Maintenance and Install Helpful Tips

The first is a foam rubber fit that pads the plug while it's in the socket. Second is the hexagonal space around the top of the socket. The hexagonal part allows a wrench to be put on the socket if there is insufficient clearance for a ratchet. Bikes generally have enough clearance for ratchets and torque wrenches, but the ability to support a wrench on the socket is useful for bikes with Fat Bob tanks and a few automotive applications (like a Corvette with headers).

For many years there have been two regular sizes of plug sockets. 80" Big Twin Evolution and Shovelhead engines need a 3/4" spark plug socket, while Twin Cams and Evo Sportsters need a 5/8" one. And then something occurred: spark plugs that needed an 11/16" socket came out on the shelves, and 11/16” plug sockets are often hard to find. We have heard people fit a strip of foam wrapping (usually used in water pies) inside of an 11/16” deep socket to use by their own. This procedure is effective and is a cost-effective approach to improvise a tool for someone that does not change a lot of 11/16” plugs.

Plug Spacing

Plug spacing is important in getting correct firing. Many people assume spark plugs are pre-gapped at the manufacturing plant, which is not usually true. But even if plugs are pre-gapped, movement when shipped may make the gap several thousandths of an inch smaller. Gapping a plug just isn't nuclear physics. What in only needs is the proper tools, a bit of repeated attempts, and a bit of determination.

To begin with, pliers and a feeler gauge are not the right tools. Our favored spacing tool is our friendly wire-loop tool where each wire loop stands for a different gap size, and the steel tabs support varied ground electrodes. Our very least preferred is the disc with the ramp throughout the perimeter. The first disadvantage in the disc type is that it exerts stress in the core electrode during gapping. The other disadvantage is usually that one part of the ground electrode might end up slightly even farther out from the middle electrode. On SplitFire and Screamin' Eagle plugs, 1 prong of the ground electrode could be higher than the other.

Observing 3 simple rules will allow you to accurately space plugs. First, don't flex the center electrode. Next, never bend the ground electrode laterally. Utilize the spacing tool to gradually walk the end of the ground electrode nearer or farther away from the tip of the core electrode. Additionally, check the correct spacing by moving the right wire loop through the gap. The spacing is right when you feel a little amount of friction as the wire moves in the gap.

Changing Spark Plugs

Right before removing a spark plug, make sure that the engine has cooled off, then start using a burst of compressed air to clear out dust and dirt away from the space around the plug. A ratchet and a spark plug socket are the recommended tools for this part of the task. Upon cautiously taking off the spark plug wire by pulling on the boot, not the wire, we will take out the old plug with a ratchet and plug socket by rotating them counterclockwise.

When the old plugs are out, you're ready to set up the nicely spaced spark plugs. Start out by applying a small amount of anti-seize lubricant around the threads of each spark plug. Modern Harley Davidsons have aluminum heads and spark plugs have a steel shell. Repeated cooling and heating from the cylinder heads may trigger a chemical reaction involving the steel spark plug shell and the aluminum cylinder head. The result is a spark plug that acts like it's welded in place.

Upon applying the lubricant (anti-seize) on the plug threads, begin turning the plug with my fingers instead of a ratchet and plug socket. A best practice that minimizes the chance of resulting in a cross threaded plug as well as the expensive damages that can be caused.
After the new plug is tight enough using your fingers, reach for the plug socket and torque wrench. The torque spec for plugs in a TC 88 is 11-18 ft-pounds, so split the main difference and opt for 15 ft-pounds.

That way, if the torque wrench is a little off with no reason in mind, you will nevertheless be within the recommended specifications. Is proper torque important for plug fitting? Generally, indeed yes! If the plug is a bit wobbly, high heat transfer within the cylinder head could be minimized, while the spark plug can overheat. If a plug is left loose, there is always a chance that it could work its way out from the head caused by rapid movements and pressure from combustion. And that is certainly very harmful. Untightened spark plugs have also been blamed for combustion chamber build ups being added to the threads of the spark plug hole.

On the other hand, making plugs excessively tight can cause other problems. If a plug is over tightened, the chances are it will probably be harder to remove. Over tightening could also grind the gasket on the gasket seat plug. Extreme over tightening can break the threads in the head and has always been the cause of deterioration.

If you don't have a torque wrench, have the new spark plug finger tight and use a ratchet to carefully tighten the plug another quarter to half a turn. This method is plainly less precise compared to utilizing a torque wrench, however it will get you at some point in the 11-18 ft-lbs. range.

As always, ensure that you travel protected and put on the needed safety equipment like carbon fiber helmets. All the best and have a wonderful ride.