Please do. Thanks.

" The click type torque wrench is wildly inaccurate and does not even really measure torque as in clamping pressure but is much more likely to measure friction between fasteners. Why are we evan talking about somthing as outdated as tourque wrenchs when we should be using degrees of rotation"---
Dave S

Dave, It is a good thing we are talking about it because you have COMPLETELY MISSED THE CONCEPT... as shown by your statements above..

NOTHING MEASURES THE CLAMPING FORCE..... and I have said this many times...and even in the last few days..... that the measurement of hold down force is only a wild extrapolation of what the engineers hope will be the corelation of the friction of the fasterner and the hole.....and THAT IS WHY IT IS IMPORTANT TO RUN A TAP INTO BOLT HOLES AND MAKE SURE THREADS ARE CLEAN AND 'LIGHTLY LUBED'.......

If you will REREAD your MB manual.... that reference to DEGREES OF ROTATION .... is only AFTER applying a specified amount of measured torque to the bolt.... let it rest.... then you use the 90 degree procedure ....

When used to torque a bolt with threads that are not frictionlesss, all torque wrenches, click type, or the traditional bar type, will result in reduced clamping pressure.

The whole process of torquing fasteners depends on very clean, friction free threads as Greg has explained. You cannot blame the click style torque wrench for a bad thread.

Dave and Greg, i think you are both largely correct about this. Truth is, we engineers have been trained to expect that joining by threaded fasteners is FOR MOST APPLICATIONS, highly variable and conservative use thereof dominates. However, in more critical and high performance applications such as head bolts, degree of rotation will provide a much more accurate measurement of joint preload. Studies have been done, such as J.C. Blake and H.J. Kurtz "The Uncertainties of measuring Fastener Preload"(Machine Design, vol 37, 9/30/65, pp. 128-131) under rather precise conditions. On a sample of 20 unlubricated and then lubricated 1/2-20 Bolts, torqued to 800 in-lb, mean values of about 7700 lb were nearly identical. However, the standard deviations for the samples were 1100 and 680 lb respectively! My conclusion - torque values give variable readings even under controlled conditions. I torque critical components and gladly use degree of rotation wherever I see it. I wish DOR was used more often, such as with the crankshaft balancer. I don't have a torque wrench that goes to 300Nm. So I went to 200Nm (the limit of my beam type), then I torqued with a 1 1/16" open end, pushing on the end-13 1/2" inches from center with a large, known mass (me). That's my take on it.

Except where MB says in the manual " add 90 degrees" .... I have never even heard of this....

I do know that a dirty sand filled hole being penetrated by a bent up bolt will pull down LESS than the engineers HOPED when they wrote down the torque numbers in the instructions....

And where gaskets are concerned that can sure make a mess...

This " DOR " has to START somewhere...... WHERE ?

Amen!!!

Hopefully from torque applied to joints carefully prepared such as the way you describe Greg. An initial torque with clean, lightly lubricated fasteners provides a good starting point because even though the variability of preload is high as a percentage of load, the variability of the final load after DOR tightening will be much lower. A combination of torque and then DOR tightening provides consistency of preload

I think it says something about those who drive/work on these cars that there is such a lengthy discussion about this torque issue.

I am not saying it is completely correct, but the only time I have ever seen any of the three mechanics in my family use a torque wrench at all was when tightening head bolts. Seems to me maybe you all are making mountains out of mole hills, but it does provide interesting reading.

Ok,,, so you are describing what the MB manual describes ?

MattDave sounded like it was a ' substitute' DOR for torque readings ...

So we still need to take the fasterners down in the number order which MB gives...

Do it incrementally.... just like all large important gasket jobs prescribe....

let it rest the amount after reaching the specified MB torque number....

Let it rest the ten minutes or whatever.... and do the ' turn an additional 90 degrees' .... perhaps twice ? ... whatever the manual says ...

So my impression is that these are used TOGETHER.... thus the question about which torque wrench... or which type....is still valid... Right ?

Habernero.... your relatives probably did not work on aluminum blocks ....or heads... Shop manuals like Subaru are careful to specify torque values for almost every bolt on the engine... and many on the car....You are probably young enough you have never had the job of trying to restore a bolt hole which had been stripped out.... never fun....

No offense but these old cars are not jet engines or F1 cars. Any torque wrench is good enough. Sears was selling a Craftsman wrench for $100 I bet you could get it on sale in the $70 range. If the manual says 30nm and your wrench is a little to high or low no big deal. You are not going to ruin a part on these cars buy having it tightened to 32 insted of 30.

$30 will get you your first torque wrench. You will be more concerned with storing it so that you can find it next time you need it, it may be a while.

I bought my first torque wrench at advance auto parts for around $30. I used it to replace a head gasket on a Dodge Daytona Turbo. It worked just fine and I still use it on my car. If I was working on internal engine components on my MB, however, I would buy something of a little better quality to be safe. For everything else on my car, I think it's good enough.

Scott

"No offense but these old cars are not jet engines or F1 cars."

No offense Hatterasguy.....but our cars have almost twice the compression ratio of those F1 cars ....and don't get taken apart between every race... not even every decade.... if done properly...
Sounds like you are too young to have experienced some of the off the wall mechanical things some of us have.... and we swear we are not going to repeat them.... thus we start trying to learn what works and what does not...

Dad was out of the game before many aluminum engines were around, but my brothers both work on modern aluminum engines all the time. Maybe they are just lucky...

And by the way I have actually had to drill and retap a few holes I have buggered. Learned my lesson eventually.

Unless you're rebuilding the engine, there is really no need for a torque wrench in working on these cars. Just cinch things down tight and be happy with the money you've saved.

Merry Christmas,