Angle torque question

[Dash01]

Bentley says to tighten head bolts to a given torque, in stages, then run the engine for 20 minutes at full operating temperature, then do final tightening of the bolts by a given angle.

Question: When doing the final angle torquing of the bolts, does it make any differnece if the engine is still hot at the time of torquing? After all, the angular amount of torquing is the same number of degrees, hot or cold, and cold would presumably be less stressful to the parts due to less heat expansion.

[DaveVoorhis]

Bentley says to tighten head bolts to a given torque, in stages, then run the engine for 20 minutes at full operating temperature, then do final tightening of the bolts by a given angle.
Is that for an M20 engine? Check the TIS. As I recall, the instructions have been superceded and no longer involve running the engine.

[genphreak]

What engine? On non-elongating bolt designs, no difference.

If the bolts are designed to stretch, it might be beneficial to have the motor cool afterwards. But I seriously doubt it.

Of course it might be a little helpful to the gasket if you tighten it up quick though. Less possibility of leakage is generally a good thing.

[winfred]

m20 m42/44 m50/52 m60/62 don't use the warm up cycle in torquing so you must be talking about a m30 (or a diesel, never done one of those), i usually do it warm just to get the job done and not stop working on it to wait for it to cool as i don't remember them listing hot or cold, may be slightly better cold but shouldn't be destructive either way

[Dash01]

m20 m42/44 m50/52 m60/62 don't use the warm up cycle in torquing so you must be talking about a m30 (or a diesel, never done one of those), i usually do it warm just to get the job done and not stop working on it to wait for it to cool as i don't remember them listing hot or cold, may be slightly better cold but shouldn't be destructive either way

M30 engine in '90 535ia. Bentley says to torque to spec, run engine for ~20 mins., then angle torque some more. This presumably to seat/squish the HG.

BTW, the same could be said of the intake and exhaust manifold gaskets, as these were all torqued to spec with new copper nuts before installation of the rebuilt head, but then found to be loose after a few heat cycles.