There is a tachometer drive on the back of the O-470. My tach drive is not used and it has a blue AN cap nut blanking it off. There always appears to be drips of oil here and running down the firewall.

Perhaps this is not the right cap? Is this area pressurized, I.e if I lose this cap will oil be spewing everywhere? Is there a specific cap for this or a blank off panel that would be better?,

I have a blue cap also. It came with the P 1000 digital tach I installed. If it is just a drip, no big deal. but there really should not be a lot of pressure there since the tach drive cable would be there instead and it would not like being pressurized. Did you try turning it tighter?

180Marty wrote:I have a blue cap also. Did you try turning it tighter?

The flat of the nut is almost right against the firewall... It would definitely hit when rotated. Just wondering what the right "cap" is before I monkey with it.

The tach drive is internally sealed. The cap is basically a dust cap when a cable is not used.
The oil is probably coming from somewhere else and blowing back there. Common.

My blue cap is knurled and is round. I put it on with my fingers and no wrench. Will try to get a picture in a few hours.

180Marty wrote:My blue cap is knurled and is round. I put it on with my fingers and no wrench. Will try to get a picture in a few hours.

Perfect, thank you

Here's a couple of pic's. Guess it's not blue anymore---painted gold when the engine was overhauled 6 years ago. Notice how much bigger the drive part of the tach is compared to the cap that goes where the tach cable used to go. Also, notice that I have an O 470U oil pump with intregral spin on oil filter. Another thing is back in the mid 90's Capehart was promoting his reusable filter with fine screen and magnets so I bit on that too. A guy let me swap my original K for the U pump if I went to the work of changing out the studs in the crankcase. Not sure why you have such a tight fit to the firewall since I have plenty of room

180Marty wrote:Not sure why you have such a tight fit to the firewall since I have plenty of room

Probably because I'm sitting on a brand new seaplanes west engine mount and new lord mounts. The drive gear actually resides back in an indentation in the firewall and the cap is outside of the depression, damn close to the firewall.

That looks similar to the tach drive cover on my lycoming.

The drive gear actually resides back in an indentation in the firewall

This is interesting since a 56 182 had a flat firewall like mine. Didn't realize that Seaplanes moved the engine back relative to the firewall. What does that do to the clearance of the prop spinner in relation to the nosebowl. I think a 520 oil pump is even deeper than the one I have and would not fit my firewall without the indent like you must have.

I'm not sure exactly why mine is like that, perhaps the product of a handmade machine with 60 years of maintenance thereafter.

The seaplane mount does not relocate the motor, but things might sit a little more proud on that new equipment than on old sagging rubbers.

After installing the seaplanes west mount, the fore/aft location of my spinner was the same however the spinner now sits noticeably higher than before. Probably 1/2"-3/4". The top of my spinner now is exactly flush, or coplanar with, the top of the cowling. (As it probably was in 1956)

The cover is just a dust cover. The seal is probably bad on the drive for the cable. You take it apart by unscrewing the hex immediately behind your dust cover and replace a little seal. easy job.