Re: Should head bolts be lubed or un-lubed? What about thread sealer?


Generally, bolts should be torqued clean and dry unless
otherwise specified. The use of a lubricant can give a wide
range of applied torque variation depending on the lubricant
used. Plain old engine oil can reduce perceived torque by
30%. Because of the multiplication effect of the thread
pitch, the clamping force and tension on the bolt or stud
can be several times the correct load. Therefore, engineers
prefer to specify torque for clean dry threads because it is
predictable and consistant. If the fastener is plated, the
specified torque will only be good for that surface
treatment.

Sorry, I do not know if your interface with the water
jacket. Most head bolts are installed into blind drillings.

Lugnut

We went through this on this newsgroup a year or two ago
and the received wisdom for American cars of previous years
were that many specified torque values with clean and dry
threads.

Some of us like to have a little antiseize in certain applications,
such as lugbolts for example. I researched the web at that time
and found that the results vary somewhat, but in general a
lubricated thread (and antiseize does have some lubricant
properties, as does engine oil, moly grease, etc). required about
15-25% less torque to achieve the same clamping tension as
a dry threaded torque sequence. (Memory...hope it is not too
far off;>)

Some GM bolts do go right through or into the water jacket.
I was always told that a little non hardening sealer around
these might be a good idea. The Ford engines I used to race
went into blind bores, AFAIR.

I have no idea what Toyota does.


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