Fix a Rough Engine with a Ground Strap?

[Jugster]

I've been dealing with a very rough engine for quite a while, now—much too rough to drive the car. We've tested everything, tried borrowed known-good coils, borrowed a known-good carburetor, replaced the ignition harness, spark-plugs, spark-plug cables, changed timer three times, rebuilt the coil-box, tested the compression (and thereby the valves), checked the timing, blew out the fuel line, bypassed the fuel system with a small portable fuel-tank, etc. Now, it occurs to me that I have gotten some little electric shocks from the top of my front door to my elbow and am starting to think it's possible I need to run an extra ground strap to the frame. I figure the easiest way to do that would be from one of the screws on the transmission's access panel to the frame. Is there a better way?

[speedytinc]

I would not put it on the inspection cover. You need to move it to pull the cover. Most guys go from a starter mount bolt to frame.
I see yo have a 15. No starter?
I am thinking upper drive shaft/transmission/4th main on the right side to frame or pan/HH corner behind the right pan to frame ear.
Do let us know if this solves your rough running & shock situation.

[Norman Kling]

If the shock is large enough for you to feel it when you touch the body, it is coming from the high tension lines to the spark plugs. You must have a carbon path somewhere in the coil box or nearby in the firewall which is conducting to the body. It might even be the route of the wire between the coil box and the spark plug. Try grounding at the spark plug with a screw driver to the head. If this changes the way the engine runs, it is not that wire causing the miss fire. If it does not change the way the engine runs, than trace that wire back to the coil. Grounding it to the frame might fix your personal jolt, but it will still conduct the spark to ground and the engine will miss fire. You must find and correct the cause of the high voltage. In cars with the wood firewall, many times when it rains the wood will get wet. If the wet wood conducts spark, it will burn a carbon track. Wood n coil box can also get wet and do the same thing.
Norm

[Craig Leach]

Hi Bob,
I run a #1 battery cable from a pan bolt to the same side of the frame the battery is grounded on but my cars have starters. Does yours? I have encountered such a grounding issue that sparks flew out of the front motor mount when cranking the engine with the starter. I'm thinking you
are getting shocked by the mag not a coil. The last time a coil shocked me I had to change my pants!
Have you tried running the car in as dark as you can get to look for sparks in the electrical system? Some times a spray bottle with water to
make things damp will help in locating spark jump.
Craig.

[BHarper]

Hello Bob,

As suggested by other posters here, a second ground strap is an easy step to take and they are never a bad idea although not always needed.

That said, I do wonder if the rough running seems to be concentrated in one cylinder or is common to all four?

The poor running and the shocks which you have felt strongly suggest that you have a significant leakage of ignition current to the body. I have reread your post several times and while it indicates that you have gone through the ignition system thoroughly, you may not have found the problem yet,

OR

your efforts and the replaced parts have, somehow , replicated the original problem.

It may be time to don your deer stalker cap and grab your magnifying glass to become Sherlock Holmes as you scrutinize every inch of the ignition system from the magneto post up and out to find where current is jumping to the body.

Good luck with your project.
Bill

[Ron Patterson]

Norman Kling is right on the mark.
If your Model T is running rough AND you can touch the car and get a mild shock you have carbon tracks either inside of the wood in the coilbox or between a coil high tension contact to ground near the metal of the coilbox.
I will never forget the first time I trouble shot a car with the problem you are having. I did all the logical trouble shooting and could not find the trouble. Late one evening I was working on the car and my wife accidentally turned off the shop lights, I was standing next to the car with hood up and saw a spark light show at the back of the coilbox.
Removed the coilbox and found carbon tracks (carbonized wood is electrically conductive) in the plywood coilbox wood. Replaced the wood with one of those non wood kits and the car ran like a top and no more shocks touching the cars metal while it was running.
Carbonized coilbox wood is is initially caused by the wood getting wet. Your initial reaction is to start the car, but all you are doing is causing the coil sparks to track over the wet wood and carbonize the wood which now is forever electrically conductive.
Trouble shooting a Model T with a coilbox that got wet is an experience you will NEVER EVER forget.
Ron Patterson

[Bob McDaniel]

Look at the bolt from the oil pan to the block just below the timer. Mine would short out a post on the timer every time I advanced the timing. I turned it around and put the nut on the other way and problem with rough running was fixed. It could send a spark up the linkage to the spark leaver and cause you get get a jolt from time to time. Worth a look.

[TXGOAT2]

Adding a good engine to frame ground may improve engine smoothness and may also improve electric starter performance.

Dirt, paint, rust, powder coating, loose bolts, and grease can cause poor electrical connection between the engine assembly and the frame. Connecting a substantial ground cable from the block to where the battery ground strap is bolted to the frame will assure that there is a good ground path at all times and will provide a reliable, low resistance path for the heavy starter current as well as for ignition and lighting current. Attaching an auxiliary cable to one of the starter bolts and then to the battery ground point ought to assure full power to the starter and a good ground for the timer.

[Norman Kling]

The timer grounds the low voltage side of the coils so would not cause a jolt when you touch the body. Also grounding the engine to the chassis would not take the jolt away. Your problem is the high voltage side of the coils, that is the side which connects to the spark plugs is grounded to the chassis on one of the cylinders. You get the jolt when you touch the car because the tires ground the chassis from the earth and you are standing on the earth so the spark goes through you! Actually, the term ground applied to the chassis, is not the same as ground, referring to the earth.
Norm