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Selection, usage and care of torque wrenches

The other day, when nobody was around, a friend asked me (rather sheepishly) to explain exactly what a torque wrench was and how it might be useful to the DIY car owner. It merely underlines the point that brandishing spanners (and the odd hammer!) for years means we can become tad complacent, bandying technical terms around that not everyone understands.

Torque wrenches are essential when working on SAABs

I told my friend that the word torque derives from the Latin toqueo, meaning to twist. In a technical sense, torque is the amount of effort required to achieve a pre-determined degree of tightness (pre load) on a fastener, typically, a nut, bolt or machine screw, when dealing with automotive components. The objective is to make sure that the fastener does not work loose but a fastener's tightness can be compromised by various factors ranging from type of material, quality of manufacture, exposure to vibration to the type of protective coating employed. At best a fastener coming loose may be expensive but at worst, the consequences may prove fatal, especially if dealing with automotive, aircraft or marine applications.

Tightening nuts, bolts and fasteners then, IS an exact science on today's cars and it is no good assuming a nut or bolt is tight because it feels OK. Some fasteners MUST be changed when they have been removed but others may be reused safely. As a rule, there are a lot of aluminium components on SAAB engines and it is essential that torque settings are adhered to strictly if stripped threads are to be avoided. Unfortunately, one torque wrench on its own is unlikely to suffice for working on your SAAB, be it a 9000 or latest shape 9-3, due to the sheer range of different fasteners involved.

Components like cambox covers, for instance don't need to be bar tight on the 9000 but if they are not tight enough they will leak and if they are overtightened, there is a risk that the cover will distort, causing... a leak! You will also find that many fasteners (main bearing caps, for instance) need tightening up in stages, with an initial torque setting followed by a final angular torque. for which an angular torque gauge is essential. This article aims to shed a little light on the subject of torque wrenches and helping the SAAB owner identify fasteners that regularly cause problems or those that definitely need replacing when they have been undone.

Torque wrenches and gauges for the job

Generally, the SAAB owner will need x3 torque wrenches and an angular gauge

Broadly speaking, for most SAABs built after 1993, at least two but probably three different torque wrenches and an angular torque gauge are required. This is because wrenches do not have a range sufficient to cover all values. It is just as important to ensure that the driveshaft nut is tight as say, a cambox cover.

Rather than buy a torque wrench or two for a one off job, you could consider hiring from a tool shop. If spending the money doesn't appeal, consider the possible consequences of NOT spending the money but there is more to tightening fasteners than achieving the right torque on a bolt or nut!

Over-tightening fasteners like studs or bolts can result in damage. Bolts, for instance, can stretch to the point that the figure achieved on the torque wrench is meaningless. Worse still, failure to follow basic procedures can result in bolts or screws bottoming out, so that the torque wrench indicates the requisite torque has been achieved when this is not the case. Another trap for the unwary is oil or gasket material being trapped in a drilling - this would cause major hassle if it were somewhere like the engine backplate (where the flywheel seal is mounted) because a leak here would mean removing the entire power unit. Unlikely? Alas, no - I've seen just this scenario.

Remember that old poem - the one that goes 'For the want of a nail, a shoe was lost...'? Well, rebuilding SAAB engines is something the maker tries to discourage because these are complex units and there is great potential for error but trying to get by without a torque wrench, especailly for achieving the lower range of torque figures is nothing short of lunacy. The author has discovered that rebuilding SAAB engines isn't a black art that involves lighting candles, drawing magic circles around your garage or hanging cloves of garlic around your car but a matter of sheer commonsense, not rushing, keeping everything as clean as possible and above all making sure that fasteners are tightened down to the correct amount.

Ten golden rules to observe:

  • don't mix nuts, bolts or fasteners up: after you remove them, replace on the engine (if possible)
  • wire brush and clean ALL nuts, bolts or fasteners (do NOT use lubricant of any kind!)
  • clean out drillings to ensure there is NO residual oil left
  • check threads on ALL drillings into alloy housings and clean up with a tap & die set (remove all swarf!)
  • clean everything thoroughly! Carbon, dirt, grit and grime are your enemies - don't let them undo your work.
  • inspect all bolts and nuts carefully! Bin and replace any that look suspect -even if it screws up your schedule
  • take care of your torque wrench: don't use it to slacken anything (use a breaker bar instead)
  • don't use solvents or cleaners that might compromise the special grease inside a torque wrench
  • after using your torque wrench, always reset it to its lowest setting
  • ideally, have the torque wrench recalibrated every 12 months/5,000 uses (or after it has been dropped)
    This is a requirement for compliance with European Standard EN ISO 6789:2003

Manufacturers' toque figures apply to DRY fasteners! If you use oil or grease you should reduce the figure by a factor of0.7 to avoid accidental over-tightening and possible stripped threads

NOT using any sort of lubricant on a bolt or nut may seem odd BUT is advisable, for the lubricant materially alters the final tightness. By reducing friction the result is a fastener that is certainly over-tightened and this increases the risk of a stripped thread.

Best practise is to assemble fasteners dry but...
If you have to use a coating of oil (or thread lock), multiply the maker's specified torque by a factor of 0.7 to achieve the correct result.


Problematic fasteners that often cause grief on SAAB applications

9000/ suspension: strut-hub through bolts. These seize and appear to face the wrong way (surely, the threaded part should face backwards, not forwards?). Removal in a hurry mushrooms the ends (great fun!). In our opinion, SAAB only sorted this out with the 2nd gen 9-5. These later cars have a much more satisfactory arrangement in which the through bolt is splined and faces the correct way!

9000/ driveshafts: there is NO need to use thread sealant on the nuts. The author has seen this schoolboy error a good few times. The thread sealant forms a vice like grip and very often, the threaded end of the CVJ is mushroomed trying to separate the driveshaft from the hub. Driveshafts used to be a fast moving line when we broke these cars regularly a couple of years ago. Change the nut and use a torque wrench to avoid this nonsense!

9000/ engine: some units use Torx type fasteners on the sump and timing case. ALWAYS use an impact driver on these, as they have an endearing habit of slipping if you do not.

9000/NG900/9-3/9-5: Change head bolts when ever the cylinder head is removed. The bolts lose their grip over time, leading to oil seepage, especially around the timing case.

Balancer shaft chain tensioners MUST be torqued down correctly to work properly.

B308 V6 Petrol V6 engine: Oil leaks will result if the cambox covers are over-tightened or under-tightened. Use a torque wrench to eliminate this problem.

D308L V6 3.0 Isusu TiD engine: On #NO# account reuse main bearing cap bolts or connecting rod bolts, unless you want the engine to let go big time on the road... NEVER, ever change a clutch on this engine without changing the flywheel, either, as they are prone to failure, resulting in the engine running out of balance. This takes some diagnosing and it would be easy to think that the diesel pump had failed but what actually happens is the engine knock sensor shuts down the fuel supply. The acid test if the car loses power on the road and won't restart is to drop the engine shield and take off the steel part of the two piece sump (the other part is alloy, by the way). Tell tale alloy swarf in the sump is a dead give away that the flywheel has failed and that the main bearings have spun in their housings.


The torque wrenches in our workshop

Our torque wrenches are a mix of Sealey Professional Tools and Halfords brands. The tool we find most useful for working on engines is the Sealey STW 1011. This is a 3/8" drive wrench with a range of 7-112 Nm.

The two Halfords wrenches are for more for general work but especially useful for ensuring wheel bolts and suspension components are tight. The Hal Pro torque wrenches have ranges of 40-200 Nm and 60-330 Nm respectively.

The angular toque gauge is by Sealey and comes in most useful for dealing with cylinder head bolts, connecting rod and main bearing caps.

All these tools have been used extensively and are recommended. Please note that the author and his family have no connection whatever with either the suppliers or makers of any tools featured on the website, so you can be sure that our appraisals are unbiased.

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