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Installing spark plugs may not be as simple as you thought

Tuesday, November 1, 2016 - 07:00
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Motor Age: What are common mistakes you see being made by technicians when removing or installing plugs?

Tim Stumpff, Product Manager – Spark Plugs, Robert Bosch LLC: Lack of proper cleaning and improper torque are the most common mistakes. Spark plugs that are worn out and require change have typically been in the cylinder head a long time. This means they can be tough to turn out. Many techs will simply thread the new plug in without cleaning the threads (in the head), which can lead to a plug not sealing properly. Threads should always be cleaned to ensure the plug can be torqued properly. A torque wrench should always be used when installing spark plugs, as over-torque can damage the plug and cause misfires and under-torque can cause the plug to loosen as the engine runs.

Michael Kollenberg, Product Manager – North American Ignition, Federal-Mogul Motorparts (Includes the Champion brand of spark plugs): Additionally, we see techs choosing and installing plugs based on a competitive interchange chart rather than relying on an application-specific catalog recommendation and not verifying spark plug gap prior to installation.

(Image courtesy of Robert Bosch LLC) Heavy ash deposits like this can be caused by the generous over use of fuel additives.
(Image courtesy of Robert Bosch LLC) The presence of an overly rich condition can cause dry deposits like this. If it looks wet and black, lean more toward some form of oil fouling caused by something as simple as an overfilled crankcase.

Jason Norwood, Technical Services Supervisor, NGK Spark Plugs (USA) Inc.: I’d just stress what Michael said earlier about proper torque. Ninety percent of our damage claims (plugs returned as “defective”) are the result of over torque.

Motor Age: The debate over using some form of “never seize” on the threads of the plug continues. What are your recommendations on the use of an anti-seize compound?

Kollenberg:  We discourage the use of anti-seize or other lubricants on the threads. First, because of naturally occurring properties of the base metals used in our shells, Champion plugs already have a certain level of lubricity built into them. In addition, the shells receive a zinc plating to provide an additional lubricating layer.

Second, even when applied with caution, anti-seize or thread lubricant often  contaminates the plug’s firing end. Torquing a plug to the vehicle manufacturer’s spec ensures that it fully seats, properly seals and assists in transferring heat to the cylinder head.

When anti-seize or similar compounds are used, you commonly end up with an over-torque condition, even when a torque wrench has been used. This is due to the difference between “wet” and “dry” torque values. Over-torquing can cause separation of the internal seat area (where the ceramic core contacts the inside of the shell). This will impair the plug’s ability to transfer heat and can lead to damaging pre-ignition or detonation condition.

Excessive gap can cause misfires and stress the ignition coil to the point of failure.
Look close. See where this plug boot has a hole burnt through? The energy is looking for an easier way home.

And Kollenberg’s fellow commentators agree. While there are a few spark plugs out there that may still recommend the use of an anti-seize compound, your best bet is to clean the area around the plug prior to removal and then clean the cylinder head threads prior to installation of the new plug. You will find some info on how to tighten a plug without a torque wrench, but as professional technicians, we know that even those procedures are less than accurate. To make sure you do the job right, use a torque wrench to install and leave the air ratchet on your tool cart. On to the next question.

Plug selection

Motor Age: Is there any truth to the idea that a technician should install the same brand of plug as the car originally came equipped with?

Norwood: In the OEM world, when we are making Dual Fine Element (DFE), Projected Square Platinum Electrode (PSPE) and other designs, it is usually for direct injection or lean burn systems, and normal spark plugs will not operate as efficiently or ignite the mixture as well.

Stumpff: The common perception is that the OE brand must be replaced with the same brand. However, this may not always be the best choice. In some instances, an OE brand may have an aftermarket version to fit the vehicle; and while it may be a less expensive choice it may not be quite the same fit/form/function of that same brand’s OE plug. In other cases, some aftermarket brands may not perform application testing. With today’s complex engines, just because a plug fits or looks like the OE, it does not mean it can withstand the stresses of high compression or turbocharging. Bosch spark plugs are tested for the application and designed to meet or exceed the OE design so a technician can install them with confidence in every application.

Kollenberg: No, but it is important to install the same fundamental spark plug technology – iridium for iridium, double platinum for double platinum, etc. – if you want to achieve the same anticipated service life as the original plug. We offer Champion plugs that are ideally suited for virtually any make or model. As long as the plug you are installing is cataloged for that specific engine application, there is no reason to be concerned about its performance versus the original brand.

Use a flexible fuel hose to get the plug started in the head to avoid accidentally cross threading the plug.

And it should be added that these guys are the same guys that make the OE original equipment. I admit, I was one of those techs that preferred OE for engine management components and I always installed the same brand plug as the car came with. But having had the opportunity to see behind the scenes at many of these big suppliers, I think the key to choosing a plug is to make sure you use a name you know and trust and choose the plug based on application and not based on an interchange chart.

In the shop

Well I learned a lot! I’ll never look at a spark plug change the same way again and I hope you won’t either. Let’s recap some points mentioned (and not yet mentioned) to keep in mind the next time you need to swap plugs on a customer’s car.

  1.  Use a spark plug wire puller to carefully remove the secondary lead from the spark plug. Inspect the boot for any visual sign of damage or arc through and service as needed.
  2. Use compressed air to clean the area around the base of the plug of any accumulated debris. Don’t want anything to drop down into the cylinder, do we?
  3. Inspect the removed plug for signs of damage and to make sure it all came out! While not as common as it once was, it’s still not a bad idea to “read” the plug for clues to any drivability issues you may be troubleshooting.
  4. Tab a small amount of grease (and I mean small!) into the fluted area of a thread chaser and carefully clean the threads in the head. Be sure to position the piston well below TDC to avoid accidental contact and watch out for any open valves! The grease will help catch small metal particles and debris and help you keep the foreign objects out of the engine.
  5. Clean the same thread chaser and run it through one more time to make sure there is no residual grease that may affect the final torque on the plug.
  6. Remove the new plug from its packaging and verify the plug gap is set to the vehicle manufacturer’s specification. Use caution on plugs with precious metal tips to avoid damage. Avoid using the wheel gauge often given out by your friendly local tool guy, and instead us a round-wire gauge.
  7. Carefully start the plug in the head by hand. I use a small section of fuel line to hold the plug as I spin it in. This avoids accidentally cross threading the plug – a problem you don’t want to have if you can avoid it.
  8. With the plug lightly seated, use a torque wrench to finish the install.
  9. Take a small dab of dielectric grease and apply it to the secondary lead boot. This grease will help act as an insulator, seal the plug contact from outside contaminants (water, oil) and make it easier to remove the boot the next time around.

I’ve watched techs rip out the old plugs with ½” impact guns and reinstall them with cordless ratchets, all in an effort to beat the flat rate. I get it – time is money in the shop – but the damage you may be causing in the process will sooner or later come back to bite you. Does it take that much longer to do it right?

I didn’t think so.

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