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I have a required torque of 30nm +100° +-5°, I have a torque-wrench 40nm-210nm. Can I convert the required setting to my TW somehow?

I'm hoping there is some kind of conversion whereby the 30nm can be adjusted to the minimum setting of my torque-wrench, which is 40nm, possibly by decreasing the angel.

The job involves torquing down a new crank pulley-bolt, after a timing-belt/tensioner replacement, on a K7M engine.

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    In principal, you could add an angle to the end of your wrench and make sure that 40 ft-lb at the vertex of the angle on the TW is the proper component to add vectors to your target torque. In practice, that would be very difficult to do accurately. I would just get a cheap torque wrench from harbor freight. It would almost certainly give you a better result that trying to use you TW with any kind of additional handle.
    – Wren T.
    Jan 18 at 7:45
  • Thanks. Hmm. I live on a different continent, so the delivery charges on a torque-wrench from HF. May be cost prohibitive. Tws in my neck of the woods don't come cheap, either. Manufactured abroad so already have import taxes that make my eyes water. I was thinking more along the lines of some sophisticated mathematical equation like... I don't know, double the torque to 60nm and halve the angle to 50 deg. Probably precisely the wrong thing to do and a bit of a long shot but what to do, right? 40nm - 30nm? Seems like a case of so close and yet so far :-) What did people do before TWs?
    – Jim
    Jan 18 at 8:06
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    Before TWs, it was probably not useful to be so precise.
    – Wren T.
    Jan 18 at 8:14
  • If you can't get a an appropriate torque wrench, you can construct the right geometry. However, I am not sure how to work it out off the top of my head. If you have a given length of bar that you can attach at a particular angle to a TW, I think you can use a dot product to setup the problem and find the unknown (which would be where on the TW to connect the other torquing bar). Does this help? math.stackexchange.com/questions/805954/…
    – Wren T.
    Jan 18 at 8:30

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There is no conversion. The reason is, the degree requirement implies a need to stretch the bolt. You cannot do that with torque alone. The initial torque is to ensure you are at the proper starting point, then the degrees gets the stretch done.

If you do not have an angle guage, the manufacturer was nice enough to actually give you a range of degrees to work with. The "+/- 5°" gives you a fairly broad range. The easiest way to do this without the angle guage is actually by eye. To accomplish this, first, ensure the engine crankshaft is locked in place and will not turn over. Next, torque the bolt to the 30nm to get it set at the initial torque. Then, with a bright marker (something clearly visible on the dark metal), mark a hash line on the bolt head so it is pointing directly up at 12 O'Clock. You only want this mark on the edge of the head of the bolt. Once marked, this should give you a clear indication of how far the bolt is turned. Since 90° is a right angle from where you started, this is very easily discernable. You'll need to go just past this, enough to show the naked eye you are past it, but not by much. This should get you to at least 95° which is within the spec. If you feel froggy and go past that point a bit, still no big deal, because you've got 10° of play to work with. You can also measure the 90° by way of the device you're using to turn the bolt. If you start it at straight up, you can see how far you've turned the bolt, then take it off the bolt and see where the line is at. Your mark should end up between the 3 and 4 O'clock position. Please note, you want to err on the side of caution and not turn the bolt too far. Reason is, there's no turning back, or rather, you can't back the bolt off to get back to the proper degree of turning the bolt.

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  • Right, makes sense. This would account for the advice to change the bolt after having removed it for the belt replacements. I cannot afford another TW though, way out of my pocket range.... cross your fingers for me. Having said that, could I not do a best estimate, put it back together and - sometime in the near future - take the vehicle to someone with the proper tools to have them check the torque?
    – Jim
    Jan 18 at 11:49
  • @Jim - Not really. I't is more or less "all or nothing". I'd bet you'll have absolutely no issues if you follow my directions. You might want to modify my instructions just a little bit. When you mark the crank bolt, mark the harmonic balancer (or whatever the bolt is keeping on the crank) at the same place. That way you can see the difference between the two marks, just incase the crankshaft moves a little while you're doing this.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jan 18 at 12:42
  • I had the sense to mark the bolt at 12 o'clock but when I tightened it, I noticed the balancer was slightly off. Now, sadly - but hopefully not too sadly - your advice came fractionally late for me, otherwise I would have been a little slower to tighten her up past the 30nm torque. Remember too, though, that my TW only starts at 40nm. Which is what the original question was about. Long story short, I had no idea this job would end up costing me so much and so the thought of yet more cost, in terms of tooling, was enough for me to go with my best judgement. Your input is appreciated though.
    – Jim
    Jan 18 at 13:01
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    @Jim - Best judgement is sometimes all you have. I did miss that in your original question, so my apologies. I know this is water under the bridge at this point, however, if you have a click type torque wrench, you could have backed it off to get to 30nm (below the labeled marking) by counting the clicks. While this would not produce a perfect reading, it would have put you in the ball park and most well enough to complete the job without worry.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jan 18 at 13:15
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    @Paulster2 Thank-you for that advice. I've learned a lot in the last few weeks. Both new belts(timing and serp') on, both new tensioners on, new crank-bolt on, spark-plugs cleaned and back in, covers, engine mounting and wheel next, and then it's disco time or crash and burn.
    – Jim
    Jan 18 at 13:41

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