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Thread: Conical mounts and bolts

  1. #1

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    Conical mounts and bolts

    Hello all,
    I changed the conical mount bushings, #71032, on my 0-320 PA-12 last Saturday. The post on this site references that the measurement from inside of the washer to inside of the washer should be 1.84".

    http://www.supercub.org/phpBB2/viewt...ighlight=71032

    Mine was 1.75". Is this critical? The AN 8-44 bolt was only showing one thread beyond the castle nut. I couldn't loosen it anymore if I wanted to.

    Technically I believe the picture shows the bushing for the 0-290 engine. It is different from the 71032. Also the above referenced post shows the bolt head aft and the castle nut fwd. My bolts were originally installed just the opposite with the bolt facing aft. I see some pix on this site with the bolt going fwd. Does this matter?

    Thanks.
    David Grantham

  2. #2
    Steve Pierce's Avatar
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    You might need a different length bolt. The bolt and engine mount in the drawing is for a Clipper or Pacer. I posted it for the compressed bushing dimension which is the same on Piper, American Champions and others. Sorry, I should have clarified that.
    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  3. #3

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    Steve,

    Which do you use when installing new engine mounts: the compressed dimension or the torque spec?

    The referenced picture appears to show the part number 60883 mount rather than the 71032 mount, does this make a difference which tightening method is used?

    Thank you,

    Vickie

  4. #4
    Steve Pierce's Avatar
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    This drawing came from the Short Wing Drawings. The dimension is also used in the Citabria manual I have. I usually torque 40 inch pounds and then check the dimension and adjust the torque to get the dimension. It has usually been very close. I do this because the clearance on some of these mounts to other parts is pretty close and I figure the compression dimension is more accurate. I hate having to repair mounts. Plus there is this new compound rubber thing that Jr posted about where the mounts are sagging prematurely. I do all this and keep my fingers crossed.

    SJ. I love the spelling checker. Now I can spell deminsion and prematurly correctly.
    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  5. #5

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    When I changed the bushings I also checked the bolt length. It is also an AN 8-44. I also checked several other manuals with regard to bushing installation. They all simply went with the 40 inch pounds.
    It appears from the other postings that the critical issue is engine part clearances from the actual mount itself. With the engine vibrating and torqued up we certainly don't want anything rubbing. I'll give it another good looking over.
    With regard to the bolt facing fore or aft, is that an important issue??
    Thanks.
    David Grantham

  6. #6
    fobjob's Avatar
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    I just put in new 71032 bushings on my O-320... 1.84 in is just not enough squeeze. The starboard lower mount sags when I take the engine weight off the crane. Also the tapered part of the front bushing is about .1 inch exposed...The bolts are all two washers short of the length that was on them with the old mounts, which lasted ten years....about .1 inches...can't accurately (easily) measure torque at that low value...but, the bushings aren't bulging any, either... I think they need to go about 1.75"....my strategy now is "tighten them till they bulge a little"...about two more turns (and washers)...

  7. #7

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    Quote Originally Posted by fobjob
    I just put in new 71032 bushings on my O-320... 1.84 in is just not enough squeeze. The starboard lower mount sags when I take the engine weight off the crane. Also the tapered part of the front bushing is about .1 inch exposed...The bolts are all two washers short of the length that was on them with the old mounts, which lasted ten years....about .1 inches...can't accurately (easily) measure torque at that low value...but, the bushings aren't bulging any, either... I think they need to go about 1.75"....my strategy now is "tighten them till they bulge a little"...about two more turns (and washers)...
    I agree wholeheartedly.

    I also turned my bolts rearward facing so it would be easier to cotter key them. I checked Univair's PA-22 manual as well as a Citabria manual and they both face rearward. Also those same manuals did not mention the 1.84" spacing but went with the 40" pounds. I gotta believe most people do as we did.
    David Grantham

  8. #8
    Steve Pierce's Avatar
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    Here is a copy of my Citabria Service Manual with the dimension.

    http://www.supercub.org/photopost/sh...=500&ppuser=58

    This drawing is what I used on my Pacer. I can't remember if I had to tighten more than 40 inch pounds or not but I did torue to the dimension.



    In my 1954 Super Cub Owners Handbook revised 1977 I did find: "Engine mount bolts should be tightened to 60-80 inch pounds."
    I wonder if different rubber compounds are the reason for different results. I installed the O-320 on my Pacer this summer and an O-320 on a Super Cub last Spring and no problems. I know Jr had some sagging problems. I got my rubber mounts from Aviall and they were factory Lycoming parts.
    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
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  9. #9
    fobjob's Avatar
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    Steve, I notice that the drawing does not accurately represent the shape of the 71032 bushings...could they be referring to an earlier engine than the O-320? I'm not going to assume anything, and check the flange dimensions on the engine crankcase....some idiots had possession of my plane in Boise in 1997 for a while, and I've been finding steamy excremental material in it ever since...

  10. #10

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    I too, have noticed that the dimension of 1.840" seems to give too much sag, so I use the torque method. The 60883 mounts (in the previous picture) are shorter than the 71032 mounts by .046" per mount pair. (I just measured several of each mount.)

    Could the dimension be for the shorter 60883 mounts and the torque for the more common 71032 mounts?

    Steve, I looked through my Univair pre- and post-1974 owner's handbooks for the 60-80 in-lbs torque specs and did not find anything. Where did you get this revised book? Or more specifically, how can I get a copy of the revised book?!

    Vickie

  11. #11
    Steve Pierce's Avatar
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    The only ones I am familiar with are the 71032. They are common to the O-235, 290 and 320 according to my parts books. What are the 60883 parts applicable to?

    The Super Cub Owners Handbook I have came from Piper. Someone told me recently that Piper still sells them.
    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  12. #12

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    The major difference between the 60883 and the 71032 is the nose dimension -- 7/8" for the 60883 vs 1" for the 71032. Same bolt diameter, though.

    I seem to sell a few sets of 60883 mounts every year. The application is related to the engine mount design, the 60883 mounts are specified in my parts book for several models of the O-235 and O-290.

    Steve -- I will follow up with Piper on that owner's manual, it sounds like a more current revision than the manual from Univair with updated information.

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    Vickie

  13. #13
    Steve Pierce's Avatar
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    Vicki, I can't find the part number 60883 anywhere in my PC-302 O-235 Series, PC-102-1 O-290-D Series, or my PC-103 O-320, IO-320 & LIO-320 Series Parts Catalogs even in the numerical index in the back.

    Last week we never got out of the 30s and this week highs in the 70s all week. Come back down and you can work on that tan. I will even let you build a cowl for a Luscombe.
    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
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  14. #14
    eslboat's Avatar
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    Steve , I know this question has been asked but I don't think there has been a definitive answer. My parts book for my 12 shows the engine mount bolts with the nuts on the forward side of the engine but I've also heard the saying nuts to the pilot . Does it matter which way the bolts face or is it just preference ? In other words are they legal either way ?

    Thanks,

    Erik

  15. #15
    Steve Pierce's Avatar
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    Structurally I don't think it matters. I put mine pointing aft. Sometimes it is hard to get them in because the intake tubes are in the way or the other way is a pain because of the exhaust. I have seen plenty both ways.
    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  16. #16
    eslboat's Avatar
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    Thanks Steve , I'm into my first rebuild and read many of your posts with great interest !

  17. #17

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    conical mounts and bolts

    The original Lycoming engine blueprints call out for the bolts to be torqued to 40 inch pounds. 1.84 inches is measured from rubber to rubber inside the steel washers. Nuts are shown on the prop side of the motor mount attach point as the "suggested mounting."

    I'm looking at the Lycoming drawings 63776 for the O-320-a,-b series and 63700 for the O-235 c, c1, c1a, c1b series.

  18. #18
    fobjob's Avatar
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    A friend of mine pointed out that since the bolt is 'gripped' by the rubber, the proper way to measure the torque would be at the nut......
    any thoughts on that?

  19. #19

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    I learned that bolts should be installed inboard down and aft. This was a long time ago, in the Air Force. I think they also covered making stone arrowheads.

  20. #20
    Steve Pierce's Avatar
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    Jay, There are some cases where that doesn't work.

    Yes, torque the nut. The bolt will have the drag of the mount, rubber bushings etc. on it.
    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  21. #21
    Gatorcub
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    Just for info, I found a Piper Service Letter dated 12/14/60 pertaining to this subject. Models affected All PA-18, PA-22 and PA-25 series aircraft equipped with Lycoming engines.

    It states that it is permissible to use torque value of 40 inch pounds to provide adequate tightness to maintain proper engine support in lieu of the linear dimension as previously specified. The mounting bushing must be free of oil and the bolt must move freely through the mount, using this torque value.

  22. #22
    Steve Pierce's Avatar
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    Thanks Gator Cub. I found my copy and posted it.

    http://www.supercub.org/photopost/sh...=14904&cat=760
    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  23. #23

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    the deal is if everything is clean and in good condition as for as the bolt is concerned and you dont have anyweight pulling on it then 1.84 inches and 40 inch pounds are one and the same thing so use 1 or the other or both but they are not 2 differant measurements

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