BOSCH:
http://www.boschautoparts.com/Resour...SparkPlugs.htm
Are Bosch Spark Plugs pre-gapped at the factory?
Most Bosch Spark Plugs are factory pre-gapped for popular vehicle applications. The gap measurements are indicated either on the box, or by the part number located on the spark plug shell.
[ul][*]X suffix = .044"[*]Y suffix = .060"[*]Z suffix = .080" [/ul]
Gaps should never by adjusted on Platinum+4 or Platinum2. Bosch Platinum+4 and Platinum2 have factory pre-set gaps, and should never be gapped by the installer.
Bosch Platinum and Super Spark Plugs also have factory-set gaps. For most plugs, the setting is shown on the plug package. These gaps are correct for the most popular applications of these plugs. There are applications, however, for which the gap setting has to be adjusted according to the vehicle manufacturer’s specifications. To avoid damage to a spark plug in the process of adjusting the gap, it is important to follow these guidelines:
[ul][*]To widen the electrode gap, use a tool that only pulls back the ground electrode, without applying pressure to the center electrode. The tool must not be wedged between the electrodes as that may cause damage to the insulator nose.[*]To close the electrode gap, carefully tap the plug, electrode first, on a hard surface, as shown in the illustration.[/ul]
If I remember correctly, gapping on Bosch Platinum plugs is only allowed on the single-ground electrode plugs, and the package used to say "After
initial gapping, no re-gapping is necessary". Not sure if they still have the same quotation.
DENSO:
http://www.densoiridium.com/faq.php
Q. Do I need to set the gap?
A. Generally, no. The DENSO Iridium Power plug comes pre-set with a protective sleeve over the firing end, to protect the gap from accidental alteration. DENSO Iridium Power’s ultra-efficient firing power compensates for normally recommended
gap settings that are smaller than the pre-set value. In the cases of vehicle modifications (nitrous, turbo-chargers, super-chargers, high power ignition systems, etc.), some adjustments may be desired. Or, if you prefer to remain consistent with factory specifications, you may adjust. However, please be careful not to place any stress on the fine center electrode during adjustment. You could accidentally break off the very hard, and therefore brittle, tip.
Q. How do I gap Iridium plugs
A. Before attempting to gap any DENSO Iridium Power spark plug, please review the specification chart to see the factory-preset gap. In most cases your Iridium Power plugs do not need to be gapped. Even with small variations in the factory set gap the ultra-efficient firing power design will compensate for those small variations. Should you decide to re-gap your Iridium Power plug, use extreme caution as improper gapping may damage or destroy the Iridium center electrode or porcelain center. To increase the gap size: Step 1 Use needle nose pliers or spark plug gapping tool to bend the ground strap up to the desired height. DO NOT LET THE PLIERS OR GAPPING TOOL TOUCH THE IRIDIUM CENTER ELECTRODE OR PORCELAIN. Step 2 Re-check the gap with a calibrated gapping tool. To decrease the gap size: Step 1 Use the same method as above, however bend the ground strap down to the desired height. DO NOT LET THE PLIERS OR GAPPING TOOL TOUCH THE IRIDIUM CENTER ELECTRODE OR PORCELAIN. Step 2 Re-check the gap with a calibrated gapping tool. WARNING: Failure to follow these directions may permanently damage the spark plug. Note: Never use a round gapping tool to check the gap or to increase or decrease the gap setting.
NGK:
http://www.ngk.com/faqmain.asp
Do I need to Gap my plugs?
Maybe, but likely not. Many plugs are pre-gapped for their most popular applications, however, the gap can be altered if the plug is dropped or mishandled in packing/shipping. Therefore even if the plugs are supposedly preset for your motor,
it is always wise to check the gap on each plug prior to installing.
Should I gap my Iridium Plugs?
The manufacturers say NO.
This is because most people do not know how to properly gap a spark plug, and the center electrodes on the ultra-fine iridium can easily snap if mishandled.
There is no warranty for snapped center electrodes. The manufacturers say an iridium spark plug will run so much better than a traditional plug, even if it is not gapped for that motor, that they would prefer you just leave it rather than risk snapping the center electrode.
Personally, we at sparkplugs.com, gap our iridium plugs for our own vehicles (weæ±*e rebels). If you insist on gapping your iridium plug, please refer to Proper Gapping for instruction.
VERDICT:
Gapping on Platinum/Iridium plugs is
generally not necessary, but can be done if you wish. However, an utmost care is required and if done carelessly, the electrodes would be damaged.
I am not here to say who's right or wrong, so take whatever you thinkis beneficialfor you. But I personally would follow the manufacturers' instructions.
JPN