NGK Spark Plug & Timing Chain FAQ: Real Answers From Someone Who's Ordered the Wrong Parts

I've been handling parts orders for an independent repair shop since 2019. In that time, I've personally made—and documented—seven significant ordering mistakes, totaling roughly $1,200 in wasted budget. This FAQ covers the questions I get asked most about NGK spark plugs, LED headlight upgrades, and timing chains. It's the page I wish I'd had before I learned some of these lessons the expensive way.

1. NGK B4 Spark Plug vs. NGK Laser Iridium 95350: What's the Difference?

The short version: they're completely different plugs designed for completely different engine families. And mixing them up will cost you money.

The NGK B4 is a standard copper-core plug with a nickel center electrode. It's been around for decades, it's inexpensive, and it's perfectly fine in the engines it was designed for—older Japanese engines, motorcycles, small industrial equipment. The "B" in the part number designates a 14mm thread with a specific reach and heat range. It's not a bad plug. It's just older technology built for older ignition systems.

The 95350 is from NGK's Laser Iridium line. "Laser" refers to the laser-welding process used to fuse the iridium tip onto the electrode. Iridium is significantly harder than nickel, so the electrode can be much finer—around 0.6mm—and still last a long time. The finer tip produces a more concentrated spark, which is why modern engines with high compression, direct injection, and tighter emission standards come with these plugs from the factory.

Here's where I made my mistake. In my first year, a customer with a high-mileage Nissan asked me to "upgrade" his spark plugs. I ordered 95350s because they were the premium plug in the NGK catalog. Turned out, they weren't the right fit for that engine—the thread reach was wrong, and the heat range didn't match. $152 with shipping, straight into the "can't return electrical parts" bin. The car sat for three days while I ordered the correct plug.

The lesson: select plugs by application, not by price. The Laser Iridium is an upgrade when it's the same part number your engine was designed for. It's not a universal swap. Use NGK's catalog or a VIN lookup before you order.

2. How Do I Know Which NGK Spark Plug My Car Needs?

Look up the part number. I know that sounds obvious, but you'd be surprised how many parts orders come in with just a vague description like "standard NGK plugs for a Honda."

NGK's part numbering system tells you the thread size, reach, heat range, and electrode construction—all in a string like BKR6EIX-11 or ILKAR7B11. The breakdown is in NGK's catalog, and it's worth learning because it helps you spot mismatches before you order, not after. Well, actually, let me rephrase that: it helps you spot mismatches if you check it. I didn't, at first.

What most people don't realize is that two engines in the same vehicle family can require different plugs. The Infiniti VQ37, for example, uses a different plug than the earlier VQ35 in some model years. Same platform, different ignition requirements. I made this exact mistake: ordered plugs for a 2010 G37 when the customer actually had a 2008 with the older engine. Six plugs and a coil that I also got wrong.

Use the VIN. Every major parts supplier—including NGK's own site—has a VIN-based lookup. It takes thirty seconds and it eliminates guesswork. I still use it every time, even now.

3. Will High-Power LED Headlights Cause Electrical Problems?

Possibly. Especially if you're also upgrading ignition components at the same time—which is exactly what I tried to do in September 2022. Mixed results.

The issue isn't the LED itself. It's the driver circuitry inside the bulb. Cheap high-power LED headlights often use poorly shielded PWM drivers that generate electromagnetic interference. That interference can bleed into nearby wiring—including crank and cam sensor circuits, which are extremely sensitive. I've seen cases where LED headlights caused ignition misfires at idle, weird CAN bus errors, and even random stalling.

To be fair, budget LED kits have improved since around 2021. The interference issue is still real, though, especially on older vehicles with less shielding in the engine harness.

Does this mean you should avoid LED headlights? No. But pick quality units and test for interference before assuming the ignition system is at fault. Our shop standard is: if a customer wants both an LED headlight upgrade and new spark plugs, we install the plugs first, verify the car runs clean, then add the LEDs and compare. It's a slower process, but it tells you exactly which component caused any new problem.

I don't have hard data on industry-wide failure rates, but based on what we've seen in the shop, about one in five budget LED kits shows measurable interference on a timing light or OBD misfire counters. Name-brand kits are better, but they're not immune either.

4. G37 Timing Chain Kit: When Should It Be Done?

The VQ37VHR engine in the Infiniti G37 uses a timing chain, not a belt. Nissan designed it to last the engine's life, which in theory means you never need to change it. In practice, the tensioners and guides are the weak points.

What most people don't realize is that a timing chain doesn't stretch the way a belt does. The chain elongates a fraction of a millimeter over time, and the hydraulic tensioner takes up the slack. When the tensioner reaches the end of its travel—or when the plastic guide rails wear through—that's when you hear the famous cold-start rattle. If you ignore it, the chain can eventually skip a tooth, and the VQ37 is an interference engine. Bent valves. Total disaster.

A "timing chain kit" for the G37 typically includes the chain itself, the tensioner, the guide rails, and sometimes the crank sprocket and water pump. Some kits also include the front cover gasket set and the solenoid seals that are prone to leaking. The parts are reasonably priced—the labor is the expensive part, usually 10 to 12 hours because the front of the engine has to come apart.

My honest advice: if you're at 100,000 miles and the car rattles on cold start, don't drive it. Order the kit and do the job. I had a customer who waited, and the tensioner failed completely at about 112,000 miles. That job went from a roughly $1,800 repair to a $4,600 repair with a used engine.

5. How Often Should You Change a Timing Chain?

"It depends" is the honest answer. Timing chains are marketed as lifetime components, but "lifetime" doesn't account for how the car was maintained, what oil was used, or whether the previous owner regularly hit 7,000 RPM on a cold engine. Yes, that's a real thing with G37 owners.

I've seen chains with 180,000 miles that were still in spec, and chains with 80,000 miles that were stretched beyond tolerance. The variables are oil change frequency and engine load. Chain tensioners rely on oil pressure—clean oil, specifically. If oil changes are late, the tensioner doesn't get the pressure it needs, and the guides wear faster.

There's no manufacturer-scheduled interval for the G37 timing chain, which is part of why this question comes up so much. Nissan calls it a lifetime part. I'd say start inspecting at 100,000 miles—not replacing, just inspecting. Listen for rattle on cold start, check for metallic debris in the oil, and if there's any doubt, have a shop scope the timing chain guides.

Think of it like this: a timing belt has a hard number because it's rubber and it degrades regardless. A chain is steel, so it degrades based on how it was treated. The relevant range is more like a spectrum—or rather, the tensioners are the part that actually wear out, and they usually show symptoms somewhere between 100,000 and 150,000 miles.

6. Should I Use OEM Parts or NGK Aftermarket for Ignition Components?

Here's where I'll be direct: for spark plugs, NGK is usually the OE manufacturer for Japanese vehicles anyway. If you buy an NGK plug for a Toyota, Honda, or Nissan, there's a good chance it came off the same production line as the one in the dealer box—minus the dealer markup. That said, there are exceptions.

Some manufacturers have updated their original part numbers with engineering changes that aren't always reflected in the aftermarket equivalent. For example, a revised ECU calibration in a later model year can require a colder heat range or a different gap. When that happens, the aftermarket part might not supersede to the updated version—at least, not right away.

My rule, developed after a $400 mistake with ignition coils: spark plugs are safe to buy by NGK part number, but coils and sensors—buy by VIN and check for supersessions. I once ordered six aftermarket coils for a Nissan that fit fine but failed within a month. Turned out the original part had a design revision that the aftermarket version didn't include. That's not NGK's fault. It's a mismatch between the aftermarket part catalog and the manufacturer's update cycle.

In my opinion, this is where a good parts professional knows their limits. The vendor who said "this isn't our strength—here's who does it better" earned my trust for everything else I order from them. That's the same mindset I'd recommend: know where NGK is the right answer, and know when to send the customer to the dealer instead.