Spark jumps to radiator hose - Alfa Romeo Bulletin Board & Forums

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Old 03-06-2012, 08:03 PM
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Spark jumps to radiator hose

The radiator hose on a 1959 Two Liter runs about 3/8" away from the #1 cylinder's spark plug. Why would the spark jump the gap from the bakelite spark plug end cap to the rubber radiator hose, rather than conducting the electricity through the spark plug? If I hold the radiator hose back further from the spark plug the engine runs normally without the visable spark jumping to the radiator hose and subsequent engine miss.

There is no metal inside the black radiator hose.
The plugs are brand new Bosch 4 prong Pt.
The plug wires, phenolic ends and wire conductors are all probably original with only 54,000 miles on them and I like to keep using them if possible.
I usually put Felpro anti-sieze compound on the spark plug threads although I did not this time. Who ever heard of a radiator hose becoming a ground?
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Old 03-06-2012, 08:13 PM
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I have! Water inside the hose is a great ground. The rubber hose may be a poor dielectric. Your hose runs close to the spark plug caps? I had to switch more than one vintage Ferrari V12 from bakelite to silicone rubber boots as when the bakelite aged, it became a poor insulator, no visible carbon tracks, but they sparked through randomly everywhere. New bakelite plug connectors solved the problem, but the silicone boots last much longer.
This is just from my experience.
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Old 03-07-2012, 08:10 AM
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Quote:
Originally Posted by Gordon Raymond View Post
Your hose runs close to the spark plug caps?
Thanks for your reply Gordon! Yes on all of the old Cast Iron, Two Liter (and probably the 1900) engines the upper radiator hose is attached to a 90 degree flange that comes up in the center of the aluminum head. The hose runs more or less parallel to two spark plugs and wires before routing under the timing chain tunnel in the head to the radiator. It is quite an impressive bit of aluminum casting work too.

I guess that I had too much faith in rubber as an insulator and suspected something was wrong with either the new spark plug, old wires or the head.
Perhaps a new set of plug wires is in order.
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Old 03-07-2012, 09:17 AM
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Now I know the engine! I suspect it could be the wire, particularly if it is carbon core. Generally, the rule is that the spark will jump the path of least resistance, so if it arcs where it should not, there is higher resistance elsewhere. Many plugs have resistors to both get a hotter spark and somewhat silence ignition RF interference. Combined with an air gap, these plugs have considerable resistance to ground. They and insulators along the way will make failure obvious with sparks where you don't want them.
Years ago I ran a Chrysler 426 Hemi engine that use rich mixtures to overcome problems wit the four step metering rods on the Carter AFB carburetors. It needed a very hot coil to avoid low speed plug fouling. So hot that even with the best (of the time) Excel ignition wire, you could get cross fire and sparks where they should not be! One humid night at the track, I opened the hood to find the ignition wires all lit up like florescent lights. St. Elmo's fire? Who knows. It was neat to watch!
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Old 03-07-2012, 11:22 AM
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I had a similar 'Frankenstein" light show on my '71 MGB about 35 years ago! The old plug wires have tin or zinc plated stranded wires inside the rubber covered with a woven insulation. The phenolic end caps can be removed and reused (pretty 'green' huh) and contain a tiny threaded brass rod with a small hole in it and a knurled nut that can be screwed down onto the wire to hold it captive in the hole. I suspect that the resistance is built up where the wire is held captive. I will try cleaning up the wire end and putting a dab of dielectric grease on the connection (or a dab of solder on the wires). Also, I found a 2" long sort of rubber insulator that is a 1/2" diameter cylinder with a half round groove cast into it that I'll use as a spacer. It perfectly matches the profile of a spark plug and may help insulate the radiator hose.
I wonder if it would help to go back to the old style Lodge spark plugs? I did not notice this problem with them...

Thanks for your imput on this and all of your prior help with my "Ethanolized" Weber's!
Mark
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Old 03-07-2012, 12:09 PM
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Many 50's era cars had copper core spark wires, and used resistors in the plugs to suppress RF noise, or in the bakelite spark plug connectors. You may just have too many resistors. Alfa's OEM spark wires - the green stuff - were copper cores.

Robert
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Old 03-07-2012, 01:00 PM
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Thanks Robert, this car has never had a radio so RF is not an issue. It does have the nifty radio blank off plate that states "Alfa Romeo World Champions 1950-1951". If there is a resistor in the spark plug connector I don't believe that it was intentional. Perhaps the newer Bosch plugs that my buddy talked me into getting have some serious resistance. I don't believe that the Two Liters came with the green color wires when new.

Mark
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Old 03-08-2012, 06:59 AM
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I had a bad ignition problem that I finally diagnosed which is similar. On an early Giulia, the upper engine (thermostat) radiator hose has a bracket spot welded on to support and guide the plug wires. The rubber insulation on the oval steel support wore thin to metal from fretting on the bottom (only 47 years old!!) and the wires were shorting there and the spark was jumping about 1/2" from the radiator hose bracket edge to the valve cover. There is a history of electrical etching marks there where sparks were jumping around like a high school science project. These were some old wires with Bakelite plug connectors. (The Bakelite connectors say 1k ohm and the wires test out at that form end-to-end.) Changed the wires for new and no more problem, but only after replacing every ignition component (coil, cap, rotor, condenser, clean dizzy, etc.) for a long trip where a one-by-one replacement would not be possible. Now replacing pieces back one-by-one.
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Old 03-08-2012, 06:35 PM
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Question grounding strap from engine to chassis?

Dear friend. Be sure the woven grounding strap from the bottom of the engine (attached to rear bolt on pan corner) to chassis is in place. Sometimes that is left out and the spark goes erratic. Of course you have it in place, but I am always ready to make comments on something screwy like that. Usually I can't even get the car to start without the strap.
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