Sparkplug query

The way I think about it, the engineers were well paid to design and test this engine. They found by testing an assortment of plugs, that certain spark plugs produce the best results. Not that they found the perfect plug, but the best compromise.

Actually that’s not the way it’s done. Manufacturers usually work with one or two plug manufacturers when designing an engine. They don’t test any other plugs.

As far as I know, every spark plug manufacturer states that the plugs are to be re-gapped if necessary and I have no reason to doubt NGK, Denso, Autolite, or any of the rest of them.

On the NGK site and in so many words, they refer to this “pre-gapped spark plug” as a myth and that the gap should be adjusted accordingly.


Thank you for that information

No matter the type of plug I always check the gap of each individual plug. In most cases with platinum and iridium plugs the gap is fine, but in a box of 8 I find there seems to be at least one and usually 2 plugs that are off by more than .002" and need the gap adjusted to get within spec for the motor.

Common sense told me the wire being so small that it could be easily damaged, but I haven’t found it difficult to regap these special plugs as long as you are careful. So far, I’ve never damaged one.

I have also heard that platinum and iridium plugs don’t need to be regapped, but I’ve found too much variation in the plugs out of the box to put a plug with an out of spec gap plug into a motor. These plugs are so hard the gap essentially never changes, so you put it in with the wrong gap and that’s the way it stays for 60 or 100K miles.

To add to Mike’s description of design processes, the engine designers will actually send the engine design parameters to the approved vendors and the sparkplug designers will recommend/forward sets of specific plugs, usually in communication with the engine designers as a joint effort. The sparkplug manufacturer’s design specifications for the plug (and there will generally be more than one) selected by the engine’s designers will (after qualification testing) then be incorporated into the engine’s design package as a “specification controlled drawing”, with the plug manufacturers’ technical details included, as well as their part number as a reference, wherein it becomes an “approved” part. The car manufacturer then orders plugs using the spec control drawing, and the plug manufacturer incorporates their own part number into the list that you see at the parts store as the correct plug for that vehicle.

It sounds complicated but it isn’t. It’s an extremely well established protocol that exists between car manufacturers and parts vendors. It’s “second nature” to design guys.

As regards the adjusting of electodes, the plugs that require care when adjusting, are the irridium plugs. The irridium electrode, the center one, is a smaller diameter and irridium is brittle. It’s easy to damage the center electrode while doing and adjustment. I do, however, generally check the gap just in case the plug came in with damage. It the plug is damaged, I simply return it for a replacement.

I’ve had applications that varied from the production gap setting and required re-gapping out of the box.

I got lazy as I got older and if they matched the application, I would just install them out of the box. Until one time… I happened to notice one was off by a huge amount. The ground strap was almost touching the center electrode. The packaging was intact and even had the circular carboard protector over the threaded end. Found 2 out of 8 in that box were similar. Been checking them religiously ever since. Kinda like finding you left the iron on once, you get anal about double checking after that. Haven’t found any gross errors since then…

In most engines, it does not matter if the spark plug has one, two, three or four ground electrodes, but I have run across on engine that you could feel a noticeable difference between a single ground electrode and multi ground electrodes. The multi ground electrodes are really side gap plugs and that may be why the engine responded differently to them. With that engine, it didn’t matter if it was a two lug or 4 lug.

Thanks barkydog for the picture, I did not see anything like that on the Bosch website though, must be a special plug, but it does not look like one of their platinum series plugs. I did run the model car in their website and teh recommended plug is the Platinum IR Fusion plug which is a 4 lug design. Go figure, the highest priced plug too.

BTW, Bosch states on the multi ground platinum plugs to NOT gap them. Its right on the box. As far as I know, it only applies to the multi ground plugs.

Plat 2 and 4 both have rebates. The plat 4 is $5 online and has $3 rebate so cost is $2 each. Plus $4 shipping for 6. I wish there was no gap war but sometimes things get sidetracked.

Single ground electrode plugs can always be gapped (carefully) but MULTI-ground electrode plugs should NOT be gapped. They are application specific and pregapped.

That being said, I am a huge believer in OEM for ignition parts. I never found fancy plugs with multiple grounds to be of any help and, in fact, were the cause of degraded performance and mileage in more than one Japanese engine I owned. For ignition parts (plugs, wires, coils, distributor caps and rotors) I always stick with OEM now. I learned the hard way.

Re - gapping plugs. I always like to check the gap, usually it is spot on, very few are off, If off I figure it might have fallen off the shelf or something and bumped the anode, proper gap for proper performance.

I liked the good old days when we used a Champion J-8 plug in everything from the LawnBoy 2 stroke mower, the rototiller with the Lauson engine, the 1952 Dodge and the 1954 Buick. However, one time I tried some dual electrode plugs from Western Auto in a car I owned that called for AC 44. The manual said that the plugs would interchange. I had problems with the plugs fouling from the first week. From that point on, I always followed the manufacturer’s recommendation for the spark plugs.

I have owned cars that the manufacturers have changed the spark plug gap in service. How can you not regap those plugs. I have also had cars whose platinum plugs came pre-gapped from the parts store for a different more popular engine.