Engine Ground Cable


In 2016, we had two different Zenith builders fly in to the same event. They had never met each other. I studied both of their engine installations, which has cumulatively about 500 hours of flight time. They were different, but both airworthy. They had an odd thing in common;  They both ad an engine ground cable that was 3 feet too long, and it terminated at the same points, the center of the firewall and the starter mounting brackets on each plane. Most people would not have noticed this commonality, but it told me something important: Both of these guys who had never met each other were listening to the same idiot on the internet, rather than following examples we show or even common sense. Somewhere out there in cyberville was a moron gleefully dispensing poor advice on ground cables. While this particular error just added weight and looked dumb, I am sure the same expert had doled out plenty of other electrical advice that was far more dangerous.



Above, the ground strap location for a Corvair engine. This is the aft end of the co-pilots side head. The head has a  3/8″-16 tapped hole, perfect for grounding, the cable is 9 inches long, it is #2 wire. You can even use wire without insulation, ( it is a ground) or go to your auto parts store and buy a premade cable, and it can even be one of the ones that look like bare woven metal, a ‘bonding jumper’.  Yes, the powder coating has to be scraped off where the 5/16″ bolt goes through, and it does have to have a metal lock nut.  Every motor mount I have ever made has a tab or a corner brace at this intersection for a ground cable.  If anyone suggests that a 4130 motor mount or an aluminum fuselage don’t conduct electricity, they are not just wrong, they are probably mentally ill, just nod politely, smile and back away slowly.


Your Vote Counts:  In the comments section, please vote for one of three following examples from my experience:


 A) “Led Zenith”  10 years ago I went to inspect a Zenith. The builder had placed a group 24 lead acid truck battery in the tail cone, (because he had made an error doing his weight and balance on a set of $10 bathroom scales.)  but he also insisted that he needed to run a 00 copper battery ground cable all the way from the battery, 12 feet to the motor, and insisted that it also had to have insulation on it. A very nice gentleman, had been a pilot for 35 years, built a number of planes, and had a long and lucrative career as a mechanical engineer.


B) “Ungrounded Claims” A second owner of a Corvair powered plane called both Dan and Myself, because his “Starter was burned out”. He was on a cross country, far from home, the starter had previously worked without a hint of a problem for years. Dan tells him to directly put the jumper cables on the starter, to isolate the starter to test it. Guy claims he did this, no dice. His solution was to rent a motel and a car, drive 200 miles to a city where he paid a guy several hundred bucks to hand rebuild the starter on a Sunday, in spite of the fact the guy said there was nothing wrong with it. About $1,000 later, the starter is back on the plane, and it still doesn’t work. Local EAA chapter experts say the issue is because it is a Corvair. After another day, he discovers that the ground cable to the motor has become disconnected, something he would have known had he actually put the jumper cables on the motor as instructed.


C) “The sticky throttle cable and $7,000 worth of starters” Back in the 1990s, when I had a lapse of moral judgement and built Lancair IVPs for rich guys, we has a guy with a flying plane call the shop asking if we could install a new starter on his TSIO-550B Continental, which, on, by the way also needed a new throttle cable every 25 hours. He had spend thousands of dollars with other shops, but he was now willing to pay our “Overpriced labor for A&Ps” ($50/hr in 1996). He initially didn’t want to use A&Ps because technically experimental didn’t require it. We solved his problem in 10 minutes: he never had an engine ground strap, and the throttle cable by default was functioning as a high resistance one. He has instead purchased one rebuilt starter for $2,500 and had later purchased a factory new starter from TCM, and it was about $4,500. The logs showed the throttle cable had been replaced 4 times. Good thing he didn’t get ripped off by trained mechanics.




32 Replies to “Engine Ground Cable”

  1. Number 3 . I love it when folks with money to burn do just that – and are perpetually pissed off at the world and everyone “who is intent on ripping them off”; when , if they took some responsibility for understanding the situation, they could remedy it themselves for a song.
    I see it in medicine all the time. They want pills to make them better, and they complain bitterly about the cost, but they won’t do a thing to exercise or improve what they put into their bodies.

  2. Your request is tantamount to asking, “which poison do you prefer?” Although at first the examples seem to go from bad to worst, the last two are just dumb money wasting ’cause- you- can’ errors. But the first one is a plane I would be scared to fly in. Weight and Balance trump proper grounding every time, no pun intended. This is only knowledge from reading and listening for me, as far as real airplanes go, but model airplane experience, especially with thermal seeking glider designs that beg for a slight favor toward tail heavy, really teach what weight and balance means. Sooner or later through operator error or experiment through greed for free altitude (ok since no live creature is involved), one experiences the nose up wallowing of a tail heavy aircraft that defies flight. Something I never want to experience from the inside.

    1. Brings to mind my wise young son’s advice he gives to W&B offenders often in our RC flying, “A nose heavy plane flies poorly. A tail heavy plane flies once.”

  3. I really don’t need to vote for any of your examples. I’ve done enough stupid crap on my own.

  4. Hard to decide. Hmmm asking the experts and then failing to follow their advice??? I pick B.

  5. The early dodge front wheel drive cars had a similar problem, the CV joints kept burning all their grease dry because there was no electrical bonding, a lot of static was building up in the joint and would use the CV balls to discharge, an easy fix add a jumper wire to the frame and no more problem,. Dan-o

  6. I looked for a reference to the ground-strap issue in both the Old and the New manuals.
    The Old manual is labeled “Corvair Flight Engines”, the new labeled “Corvair Conversion Manual”.
    I am not sure if these are supposed to be equivalent. The Old manual is copyright 2006, the new manual is dated 2014 in the title sub-head.

    In any event, the only reference to the proper grounding of the engine to the motor mount that I was able to find was in the 2014 version on page 132 in a Commentary within the section 3500 Airframe charging group.
    Is that information to be found elsewhere in the manuals you have produced? If so, where?

    Inasmuch as technical people tend to think visually, are there drawing and diagrams of these systems? I notice in the old manual there are drawings done by a David York, anything more from him or similar talents?


  7. All three have so much to offer in education and entertainment, but B takes a special dose of ego to not want to admit you did not think of such a simple test, and instead lie which cost you a bunch more money.

  8. All three show the same lack of inquisitiveness relying upon either faulty or imagined information. “A” is very interesting as the person could have used their experience and assumed knowledge to effect a better solution or pay attention to what has been proven to work.
    Having said that I’m glad for the post and picture about a very simple solution.

  9. Being a motorcycle/small engine mechanic I feel the pain. People rarely understand mechanacle things anymore. People hear about a third of any explanation you try to give. Engine break-in proceedure is a big one. Thank God my customers stay on the ground! My flying is truly an escape. Oh, A is a smoking hole waiting to happen.

  10. I have a corvair powered VW beetle that I bought. One day a friend noticed the clutch cable glowing like a toaster element. I quickly added a heavy ground strap. Funny thing is is always cranked over well !

  11. As a Mr. Goodwrench for many years…I saw an engine swap in a ’65 stepside that someone did that ended the life of several sets of U-joints in a two year period as well as some “mysterious bad weather starting issues”. Imagine the customer’s disbelief when I pulled a copper ground strap up from the firewall and said: here you go. He could no fathom how such a small thing could cause these issues. Surely the ground will carry through the metal. You mean the rubber engine and transmission mounts? What’s next in line? Yep the driveshaft and the best contact is no a greasy roller bearing surface…or a horribly pitted dry one either.

  12. I think all three are worthy of a Darwin Award, just remains to be seen who meets the one remaining criteria first.

  13. Well, I vote for the throttle cable ground! While I can somewhat see the ground cable thing (non technical types think chassis ground is too high a resistance, while the opposite is true), it is really hard to believe the throttle cable fiasco.

  14. I’ll take “Ground Straps” for $7,000 Alex.
    In this 1996 tale of failing throttle cables an experimental aircraft owner learns a valuable lesson.
    What is “Aircraft wiring 101”

  15. When I was a young student in automotive shop class one of the test questions asked was, “whcih cable should be removed first from a 12 volt negative ground battery,and why?” I was the only one in a class of about 30 students to correctly answer.

    For the record … my Cleanex has a PC-680 in the tail and uses the air frame for ground. Works well so far. Currently at 137 hours.

  16. I’m voting for “c” to be the worst offender with “a” as a close 2nd. As I built a Varieze and now a Vision, my research for electrical wiring of composite airplanes showed that it is clear that for a starter to work the engine must be grounded. My Varieze’s engine was not grounded with more than a 20 gauge wire until I put a starter on it. My Vision’s engine, with the Corvair, is grounded direct to the battery on the firewall as there is no need for electricity to run through the motor mount. Hard to believe a Lancair IV was wired without understanding the need for grounding the engine.

    1. Alan, if you met the owner of the Lancair, you would understand his plane was the product of a series of unskilled shops, and the owner never sought one person, and refused to be, the one person in charge of the project. But it was painted nicely, so most people thought it was a “safe” plane.

  17. A little education in electrical systems and some common sense would have save a lot of time money in all three. These can be considered tuition in the college of life.

  18. I pick number 3.
    Saw this before with an old Chevy pick up with manual choke cable glowing red during start up.
    Bonding straps corroded off the truck.
    Thanks for the great work you do.

  19. The best part of this whole post is the picture. I have done a screenshot to save it, so I don’t have to ask. I will just know. Thanks for sharing more of your knowledge to ignorant builders like me.

  20. I have seen a lot of GM cars with floor shifters (factory) that keep needing to have new cables installed. Same problem. The owners would not hook up the small ground cable from the engine to the body. Shifter cable becomes the defacto ground cable.

  21. believe it or not, true story, it was a chilly spring evening in 1982 when a regular, satisfied customer rolled up the drive with smoke pouring out of the engine compartment of her ’71 Pontiac Bonniville Brougham. the rag joint in her steering coloumb was smoldering and actually burst into flames when I lifted the hood…

    1. After driving her home in the wrecker and getting her calmed down, I checked the service jacket and discovered that a new starter had been installed a couple months earlier, and a battery the previous July.

      1. …Yes, the fire was electrical, not caused by a cracked exhaust spewing hot fumes onto the steering column… but it was not immediately obvious

      2. at some point the battery cabol had been replaced and not securely mounted along its lemgthand was laying across the column, which had eventually rubbed thru the insulation, contacting the unfused conductor. the dead short to ground, thru the steering gear had enough resistance to cook the tough rubber rag joint, and cause the fire,,!

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