Torque Wrench

[jackellis]

The why is a long story but I'm going to be changing a bunch of spark plugs on my airplane in the next week or two. They have to be tightened to exactly 30 foot pounds, so a torque wrench is called for and I don't have one.

Since I don't expect to be using this tool every day, I'm looking for something that strikes a reasonable balance between quality and economy.

Any thoughts?

[Black wallnut]

If you must have exactly 30 pounds of torque then I suggest forgetting about economy and only buying quality.

Methinks uniformity is more important than exact torque but I'm not an aircraft mechanic. If you only need uniformity then you may be happy with a Craftsman click type.

[cwsmith]

I've had a Craftman MicroTorque for years and it works quite well. It's a "click-type". They also make a DigiTorq, but I'm not familiar with it.

But a question for you: Can you do that yourself? I've always been under the impression that any work on your engine had to be by a certified aircraft engine mechanic. Same with work on the fuselage requiring a certified airframe mechanic. Am I wrong in that, or is it for more indepth, specific types of maintenance?

Thanks,

CWS

[phi1l]

But a question for you: Can you do that yourself? I've always been under the impression that any work on your engine had to be by a certified aircraft engine mechanic. Same with work on the fuselage requiring a certified airframe mechanic. Am I wrong in that, or is it for more indepth, specific types of maintenance?

Thanks,

CWS

I am no expert, but I believe it depends on the classification of the airplane. If it is "experimental". I think you can do some things yourself, but inspections are required..


I got a torque wrench in a combo tool set about 35 yrs ago, and have yet to use the thing. But if I ever need it, I have one

[Bill in Buena Park]

+1 on the Craftsman models. I own one each of in-lb and ft-lb "click" types, and they work well.

If you can live within 10-75 ft-lbs, this model is affordable.

[jackellis]

But a question for you: Can you do that yourself? I've always been under the impression that any work on your engine had to be by a certified aircraft engine mechanic. Same with work on the fuselage requiring a certified airframe mechanic. Am I wrong in that, or is it for more indepth, specific types of maintenance?

There are twenty-odd items owners of certificated (production) airplanes can perform themselves, including changing, cleaning and gapping spark plugs; changing oil, replacing fuses and batteries; replacing and repairing non-structural parts. Owners can do many other things under the supervision of someone with an inspection authorization (IA). Owners of experimental (homebuilt) airplanes can do pretty much anything they want

I'm going to be doing this under supervision even though I don't have to. It all started when I had to cancel a flight due to a fouled spark plug. I identified the problem (engine monitor tattled) quite easily and had the tools but I didn't have a replacement plug and I'd never removed or installed a plug before. Another local pilot helped me fix the problem that evening, and that's when I realized there are some simple maintenance items I need to be able to do myself, especially if I happened to be at an airport that did not have a mechanic available. The local mechanic works weekends and takes Mondays and Tuesdays off.

Bill, thanks for the suggestion. Ebay has some Snap-Ons, Matcos and SK Tools wrenches at reasonable prices. There's also one model from Northern Tool that gets good reviews from folks who consider themselves pros. Hopefully a few others will weigh in with their suggestions.

[LinuxRandal]

I own several torque wrenches. (Craftsman, Proto, one no name from Wards, and a Facom)
I did some work on a friends fathers van, and didn't charge him. He, in exchange, took my torque wrenches in and had them calibrated, when he had his done. (yearly for his tools, FAA requirement for his size/type plane).
My BRAND NEW Proto, had evidently had a rough time getting to me, it was way out of spec. His son had two HF (3/8" and 1/4") torque wrenches that he didn't use often, and they were within spec.
Personally, a plane (your life) is not something I would go cheap on. I would find out at the airport, who calibrates them, and take THEIR suggestion, and see if they sell them.

Now a friend of mine is a machinist, who built a Legal Eagle (experimental plane) and he used a cheapy that he has had for some time, and he keeps it in spec. (similar to my old Wards one)

[woodturner]

They have to be tightened to exactly 30 foot pounds, so a torque wrench is called for and I don't have one.

My first suggestion would be to check the specification. It cannot be "exactly" 30 ft-lbs. Torques are usually specified as a range. For a value in that range, one might expect a spec of 28 to 32 ft-lbs, or something like that. It's impossible to set exactly 30 ft-lbs, and that level of precision is not needed.

There are two types of torque wrenches - the click type and the beam type. The click type have to be calibrated regularly and will have a built-in tolerance - so you would want to make sure that the tolerance of the wrench is within the spec range you need. A 5 ft-lb tolerance click wrench will not be able to achieve a +/- 2 ft-lb spec.

The beam time is less expensive, trivially easy to calibrate yourself, and is inherently more accurate. The beam type works by physical principals, the bending of a beam of metal. However, one has to watch the pointer and judge when the pointer has reached the required torque mark on a scale. It's not difficult, but if the fastener is oriented such that you can't read the scale straight on while turning the wrench, a helper will be needed to meet the scale. Beam type wrenches are often accurante to 1/2 ft-lb.

Torques is defined as force at a distance - 1 ft-lb is a 1 lb force at one foot from the fastener. As a result, you can add straight extensions without distorting the measurement, but anything that extends the length of the beam will change the torque reading - so don't use crow's feet, u-joints, etc. with a torque wrench.

It's common to use anti-seize on the spark plug threads for automotive engines. I DON"T KNOW if that is appropriate for aircraft engines or not, but might be a question to ask an aircraft mechanic. The purpose of the anti-seize is to keep the spark plug from seizing over time and also to provide lubrication to ensure the torque spec is met and not distorted by friction (torque on a faster is primarily a way of measuring how much the fastener has stretched, which directly relates to the force required for it to come loose).

[jackellis]

I just re-checked the service manual (instead of relying on word of-mouth) and the spec is 330 in-lbs, + or - 10%. There's only one aircraft repair station up here, and I forgot to ask him what make wrench he uses. Same for the guy who helped me earlier in the week - he said he paid around $80 for his. My wife's BIL is a machinist and he would also probably know.

We do use anti-seize plus new hard copper gaskets each time the plugs are gapped and cleaned, or replaced.

I think I'm going to stick with the click-type tool. Others seem to be able to use them successfully and they're easy to work with, especially for inexperienced users. If I was overhauling an engine, different story.

Thanks for all of the suggestions.

[JoeyGee]

When I worked in a factory, the maintanence guy's favorite expression for "close enough" was always "We ain't building airplane parts". I guess you can't use that in this case...

[JimD]

I use HF torque wrenches. Often available for $20, sometimes even less. This job calls for a 3/8" or maybe even a 1/4". You might not want to go that cheap on this job. I use mine for little things (I torque the plugs in my vehicles, for instance, and a I use my 1/2 inch on my car wheels).

If you've used a click type before you probably do not need this information but all commonly available torque wrenches will allow you to pull past the setting. You get a click but it is not earthshatteringly loud or anything. And if you keep pulling to torque will be above the setting. It could be worth practicing, like by dropping the setting and torqueing the plugs or just torque a bolt in a vise, just to be sure you recognize the "click".

I have a beam type, a Craftsman, that I don't use anymore. I can see where it would be easy to calibrate but you need a standard to calibrate it with. It also seems easy to knock out of calibration.

Jim

[Black wallnut]

One other tip if you buy a click type. Always store it set to zero. If you can find a good deal on a Snap-on / Mac / Matco on ebay that might be what to buy. IIRC Snap-on dealers will re-calibrate theirs for free. Their life time guarantee is good no matter how many times the tool changes ownership.

[Tom Slick]

Does your torque wrench need a certificate of calibration? When I was in the USAF as a turbine engine mechanic our wrenches had to be certified as calibrated every 6 months.

PDI and Proto wrenches are also very good.

[woodturner]

the spec is 330 in-lbs, + or - 10%.

FWIW, by my calculation that is 24.75 ft-lbs to 30.25 ft-lbs. A good click type torque wrench should be able to achieve that tolerance if properly calibrated.

BTW, Autozone and Advance Auto loan out torque wrenches - you "rent" them for the purchase price, use them, then return them for a full refund. AZ calls it "loan a tool", not sure what AA calls it.

If you aren't doing this very often, might be a way to use a higher end tool than the usage might justify.

[woodturner]

I have a beam type, a Craftsman, that I don't use anymore. I can see where it would be easy to calibrate but you need a standard to calibrate it with.

Unlike click type wrenches, beam type wrenches don't need a standard for calibration. Since they work by the physics of the material, the "calibration" is simply making sure the pointer is pointing to zero and adjust it to point to zero if it is not.

Once the pointer is at zero, it's the bending of the metal beam that determines the torque reading.