How much to tighten spark plugs

[Ronnie]

So there are a few threads on this already but I can’t recall one with pics of the manufacturers instructions.

I tried to do this with a torque wrench once, once because I tightened the plugs a lot more than 1/2 to 2/3rds rotation passed hand tight when I used the torque wrench. May be I had a faulty torque wrench.

What do you think the last image is of/means?

 

[InmyElement]

I'm assuming that what it means, but I've gone with Yamaha's recommendation 18.5 ft lbs on the plugs and 6.2 on the coil bolts since it was new. Never an issue getting plugs out or over tightening, which I have a bad habit of doing. I even torque the oil filters.

3/8-in Drive Digital Torque Wrench | CRAFTSMAN

3/8-in. Drive Digital Torque Wrench provides convenience to the user by converting torque from ft./lbs. to in/lbs. to Nm with a touch of a bottom. An LED backlit screen makes it easy to see every ...

www.craftsman.com

 

[Ronnie]

I'm assuming that what it means, but I've gone with Yamaha's recommendation 18.5 ft lbs on the plugs and 6.2 on the coil bolts since it was new. Never an issue getting plugs out or over tightening, which I have a bad habit of doing. I even torque the oil filters.

3/8-in Drive Digital Torque Wrench | CRAFTSMAN

3/8-in. Drive Digital Torque Wrench provides convenience to the user by converting torque from ft./lbs. to in/lbs. to Nm with a touch of a bottom. An LED backlit screen makes it easy to see every ...

www.craftsman.com

Although I believe this tool would, if used properly, tighten the spark plugs to Yamaha’s recommended specifications, at a cost of over $200 including sales tax in CA (or even at $190 out the door), I’m going to keep following the directions on the box since I don’t have to spend any more money to do so. I’m willing to invest some money into a decent torque wrench but not that much money.

 

[drewkaree]

@Ronnie here's a decent torque wrench for you. I've got all 3 common sizes (1/4, 3/8, 1/2). Decent value

https://www.amazon.com/TEKTON-24330-8-Inch-ft-lb-13-6-108-5/dp/B00FMPKAD0

 

[mpecoraro]

@drewkaree and @Ronnie do you find that those wrenches are accurate on the low end range? I'm looking for a torque wrench in the 5-50 ft lb range. Bonus points to somebody that knows of one made in the USA. Thanks!

 

[drewkaree]

Mine is good enough for low end ranges, I never found anything that went lower, for reasonable prices. I think my plugs were 13 ft/lbs, so Ronnie's wrench wouldn't even work in my case.

 

[2kwik4u]

@drewkaree and @Ronnie do you find that those wrenches are accurate on the low end range? I'm looking for a torque wrench in the 5-50 ft lb range. Bonus points to somebody that knows of one made in the USA. Thanks!

I've had Tektons Verified/Calibrated before for Space Flight Hardware Assembly. They typically show up in spec, and stay that way if you don't beat them up. Don't use them like a ratchet, and don't loosen bolts with them. Use a ratchet to get close (in either direction), then use the Torque Wrench to finish them up to spec.

If you need a "lower range" torque wrench get a smaller version, and try to stay in the "middle" of the available range. I've used these for in-lbf level use in the past with good success.

Remember you can easily convert from in-lbf to ft-lbf by multiplying/dividing by 12. for Example 10ft-lbf is 120in-lbf. So the smaller wrench I have linked above will get you 1.6ft-lbf to 16.7ft-lbf (20-200 in-lbf).

As for spark plugs. Either method is fine. And to risk opening a can of worms, so is Anti-sieze. Either is fine. Use what you're comfortable with, we're all in the same ballpark here.

 

[WREKS]

9.4 ft lbs on MR-1 plugs. 6 bolts holding cylinder head cover screw into camshaft caps. Be very careful with those. They strip so easy. Each time they are torqued may change the torque value. I do not know if camshaft caps are even available.

 

[Ronnie]

I may be buying a full set of Tekton torque wrenches in the future (if I can’t borrow a good one from my retired mechanic neighbor) but don’t plan on using them to install spark plugs. In my opinion there is little or no risk of over tightening spark plugs by using the hand tighten plus 1/2 to 2/3rd rotation with a standard ratchet wrench method. In this scenario I don’t have to have a properly calibrated torque wrench nor do I have to look up the recommended torque spec, just follow the instructions on the box to collapse the crush washer, done.

I think the last image on the box is that of an ultra light and small plane analogous to a personal water craft and the instruction is not to use the spark plugs in such craft. What do you all think?

 

[Babin Farms]

Changed thousands of plugs and never used a torque wrench. Good-n-snug by using just the right hand only on the ratchet and after so many times you just know the feeling when it’s enough. Don’t overthink this, they’re just spark plugs.

 

[HangOutdoors]

I have been doing Snug then 1/4 turn. I bought a 3/8" Torque wrench when I did my front brakes over the summer. Was thinking of using that next time. It goes down to 5 ft. lbs.

 

[drewkaree]

I may be buying a full set of Tekton torque wrenches in the future (if I can’t borrow a good one from my retired mechanic neighbor) but don’t plan on using them to install spark plugs. In my opinion there is little or no risk of over tightening spark plugs by using the hand tighten plus 1/2 to 2/3rd rotation with a standard ratchet wrench method. In this scenario I don’t have to have a properly calibrated torque wrench nor do I have to look up the recommended torque spec, just follow the instructions on the box to collapse the crush washer, done.

I think the last image on the box is that of an ultra light and small plane analogous to a personal water craft and the instruction is not to use the spark plugs in such craft. What do you all think?

View attachment 167256

Too blurry for my old eyes, even with glasses

 

[TreeRX]

18.4 ft. lbs. for the plugs
ignition coils 5.9 ft. lbs. These bolts are also supposed to get thread sealer as per the service manual.

 

[Can0n11]

I may be buying a full set of Tekton torque wrenches in the future (if I can’t borrow a good one from my retired mechanic neighbor) but don’t plan on using them to install spark plugs. In my opinion there is little or no risk of over tightening spark plugs by using the hand tighten plus 1/2 to 2/3rd rotation with a standard ratchet wrench method. In this scenario I don’t have to have a properly calibrated torque wrench nor do I have to look up the recommended torque spec, just follow the instructions on the box to collapse the crush washer, done.

I think the last image on the box is that of an ultra light and small plane analogous to a personal water craft and the instruction is not to use the spark plugs in such craft. What do you all think?

View attachment 167256

Just curious on if you have been using Iridium plugs and if so what kind of wear you are seeing in those plugs. We are seeing plugs making TBO @2000 hours in our aircraft as opposed to 400 hours for standard plugs. We live or die by manufacture manuals and have to document torque etc so I am inclined to follow the Yamaha manual that specifies torque that Tree provided in his post. Most of our aircraft manuals provide for torque values for wet torques but my FSH manual and Tree's doesn't state the use of anti seize so I would be hesitant to use it. Another ignition best practice is cleaning and drying your harness boots which is essential to prevent well flash-over, Not so much an issue probably with this type of ignition harness used by Yamaha and I have seen other poster's suggestions (in other posts) of dielectric grease to prevent this. That is also another compound not listed in the manual. I haven't had to replace plugs yet in my boat and am interested in the longevity of iridium in these higher RPM engines.

 

[Ronnie]

Just curious on if you have been using Iridium plugs and if so what kind of wear you are seeing in those plugs. We are seeing plugs making TBO @2000 hours in our aircraft as opposed to 400 hours for standard plugs. We live or die by manufacture manuals and have to document torque etc so I am inclined to follow the Yamaha manual that specifies torque that Tree provided in his post. Most of our aircraft manuals provide for torque values for wet torques but my FSH manual and Tree's doesn't state the use of anti seize so I would be hesitant to use it. Another ignition best practice is cleaning and drying your harness boots which is essential to prevent well flash-over, Not so much an issue probably with this type of ignition harness used by Yamaha and I have seen other poster's suggestions (in other posts) of dielectric grease to prevent this. That is also another compound not listed in the manual. I haven't had to replace plugs yet in my boat and am interested in the longevity of iridium in these higher RPM engines.

I can’t speak to how much longer an iridium plug lasts compared to a non-iridium because I used to replace iridium plugs every two years now I replaced the plugs every year with the same model (non iridium) that came with the boat. What I do recall is that iridium were $12 each the last time I bought them (pre Covid plus a few years). Whereas I just paid $8 per conventional plug.

I have always read that you cannot legally use auto parts in aircraft. I met a private heli pilot years ago who was a member and landed his helicopter at the rc airfiled. He showed me car starter or alternator that he installed on his heli and said the only difference was the aviation model was certified/faa approved and cost three time more than the auto model. Dielectric grease isn’t in the manual but it makes sense to me so I use it along with stabil and anti seize. The latter is discussed by several posts here but summarily sometimes the plug in cylinder three gets stuck and / or it breaks apart when it is removed, anti seize is supposed to reduce the chances this will happen.

 

[2kwik4u]

@Ronnie I think you're right. I wouldn't use those plugs in an airplane or personal aviation device based on that graphic.

Have a buddy that builds his own airplanes (he's on #3 now). I'll shoot him a message and see what his thoughts are on WHY you shouldn't do that.

 

[Can0n11]

You definitely cant use non FAA-PMA approved parts in a certificated aircraft. Our Continental IO360 engines use 2 Iridium plugs per cylinder that are ridiculously expensive but work great. A great deal of care must be taken when cleaning or adjusting gaps. Cleaner and tester units are really nice bench additions but you are looking at 600-2k$. If you use anti seize type is important, and over torquing can cause plug failure as well. Our engine manuals spell out wet torque and use of specific oil or anti-sieze as do our Champion manuals etc. The AC circular 43-13-1A and 2B are great reads for you motor heads and modifiers. Interesting to note that your Lowes Hardware bolt might have a tensile strength of 50000 psi and the same size AN Bolt strength would be upwards of 120,00psi.
As far as torque- Section 7-40 is good stuff, as it relates to aircraft. http://rvplane.com/pdf/AC43.13-Chapter 07.pdf

 

[Ronnie]

@Can0n11 , wow, a few more document references and I’d be asking the moderators for an “over my head” emoji/pictorial response . I’m glad people like you exist and hope people like you maintain the planes I fly on.

 

[tkeru408]

@drewkaree and @Ronnie do you find that those wrenches are accurate on the low end range? I'm looking for a torque wrench in the 5-50 ft lb range. Bonus points to somebody that knows of one made in the USA. Thanks!

I use the smallest wrench on that Amazon link for my mountain bike and it always seems to work fine, though I've never specifically tested its accuracy. It's 20-200 inch-lbs (1.67-16.67 ft-lbs), so even on the low side of what you mentioned.

 

[RobbieO]

So there are a few threads on this already but I can’t recall one with pics of the manufacturers instructions.
View attachment 167219View attachment 167220
I tried to do this with a torque wrench once, once because I tightened the plugs a lot more than 1/2 to 2/3rds rotation passed hand tight when I used the torque wrench. May be I had a faulty torque wrench.

What do you think the last image is of/means?

I wouldn't use a torque wrench, unless you have a torque spec. The illustration is deceiving IMO. It doesn't even illustrate a 1/2-2/3 turn.