For those of you that use Iridium plugs, did you gap them before installation? There are a few different makes of Iridium plugs on the market these days (NGK, Autolite, Denso etc). It seems a lot of people on the forum like the NGK plugs so I was thinking about buying a set. There seems to be varying opinions regarding plug gap. I’ve read that some people install them out of the box because they are already gapped correctly from the manufacturer while others still set the gap to Harley’s recommendation (38 t0 42mm). I’ve heard that the default gap for the NGK Iridium plugs that fit Harley’s is about 20mm. If you use Iridium plugs did you gap them or install them straight from the box?

 

no they come pregap,

 

Always check the gap. Unless they're packed really well with the end protected I would at least check the gap. I've seen some that were probably dropped or hit on the end and had the gap too small, it only takes a second to verify.

 

yes no matter what plug you buy always check the gap.

 

I Gap Mine using a feeler gauge at 040 .. Never found one dead on yet..

 

Even thought in most situations they come pre-gaped - It is a good idea to check and adjust if needed.

 

Thanks for the replies. I certainly understand the need to check the gap but I was curious if people gap Iridium plugs. The pre-set gap on Iridiums is about 20mm less than what Harley recommends a standard copper plug be set at.

Do most people that install Iridium plugs leave the plug at the pre-set gap (around 20mm) and install it or do they gap the plug at 40mm before installation? That's what I'm trying to find out.

Thanks.

 

Iridium plugs are overkill in most cases. I am a NGK fan and user, but when my plugs need changing I will go for the standard NGK U-groove plugs. A local speed shop owner here has one of the counter top splitfire plug sparking devices which lets you see the type of spark you will get out of any plug. Steve claims that the NGK U-grooves proved to be as good or better performing plug than the mighty expensive "Splitfires" and many others. The U-grooves can be had for a fraction of the price of many newer plugs on the market. I wish I could give you the part number, but I have only recently begun to consider changing mine.
I will post back when I find the correct part number for the 88 TC motor.
$0.02

aka Bob

Addendum; If an Iridium plug is designed to go into the Harley, I would consider the gap they use. Just check them both for consistency.

 

Always check the gap, the same plug for your v-twin will also be used in many other applications from Ferrari's - Ducati's - ATV's - Outboard Motors & Snowmobiles all will have different head/piston designs & compression ratio's. When I used an NGK Irridium plug, they were factory gapped at .18!

 

I agree, always double check the gap. Also, I was told that if they need to be gapped, use a tool that won't mar the Iridium finish. It's a very thin layer and can easily be scratched away. You paid good money for them, there's no sense in ruining them before they even make it in the bike.