Re: Head Bolts

• Subject: Re: Head Bolts
• From: casey@domain.elided
• Date: Thu, 26 Sep 96 19:17:07 -0400

warrer@domain.elided (Ryon C Warren) writes:

>I believe the head bolts on my '81 528i are stamped 10.8, which
>if memory serves correctly is 10,800 psi tensile strength.
> All this talk of head bolt failure has me slightly paranoid,
>and wonder if I should change to higher strength bolts.
>
It is not that the "new" bolts are stronger, it is that they
are "stretch" bolts (they have a turned down shank). They will
stretch and shrink in lenght when the head expands when hot and
contract when it cools. The "old" bolts will fracture just under
the head when forced by the expanding head. Usually when when (even
slight and/or repeated) overheating has occured.

NOTE: It is recommended they be angularly torqued, not just torqued
      to X ft/lbs.


Drive well,

Shawn...
casey@domain.elided

'83 BMW 320is (E21)
BMW CCA Member - Boston Chapter

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