Big End Bolt Torque Setting

[DavidBrough]

I'm putting my engine back together and would like to check on the correct big end torque setting as my Haynes manual just says 44ft lbs but the BBB refers to 4+1 mkp followed by 90+10 degrees rotation. I'm inclined to go with the BBB figures but don't really understand the scale as the variance between 4mkp plus 90 degrees is very different to 5mkp plus 100 degrees which seems to be the suggested scale. Does anyone know what the correct setting should be?

[tel76]

Hello David,
We seem to be doing the same operations on our projects,i have just done this on my engine,i used the following which i obtained from the Mercedes Benz, Maintenance Manual CD. and information given by JA17.
  Initial torque - 29ft lbs.
  2nd      "      - 36ft lbs.
Followed by 90 -100 degrees angle of rotation.

[DavidBrough]

Thanks Eric, the BBB torque statement now makes more sense as I'd initially read it as an allowable variance not a staged process. I do have one extra question though as the initial 29/39 ft lbs is a two stage process you quote the angle torque as a single stage approximation, should that part also be two stage i.e. first to 90 degs then an extra 10 degs?

[tel76]

David,
The angle of rotation is a one step operation,after the 36ft lbs turn the nut 90 to 100 degrees,its the tolerance,not less than 90 and not more than 100.
After the 36ft lbs operation i used some tip ex to mark the required angle(i used 95 degrees)on the con-rod and using a socket and bar to turn the nut to the required mark(do not use the torque wrench) and make the operation in one movement,it is not acceptable to back off the nut if you over tighten.
Hope this helps.

[DavidBrough]

Thanks Eric, now all torqued down properly.

[ja17]

Hello,

Yes, a simple 1/2" braker bar can be used for the final angle of rotation. You can get a scale and pointer to use with it, but not really needed as long as you can refference the angle and you know what 90 degrees is. Start with the breaker bar parallel with the block and end up with it perpendicular to the block (90 degrees)

I also use some paint to mark the nuts after final angle setting, because you have no way to go back and check them if you lose track of where you are.