Hello all. Been using torque wrenches for over 50 years. Always store them with the spring backed right off, but not so loose that it rattles. (Been doing this since I got a hefty clip round the ear'ole in the '60's whilst at college, for handing one back to the storeman with it still tensioned!)
I started college with a cantilever box of, mostly poor quality, mixed spanners and screwdrivers I'd collected as my juvenile interrest in cars, motor bikes and Go-carts grew. It wasn't long before I got involved with building beach buggies and fast road cars, Minis, Anglias, Mk1 Cortinas, etc for which I needed some better tools. I think it was a small tool shop near Chiswick Bridge where I bought my first "quality" tools - A large, Kampmann brand, A/F and Whit socket set, German made and of excellent quality which I still have, with a free beam type torque wrench 0-150 lb ft. Wowee! As I settled down to working in the garage trade I bought mostly Britool branded tools and so, about 8 years later, when I noticed that the beam of the torque wrench had a very slight bend in it after use on a hub nut. (150lb ft had been too much for it!) I bought a "click type" Britool 20-100 lbs ft torque wrench (the one you see everywhere with the red bobble on the adjusting lever - expensive purchase at the time with a growing young family in tow!). Many years then went past and I never gave calibration much thought, although I did, Very occassionally, put it "back to back" with the current shop tool and see if they both clicked at approx the same point. Never had any known problems. No blown head gasket comebacks or brake caliper carrier bolts coming loose!
By the late '80's early '90's I was much less on the tools from day to day but still very active at home on classic stuff (Hillman Imps featured heavily), old horticultural machines and modern family vehicles. These all have one thing in common, a lot of aluminium castings which don't take kindly to overtightened fixings. So I had a good think because I had had a few stripped out threads when using the Britool wrench. Thought that getting it checked over and recalibrated would be a good idea but got a nasty shock at what was being charged! Wish I lived near you Liftex, £10 sounds like a dream! Anyway at that time I was friendly with the local Halfords workshop manager (back in Edinburgh at this time), who told me that a lot of the local mechanics just bought a new "budget" brand torque wrench every two years rather than paying to recalibrate as the cost worked out the same. So this went round in my head for a while until I had an Imp engine to rebuild. Imp head bolts are notorious for stripping threads so I went out and bought a Norbar 20-110 lb ft wrench! I know, not a cheapie, but I wanted reliability. Must have been "high" on the experience because a short while later bought a small 3/8" drive Halfords (actually, I think, made by Norbar?) 6-44 lb ft wrench because there are now so many small (10mm etc) nuts and bolts on cars and horticultural stuff these days. In my opinion a very good wrench by the way! Around about this time I was also given a 50-250 ft lb Britool torque wrench (nick named "Big Bertha" immediately) all in pieces, in a large cardboard box! I was told it was "all there" - He lied, but it was free!
Ok, fast forward to just a few years ago. Even the "new" wrenches are now at least 15 years old and, although they are only seeing "hobby" use, I started wondering if they were still accurate? Biggish jobs comming up on my older boy's Punto and younger one's Astra. Well maybe I should get just the Norbar 20-110 lb ft wrench checked out? (I particularly like the feel of this wrench and it has a ratcheting mechanism which the Britools don't) Then I came accross a site on You Tube which showed someone checking out a click type torque wrench using a digital torque adaptor. Hmmm. This looks interresting? So I started looking around to see what's available and how much they cost. At the same time I had a CV joint to do on younger son's Astra and, for reasons not worth mentioning, I had to remove and refit a driveshaft on my wife's '92 Panda Parade. With the Norbar only going to 110 lb ft I would ussually do up the hub centre nut with my 3/4 drive sockets and a short leangth of scaffold pole on the "T" bar handle. I turned up a thing called a Clarke Pro 1/2" drive Digital Adaptor which went from 22 to 265 lb ft. It was reasonably priced (can't actually remember how much) but it was even cheaper when I bought it from Machine Mart on one of their VAT free events! As it is interposed between the socket and the "T" bar it adds considerably to the working depth of the head of the tool but worked beautifully on the hubs.
Having, at that time, finished the current crop of maintenance tasks I then had time to think about using the Clarke to check the wrenches. The output side of the adaptor (1/2" square drive) needs to be very securely held. I though of simply gripping it in my vice but that would mark up the faces. Then I realised I could hold my oxygen sensor socket, which has a cut away side, in the vice with my aluminium soft jaws to prevent marking and insert the adaptor into the top of this. I decide to do a first test, at mid range, on all the wrenches. So set up the Norbar for 65 lb ft, stuck it in the top of the adaptor and, slowly and as smoothly as I could, pulled it round to the click whilst watching the scale reading on the adaptor. You can "tell" the adaptor to indicate actual torque being applied (in which case it displays the actual increasing value as you pull harder and harder - useful for this) or you can set it to "beep" when a set calibrated figure is reached (useful if you are using the adaptor on its own as a torque wrench in its own right). I found that, at first, I was not getting very repeatable readings but as you do it more and get smoother at doing it, the readings get more consistent. Once I'd got used to it I found that by repeating each sample 5 times and taking the 3 nearest readings I could get a pretty consistent reading. - you get better at it the more you do it.
So what was the outcome? The 2 Norbars (20-110 and 6-44 lb ft) were pretty much spot on. Perhaps that was predictable as they are the youngest but seems to support that winding back the springs for storage is the way to go. My trusty old pal the 20-100 lb ft Britool gave me a surprise. As it was so old I had been expecting it to read low as it is logical to expect the spring to have relaxed somewhat. But none of it! the readings were measureably higher! Well that explains the occassional stripped fixing I was getting. But why? Having "Big Bertha" in pieces in a box (mentioned earlier) I could see exactly how to overcome the safety stop that stops you unwinding the handle all the way. So, as I have the Norbar anyway, I stripped the Britool right down. It was filthy inside. Dirt and dust and congealed lubricant actually meant I had to make a stout wire hook to fish the spring out with! I was shocked because I thought I'd looked after it! I cleaned it all up with solvent and lubed it with silicon oil as I thought this would attract dirt and dust less than conventional oils. I then reassembled it all and, on test, it reads just very slightly low which was to be expected and, as I now know what it's doing, makes it a very useable spare. Out of interrest I then tested them all at 1/3, 1/2 and 3/4 scale deflection. If you draw a graph of the results there is slight non linearity in the results. I believe most of the manufacturers say that settings at either extreme of the range are not especially accurate so that was why I chose to do my checks in this way.
Close inspection of "Big Bertha" in comparison with "Little Bertha"? (the smaller Britool) would seem to confirm that everything is there except the little locking pin that stops you unwinding the handle fully. Strangely the tiny spring is still hiding down it's hole! Most annoyingly, the shims for the main spring which allow you to fine tune it, are missing. If I can find a source of shims I'm going to have a go at rebuilding it. The Clarke tool is quite bulky so it works well on something like a hub nut but is unuseable in tight corners. Having Big Bertha available would give me good options for doing, for instance perhaps, crank pulley bolts and the like where space is at a premium. I may however, have to do a weight lifting course to build up enough muscle to pull anywhere near 250 lb ft!
I rang Clarke, the manufacturer of the digital torque adaptor, as there were a few things I wanted to ask them. I hope I have understood correctly as I asked questions on a number of points, but I believe there is no need to periodically have the device checked for calibration, or not 'till it gets really old anyway. You do need to do a periodic reset though - simply requires two buttons to be pressed at the same time - This allows the device to reset as battery voltage falls slightly in use and improves its accuracy. There is a seperate warning display on the panel for when the battery needs changing.
So there you are. An inside glimpse into just one of the exciting activities that is my life since retirement! Hope at least one or two of you are still awake? This digital adaptor is proving really useful and I've used it, mostly on hub nuts, a few times now to good effect. Well, my turn to make the tea tonight so I'm off to make Panini pizza slices. Salami, cheddar cheese and, sliced in quarters, baby plum tomatoes on halfed Panini rolls toasted under the grill. Yum Yum!
