How do I increase the spark plug gap?

[RobertE]

OK, so I've got a new set of plugs sitting here and need to gap them at .018 - .022. But from the factory they seem to be .015. So how do I increase the gap? The tool I've got works for reducing it but not increasing it.

Follow up is, what's the likely consequence of too small a gap?

Thanks.

[mooney389]

As long as they are at least .015 they should be fine. Most likely to damage them if you try to widen the gap.

[NotarPilot]

Yup, I agree.  Leave them at .015, fly the hell out of it and let nature take its course.  Meaning, they will increase in gap size the more the sparkplug fires.

[Super Dave]

I'm no mx guru, but I just happened to watch the Mike Busch (a real mx guru) webinar on spark plugs. He agrees with mooney389 and NotarPilot, no way to increase gap other than use. He also said most engines call for .016, but .015 should be just fine.

[RobertE]

Thanks, guys. Just one f follow up. Does anyone know what the flight consequences are of too small a gap vs too large? I assume the later will misfire at high altitudes? How about the former?

[Super Dave]

Again, according to Mike Busch... To small of a gap results in weaker spark. To large of a gap makes it hard for the plug to fire, making for hard starts. Also, he says a wire gauge is the only way to check the gap. .015 should barely pass through, .019 should not fit.

[Mooneymite]

http://www.aircraftspruce.com/catalog/topages/hdsprkpluggrapkit.php?clickkey=210324

[NotarPilot]

If you're only dealing with a .015 gap I doubt you'll have any problems.

[Piloto]

Is not big deal increasing the gap. Just insert a good steel small screwdriver underneath the electrode and lever it against the plug rim.  Apply minimum force and it will open the gap. I have done it a dozen times with no side effects. A too small gap is subject to fouling and oil and will cause misfire.

 

José 

[wiguy]

 I just put some new Tempest 'Massives' in. The gap looked much tighter than my moderately worn plugs. I didn't want to mess with them, they are working fine.

[Uncleger]

Hey guys saw your posts regarding opening the gap on aviation plugs.  What you may or may not know, a lot of guys myself included are going to Surefly or Electro Systems electronic ignition.  These systems need .22 to .35 gap.  Need to find a way to safely gap the plugs.  FYI Electro Systems sells plugs to proper gap. Not everyone wants to buy expensive plugs after nearly 6k plus installation for their stc.  Surefly is around 2800.00 for their stc.  No plugs to date. is around 

[EricJ]

5 minutes ago, Uncleger said:

Hey guys saw your posts regarding opening the gap on aviation plugs.  What you may or may not know, a lot of guys myself included are going to Surefly or Electro Systems electronic ignition.  These systems need .22 to .35 gap.  Need to find a way to safely gap the plugs.  FYI Electro Systems sells plugs to proper gap. Not everyone wants to buy expensive plugs after nearly 6k plus installation for their stc.  Surefly is around 2800.00 for their stc.  No plugs to date. is around 

The tool kit linked above with the gapping tools includes a little lever tool to pry the legs of a massive plug out to increase the gap.   Piloto suggested using pretty much any lever tool, like a screwdriver.   That can work, but putting a side load on the center electrode should be avoided.   It's also easy to crack the ceramic nose doing this, so it's a good idea to practice on old plugs first.

Aircraft Tool Supply sells a "plug ungapper" that also works well and keeps the loads symmetric and off of the ceramic nose, as long as you're careful.   I've used this one sometimes, but they're all kinda tricky and require practice to avoid damaging the plug.   

It's not unusual to have to open up a gap if you get it a little too small during a normal regapping process.   Opening it up as far as they want for the sure fly will require some practice to perfect, I think, but it's definitely doable.

https://www.aircraft-tool.com/Detail?id=SPGE1