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Discussion Starter #1
Anyone have any tips on how to use the torque wrench when replacing the spark plugs on slk 320? Since it has to be in on one long, fluid motion until you hear the click, how do you guys do it? I can only get about a 1/4 turn on any wrench due to the space issue, not sure how to get close enough to the right torque to be able to switch out the regular socket wrench for the torque and get it to click in the limited amount of turn before running out of space?

I have put them in and threaded them by hand to make sure they are not cross threaded, then finished tightening them using a regular wrench to the point that they give resistance and require pressure. I then tried using the torque but did not have enough room to turn the torque far enough to hear the click.
 

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Jbanks15-Sorry, that does not help. I do not need a tutorial on how to use, or why to use a torque wrench. I need specific tips and trick from the owners that have the M112 engine and have changed their spark plugs and run into the space issue when trying to get the "click" on the torque wrench when you can only turn the wrench a short distance before you run into an immovable part and have to reset the wrench.

I have looked up torque wrenches in tight places and the general rule is "guess". I know that someone here on this forum has successfully used a torque to change the plugs.

Jbanks, I do think that link would make a good sticky for why you use a torque wrench when changing plugs and not just "wing it":tu:
 

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What kind of torque wrench are you using? The ratchet head click type and the proper combination extension combination shoul allow you to torque in thetightest of spots.

You are very wise to torque your spark plugs in an aluminum head engine. It is also best to use a VERY THIN coat of copper based anti-sieze compound on the THREADS ONLY.
 

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You need one of these. 104405520.gif A handy dandy genuine
M-B spark plug wrench. Otherwise you can do it the way that I do. Tighten finger tight. Then tighten each plug 180 degrees with spark plug wrench. Then tighten each one another 90 degrees. They are all the same then. If you don't feel comfortable with that method, you could try a swivel adapter between your torque and your plug wrench.
 

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You don't need a long continuous swing to get the torque correct. With your clicker type torque wrench, all you need is enough room to tighten it enough to get it to click and that's not very much.
 
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If you use an anti seize be reminded that your torque values are for dry applications. Adding a lubricant increases the torque over the actual reading.
 

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Discussion Starter #7
Sokoloff. Thanks I did not know that but it worked:Beer: new to the torque tool and had only used it or seen it used when it was just one long stroke (like a lug nut)

CarolinaBlueTec- I tried a swivel/ wobble joint and really did not like the loss of feel with it. I could not tell if I have the right angle on it to get the plug in or out straight. With just the socket and the extension I could get a much better feel that there was no resistance that might indicate a cross thread. Others on the forum had recommended the swivel as well, so I did try it and with more experience, I could see how being able to use the swivel would speed up the process.

I did get the MB boot tool and it was well worth the $18. I had all the coils off and the boots pulled in 15 minutes.

MBDiagMan - I originally purchased the anti-seize for the plugs but someone pointed out that the Bosch plugs are designed to be used without it, so I did skip that step. Hopefully the Bosch will perform as advertised and I will not have to have an Indy do the job the next time because I cannot get the plugs out.

BTW-You guys all rock on this forum. I would have never tried his with the help and support on this forum
 

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Tightening any bolt correctly.

To complement (and compliment) the comments above:

If you use a long extensions on the torque wrench side of the swivel, it allows you to hold the extension like a shaft and to have a "pure torque" that goes through the swivel into the target item.

The torque value is intended to give the correct longitudinal/axial force for the thread, and includes pitch of thread, contact areas, etc in the calculation, and also has assumptions about the cleanliness and lubrication of the thread. More dirt or less lube will mean the effort is spent on the thread, and not on the axial force, so the same torque will not provide enough holding force. And for the example mentioned, adding lube will reduce the thread friction, so the torque will spend less effort on the thread friction, and more will go into the axial force, so the correct torque will provide a higher fixing force, which may exceed the strength of the threads.

Spark plugs have a much simpler system; the washer at the base of the thicker section is a crush washer, and will provide a good axial force over quite a range of crush. Hence the plug should be done to (for example) finger tight, and then 90°, then 45° more. (See the plug manufacturers instructions for their crush washer). For a spark plug, if the plug has been removed and refitted too many times, then the crush zone may have been exceeded, and this method will result in over-torque, and hence strip the threads and result in a need for a heli-coil re-threading. Therefore, the use of a torque wrench is advised; this is set to the maximum value, and if you hear the click, the next time you will need new spark plugs (or at least the crush washers, which don't tend to be available separately).

In place of a torque wrench (or to compliment its ultimate safety) it is possible to get an protractor to measure the turn of the bolts; as long as this is downstream of any ratchets, it can show the angle of rotation, so the wrench can provide the torque to turn the bolt, and the protractor provides the control.

(Note this philosophy is very similar to that of stretch bolts; use the bolts, tighten to angles, so the bolt has entered the plastic deformation range, and then all the forces will remain at the maximum of the plastic deformation, and not exceed the thread loading. However, once installed, the bolts have started to stretch and work-harden, so they cannot be used again.)

You had all the answers from (almost) all of the big hitters above; just a bit of detail that might help you understand the different methods of ensuring a bolt is fitted correctly.
 

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One trick the R170 has that is not common; the bonnet can be lifted to vertical, so it should not impede operations on the rear of the engine compartment.

First stage is to open the bonnet as normal.
Now run your fingers up the rear side of the bonnet stay, and at the last couple of inches, you will find a large smooth button. Take the weight of the bonnet with your left hand, and press this button in. Push harder with the left hand, and the button will disappear down the outer tube of the stay. Keep pushing, until the bonnet is vertical, and the button will reappear in the hole about 6" from the bottom of the stay outer sleeve.

Lowering is similar; support the bonnet with left hand, press buton with right hand, allow bonnet to drop down (slowly) until it latches again, when you can then shut the bonnet as normal.

HTH,
Anon
 

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One trick the R170 has that is not common; the bonnet can be lifted to vertical, so it should not impede operations on the rear of the engine compartment.

First stage is to open the bonnet as normal.
Now run your fingers up the rear side of the bonnet stay, and at the last couple of inches, you will find a large smooth button. Take the weight of the bonnet with your left hand, and press this button in. Push harder with the left hand, and the button will disappear down the outer tube of the stay. Keep pushing, until the bonnet is vertical, and the button will reappear in the hole about 6" from the bottom of the stay outer sleeve.

Lowering is similar; support the bonnet with left hand, press buton with right hand, allow bonnet to drop down (slowly) until it latches again, when you can then shut the bonnet as normal.

HTH,
Anon
great tip bud thanks
 
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