Results 1 to 9 of 9

Thread: Staying well grounded

  1. #1
    wireweinie's Avatar
    Join Date
    Aug 2013
    Location
    Palmer, AK
    Posts
    4,142
    Post Thanks / Like

    Staying well grounded

    Just need to put out a reminder to check out your ground path from the engine to the airframe. Do it at least each annual. Please.

    Two days ago I had to do some wiring repairs due to poor engine grounding on a very nice C-180. I was originally called because the alternator was not charging and the field breaker would pop as soon as the master was turned on. I was busy, so I attempted to troubleshoot the system over the phone. When that did not work, I went to the aircraft. The aircraft was tied to a good solid dock and had the top cowl removed (greatly appreciated!). The very first thing I saw was the regulator ground wire had NO insulation left on it due to overheating.

    Some of you will remember MCS Mike and I telling about 'bad things' happening due to poor engine grounds. Here was another example. There was no ground strap connecting the crankcase to the airframe. I didn't remove the lower cowl to check but it appears that the aluminum ground straps that wrap over the Lord mounts on the engine had finally broken (this charging system has been working fine for a couple of seasons). This means that when cranking the engine or when the alternator begins to charge, the path to ground for the starter or alternator will be things like primer lines, control cables, etc. Since I run the regulator ground wire (20 gauge) to the back of the alternator for Plane-Power systems, this little wire was the first victim. Current to the starter motor trying to go through this little wire had made it hot enough to melt the insulation off and let it melt into the field wire it had been bundled with. The dead short between these wires was the reason that the field breaker would pop when the master was turned on.

    The repair was actually fairly simple. I printed new regulator ground and field wires and installed them. Then I installed a braided ground strap from a stud on the accessory case to one of the 1/4" bolts that hold the regulator to the firewall. I also installed a new start relay due to an unrelated issued that was found during troubleshooting (loose battery connection had messed up the threads on the terminal) and then the owner started the engine. Low voltage light went out and the ammeter showed a positive charge. After shutdown, no burn't ground wires or primer lines were noted.

    This issue has actually started fires in the past. I've also been told about control cables 'welded' immovable from this. So, please check this item out on your aircraft and avoid the extra down time for repairs.

    Web
    Life's tough . . . wear a cup.

  2. #2
    JWE's Avatar
    Join Date
    Jan 2018
    Location
    NC
    Posts
    159
    Post Thanks / Like
    Thanks for the heads up.

  3. #3
    mvivion's Avatar
    Join Date
    Jun 2003
    Location
    Bozeman,MT
    Posts
    11,746
    Post Thanks / Like
    As usual, good solid advice. Might save someone from camping involuntarily in a bug infested swamp.

    MTV

  4. #4
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    11,477
    Post Thanks / Like
    There was a bulletin addressing this very issue 30 or 40 years ago making it mandatory to install a separate ground wire from the engine to the airframe. I don't recall if it was a Cessna bulletin or an AD. I think it was an AD.
    N1PA
    Likes bfd777 liked this post

  5. #5
    Eddie Foy's Avatar
    Join Date
    Dec 2014
    Location
    South Florida
    Posts
    3,764
    Post Thanks / Like
    I ditched the lord mount thingies and installed a ground wire like you did.
    "Put out my hand and touched the face of God!"

  6. #6
    hotrod180's Avatar
    Join Date
    May 2008
    Location
    Port Townsend, WA
    Posts
    3,694
    Post Thanks / Like
    Quote Originally Posted by skywagon8a View Post
    There was a bulletin addressing this very issue 30 or 40 years ago making it mandatory to install a separate ground wire from the engine to the airframe. I don't recall if it was a Cessna bulletin or an AD. I think it was an AD.
    Any way you could provide a copy of that?
    On the early model 180's, besides the ground strap(s) from the engine case to the mount,
    there are a set of those "Lord mount thingies" (bonding straps) at the rubber bushings where the mounts bolts to the firewall.
    Even though I replaced the rubber firewall bushings with a set of solid aluminum seaplane bushings,
    I went ahead & ran a separate ground from engine to firewall, as others have described.
    Last edited by hotrod180; 10-02-2021 at 09:25 AM.
    Cessna Skywagon-- accept no substitute!
    Likes wireweinie liked this post

  7. #7
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    11,477
    Post Thanks / Like
    Quote Originally Posted by hotrod180 View Post
    Any way you could provide a copy of that?
    On the early model 180's, besides the ground strap(s) from the engine case to the mount,
    there are a set of those "Lord mount thingies" (bonding straps) at the rubber bushings where the mounts bolts to the firewall.
    Even though I replaced the rubber firewall bushings with a set of solid aluminum seaplane bushings,
    I went ahead & ran a separate ground from engine to firewall, as others have described.
    I looked at the FAA's AD list and all I could find was AD 79-25-07 which refers to grounding the alternator. I no longer have the 185 and it's records so can't refer there.
    Long ago there was something which referred to those straps which bridged the rubber lord mounts. They are made of aluminum and are prone to breaking. Once broken there is no suitable ground for the starter. They can become twisted when torqueing the engine mount bolts. This twist stresses the strap eventually causing breakage.
    N1PA

  8. #8

    Join Date
    Jan 2017
    Location
    Utah/Alaska
    Posts
    362
    Post Thanks / Like
    do you solder the ends on that flat braid or use a hammer to just flatten them?

  9. #9
    wireweinie's Avatar
    Join Date
    Aug 2013
    Location
    Palmer, AK
    Posts
    4,142
    Post Thanks / Like
    solder

    Web
    Life's tough . . . wear a cup.

Similar Threads

  1. Replies: 46
    Last Post: 08-28-2018, 08:22 AM
  2. Advantage to staying with same AME??
    By Gordon Misch in forum Medical Matters
    Replies: 9
    Last Post: 08-06-2013, 10:36 AM
  3. Almost Grounded
    By Jerry Gaston in forum Cafe Supercub
    Replies: 2
    Last Post: 09-06-2006, 08:46 AM

Bookmarks

Bookmarks

Posting Permissions

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