The International Cessna^® 170 Association

Other than purchasing the $280 tool from Spruce, has anyone removed the tach seal from the housing? My O-300s never ending oil leak was finally traced to a worn tach seal.

My original housing was also damaged so I purchased a salvage tach seal housing from E-Bay and guess what it came with a visibly worn tach seal we need to remove without scoring the internal wall.

Thanks- Jim Layman
N9534A
'49A

I have drilled 2 small holes for sheet metal screws and then pulled the seal.

John

I've removed a couple of them with a flat screwdriver and simply pried it out. You can also put a flat-washer on the end of a bolt held loosely by a nut. the washer should be just small enough to slip past the rubber seal and grab the metal seal-surround and the bolt can then be placed in a vice and the housing jerked away leaving the seal.

I broke an ear off the housing once trying to get it off the accessory case.

I'm sure you know how it happened Tim ... but sometimes it can be cracked previously and a person might think they did it on removal. (Clearly if one used a screwdriver or scraper to remove a housing and had to get rough with it ... that can certainly crack them... but-also):

Aluminum housings such as the tach-drive-adapter, pushrod-tube-housings, etc. which have mounting "ears" thru which studs pass to be held by nuts are easily broken/cracked when installed and the crack not evident. This usually happens when they are either overtightened (in efforts to stop a gasket leak) or when first-installed and tightened-down un-evenly onto home-made (flexible/thicker than necessary material such as cork) or if too much gasket-paste such as Permatex No.2 is used. Only a very thin "paint" of gasket paste should be used when it's deemed necessary.

During the Mx Seminar at Cody Convention I showed a pushrod housing from our recent 172-purchase which had a crack at one ear which was virtually invisible...but leaked almost a quart every two hours in-flight. It made a real mess on the firewall and belly, and masqueraded as a bad pushrod "rubber". The previous owner had smeared RTV all over the rubber and housing in a sloppy attempt to stop the oil leak.
It had been installed using a blue EPDM/Silicone gasket at it's recent overhaul and had likely been torqued unevenly during installation...or insufficiently, which resulted in a leak that subsequently was re-tightened un-evenly. Either method likely resulted in the crack. (Hint: Even experienced mechanics will sometimes rely upon their "wrist-torque-meter" when installing what seemingly are simple items such as pushrod housings. I was taught it's a bad practice. All bolts and studs have torque specifications and if an inch-torque-wrench/meter is used during initial-assembly a more-even application of torque will avoid this mistake. By "initial-assembly" I am referring to the first effort at installation. The common practice is to assemble the parts by hand... then use a wrench to tighten further...THEN pull out the torquemeter and "check" for final torque specification. I'm suggesting that after the hand-assembly that the torquemeter should come out and be used for the initial tightening, in order to assure than an even-amount is applied sequentially at this first attempt. There are three major types of torque-wrench: The old "needle-and-scale", a "clicker", and a "meter". Most guys/gals these days have "clickers" which is fine for most work that does not involve delicate assembly. But I use all 3 types and recommend an inch "needle-and-scale" or a meter for initial-assembly of delicate items on delicate work such as aluminum housings mating to castings like this, and save the clicker for final torque-checks on most other items.)

Hope this helps.