Hello Erick,
I have not had any issues with reusing the old rod nuts and stretch bolts, but they should be checked. Defective, fatigued or over torqued stretch bolts will become permanently deformed and be too narrow. These bolts can be checked. The "new diameter" of the small section of the bolt is listed in the BBB at 9.0 mm. The minimum diameter of a used rod stretch bolt is 7.8 mm. Connecting rod stretch bolts below this 7.8 mm diameter reading should be replaced. *BBB 03-0/2
Once the bolts have been checked , a torque setting of 29 ft. lb. (first pass) on each rod bolt, then bring each one up to 36 ft. lbs.(2nd pass), then 90 to 100 degree angle of rotation (third pass) on the M129 (250 series) and M130 (280 series) connecting rods. I like to mark each rod bolts with some paint after the angle of rotation pass because there is no way to go back and double check these since you do not have a final toque figure.
The 230SL engine M127 is a different story (also same in 190SL). The diameter of the rod stretch bolts is smaller. The length of the rod bolt is measured before torque and after torque. When the bolt stretches .1mm it is correct. This .1mm of stretch will occur between 28 and 35 ft. lbs. normally. Working with one rod at a time, I usually start measuring each bolt length. After two passes bring the torque up to 28 Ft lbs. and measure the new length of the connecting rod stretch bolt, and continue if needed until .1mm stretch is achieved. If the .1mm stretch occurs before 27 ft. lbs. or after 34 ft. lbs. I replace the stretch bolt. No angle of rotation is used on these engines. Needless to say you need to be good with a micrometer to achieve desired results! If a rod bolt stretches beyond the .1mm before 27 ft. lbs. is achieved, the bolt should be replaced since it is fatigued. A more detailed explanation of the process is covered in the "Type 190" BBB page 01-4/32 also covered in the "Type 220" BBB. I am sure most shops are just torquing these rods in at 28 ft. lbs. which normally is sufficient.
After torquing, I always check to make sure that the connecting rod assembly is free and not binding after the final torque.
