Correct spark plug gap for rc

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Losi125

Losi125

Well-Known Member
Messages
193
Hello everyone I have a question I should have asked a long time ago in the past I would just purchase ngk cmr7h and just drop them in run and go . So I needed to purchase some spark plugs and I go to eBay and purchase some and the gap says .040 I go to the ddm site and they recommend .029 gap I have in the past purchased spark plugs from ddm but I never really checked the gap I just drop them in and roll . Does ddm spark plugs come gapped at .029 ? Or do you have to re gap them ? Or Do you just drop them in and go without checking? In the past I never had any problems just dropping them in but now I am going to make sure they are gapped properly .
 
Polar_Bus said:
I've never checked/changed a plug gap in my life unless I dropped the plug on the floor smashing the gap closed !
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That's exactly what I was doing I'm just wondering should we be checking and if the gap is .029 would anything else Rob you of a slight performance
 
Losi125 said:
That's exactly what I was doing I'm just wondering should we be checking and if the gap is .029 would anything else Rob you of a slight performance
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Im not sure how much slight variations effect performance, and im also not sure why DDM would recommend a different gap than the plug manufacturer. I've always just done it because its simple, and its what I was taught to do as a kid. I would assume a proper gap would lead to at least slightly better results, and perhaps longer plug life. I really don't know though. Perhaps one of the mechanics will chime in.
 
I can't remember where I read this info but in certain types of electrode design configurations the mfg. specifically tells you do NOT attempt to jam a gap tool in the electrode or attempt to bend the electrode to adjust the gap as the ground electrode can crack and break off.
 
I vaguely remember from shop class that too narrow a gap can cause poor fuel economy due to a small spark, and too large a gap can cause poor performance due to the fact that the plug doesn't have enough voltage to properly jump the gap. How much of a difference in the recommended gap we are talking about, I haven't got a clue
 
RENOV8R said:
I vaguely remember from shop class that too narrow a gap can cause poor fuel economy due to a small spark, and too large a gap can cause poor performance due to the fact that the plug doesn't have enough voltage to properly jump the gap. How much of a difference in the recommended gap we are talking about, I haven't got a clue
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Ngk manufacturer says .030 ddm says.029 then I saw something on eBay at. 040 I have had bad spark plugs straight out of the box but I have never ever checked the gap now I'm wondering.
 
21bangbang said:
How did you come up with that number? This thread is the first time I've heard of people not using manufacturers specs. Kinda curious now if it does matter if its correct. Doesn't really appear to matter much. Any mechanics on here with spark plug knowledge?
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Can't remember now but it may have been the NGK site.
I vaguely remember it saying 0.23 - 0.27 so I just went 0.25.
At the bottom of this Zenoah torque chart it says gap 0.6 - 0.7 mm which is 0.23 - 0.25 inches.
I run all my 2 stroke motors at that and never had a problem.
G320TorqueSpecs.jpgh
Losi125 said:
Ngk manufacturer says .030 ddm says.029 then I saw something on eBay at. 040 I have had bad spark plugs straight out of the box but I have never ever checked the gap now I'm wondering.
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I've found they're usually 0.25 out of the box.
Losi125 said:
Ngk manufacturer says .030 ddm says.029 then I saw something on eBay at. 040 I have had bad spark plugs straight out of the box but I have never ever checked the gap now I'm wondering.
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I've found they're usually 0.25 out of the box.
 
Last edited:
So I'll try to give a brief explanation of why plug gap isnt all that important (anymore) first most if not all plugs are pre gapped from the factory for optimal performance with a MODERN ignition system. Those of us who were told we needed to gap every plug, was (in most cases) because they, or the guy teaching you, had learned about plugs when point systems were still prolific. A points system isnt really a high energy system. (Yes there were exceptions) so the plug gap mattered a lot more, too little the spark wasnt good enough, too large and the spark wouldnt jump the gap. With the advent of transistorized magnetos and high energy ignitions the gap became less important. Also a good point to note is the advancement in plug technology. We went from copper core plugs that need replaced ever few thousand miles to plug's that will (basically ) last most of an engines life. With modern plugs ( ie iridium and platinum) gapping the plugs is about the last thing you want to do. The electrodes have become so small it easy to break a strap or misalign the electrodes. So I guess what I'm getting at is yes check if it makes you feel at ease, but it should be set to the plug mfgs spec from factory.
 
Seandonato73 said:
So I'll try to give a brief explanation of why plug gap isnt all that important (anymore) first most if not all plugs are pre gapped from the factory for optimal performance with a MODERN ignition system. Those of us who were told we needed to gap every plug, was (in most cases) because they, or the guy teaching you, had learned about plugs when point systems were still prolific. A points system isnt really a high energy system. (Yes there were exceptions) so the plug gap mattered a lot more, too little the spark wasnt good enough, too large and the spark wouldnt jump the gap. With the advent of transistorized magnetos and high energy ignitions the gap became less important. Also a good point to note is the advancement in plug technology. We went from copper core plugs that need replaced ever few thousand miles to plug's that will (basically ) last most of an engines life. With modern plugs ( ie iridium and platinum) gapping the plugs is about the last thing you want to do. The electrodes have become so small it easy to break a strap or misalign the electrodes. So I guess what I'm getting at is yes check if it makes you feel at ease, but it should be set to the plug mfgs spec from factory.
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Yep my Navaras run Iridium and you just change them every 100.000ks and forget about them.
 
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