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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Martin on November 18, 2016, 02:42:22 PM

Title: Spark plug wire earth harness.
Post by: Martin on November 18, 2016, 02:42:22 PM
If you need to do a compression test, or crank over the engine with the spark plug leads disconnected it is important that you earth the leads. Failure to do so could result in the failure of the ignition module. I made up a harness, made of heavy gauge wire. Crimped and soldered  a tubular wire connector to one end of the wire with 4mm bolt with the head cut off inserted and soldered into the other end of the connector. Cover the connector with a piece of heat shrink with enough of the bolt thread exposed to take a spark plug nut. If your bike is fitted with spark plug wires that require spark plug nuts, acquire four old nuts from discarded spark plugs. Do this four times then insert the other end of the four wires into a wire clamp and solder. You now should have a harness that does 2, 3 and 4 cylinder engines with or without spark plug nuts. If you make 2 harnesses you can do 5, 6 and eight cylinder engines.
Regards Martin.
Title: Re: Spark plug wire earth harness.
Post by: kris on November 19, 2016, 04:21:15 PM
Interesting....thanks Martin. So, without discharge the power simply backs up into the coil? Is that it?
Title: Re: Spark plug wire earth harness.
Post by: Martin on November 19, 2016, 04:48:52 PM
It overloads the ignition control unit (ECU) and burns out components. What components it burns out and whether or not you can get into them and repair them I do not know. Possibly RBM or Inge can shed some light. If I ever blow one I might get a mate to have a go.
Regards Martin.
Title: Re: Spark plug wire earth harness.
Post by: kris on November 19, 2016, 05:54:53 PM
I'll go with the ounce of prevention...I'd be over my head otherwise.
Title: Re: Spark plug wire earth harness.
Post by: Bill on November 19, 2016, 06:11:25 PM
An ignition coil is really just a special transformer .... current is induced in the secondary winding when the magnetic field collapses and it has to go somewhere ! If it can't go where intended well ..... you can guess it will go where the damage is most expensive !
Title: Re: Spark plug wire earth harness.
Post by: Filmcamera on December 16, 2016, 10:06:04 AM
When doing a compression test can't you just disconnect the entire injectors/coil loom portion so no power goes to the coils in the first place?
Title: Re: Spark plug wire earth harness.
Post by: Martin on December 16, 2016, 08:00:19 PM

Maybe pulling the fuse I will look into it. But when I  made the harness it was for cleaning and checking the injectors and I had the spark plugs out, and I didn't want an errant spark .
Regards Martin.