Connecting Rod Assembly problem

[dnadanny1]

Hi there.
I am overhauling  a 1966 M127.981 engine.

As I am reading through the MBEngineSpecs.pdf, it said from 1968 onward, connecting rod bolts are stretch bolts, and I need to install connecting rod cap and torque nuts to 36 ft. lbs, and further tighten an additional 100 degree of wrench rotation.

As the tightening specification suggested the connecting rod bolts should be tightened at 27 ft. lbs, it confuse me that should I add 100 degree of wrench rotation to 36 ft. lbs or/and 27 ft. lbs?

As I dont know whether the bolts has been changed by the previous owners, How can I tell whether the bolts in the engine are stretch bolts?

Thanks a lot.

Regards,
Danny

[Benz Dr.]

If you have a 127 engine torque the bearing cap bolts to 27 ft-lbs. I think these should use 14 mm nuts.

Later engines us 15 mm nuts. stretch screws and angle of rotation after initial torque is reached.

[dnadanny1]

Thanks for your information Dr.

What really confused me is that I am sure my engine is M127.981. But the Connecting Rod nut is 15mm, please check attached pictures.

So I should go with 27 ft-lbs or 36 ft-lbs & further tighten an additional 100 degree of wrench rotation?

Thank you again.

Regards,
Danny

[ja17]

Yes do not use the extra "angle of rotation" on early M127 engines.

[ja17]

Maybe you can provide a picture of the connecting rod casting number. Latest version rods for these engines may use the newer bolts? The 15mm nut size does indicate this might be the case.

[Benz Dr.]

Late 230SL connecting rods are not gun drilled down the center of the rod to accommodate piston pin bushing lubrication. If your piston pin bushing is lubed through the top of the connecting rod it would be the 3rd version.

[dnadanny1]

Thanks you all for your reply and help.

For better clarification, I have disassembled my connecting rod, and taken some photos of it.
Please find attached are the more-detailed pictures of my connecting rod.

How much torque should I apply to the connecting rod?

Thanks again.

Best regards,
Danny