Exhaust manifold install : I forget how

[M. Hinrichs]

OUCH ! I forget the torque specs, as well as when final torque is applied. Hot or cold? I thought it was hot (steele with alum;dont want cracks). Someone straighten me out . Thanks
-M

[Robert Goodwin]

Well now. That all depends on what kind of engine we're talking about here. If it's gas, the MB manual either does not specify, the info is hidden or you use the standard torque value for that size bolt (nut). If it is a diesel it is 20nm, 30nm or maybe even some other number depending upon which diesel engine you have. Basically, we need a little more info here. As for hot or cold, the manual makes no mention of temperature for the gas or diesel engines, so I would do it cold (doesn't hurt as much) unless someone else has some better information. The year of the engine also points to a type of nut that is used as I think there was a production change for the nuts in the gas engines.

[Robert Goodwin]

I have not been able to sleep since you raised the torque question. Well, I did get some sleep The plot thickens. There are torque specs provided for some, if not all, of the diesel engines. Gas engines are treated somewhat differently with a phrase such as remove nuts, reinstall nuts. I checked my maintenance documentation back to the 190c, 200, 190dc and similar series. The most definitive statement was in the Haynes manual for the 123 (another diesel) which said to tighten the nuts securely. Haynes also provided a chart at the begiining of the manual with torque values for bolt/thread sizes:

M-6 6-9 ft-lb 9-12nm
M-8 14-21 ft-lb 19-28nm
M-10 28-40 ft-lb 38-54nm
M-12 50-71 ft-lb 68-96nm
M-14 80-140 ft-lb 109-154nm

My research of the diesels gave torque values of 20-30nm and the nuts are probably M-10. That leads me to believe that the torque values in the chart are for iron to iron. The almost 50% reduction in torque seems to be attributable to attaching steel to aluminum. At least that's the way it appears to me. There must be at least one "real" Mercedes mechanic out there who knows the real answer, even if it's remove/reinstall and tighten securely.

If you ever knew the torque specs, I would suggest doses of truth serum but all the places I used to go to get it in West Memphis have probably fallen down or burned down and not necessarily in that order. The Cotton Club comes to mind.

[M. Hinrichs]

Thank you Robert for your inputs. I have been delayed with P.C. problems until now. I have hit up MBUSA with the same question. I will keep thread readers posted on the outcome. Since I have done some interesting reading of tech value from Dana Clevite on the subject.

(on the flip side, the land marks of your memories of here have been slowly erased with time in the same fashion of mine regarding various establishments on Atlantic and back gate Oceana)

[Robert Goodwin]

Peppermint Beach Club is no more and the back gate of Oceana is at an industrial park.

Looking into removing the exhaust manifold on my 300SDL, I learned that the nuts are copper. MB does, as I mentioned, provide torque values for mine. If yours are copper, "tighten securely" may be the best advice MB is willing to give. Remember, if you want a really good guarantee, go to K-Mart and buy a toaster.