Correct torque for C220 CDI injector bolts

[panason1c]

Not to mention that if a stretch bolt is overstretched due to overtightening it (and doesn't snap or strip) there is the probability that it will lose its tensile strength due to its 'overstretched' condition resulting in an 'undertorqued' component situation.......in this case, the injector possibly being clamped less tightly after two x 90 degrees than it would be on one x 90 degrees tightening.

 

[kebo57]

Not to mention that if a stretch bolt is overstretched due to overtightening it (and doesn't snap or strip) there is the probability that it will lose its tensile strength due to its 'overstretched' condition resulting in an 'undertorqued' component situation.......in this case, the injector possibly being clamped less tightly after two x 90 degrees than it would be on one x 90 degrees tightening.

Hi John the MB bolts are thread rolled & have neck diameter of 5.23mm so as you state "it will lose its tensile strength" if you over tighten, thats why I left some of the standard long series cap head bolts in which have a neck diameter of 5.90mm & are high tensile

Kevin

 

[brenner]

bolt

I know that it's 2015, and 7 years have passed since this was written. But just in case someone reads this now..... According to MB, the torque is 7 Ntm + 2 X 90 deg. BUT, tests have shown, that the 2nd 90 deg does not help in holding down the injector. But it CAN make you strip the threads in the aluminum hole. I have talked to many MB mechanics, and none of them would do the 2nd 90 deg. If you have problems with leakage, try annealing the copper gasket. Heat with propane to cherry red hot, and let it cool. This makes it softer, and seals better. Look it up in Wikipedia. 2nd, don't use a regular bolt! The clamp that holds the injector has a concave seat, the bolt head bottom is convex and fits into the concave seat. This makes for 100 % contact! Even if the bolt is not 90 deg with the clamp. If you use a normal bolt, the bottom of the bolt head touches in only one spot, and therefore can quickly come loose! Look at the clamp and the bolt head, and you will see what I mean.....

 

[mercedes13156]

In my old C Class 220CDi Coupe I had the black death on Pot Nr 4. I cleaned most of the tar away by heating the engine up, leaving it idling for half an hour to let it soften a bit and peeled most of it away with a screwdriver. I got the injector out and removed the rest of the muck. The bolt hole was full of muck, so I filled it with WD40 and scooshed it out with compressed air several times along with running the old bolt down until I saw the bright metal at the bottom of the hole. (That took most of the day, off and on).

I cleaned out the injector hole with a reamer for a Peugot diesel which fitted perfectly. The injector went back in fine and I torqued the bolt as per dealer instructions to 7NM then twice plus 90 degrees but very slowly and half an hour between the two 90s. On the second 90 there was a "Click!", the thread stripped and came out with the bolt. I had to cut a new hole, helicoil it and enlarge the hole in the retaining fork for a 40xM8 black steel allen bolt torqued up as above with one turn of 90 degrees. Within a week, it had loosened itself and was puffing away. I removed it all cleaned it again, put in a new washer and used threadlock on the bolt. Perfect. It stayed put and didn't move again.

I wouldn't risk a second 90 degrees, but if you notice, the new bolts have a bit of threadlock on them and if you dry assemble the injector and fork, then measure the depth of the hole, you'll find that the MB bolt doesn't go all the way to the bottom of the bolt hole. If you've done everything else right, the bolt will hold the retaining fork and the injector nice and tight. Added to that, there is a large degree of stiffness in the two bolted connections on the steel fuel pipe between the rail and the injector. Adding that kind of inertia to the injector adds significantly to its reluctance to move, as long as everything else is correct.