A Low Cost 300 ft-lb Torque Wrench - DIY Shop-Built

Bambusiero

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Here is a low cost 300 ft-lb DIY shop-built torque wrench - to handle re-installation of that big 30mm 304 ft-lb harmonic balancer - crankshaft bolt.

This is needed when you replace the front main seal and / or the oil pump cover plate o-ring, which are common oil leaks at the front of the 80-Series 1FZ-FE engine.

Principle of Operation :
The well known "torque wrench extension". Usually, this is used to compensate the wrench's setting for the added length caused by some special tool end added to the wrench, like an open end crows foot.

In this case, however, the usage is a long cheater bar added to your regular 150 ft-lb 1/2" torque wrench, multiplying it's torque setting. The torque applied by the overall tool is the torque wrench click setting, multiplied by the leverage ratio of the total length of the tool, relative to the wrench length. Wrench length is to the middle of the handle, not the full handle length.

Lw = Length of wrench = 16" to middle of handle (overall length is 18")
Lt = Length of tool (cheater bar) = 28", from pivot to pivot.
M = Multiplier ratio of your wrench's torque click setting
Tt = Torque applied by the tool, overall
Tw = Torque wrench click setting

M = ( Lt + Lw ) / Lw = ( 28" + 16" ) / 16" = 2.75

Tw = Tt / M = 304 ft-lb / 2.75 = 110.5 ft-lb (Torque wrench click setting)

Tt = Tw * M = 110 ft-lb * 2.75 = 302.5 ft-lb (close enough to the 304 ft-lb spec)

Maximum torque capacity with this 2.75 multiplier would be 412 ft-lb (at 150ft-lb setting), if you have use for such a monster.

I chose 2.75 because 3.0 (32" tool) looked like the wrench handle might hit the hood latch. Effort to get "click" at 110 ft-lb setting was no problem.

Tools and Materials Required :

1) 3/4" drive breaker bar.
2) 30mm x 3/4" drive 6-point socket, standard depth.
3) 1/2" drive 150 ft-lb torque wrench.
4) 7/8" or 1" x 1/2" drive socket, to be sacrificed by welding to the tool.
You could get one from the junk tool bin at your friendly neighborhood pawn shop, for instance.
5) 1.75" or 1.5" O.D. x 1/8" heavy wall steel tubing x 27 3/8" long.
Just make sure it's inside diameter will fit over the handle of the breaker bar.
6) Welder - MIG, stick - whatever you have.
7) Angle grinder, files, band saw, etc. - for weld fit up.
8) shop press, big vice, big hammer - something to squash the pipe a bit at one end.

Figure out the tube length needed, subtracting for the breaker bar hinge at the socket end, so the length to center of rotation comes out right. In my case, the tube length was 5/8" shorter than the tool design length.

Flatten one end of the tube so both sides of the tube can be welded to the 1/2" socket.

Cut or grind out a weld fit-up pocket into the flattened end of the tube to fit the outside diameter of the 1/2" socket.

Weld the socket onto the tube.

Torque on, dude!

In use:
TorqueWrenchExtension_InUse1.jpg


Tool assembly layout:
TorqueWrenchExtension_Assembly.jpg


The socket end:
TorqueWrenchExtension_Socket.jpg


1/2" adapter end, side view (squashed):
TorqueWrenchExtension_AdaptorSide.jpg


1/2" adapter end, top view:
TorqueWrenchExtension_AdaptorFace.jpg


p.s. One could use this same principle in reverse, to reduce the torque of a common 150ft-lb wrench to some much smaller range. % error would scale down as well, so accuracy should be good. Details left as an exercise for the reader.
 
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IIRC an impact socket should not be used when torquing fasteners because they are softer than standard sockets and this can impact measurement. Setup looks really cool though, a better system than slipping tubing over the torque wrench.
 

bloc

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IIRC an impact socket should not be used when torquing fasteners because they are softer than standard sockets and this can impact measurement. Setup looks really cool though, a better system than slipping tubing over the torque wrench.
Really? Ultimately the same amount of torque is getting applied, correct?

Granted, there isn't the pulsing/hammering action that they are designed to survive..
 

Bambusiero

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"IIRC an impact socket should not be used when torquing fasteners because they are softer than standard sockets and this can impact measurement."

It had no "impact" on the matter. :D
 

LINUS

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IIRC an impact socket should not be used when torquing fasteners because they are softer than standard sockets and this can impact measurement. Setup looks really cool though, a better system than slipping tubing over the torque wrench.

I've never heard this way, --working in chemical refineries as both an operator & as a mechanic where each step of a job done has a S.O.P. - in fact, if only one socket was packed to a jobsite, (common when 3/4" or 1" drive) impact was all there was in the tool / shop inventory, esp for some larger sizes like 1 1/4" or larger studs that use 2 nuts on flanges & you rigged the impact gun prior to packing it to flange being worked (guns use a rubber ring w/ a steel cotter to hold socket in gun, hard to do with gloves on, so we did in shop beforehand when gathering tools) - maybe the larger size socket have the mass to be rigid enough? (Total guess)

I have heard the flipside, not to use std chrome dipped ones for impact - but the myth was fear of the "socket exploding" - real world never saw more than splitting longside in the wall where thin between the thicker "flats" that grab the nut, or rounded corners of the drive end square hole. I only have experience there with 1/2" drive max though, no larger.

------
@ OP - like that idea, brains over $$$ solution! I honestly never learned the math to do as you did, so I envy your skill / ingenuity there!
 

bloc

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I have heard the flipside, not to use std chrome dipped ones for impact - but the myth was fear of the "socket exploding" - real world never saw more than splitting longside in the wall where thin between the thicker "flats" that grab the nut, or rounded corners of the drive end square hole. I only have experience there with 1/2" drive max though, no larger.
My cordless 3/8" impact rounded the square corners on a number of my regular chrome sockets before I invested in a set of 3/8 deep metric impact grade ones.. but no explosions.


Btw that 3/8" 20v dewalt cordless impact is an incredible time saver when doing anything with more than a few bolts. Front end rebuild, part-time install, even zip off fully torqued lug nuts. I'll usually use the 1/4" impact for reassembly.. gets things nicely into the "before I get the torque wrench" range.
 

tominboise

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Very interesting. Another option would be to use a breaker bar / cheater bar of known length and a fish scale at the end to measure the force applied. 300 ft lbs with a 36" total length wrench = 100 pounds applied at the end.
 

dogfishlake

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Very nice work. I will probably have one of those on the tool wall next time i need to remove the balancer bolt. Thanks for doing the math!
 

Bambusiero

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In all fairness, I didn't invent this thing. The idea has been around forever. I wasn't really aware of that, but it has.
In fact, after finding the basic formula on wikipedia, if I recall, I also found it on the instruction sheet for my torque wrench.
Not as a cheater bar multiplier, mind you, but the formula is the same for correction factor of an add-on tool end.
I might venture to guess that every well trained automotive mechanic has probably seen it in a text book, and maybe forgotten it.
Another fellow in the tools forum did something similar with a big flat bar welded to socket extensions.

I think I mulled over this job for several weeks, wondering where I was going to get a big-ass torque wrench, like many others here suggested.
I thought about the fish scale idea. But I don't have a 100 lb fish scale either. Buy one? The idea sours.
How about a small jack on a bathroom scale? Nuts! ("Not MY scale!", the wife said.)

But, you need the 3/4" drive breaker bar anyway, to get the thing off in the first place, lashed under the frame & bump the starter.
That idea works beautifully, BTW.
At some point, the thought of "leveraging" that same breaker bar just made sense (pun intended).

This tool probably took me 3 hours to build, scrounging around for likely materials and all, and about 5 minutes to use. Done. :beer:

Anyhow, lots of folks have to do this job, so hopefully, this will make it easier for someone.
 
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Hornd

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I was going to do the same, but didn't want to invest 3 hours for a tool I will likely never use again.
Slipped a pipe over the HF 3/4" Breaker Bar and went till I felt it was good and tight.

I called the dealership, I called the CAT Dealer, I called the Tool Rental Shops. The dealership told me that would tighten the bolt at 1 hour labor. Then I had to tow it there from my house.

Thou I will likely never know the final torque; I feel comfortable with it. Unless your checking every bolts torque on your used rig your taking the same risk. If your worried, paint mark or Sharpie Witness mark bolt, and check it every time you check your oil.
 
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