Tach seal removal

How to keep the Cessna 170 flying and airworthy.

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james_layman
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Joined: Sat Jan 29, 2005 4:15 pm

Tach seal removal

Post by james_layman »

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
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n3833v
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Re: Tach seal removal

Post by n3833v »

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

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GAHorn
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Re: Tach seal removal

Post by GAHorn »

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.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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mit
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Re: Tach seal removal

Post by mit »

I broke an ear off the housing once trying to get it off the accessory case. :cry:
Tim
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GAHorn
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Re: Tach seal removal

Post by GAHorn »

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.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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