How do I not overtighten or undertighten spark plugs for a 2002 Corolla?

General Discussion
1

I am changing my own spark plugs for the first time. I have a spark plug wrench, dielectric grease, anti-seize compound etc.

I have a Haynes manual for my 2002 Toyota Corolla. The book was written before Irridium plugs were used. Should I tighten the spark plugs to the same torque specifications as regular plugs? The book says 158 inch pounds. How do I know I have tightened them to the right amount?

How do I avoid cross threading the spark plugs? What happens if you cross thread the spark plugs (assuming the car seems to be running fine)? Would I need a new engine or expensive repair when it is time to replace the spark plugs again?

2

you need a torque wrench, first of all.

There is a technique to avoid cross-threading. but first:

  1. Clean the spark plug hole in the cylinder block with a clean, lint-free cloth.
    Wipe away from the hole; don’t shove any dirt into it.
  2. Lightly coat the threads of the spark plug with a drop of oil from the dipsitck.

One that I use:

  1. Place the plug in the opening, Keep it perpendicular to the block surface.
  2. Turn it CCW (backwards) with your fingers until you hear the threads click several times.
  3. Carefully turn it CW (Clockwise) with your fingers until it is completely inserted. If you feel any resistance, stop, back it out and try again. If the threads are damaged, there are tools to clean them up.
  4. Continue tightening it with the torque wrench to the specified number.
3

You can’t cross thread a spark plug with your fingers, at least not to the point of doing damage. If it is just getting started and you can’t turn the plug with your fingers, then back it off and repeat Bill’s advice above.

If you are using NGK or Denso plugs, do not use anti-seize on them. They have an anti-seize plating that is not compatible with anti-seize compounds. If you are using another brand, you will need to check their web site. A general rule is that if the threads are silver, don’t use anti-seize, if they are black, use anti-seize. That may not be universally true though. Champions are silver and I would use anti-seize on them.

If your spark plugs are in holes that make it difficult to get your fingers on them, then I like to use a 1/4" or 3/16" reinforced tubing, like fuel line. You can get it at any parts store. Cut about a foot of it and slip it over the contact of the spark plug. Now you can guide the plug into the hole and start threading it. You can only go a few turns before the resistance gets to be too much for the tubing to turn the plug any more. It will not start threading in if the threads are not perfectly aligned.

Once you have two or three turns, you can switch to the socket. Put an extension on the socket and the plug should turn easily with your fingers until it bottoms out. It’s not a solid hit, but you can tell. Turn it as tight as you can with your fingers. Now put the ratchet or flex handle on the extension. If you have both, use the flex handle. Not the position of the flex handle and pick a point that it would be pointing too that is about 3/4 turn (270 degrees) from the start. Now turn the handle to that position and the plug will be just right. If for some reason it gets really hard to turn and you have gone past 1/2 turn, it is OK to stop.

Note: I’m pretty sure your plugs have a gasket on them. It looks like a metal o-ring that can be removed from the plug. Do not remove it. If you are doing an engine that uses a tapered seat instead of an o-ring, then you only turn the handle about 1/8 th turn.

If you use a torque wrench, still use the 3/4 turn as your guide. If the torque wrench doesn’t click or reach the desired torque, stop at the 3/4 turn anyway. If it clicks a little before, then stop there.

If you put any oil on the threads, which I would not do, then you probably will not reach the torque before the 3/4 turn.

4

You should use the same brand and model plug you cr came with. No advantage to changing.

5

The 2002 Corolla uses the same engine as the 2003, and the 2003 came with NGK Irridium plugs that are good for 120k miles.

6

Make sure before inserting the new ones the spark plug holes and threads are free of any debris. Use good lighting, might need to use a combinations of flashlights and mirrors, etc. If some debris near the hole is difficult to remove I’ll get out my shop vac with appropriate adapter and suck it out that way. That’s usually not required on my Corolla though b/c with the spark plug cable top hat there’s no easy way for debris to get down that hole. If necessary, I usually do the vacuum thing with the old plugs still in.

Yes cross-threading the plugs is fixable but will cause you a lot of expense and grief, so best avoided. To reduce the chance of cross threading what I do is find a piece of rubber or plastic tubing – like fuel hose, a big straw, etc – that is sized so I can fit it tightly over the top of the spark plug. Then I hold onto only that with my fingers when I thread the SP into the threads. Then if it starts in askew and begins to cross thread the plastic tube will yield and won’t twist further. To avoid the plugs seizing I’ve always put on a tiny dab of moly lube on the spark plug threads, but not everyone here agrees with that technique. On the plus side, the plugs have never seized.

If your Corolla is like mine you may have some difficulty b/c the plugs are way down in a long narrow tube. I have to duct tape the extensions together so they don’t come loose and stay down there in the hole. One other caution: My spark plug socket is probably similar to yours and has a rubber insert and sometimes that insert stays down on top of the spark plug after I’m done tightening it. Make sure that doesn’t happen otherwise the spark plug won’t work. If it does happen, I have a pair of very long and narrow nosed forceps on hand to extract it from the hole. Suggest you secure such a tool before starting the job. I sometimes have to use that same tool to get the old spark plug out of the hole once it is unscrewed.

About tightening: I can’t speak to the particular plug you are using, but when I do this on my Corolla I first look up the tightening torque value in the service manual, then I’ll use my torque wrench to snug it up. I usually snug it up in two or three steps. If I want 12, I’ll first snug all to 6, then to 8, then to 12. I usually re-torque the plugs after a couple of drives, maybe a week later. Sometimes they’ll loosen a bit at first.

If I can’t find my torque wrench I’ll bring my bathroom scales out to the shop. I’m a diy’er, not a pro as you might can tell. If say the specified torque value is 12 foot pounds. I’ll find a ratchet that is about one foot long. Then I’ll press on the scales to get a feeling how much force 12 pounds is. Then I’ll use that to judge how tight to push on the ratchet. Better of course just to use the correct tool, but it works pretty good as a back-up. Best of luck.

7

I have worked on lots of vehicles where the plugs wore out and caused misfires . . . long before the book would have you change them out

The maintenance book is only a guideline. It’s not the bottom line in all cases

8

I don’t use any lubricant on the threads because it messes up the torque values. I use a beam-type torque wrench (just a personal preference) and torque the plugs in two or three steps. It usually takes two steps to get it to spec and I double check them all after doing the last one.

NOTE: Never use a U-joint with a torque wrench. It’ll mess up the torque readings.

Because of the long tube mentioned in another post, you want to be sure you have a proper size “spark plug socket”. It’ll have a rubber piece inside that’ll hold the plug without damage and allow you to pull it up the tube. And it’ll hold the new plug for ease of installation in the bottom of the tube. I have one taped to the end of the proper size extension. These spark plug tubes are common in dual overhead cam engines, because the plugs has to seat down between the camshafts for its electrodes to protrude into the cylinder.

Toyotas should get only NGK or Nippon-Denso plugs. Those are the suppliers Toyota uses. I once tried another brand with poor results, and had to replace them with NGKs. I like NGKs. Check the website for the proper torque. I try to hit the middle of the specified range.

Preventing cross threading is a matter of “feel”. By starting the plugs with a delicate touch, you can feel when the threads begin to properly catch. The plug should then screw in with only finger force.

Toyota uses spark plugs with a flat base and a hollow metal “crush washer” at the base. Once installed, the plugs should not be removed and reused. Lots of people do so, but the plug manufacturers recommend against it, because it risks poor sealing of the plug’s base.

Sparkplug threads damaged can be repaired by a competent shop.

  • If it’s only the lead threads, there are “backout taps” that can be used. They’re like standard taps sliced into three or four segments and collapsed, with a conical hollow inside. There’s a cone that gets pulled into the center of the thread segments and expands them to the proper size. It’s inserted into the hole, them expanded by pulling the cone up with an included bolt. When it reaches full diameter, it’s gently backed out of the hole, cutting new lead threads as it gets to the top of the hole.
  • Badly damaged holes can be tapped out oversize and “helicoils” installed. It’s a helical steel piece that creates brand new threads. They make special ones specifically in spark plug size threads, specifically for repairing bunged-up sparkplug holes.

Summary:
Get the proper size spark plug socket.
Get a torque wrench. Attach a proper length extension to it. Use it.
Get either NGK or Nippon-Denso OEM replacement plugs. The listing at the parts store will tell you which is the OEM replacement choice.
Look up the proper torque spec on the plug manufacturer’s website.
Use a gentle touch and care.
Use care and common sense, but if you do mess up, its is repairable.

9

I’ve never used a torque wrench for the hundreds if not thousands of plugs I’ve replaced…and ever damaged one. If you’ve never replaced spark plugs before…then a torque wrench might be a good idea so you can get a feel as to how tight they should be.

10

I never used to use a torque wrench, but as engines evolved to where they all had aluminum heads with the plugs deep down in spark plug tubes I began to feel more comfortable using one. Now I wouldn’t do the job without one.

But I agree, after hundreds or thousands of plugs a torque wrench isn’t really necessary, but for a beginner I definitely recommend one.

11

I never used a torque wrench either. Now I use it because I have one!! So far, both methods worked fine for me. When I use the torque wrench, since it is a click type, I usually set the torque a bit lower than the book and get a feel for it. Then I decide if I want to tighten it more or leave it as is. With today’s extended change intervals, I think for every car I own, I will only change the plugs once and by the second plug change the car is probably not worth the new plugs.

12

I’m home baby

13

Your best best is to forget the torque wrench and work by feel so to speak.

With tapered seat plugs run them down until they touch. Then just snug them up a little.

With gasket seat plugs run them down until they touch. Then go maybe another half a turn.

You can go onto the websites of some spark plug manufacturers and in their tech info they will say the same as above.

One for example is that some plugs have a recommended torque range of 7 to 15 Ft. lbs. Working by hand is much preferable to that and it should also be kept in mind that when dealing with low torque values a torque wrench (especially a 1/2" drive) is not going to be down to the pound accurate anyway.

14

I use a torque wrench for most things but not spark plugs. With copper plugs I always used never-seize and if you then used a torque wrench, it just seemed you were turning the plug far to much after it was seated.

I just hold my 3’8 drive ratchet by the head with the handle sticking out between my index and middle finger and twist firmly with my wrist.

In 60 years of doing this, I have never had one blow out and never had any trouble getting one back out.

In the 50s , plugs came out every 5000 miles, first to be cleaned and re-gapped, next time
replaced.

When I worked in a gas station, we charged $0.25 to clean and re-gap a plug and @1.00 for a new one.

At 10,000 you also replaced the points and condenser and inspected the cap and rotor.

Some people bragged about not doing this, the same people that called me wanting help in the nastiest weather because their car wouldn’t start.

They then would say I knew I shouldn’t have bought a xxxxxxx - they never start in the winter.

15

Funny, I used to use a torque wrench, now I don’t, except as a safety check. I put the new plugs in dry and I set the torque wrench, just in case. I go snug then either 3/4 turn for plugs with a gasket or 1/8th turn for tapered seats. If the torque wrench clicks a little early, then I stop.

If I have to remove a plug today, a new one is going in. I do remember the days of removing the plugs and sandblasting them in a special sand blaster just for plugs. I usually took a points file to the points to give them a quick dressing between full tuneups as well. Also blew out the air filter from the inside with compressed air. Oh yeah, and the oil changes and lube job every 1500 miles.

16

OK4450 and I have debated the use of torque wrenches numerous times. Our opinions differ on this.
For a newbie I definitely feel you should use one. You’re gonna have to decide your own tolerance for risk.

17

Yeah I don’t use a torque wrench either, just do it by feel with the ratchet. Seems like snug and a quick tug does it. Everyone has a different strength level though. The problem is on the rear plugs anyway, you can’t see them and barely feel where they are to get a wrench on there, let alone get a torque wrench down there and be able to see it. Just no room to work.

18

Keith, you didn’t use air to blow out a filter when I worked in a gas station- they were all oil bath:)

I also remember the 37 Pontiac we used to service regularly because it had 37 grease fittings, including one on the water pump.

19

My 55 Chevy and 57 Olds had oil bath filters originally, but I went to a junk yard and got newer paper filters for them.

20

How does the reinforced tubing prevent cross threading? A book mentioned the same thing. I don’t understand what the tubing would do. I should not use a spark plug socket, I should buy a torque wrench? Do they have electronic readouts? How will I know I use the right torque (158 in pounds)? Mechanics take out spark plugs to look at them and tell me if I should replace them. Should I tell them to stop?