Continental 0300 D Tach Cable Connection

[Darrell Hamilton]

I have a newly overhauled 0 300 D. It continues to have a small oil leak where the tach cable connects to the engine. Has anyone had this issue?

 

[Dan Thomas]

I have a newly overhauled 0 300 D. It continues to have a small oil leak where the tach cable connects to the engine. Has anyone had this issue?

There's a small seal in the tach drive adapter on the engine. Your seal is leaking. #36 in the picture:



Three nuts to remove the adapter, and the seal can be replaced. The driveshaft (#31) might have a groove worn in its seal shoulder, making the seal ineffective, though. Got to look for that.

The overhaulers might not have replaced the seal. Or they installed a new one with no sealant on the seal's OD where it fits in the adapter. Been there, seen that.

 

[Darrell Hamilton]

Thank you.

 

[3393RP]

Dan, your knowledge always impresses me.

 

[Capt. Geoffrey Thorpe]

Dan, your knowledge always impresses me.

That.

 

[Dan Thomas]

Dan, your knowledge always impresses me.

Thanks, but the range of my knowledge is very narrow. There is so much I don't know, even in aviation. What I do know comes from a passion to be as knowledgeable as possible in whatever career I was in, and there have been several.

We often forget this:



That red slice is being really generous. For most any of us, it would be pretty much invisible.

 

[Magman]

Improper installation techniques for the seal in the adapter can result in a cracked adapter too.

Don’t ask!

 

[Let'sgoflying!]

Can those seals be installed backwards? Or would that be Exxon Valdez vs just a 'small leak'.

 

[Dan Thomas]

Can those seals be installed backwards? Or would that be Exxon Valdez vs just a 'small leak'.

Backwards sure wouldn't help, especially if there was a bit of crankcase pressure from a restricted breather tube. but if everything else is OK, an inverted seal would still do the job.



Oily side on the left, tach cable side on the right. One can see that any pressure in the case would force the seal more firmly onto the shaft.

 

[Eagle_]

You should contact the overhaul shop, I guess they gave you a warranty so they are obliged to either send you a new seal and pay for the work this has cost you. Or just pay for you buying a new seal + work involved.
It’s not uncommon to have an oil leak on a freshly overhauled engine, this happens a lot on varying locations. Don’t use silicone unless that’s your only option.

 

[Dan Thomas]

You should contact the overhaul shop, I guess they gave you a warranty so they are obliged to either send you a new seal and pay for the work this has cost you. Or just pay for you buying a new seal + work involved.
It’s not uncommon to have an oil leak on a freshly overhauled engine, this happens a lot on varying locations. Don’t use silicone unless that’s your only option.

Getting that old seal out without damaging the housing is really tricky. That shop should send him a housing, in good condition, not scored up inside, with a new seal, properly installed with a sealant specified by Continental, and Continental does not specify silicone. Silicone has been blamed for engine failures. Gobs of it break off end get into places where is blocks oil flow. Great for bathtubs and windows, not so great for engines or fuel or oil systems.

What the FAA thinks of silicone (RTV):

http://www.aero-news.net/index.cfm?do=main.textpost&id=c9a9aeb5-b68e-4724-834a-91d35f8e32e6

 

[Bell206]

Getting that old seal out without damaging the housing is really tricky.

FYI: there are small specialty pullers out there for removing dynamic/Garlock seals that will work on some tach housings depending on configuration even with the engine installed.

Can those seals be installed backwards?

Yes. Whether they leak will depend on a number of things like if the shaft has a specific diameter in the normal seal position or if the seal material is directional. Regardless, if installed backwards the lifetime of the seal is usually shortened in my experience.

 

[Magman]

It’s been a while but I recall moderate heating helpful with removal and installation. NOT a torch but hot air. Wearing gloves of necessity.

While you are in there you may want to check the end of the Tach Cable for a drain hole. Lack of this feature may fill your Tach with oil if the Seal is bad.