Welcome! Becoming a registered user of ShortWingPipers.Org is free and easy! Click the "Register" link found in the upper right hand corner of this screen. It's easy and you can then join the fun posting and learning about Short Wing Pipers!

Page 1 of 12 12311 ... LastLast
Results 1 to 10 of 113

Thread: Carb Heat Box

  1. #1
    crazyivan's Avatar
    Join Date
    Feb 2009
    Location
    Absolutely Temporarily Pensacola
    Posts
    102
    Post Thanks / Like

    Default Carb Heat Box

    I have a PA-22/20 with the 150hp O-320. Flying back from a fly-in today I suddenly lost 300 rpm and the engine started running rough. I switched tanks, went full rich, checked engine instruments, turned toward the closest airport, and pulled out on the carb heat. The carb heat knob pulled with no resistance and no stop. I figured the cable broke and I full carb heat on.

    After I landed I crawled under the cowl and found the cable hanging unbroken and the linkage arm completely gone. It looks like the shaft sheared off due to corrosion and the connecting screw let go.

    What parts do I need to fix this? I see that there is a repair kit for Continental engines, but nothing listed in Univair or Aircraft Spruce for the O-320. There is a Carb Heat Box assembly for sale, but the picture of it has a drain pipe that won't fit under the cowl.

    I need to fix this ASAP before the snow sets in!

    Help![attachment=1:38s09s37]Aircraft Spruce Carb Heat Box.jpg[/attachment:38s09s37][attachment=0:38s09s37]100_0354small (Medium).jpg[/attachment:38s09s37]

  2. #2
    Administrator Steve Pierce's Avatar
    Join Date
    Nov 2007
    Location
    Graham, Texas, United States
    Posts
    11,864
    Post Thanks / Like
    Blog Entries
    1

    Default Re: Carb Heat Box

    Spruce sells one that doesn't have the tube but the quality is very questionable. I talked to McFarland Aviation who makes the repair kits at OSH. I need to get back with them on the dimensions for the Piper air box to see which kit wil fit. I will check this on Monday. I have seen them where the bushings out but never seen one shear from corrosion. You will need the bug nut assembly as well. It is shown on the engine installation drawing.

  3. #3
    Stephen's Avatar
    Join Date
    Nov 2007
    Location
    Lopez Island, WA
    Posts
    3,171
    Post Thanks / Like

    Default Re: Carb Heat Box

    Quote Originally Posted by Steve Pierce
    Spruce sells one that doesn't have the tube but the quality is very questionable. I talked to McFarland Aviation who makes the repair kits at OSH. I need to get back with them on the dimensions for the Piper air box to see which kit wil fit. I will check this on Monday. I have seen them where the bushings out but never seen one shear from corrosion. You will need the bug nut assembly as well. It is shown on the engine installation drawing.
    Steve, I think Spruce has an almost exact copy, not sure about the tube you are refering too...But, the quality seems equal or better than the original too me. BUT, it is not a PMA'd ceritified replacement part and therefore it would not be legal to use...
    "You can only tie the record for flying low."

  4. #4
    crazyivan's Avatar
    Join Date
    Feb 2009
    Location
    Absolutely Temporarily Pensacola
    Posts
    102
    Post Thanks / Like

    Default Re: Carb Heat Box

    The picture above from ACS shows the box upside down. The tube sticking straight up would be going straight down when mounted on the carb and wouldn't fit in the cowling. I saw the non-PMA boxes without the tube, but I want to keep it legal.

    I'm considering spending the few hundred bucks to replace the whole heat box but can't find anybody that sells a PMA one that fits. I hate corrosion. If McFarland has the proper repair kit (thanks for that tip Steve) then I'll probably drop the box, strip it, paint it, then reinstall it.

  5. #5
    Administrator Steve Pierce's Avatar
    Join Date
    Nov 2007
    Location
    Graham, Texas, United States
    Posts
    11,864
    Post Thanks / Like
    Blog Entries
    1

    Default Re: Carb Heat Box

    The boxes from Aircraft Spruce will work but inspect for quality. I returned 4 of them on another project and ended up with a Univair part. Univair makes an airbox for the Super Cub that is the same except that the carb heat inlet tube is at an angle.
    Here is:
    PART 21—CERTIFICATION PROCEDURES FOR PRODUCTS AND PARTS
    Subpart K—Approval of Materials, Parts, Processes, and Appliances
    with a section on owner produced parts:
    http://ecfr.gpoaccess.gov/cgi/t/text/te ... .2&idno=14

    Here is a great article from one of the FAA's best ever, (RIP Bill O'Brien):
    http://www.amtonline.com/publication/ar ... &pageNum=1

  6. #6

    Join Date
    Nov 2007
    Location
    Langwarrin - Victoria, Australia
    Posts
    1,345
    Post Thanks / Like

    Default Re: Carb Heat Box

    This is the same "s...box" that caused Patsy's prang!
    In that case the "flap" inside simply broke off, got sucked up and blocked the carby inlet. This was about 400 odd hours since engine overhaul.

    Are these things changed or inspected at overhaul?

  7. #7
    Administrator Steve Pierce's Avatar
    Join Date
    Nov 2007
    Location
    Graham, Texas, United States
    Posts
    11,864
    Post Thanks / Like
    Blog Entries
    1

    Default Re: Carb Heat Box

    I inspect them at every annual but they are normally sealed off at the ends. Not sure how the water got in Dave's. I flew it for 200 plus hours. What I usually find is the shaft rattling around in worn out bushings or the flange that holds it to the carburetor cracked.

  8. #8
    crazyivan's Avatar
    Join Date
    Feb 2009
    Location
    Absolutely Temporarily Pensacola
    Posts
    102
    Post Thanks / Like

    Default Re: Carb Heat Box

    My guess is a combination of factors. I assume that is the original box. My theory, it developed a small score on the shaft after using it for the first 10 years of its life. It sat in an Arkansas barn for another 24 years absorbing that humid salty air. The scoring developed some corrosion and then failure was a matter of time. Or I'm completely wrong.

    The only thing that I don't understand, was it a coincidence that the shaft failed and the bug nut let loose at the same time? I would think that the bug nut would have secured the arm to the actuating cable. It worked on preflight so it all let loose during the 30 minutes in flight until failure.

    Steve, the Univair part you mentioned, is it 11950-007? Also, where do I get the engine installation drawing?

    Thanks a million.

  9. #9

    Join Date
    Nov 2007
    Location
    Langwarrin - Victoria, Australia
    Posts
    1,345
    Post Thanks / Like

    Default Re: Carb Heat Box

    Steve - you inspect them at every annual so does that mean that things like carby, mags, plug leads, generator, starter etc. (i.e. the bolt on bits) are not renewed/overhauled when the engine is overhauled?

    I was a little surprised when I pulled the carby off as it looked pretty old and dirty inside even tho' the engine has only done 400 odd hours since overhaul. So I suspect that it wasn't even cleaned before refitting. I guess I had better drag out the engine logbooks and have a real close read and see what was or wasn't done.

    And after seeing the photos you posted of the misfitted bearings, I am pleased that the case will have to be split to replace the crankshaft. We can have a good looksee at what the inside condition is like and make sure that the new bearings are fitted correctly.

  10. #10
    Administrator Steve Pierce's Avatar
    Join Date
    Nov 2007
    Location
    Graham, Texas, United States
    Posts
    11,864
    Post Thanks / Like
    Blog Entries
    1

    Default Re: Carb Heat Box

    Usually all the accessories are rebuilt at overhaul.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •