upstate bob

old sears craftsman beam bar and some harbor freight clickers.

jcorenman

Fred,

Cylinder heads are basically clamped in place by the tension of relatively long bolts or studs. The blocks and heads are aluminum in this case (different alloys) and secured by steel fasteners, all with differing coefficients of expansion. So the elastic nature of the bolts/studs is very much part of the equation. The tension must be high enough to properly clamp the head against combustion pressure over a wide temperature range, but not so high as to exceed the elastic limit of the fasteners. And it must be able to be properly reassembled by your average trained tech at the dealership.

The WSM, as updated over the years by the various Tech-Spec booklets and Tech Bulletins over the years, specify either torque or angular tightening-- but not both. In the early references an initial torquing to 20NM is specified, followed by two rounds of progressively higher torque values without regard to angle. In the later references the same initial torque is specified, but the subsequent tightening is by angle without regard to torque.

Clearly, if the goal is to tighten a fastener to a specified amount of stretch, then in theory either the tension (i.e. torque) or elongation (i.e. angle) can be measured. The torque represents the desired tension, the angle represents the desired amount of stretch. For a given set of bolts or studs, the relationship between tension and torque is known in theory, as is the elastic limit.

The problem with torque is friction: in practice a large fraction of the applied torque goes into friction of the threads, which subtracts from the torque that is related to tension. The WSM specifies "light machine oil". Grease the threads instead, or simply use anti-seize, and the tension goes way up for the same torque and the threads will fail. Similarly, if assembled with dry threads then more torque goes into friction and the tension on the fastener goes down. Used fasteners (with worn/polished threads) will likely behave differently from used ones. The differences are like 20-30%, non-trivial.

The problem with angle is that the relationship between tension and stretch for the fastener is a complete unknown, in practice. For new fasteners, at the factory, this was simple-- the engineers did some tests and told the assembly techs what to do. As Greg said, it is a different story now. Used parts may be new or old style (hopefully not mixed), may have been stressed beyond the yield point (overheated engine, anyone?), threads (male or female) may or may not be damaged, new parts may or may not meet the original spec.

So measuring both torque and angle is the only sensible way to know whether the parts are behaving as designed. If the torque falls off as the fastener is tightened then either the fastener is yielding or the threads are failing. If the torque gets high then the fastener is work-hardened and brittle, and the threads will fail before the angle is reached.

The Gear-Wrench angle wrench, and the Snap-On "TechAngle" wrenches referenced above are both perfect for this job. A "beam" wrench or the older Snap-On "Torqometer" wrenches will do the torque job, if you add some way to measure angle with sufficient accuracy. I bought a lightly-used Snap-On TechAngle (ATECH3FR250) on eBay a few years back for less than $300, a very nice tool.

Personally I would take a used Snap-On over a new anything for the same price, and good ones do come up on eBay with some frequency.

jeff spahn

I have the 1/2" tech angle from Snap On. Was expensive and it works well with one caveat. It is susceptible to damage on the end where the batteries screw in. I am on my second one. You CANNOT hold the wrench except on the handhold. Don't let your hand overlap the end or you will end up breaking the battery connection and the wrench will turn off. A very weak point IMHO. I am trying to figure out a way to keep this from happening as it can if you just set it down and something bumps the cap on the end of the handle.

BC

Oh, nice. Note sure what the small one would be good for:

http://pages.ebay.com/link/?nav=item...d=381475080705

Daniel5691

Jim:

Just WOW. What a clear, concise, helpful description of the problem and solution.
Yours is one of the best posts I have ever read.... and given the depth and breadth of
expert information we see here regularly, that's saying a lot.

If you can explain something as subtle as this to an uneducated person such as myself, you
have really done something. Thank you so much. This is so helpful.

Hilton

Brendan, those are Techwrench models, not Techangle.

They won't measure degrees.

The model number you want for degree measurement starts with A.. e.g. ATECH3FR250

BC

OK. Tech angle. Thank you

FredR

Jim,

Excellent post and thanks for taking the time and effort to prepare. The mechanics of course I fully understand - the bit I was "missing" was not really missing at all given your input.

As you rightly say we are given a torque value or a rotation value to work with but I have never seen a "target torque value" specified to reflect the expected value when the specified rotation is achieved. All one can say for sure is that as the item is wound in the torque should increase proportionately [Young's law] and in our [oil] business, the only approach we tend to use is controlled bolt stretch wherein a pre-tensioning device is applied to the studs, they are then stretched to the pre-determined amount [measured], the nut is then wound in and the tensioning device released so that the stud or bolt then takes the strain.

Clearly if the torque applied does not increase with the rotation then something is clearly wrong. My interest in this matter specifically applies to an incident I experienced some time ago on my 928. I have the 928 Motorsports lower frame brace fitted and that is attached to the inner most front bolts of the lower A arms. The kit has a longer bolt than stock to ensure the thread engagement is sound when the additional elements are introduced. I had to release this to work on the alternator and when refitting it I made the cardinal error of not checking the specified torque values as I was sure the correct value was 85 ft lbs which is quite reasonable for a bolt of that size. As with any controlled torque joint I usually do the initial tighten using my ratchet and then take another two or three steps, so for 85 ft lbs i would typically do something like 40 ft lbs, 60 ft lbs then finally 85 ft lbs. I was just past the 60 stage- presumably approaching 70 ft lbs and I could feel something was not right so I backed off and horror of horrors the rear bolts on the lower arm were 85ftlbs but the front ones were 50 ft lbs. I crapped razor blades when I realised my mistake! Fortunately it seemed as though I had stretched the bolt- whether I stretched the threads I was not sure but with a new bolt it seemed to torque OK at 50 ft lbs and no problem since.

So indeed I can see the value of having a dynamic torque readout. presumably the angle readout is zeroed and then the device measures the ratcheted increment applied. If I have a bolt that is controlled by rotation I put a spot of paint on it and carefully check the amount of degrees as these are usually specified in increments of 90 degrees. Had I had such a torque wrench at the time I would have seen the torque dropping off or plateauing earlier than I did so indeed I can see the value of such.

Lesson learnt- always check the specified torque no matter whether you think you know the correct value!

rgds

Fred

davek9

Don't waste ur $ on this one, it only lasted a few times for me, now won't switch modes when needed.

'm leaning toward this Eastwood product,
http://www.eastwood.com/digital-elec...Ea4aApV58P8HAQ
but at $99 wondering if it's too good to be true LOL...

I only use new studs or bolts, once you have had one stretch during assembly you learn it's not worth the time and $ saved trying to re-use torque yield bolts (S4) or Studs on the S3 and 16v).

Dave K

worf928

Several years ago I "invested" in a set of the Snap-On electronic torque wrenches and within a few weeks of use they were all useless due to the above.

If anyone ends-up with one of these POS Snap-on electronic wrenches, the only way to make them last is to unscrew the end of the battery box after every use. The spring is so weak that it won't last if you don't.

For angle-torquing my 1/2" Gear Wrench is the go-to tool.

For my Christmas present I'm going to look-in to something Stahlwille.

Doug_B_928

Taking the Snapon techangle as an example, the 3/8" is 5-100 ft-lb and the 1/2" is 12.5-250 ft-lb. If you could only have 1 for automotive use, which would it be? Does the angle requirement tend to be for fasteners that require higher torque as well so the 1/2" would be the better bet?

Bmw635

Great timing on this topic.

I am helping my friend start this company as he was the patent holder to a lot of the CDI (Consolidated Device Inc) and Snap On torque technologies and left SnapOn couple years ago. Currently, we're selling to Bosch, Tesla, Space X , OshKosh, Siemen, Schlumbeger, etch...... and growing.

These items will have 200-300 hrs of battery, 1% accuracy, angle and torque built-in. The SPA is professional version and the TA is consumer version. You can use your ratchet and turn these adaptors into pocket torque / angle tool. You can call and ask for special pricing letting them know that Peter on Rennlist/ Porsche 928 referred. We're still working on the ecommerce to allow buying online.

There I've disclosed my associations.

http://digitoolsolutions.com/products/

jcorenman

Doug, do you mean one torque wrench period, or one angle-measuring wrench? For the 928, angle-torquing is pretty much limited to cylinder head bolts, that's an M12 which is less than 100 ft-lb yield. (The "old" torque spec was 90NM = 66 ft-lbs).

So unless you are contemplating an engine-rebuild (or just like tools) it is hard to justify the expense at all, over a good set of basic torque wrenches (e.g. 1/4, 3/8 and 1/2" click-type). But I think either a 3/8 or 1/2" would work for cylinder heads.

The other place I've run into angle-toque is front-axle bolts on Audi's, M14 bolts are 85 ft-lbs plus 180 deg, M16 140 ft-lbs plus 180 (one-time use bolts). Big numbers but arguably less critical than head bolts, and a 1/2" clicker and a big breaker-bar for the last 180 would do it. I used my 1/2" tech-angle and was happy to have it.

I've never had any trouble with it, but I've also never had occasion to use the battery-cap as a handle. I can see where that might happen but it has not been an issue for me.

I went with the 1/2" (250 ft-lbs) because

Doug_B_928

One for angle-measuring. Good info...thanks. Your post was cut off. Why did you pick the 1/2"?

jcorenman

Ooops... fat-fingered it. Because most angle-torqued fasteners seem to also be large, M12 and bigger.