Occasionally I come across a product which was sold for a particular application, but the product marketing team didn't do their homework, missed a trick and a potential market for other uses.
I've wrestled with high torque fasteners on my K-bike for a while now and when I met the 200Nm 150 ft-lb torque on the pinion nut decided to look into other options. Last time I was fighting the reaction torque from a very long bar and got bruised knuckles after the socket slipped.
I've had Norbar clicker type 1/2" torque wrenches for years. They are workshop quality and I check their calibration against my spring balances after extending the normal grip handle to about 3-4 feet.
My highest torque wrench limits out at 150 Nm (110ft-lb). After doing research, I find the max torque spec. for most affordable wrenches is 200Nm (150ft-lb). However their accuracy at that level can be questionable and they often come with short 18" handles. That's just not enough when you are tightening a pinion nut to 200Nm. Ideally you need a 2-3 foot handle. After more research I find the pro shops working with high torques on commercial vehicles use a 3/4 drive and 3 foot long torque wrenches. But these are expensive tools.
Another issue I have is the torque 'reaction' - That's the effort you are putting on the torque wrench and the strength of the support that's holding what you are tightening. For a rear drive pinion nut you definitely need a BIG strong vise fixed to something substantial.
Now I've been interested in impact wrenches for a while. They apply torque in stages using a balanced small hammer system. This means there is virtually no 'reaction' at the handle for very high torques. However the thing you are tightening still has to be fixed rigid preferably with some mass like a heavy vise.
The downside of impact wrenches of the air type is their setting torque is rather nebulus and results are rarely repeatable. That's why your car lug nuts are often over tightened by the tire shop.
******Then I come across a 12 volt dc impact wrench with a 3 digit electronic torque display readout and auto torque shut off. They marketed them to petrol heads for tightening wheel nuts originally for around £80, but they are now selling for £30. Their torque range is 80-350Nm (59-258 ft-lb)******
So I'm thinking probably Chinese, may be not well made and with simple ineffective innacurate electronic torque control.
I ordered one for £30 from these people, but they seem to be sold under different names. If they look like mine then they are probably the same and I've seen them on USA sites and Fleabay. My unit says it's a TT607C
When it arrived I was surprised at its weight and overall quality. Time to pull it apart and see if it has potential as a high torque wrench tool. What I'm after is accuracy close to my present clicker wrenches or better and important repeatability.
I've attached some pics of the internals. The 12 volt dc motor is connected by steel stepdown gears to a cylindrical assembly containing 3 'hammers'. As the assembly rotates, the hammers put a rotational impact on the socket shaft. A power mosfet in series with the dc motor is controlled by a microprocessor which also runs the 3 digit led display. The motor current appears to be sensed on the controller board and they are probably using this as the torque feedback to compare with the preset value.
I've been practising on a spare RD pinion nut with a spec torque of 200 Nm. At 100 Nm the tool whirrs for about 2 seconds, the first impact blow occurs giving a torque reading of about 30 Nm. Then a second impact blow occurs sending the torque reading to 70Nm and finally a third impact put up the message END. For 200Nm torque there are 5 stages of impact blows.
Now the burning question: 'Is it accurate and repeatable?'
I tested my impact tool from 80-200Nm by tighting the pinion nut in 10Nm steps from 80Nm and checking with a 4 foot socket bar and spring balance for the point when the nut could be just moved up from the torque set by the impact wrench. This point was consistently similar with a 5-10Nm error when checked against the spring balance, and my clicker torque wrench up to its max setting. I could not say if other tools will perform the same and it's probably best to make your own calibration checks. I cannot see there is anything to drift out of calibration, but the voltage source is probably important. I used a full charged battery, but I'm about to try a 12V dc regulated mains power supply like this:
Here is a list of high torque specs for the KRS from Clymer:
Rear wheel mounting bolts 105Nm
Clutch nut 140Nm then 50Nm and 60 degrees
Upper Fork Bridge
Front suspension ball joint 230Nm
Front suspension ball joint hex nut 130Nm
Lower Fork Bridge
Ball Joint 230Nm
Ball Joint nut 130Nm
Suspension A arm
Ball joint at lower fork bridge 130Nm
Pivot shaft nut at frame 107Nm
Pinion nut 200Nm
Threaded ring 118Nm
Final Drive to Swingarm
Fixed bearing journal 160Nm
Float bearing journal locknut 160Nm
Rear swingarm to frame
Left & right bearing journals 160Nm
Right side (?) 200Nm
Overall, I was impressed by the build quality, design and performance for a price that seems a steal. It appears to set high torques consistently on fasteners other than wheel lugs.
However I would add a note of caution. If there are fasteners being undone which may have been Loctited, you have no 'feel' or feedback when threads may still be locked and require more heat. There is a risk, particularly on the swingarm journals, that the aluminium threads could be chewed up if the removal torque is set too high.
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