Spark Plugs and the VTX 1800

Posted by Bare | Last Updated January 20, 2011

Plugs tend to be a topic of controversy on the VTX – from the famed “broken electrode” Bosch plugs to the “overpriced” Uber plugs to the “required” iridium plugs from NGK. I find that each plug has its place depending on the rider’s choice, riding habits/style and the bike itself. I personally run the Bosch +4 4419 plugs with no ill effects and the cost is just right for me – but everyone’s experience tends to be a bit different, they say variety is the spice of life…

Here are the facts about plugs and the VTX 1800…
The shallow plugs on the VTX (front right and back left) tend to look nicer than their counterparts, the deep plugs (front left and back right). This is typically a side-effect of the break-in on the motor and tends to “work it’s way out” after the first 6,000-8,000 miles. If you take apart a cylinder head and look there is no discernable difference between the 2 plugs positioning in the head, they are very symmetrical. Each plug is set next to an intake valve on the outer edge of the combustion chamber and they both have the same distance from the exhaust valve. Based on that information there should be no difference in fouling between the shallow and deep plugs in a new engine, but let’s take this one step further… There are two oil jets in the crankcase set at the base of the cylinders that spray oil onto the connecting rod’s wrist pin area, these oil jets not only lubricate the wrist pin to piston connections, but also lubricate the cylinder walls and help keep the piston itself cool. In a new engine the rings are not seated in yet and the over spray from the oil jets that go into the cylinder walls can get past these unseated rings and up into the combustion chamber. There it is burned off, but it can first contribute to plug fouling. The oil jets on the VTX face the “deep plug side” of the cylinders and therefore may be a contributing factor in the deep plugs looking worse that the shallow ones on newer engines.

The 2002 VTX’s came with a plug that is one step colder than the 2003’s and up. These bikes are not known for producing pretty looking plugs to begin with, so these colder plugs were renowned for fouling early and often. One of the culprits that compounded this fouling problem is the lack of a good ground on these bikes. Most of this problem can be remedied by reworking the grounds as detailed in this article, but even that is no sure fix for all riders in all conditions and environments. I generally tell people that if you’re running the colder plugs (which were stock for 02’s) and have good results (i.e. nice, pretty, tan plugs) then stick with it. I believe that “if it ain’t broke, don’t fix it”.

Now for those with 02’s who are still fouling – even after reworking the grounds, checking your coil connections and making sure the plugs are properly installed – then go ahead and swap to the hotter plugs which are stock in the 03+ VTX’s. Generally speaking this solves most people’s problems with fouling, or at least makes them as good as can be expected from these bikes. On rare occasions if someone with an 02 has really good looking shallow plugs but badly fouled deep plugs I have recommended sticking with the stock 02 (colder) plugs in the shallow holes (if it ain’t broke…) but running the 03 (hotter) plugs in the deep holes. On these rare occasions it seems to work better than all cold or all hot plugs across the board – just a little “food for thought”.

Proper installation of plugs
The most common mistake I see when guys install plugs on their bikes is that they flip open the manual and see 13 ft/lbs as the recommended torque and go straight to work changing plugs without realizing they’re making a mistake. The manual spec for a plug is 13 ft/lbs but this pertains to old plugs which have already been installed and seated properly. When installing new plugs you have to seat them finger tight first and then use a ratchet to tighten them 1/2 a turn further. Doing this seats the crush washers properly and will eliminate the possibility of oil blow-by coming up the threads while the motor is running. Oil blow-by will prevent the plugs from getting a good ground and further assist the plugs in fouling. When you install a new plug properly you will actually feel the crush washer seat at roughly 1/2 a turn past finger tight and it gets much tougher to tighten after that – that’s when you stop. Once your plugs are properly installed you can pull and check them anytime you want and then reinstall them using the manual spec of 13 ft/lbs. Always use a little bit of anti-seize on the plug threads before installing them, and NEVER install plugs into a hot (or even warm) motor.

Something to watch for when installing plugs – do NOT cross-thread them. With steel plugs and aluminum heads it is sadly too common an occurrence to see. If you’re a new “wrench” and afraid you might make this mistake then go to the auto store and get yourself about a foot of 3/8″ fuel line. It will cost a couple bucks but you can slide it over the insulator on the plug and use it to thread the plugs into the heads. What makes this fool-proof is that if you do actually start to cross-thread the plug the fuel line will slip on the plug before it will ever actually cross-thread into the head. It also helps with getting those deep plugs started if you don’t have a plug socket.

Spark plug cross reference
for the VTX 1800
Manufacturer OEM (03+ stock) Cold (02 stock)
AC Delco* 41-806 41-801
Autolite APP3924 APP3923
Bosch Platinum +4* 4419 4418
Champion Copper* RC9YC4 RC9YC4
Champion 7346
Champion Double Platinum RC10PYP4
Denso VK16PRZ11 VK20PRZ11
Denso PK20PR11
Denso Iridium* IK16
NGK Iridium BKR5 EIX-11 BKR6 EIX-11
Splitfire* SF522D SF392C
Splitfire Platinum* TP522D TP392C
Uber Power* FZX5iL FZX6iL
Gap 1.0 – 1.1mm (.038″ – .043″)
*I tried to verify as many plug numbers as possible but ran into problems finding any concrete answers from many plug manufacturers. The plugs with “*” next to them are verified by the manufacturer as a direct cross-reference, the others are old numbers that were floating around the VTXOA.

5 Responses to “Spark Plugs and the VTX 1800”

  1. Broka says:

    Thanks great info. cross reference chart shows NGK plugs Cold 02stock IFR6L11? This is the Hot plug. IFR5L11 is the OEM cold plug. Highly recommend Hotter plug for 02 models.

    • Bare says:

      I’m not sure where you’re getting that idea from, but you’re wrong. This is directly from NGK’s website:
      “The heat range numbering system used by spark plug manufacturers is not universal… For NGK, Denso and Pulstar, the higher the number, the colder the plug.”
      Do your homework and know what you’re talking about before you post assumptions on the internet to guide other people.

  2. Jimmy Carter says:

    Hey man, I did everything you said, it went great! The only thing is the “1/2 Turn past finger tight with the rubber hose. There is no way that I can get a half turn. All of them were tight at less than a quarter and they were tight.

    • xcalibur says:

      I’m fairly sure the only time you need the hose is to start the plug into the thread. Once its a quarter way in turn it by hand til it threads as far as you canby hand. Then ttighten the plug half a turn with a “socket” 🙂

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