crankshaft. Its worth giving it another tap or two.

Mike

Mike Kelly makes a good point regarding the welch plug. You could try putting some sealer over it. Oil leaks on aircraft are difficult to find due to the pressure cowl which tends to push oil all over and you can't really run the engine and look for leaks due to the prop and airfow. If it's not 'obvious' about all you can do is check the usual places as you described. I use only the 'reusable' rubber v/c gaskets now. The cork doesn't seem to hold up over the long haul. Also, I have all the valve cover retaining screws safety wired to prevent them from backing out. It seems once the rubber boots on the push tubes are on properly and sealed they don't give any more trouble. However, the upper part that's swedged into the cylinder seem to be leakers on occasion. They can be 'reswedged' though.

MikeB

Hi Mike,

What is a Welsh Plug? Is that the fitting on the end of the tapered crank shaft?

Regards,

Sam Burke N6404C L16A

sburke wrote:Hi Mike,

What is a Welsh Plug? Is that the fitting on the end of the tapered crank shaft?

Regards,

Sam Burke N6404C L16A

If you have a tapered shaft the crank plug screws in, I doubt it's leaking there. Just because you installed a new seal don't assume that fixed the problem sometimes it takes a couple attempts to get a main seal to quit leaking if there's a groove worn in on the crank. Might try another seal and leave it out a 1/16 of an inch.

I don't see any oil around the new main seal.
Regards,
Sam

If it is a Continental it is going to seep oil..It usually comes from the push rod housings, especially if they have not been upgraded to the new type. I have had 4 cylinder and 6 cylinder Continentals and always treated it as pretty much a normal thing after you get some weat and tear on them. O-300's are famous for it. How long have you had it?

Doug

Hi Doug,

I have had the airplane since January of this year. The engine has over 600 hours SMO. I do see some oil coming from the top of the pushrod tube at number 2 cylinder.

Regards,
Sam

If that's the case, the push tube can be reswedged with the proper tool. I'd guess most engine shops and probably a lot of techs would have it. Fairly common operation but that doesn't always work long term either. You can also try sealing it from the outside with some sealer (Permatex, silicone, etc.).

MikeB

I realize this post is 6 months late but, do a differential compression test, worn/stuck/broken compression rings cause high crankcase pressures and that "heavy breathing" pushes oil out from almost every gasketed surface.
Leon

I used the swage tool shown in the attached photo. My oil leaks are a thing of the past, thanks. I also used the silicone Real Gaskets for the valve covers (RG-530162-4), mind the torque.
Regards,
Sam N6404C

The best way to find an oil leak is to gunk the engine until it is oil free, then spray soft and dry powder deodorant or any deodorant that has talc in it around all the gaskets and seals until it is covered in white powder. Run the engine for a few minutes and wherever the leak is starting will turn dark quickly, plus it will make your engine smell good too....It really works, it is an old trick a Pratt and Whitney instructor taught me years ago. Jim