Technique: Setting Plug Gap, And, Why No Feeler Gauge? (4 Viewers)

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Hi folks, I searched and saw several threads that mentioned the spark plug gap setting of .8mm but what I'm wondering here is what is the consensus towards which technique is the best for setting gap?

For years I relied on the old tool that had the little loops of gauged wire and the little crows foot contraption for bending the electrode but then a friend told me that method was crap because when you bend the electrode that way you end up with an angled electrode where only part of it, usually the tip, is the right distance from the center electrode while the rest was angling further and further away. He insisted on using feeler gauges for the exact measurement and he would squeeze the feeler gauge between the two electrodes softly with a vise. His electrodes were almost always parallel but I wondered about squeezing ceramic, even slightly? Recently I read somewhere a site (bosch maybe) where they specifically stated not to use the feeler gauge for this but they did not elaborate any more on why????????

I have also used the method that I think my father showed me which was lightly tapping the plugs electrode on a piece of wood at an angle and then using that circular ramp up gauge that goes from skinny to fat to essentially re-widen the gap to the right amount. The thing I wondered with that method (which usually produces relatively parallel electrodes if you tap at the right angle) is where to stop on the gauge? IOW, as you ramp up do you stop when the first edge of the electrode is at the number, or do you go to the center of the electrode, or to the next edge? I would assume it makes a minor difference at least and also the thing with that method is that the electrode seems to spring tighter so that you actually ramp past the number by several bars so that you can slightly squeeze the corect mark in and out.

I have also wondered about those plug gapping pliers, seems like the best of both worlds - a safe way to squeeze the electrodes very parallel to each other but for the fifty bucks or so I see them for, I gotta wonder if its worth it for the once a year or so I change the plugs on any of my vehicles?

As always I'm probably over-anal-izing this, but I am interested in what techniques you all are using for gap? Thanks. :cheers:
 
I also used to agonize over this until I bought my first plugs for the Cruiser. Through Toyota dealers, the plugs are pregapped, and they're right on. Just did this 2 weeks ago for the 97 and checked them before installing. Dead on for $1.72/plug. Plus you're getting the OEM specified plug, proper heat range, etc...

DougM
 
I have the Jacobs gapping pilers and IMHO they are not worth the money. The handles kept slipping off and it just easier and more accurate using the feeler gauge. I always just ended up doing your buddy's method.

I have to change my spark plugs in my turbo car about every 2500 miles. I gap .032 down to .028 with no problems using the feeler gauge.
 
MacLean216 said:
I have the Jacobs gapping pilers and IMHO they are not worth the money. The handles kept slipping off and it just easier and more accurate using the feeler gauge. I always just ended up doing your buddy's method.

I have to change my spark plugs in my turbo car about every 2500 miles. I gap .032 down to .028 with no problems using the feeler gauge.

So MacLean, thanks for the response, just to make sure I understand, you are squeezing the two electrodes together with a feeler gauge in the middle right? I guess technically or theoretically, you are not actually putting any pressure at all on the center electrode until the two electrodes and the feeler gauge are all squeezed as one? Have you ever had a cracked ceramic when you went to remove them? By doing that I'm sure the two electrodes are extremely parallel. Have you ever measured the gap after using them?

Also, to make sure I understand, you are changing the plugs that frequently? That must get real old real fast. My Safari literature recommends 20K kilometer intervals which is still less than the 30K mile intervals for most vehicles. s***, every 2500 miles makes the lube oil filter and plug routine a real chore!

Anyway, thanks again for the response man, I appreciate it. If you could just clarify the feeler gauge method I'd appreciate it. Thanks! :cheers:
 
IdahoDoug said:
I also used to agonize over this until I bought my first plugs for the Cruiser. Through Toyota dealers, the plugs are pregapped, and they're right on. Just did this 2 weeks ago for the 97 and checked them before installing. Dead on for $1.72/plug. Plus you're getting the OEM specified plug, proper heat range, etc...

DougM

Yes that would be wonderful but I must use a special plug that is one heat range cooler than stock, and with some other specifications that make it more appropriate for turbos. I'm not an expert at plugs but basically I think they are trying to avoid predetonation with a plug that runs too hot. They are all NGK but they were all gapped around 1.0 instead of .80 . The Safari literature is very specific about this particular plug, but, interestingly they make no mention anywhere that I can find about plug gap so I went with the .80 from the FSM. In general for forced induction you typically decrease the gap slightly - there was some formula from way long ago which stated for every extra 50HP you should decrease the gap .004 I'm not doing this with the plugs on my rig but perhaps I should convert that .004 and use it times what 3 or so? Anyway, in the absence of pre-gapped plugs, I gotta find the right way to gap them. Thanks this is cool! :cheers:
 
turbocruiser said:
Hi folks, I searched and saw several threads that mentioned the spark plug gap setting of .8mm but what I'm wondering here is what is the consensus towards which technique is the best for setting gap?

As always I'm probably over-anal-izing this, but I am interested in what techniques you all are using for gap? Thanks. :cheers:

I have a little round, silver thing that looks like a coin and it says Champion on it, metric on one side and SAE on the other. I think I paid .25 for it back in 1982 in high school when I built my supercharged '76 Bronco. Since then I have used it on at least 3 Vettes, two Porsche Turbos, some BMWs and Jags, a 38' Scarab with twin Hawk 750HP engines, and most recently two weeks ago, my 8th Land Cruiser. I have never had one single issue with spark plugs or obtaining a correct gap.

Jim

P.S. Oh yeah, I forgot that I used it once on my Honda pressure washer. :D
 
turbocruiser,

I run NGK plugs one heat range cooler than stock.

you are squeezing the two electrodes together with a feeler gauge in the middle right?

Yep. I have never had a problem with damaging the ceramic. I push hard but I am very carefull.

Unless your missing uptop or having idle issues, I would stay with your current gap. But if you want to play around with gap, you can gap down .002 inch until your idle gets rough. Then increase gap .002" and you should be good.


Its a small pain changing them frequently but I run the car hard with lots of boost 20+ psi. Supras eat spark plugs and clutches for breakfast.
 
If you are running the correct plugs, then they should be gapped correctly when the electrode is parrallel. Any gapping is really just checking them and getting them back to correct if they were not from the factory.

Light tapping the side electrode should not damage anything to close the gap. Don't put anything in there. Just measure it and if it's wide tap lightly and recheck.

I wonder if Bosch didn't want a feeler gauge scraping the platinum chips off of the electrodes?
 
Gumby I think you nailed it.
Whats the use in buying an expensive platinum plug if your going to scratch it off. Seems like they would be a little tougher than that but who knows.
I am using NGK and use that little coin deal but it been years since I had a plug that was off gap.
Interesting difference with the turbo setup. I had not heard that before but thinking I may try a plug on heat range cooler to offset the spark knock I have.
:banana:
 
elmariachi said:
I have a little round, silver thing that looks like a coin and it says Champion on it, metric on one side and SAE on the other. I think I paid .25 for it back in 1982 in high school when I built my supercharged '76 Bronco. Since then I have used it on at least 3 Vettes, two Porsche Turbos, some BMWs and Jags, a 38' Scarab with twin Hawk 750HP engines, and most recently two weeks ago, my 8th Land Cruiser. I have never had one single issue with spark plugs or obtaining a correct gap.

Jim

P.S. Oh yeah, I forgot that I used it once on my Honda pressure washer. :D

Okay good, thanks Jim, I too used this method many times on everything except the pressure washer!

What I'm wondering with this method, again from the first post, is where to stop on the gauge? IOW, as you ramp up do you stop when the first edge of the electrode is at the number, or do you go to the center of the electrode, or to the next edge? I would assume it makes a minor difference at least and also the thing with that method is that the electrode seems to spring tighter so that you actually ramp past the number by several bars so that you can slightly squeeze the corect mark in and out.

Is this the way you do it and have you ever measured the gap after taking the plugs out at 30K? Thanks again, I appreciate it. :cheers:
 
turbocruiser said:
What I'm wondering with this method, again from the first post, is where to stop on the gauge? IOW, as you ramp up do you stop when the first edge of the electrode is at the number, or do you go to the center of the electrode, or to the next edge?
Is this the way you do it and have you ever measured the gap after taking the plugs out at 30K? Thanks again, I appreciate it. :cheers:

I have always tried to stop at the very center of the mark vs. the center of the electrode. On pre-gapped plugs I always check them first. If they are too wide, I tap on them with the coin and then slide the coin edge in to check. If I need to open it up, I don't do it with the coin edge (which could damage the spark tip), I use the little pry hole on the inside of the coin to open it up. And for those who trust pre-gapped plugs, 2 of the 6 I just bought from Toyota were off.

I have measured the gap when removing and usually the number is a bit bigger, I assume due to heat and wear on the electrode.

Jim
 
Gumby said:
If you are running the correct plugs, then they should be gapped correctly when the electrode is parrallel. Any gapping is really just checking them and getting them back to correct if they were not from the factory.

Light tapping the side electrode should not damage anything to close the gap. Don't put anything in there. Just measure it and if it's wide tap lightly and recheck.

I wonder if Bosch didn't want a feeler gauge scraping the platinum chips off of the electrodes?


Thanks Gumby, makes perfect sense. My plugs are the correct plugs for my rig but they are all at approx 1.0mm (some were .9, some were 1.1) and even the NGK site mentions that this particular plug is used in many turbo applications and is pre-gapped "for the most common" of these applications. Maybe they meant pre-gapped "for the three most common" of these applications!

I'm also wondering about the scraping of the platinum chip on platinum plugs; that also makes perfect sense along with the fact that most platinum plugs insist that you do not "adjust" the gap after any use for fear the hardened platinum has the chance to pop off. However, in this case, I think they were referring to any plug at all and one other thing I remember them saying was to never put pressure on the center electrode or the ceramic center of the plug, and something about pulling up on the side electrode as opposed to using the center electrode as a fulcrum point. So, all that made me think that the center electrode and center ceramic were both basically hands off and that anyhting I did to gap would have to touch the side electrode only.

Thanks again guys, this is great. :cheers:
 
turbocruiser said:
So, all that made me think that the center electrode and center ceramic were both basically hands off and that anyhting I did to gap would have to touch the side electrode only.

Thanks again guys, this is great. :cheers:

I guess this goes without saying, but when it comes time to put the plug down into the cylinder head, even the slightest tap on the tip of the plug, heaven forbid it actually dropping out of your socket, will require regapping.

Jim
 
elmariachi said:
I guess this goes without saying, but when it comes time to put the plug down into the cylinder head, even the slightest tap on the tip of the plug, heaven forbid it actually dropping out of your socket, will require regapping.

Jim

Yes, agreed, the way that I prevent that problem is I never try to lower the plug to the hole with a socket and extension. Whenever I try to lower it that way the plug almost always falls out and smacks the bottom of the spark plug hole. What I do instead is put the plug's top into the inside of some stiff heater hose and lower it down and screw it in slowly. This way I find the center of the spark plug hole super easily, there is virtually no chance of stripping it in cause way before that point, the hose starts spinning on the plug, and if the hose does start spinning indicating a cross threaded plug, you can just push down a little to go further down the plugs taper, reverse thread the hose and almost always the spark plugs spins out undamaged and ready to retry. As soon as the plug threads in a few turns, I pull the hose off, finish it up with a 16mm and 8" extension by hand and without the ratchet and then put the torque wrench on it to 14 lbs. Perfectly fool proof, and hey, I'm not to proud to admit that's exactly the type of method for me!!! :D
 
turbocruiser said:
What I do instead is put the plug's top into the inside of some stiff heater hose and lower it down and screw it in slowly. :D

After Santa brought me my Craftsman tool set, I JB-welded my junker socket with the rubber keeper onto the long extension. Now I have my own "Special Service Tool." :D

Jim
 
Bosch has a special tool to gap platinum plugs. It grabs the ground electrode at the base and you bend in either direction to increase or decrease the gap. I was a Bosch distributor for a number of years and was unable to purchase one. I finally convinced my rep. to get me one and he did. This isn't much help other than to tell you that there is a "proper tool for the job. I almost never gap an NGK plug anf I only use Bosch platinum for problem cars. Oil burners, low compression, anything domestic etc.
 

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