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Thread: Front crank Seal

  1. #1
    Bayport Piper's Avatar
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    Default Front crank Seal

    I have a front crank seal that gave way last week. It was a split type seal. I had it replaced by a buddy of mine who is an A&P with another split type seal. Yesterday, after the 2nd test run around the patch, it gave way once again. Does anyone here have any input as to whether I should be using a different sort of seal or maybe the problem stems from something else? Until now I had absolutely no problems in the engine area of the plane. It has 60 hours since an oil pump AD fix, but thats all. Any input is appreciated. Thanks

  2. #2

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    Default Re: Front crank Seal

    Check for an obstruction in the overboard dump line that comes off the top of the engine (the "crankcase breather tube"). It's the 5/8" (or so) aluminum tube that vents out the bottom on the cowl at the firewall and it is connected to the fitting on the engine with a short piece of rubber hose. Most engines, you can find the top end inside the left cooling air inlet in the nosebowl. If this tube is plugged, it will DEFINATELY blow the prop shaft seal! Usually it takes just about enough time to warm up the engine, do a runup and take off for the pressure to build enough to jettison the seal. Instant "windshield oil"! Been there...done that.

    This is a known problem when airplanes are used a lot for ski-flying since water vapor can -and does occasionally- freeze down at the lower (exit) end. There SHOULD BE a "whistle slot" in this tube for just this reason. But if the tube is plugged ABOVE the whistle slot by something really stupid (like a certain type of "Mud Dauber") your solpoution is to remove the stoppage.

  3. #3
    Administrator Steve Pierce's Avatar
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    Default Re: Front crank Seal

    Excess crankcase pressure (blow-by) can cause the nose leak or as John posted a crankcase vent obstruction. I have had a few problems with getting the seal to hold. I have used this Continental Service Bulletin to remedy the problem.

    http://www.supercub.org/photopost/showp ... &ppuser=58

    http://www.supercub.org/photopost/showp ... &ppuser=58

    http://www.supercub.org/photopost/showp ... &ppuser=58

  4. #4
    Bayport Piper's Avatar
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    Default Re: Front crank Seal

    Good advice gentlemen. I'm heading out to the field today to inspect the breather tube. I'm also going to look if anyone would have a stretch over type seal I'll purchase both types to have them on hand. I'll keep you posted. Thanks John

  5. #5
    Bayport Piper's Avatar
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    Default Re: Front crank Seal

    Well, its a spun seal once again. I have a feeling it was installed incorrectly. Even my hangar mate says he believes they didn't use the right or enough adhesive. I checked the breather tube and its free and clear. I'm going to try a stretch type seal next with the right adhesives and making sure things are going in the right way. One other question, does anyone know about the removal of the shocks from the hydrasorb system in order to smooth out the landing impact?

  6. #6

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    Default Re: Front crank Seal

    I have to assume that you have the correct bungee cords installed? The PA-20 EARLY used a slightly different setup than the later ones, but if you have HydroSorbs and two cords on each one, you have a "later -20". The HydroSorbs are simply shock absorbers and were in fact originally made by Monroe. Lots of people don't realize that shocks only effectively "dampen" in one direction. What you may intuitively think is that they would dampen in "compression" (thinking like you were in your car) when you hit a rise in the road (or drop your airplane onto the ground from four feet) and that would put you among the general populace... wrong. "Shocks" dampen in REBOUND...when they RETURN from the "upward shove on the wheels". As it turns out in "real life", shoving your ShortWing's wheels "up" actually LENGTHENS your hydrosorbs instead of compressing them, like in your car, but the bulk of their "dampening effect" by design is when the wheels "return down" and they shorten again. Believe it or not. It didn't take much for Monroe to make the shock dampen in the "other direction"; just a matter of putting "the works" on the "other end". This method of "absorbing the energy" gets rid of the "pogo stick effect" just as well as the shocks on your car "kill the bounce", by controlling the REBOUND. Without the hydrosorbs installed, you would get a GREATER flexation of the "rubber bands" (bungee cords) because the shocks aren't actually "not doing anything at all" in that direction, but they are doing "less". But if they are removed, or worn out completely, you would then have to deal with a good deal larger WALLOP when they rebound(ed?)... AND, you would get tossed back up in the air. You don't want to do that...it isn't as much fun as one might think. If that is in fact your real "problem", it's time to put new HydroSorbs ON, not remove the old, tired ones. Bzzzzzttt! Wrong answer, try again. :mrgreen:

    Chances are that the problem is really very easily fixed (just throw some money at it). If your HydroSorbs are in fact doing what they are supposed to be doing,then what you have to do is "take care of the loose nut on the controls". In other words, "tighten up your landing technique" Stop doing Carrier landings! I got two thousand words about why wheel landings are NOT the right way to land, but I'm gonna "spare you" (mostly because Pacer pilots already know, but if you don't as of yet...well, you're learnin'). Full stall.

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    Default Re: Front crank Seal

    I use Aviation Permatex on the nose seal and lubricate the shaft where it contacts the seal.

    I use a 1080 and 1280 on my Pacer.

  8. #8
    Bayport Piper's Avatar
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    Default Re: Front crank Seal

    As far as suspension goes. I don't know why I wasn't thinking of it that way. Well said. I do wheel landings on occasion if there are any cross winds and 3 pointers on nicer days. To the seal. I'll see what was used as far as chemicals Thanks gentlemen.

  9. #9
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    Default Re: Front crank Seal

    Last time I did a front crank seal was over 10 years ago. I believe I used 1300L to coat the area in the case recess. attached is a portion of the Lyc SB that discusses what to "glue" it in with.
    "Progress is our most important problem"

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    Default Front oil seal

    The front oil seal split in half and blew out on my O-290-D2 yesterday.Probably a result of the motor sitting for 20 years or so. It looks like there are two types of replacement seals. A two piece or a one piece extra stretchy, to stretch around the propeller flange. Which one is preferred?

    Thanks, Scott

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