[Supras] Question about head gasket (hopefully last)

[berniek at technicaldevelop.com]

Your last question relates to why most head gasket failures involve cylinder
#6 rather than #1.  I believe the reason involves greater heat, higher
temperature at the rear of the engine, as it is further removed from the
water pump.  In years past, inline engines had steel water distribution
tubes within the block.  From all appearances, that does not appear to be so
with the 7M.  Higher temperature at the rear of the engine is also reflected
in part in greater cam journal wear (complete disappearance of the soft
"mystery coating") on the exhaust side of the engine at the rear, probably
from thinning of oil.  I've experienced this, as have others I've
corresponded with.  One other problem I've had and others have written about
is a slow coolant leak from between the head gasket and the block, again at
the rear of the engine.  This, too, would indicate presence of higher cold
to hot temperature differentials at the rear of the engine as opposed to the
front.

            BernieK


----- Original Message ----- 
From: "t72pwrd" <nholden1 at woh.rr.com>
To: <berniek at technicaldevelop.com>; "Craig Thommes" <cthommes at adelphia.net>
Cc: <Supras at supras.com>
Sent: Sunday, June 04, 2006 7:35 PM
Subject: Re: [Supras] Question about head gasket (hopefully last)


> IIRC the 1/2J motors came with MHGs from the factory.  I think that was
the
> biggest reason they don't blow as frequently as a 7M with a composite
> gasket.
>
> Don't worry about adding fuel to a flame war, this list can certainly
> withstand it.  I actually miss the frequency of the flame wars from a few
> years back.  They were entertaining, fun to engage in, occasionally
> educational and always resolved peacefully :-)
>
> BTW, if it was "cumulative end to end differential expansion" why doesn't
#1
> blow too?  Put that in your pipe and smoke it you lousy &#@!#$$%^%!  LOL!
>
>
> ----- Original Message ----- 
> From: <berniek at technicaldevelop.com>
> To: "Craig Thommes" <cthommes at adelphia.net>
> Cc: <Supras at supras.com>
> Sent: Sunday, June 04, 2006 6:24 PM
> Subject: [Supras] Question about head gasket (hopefully last)
>
>
> > Inline 6 cylinder engines are probably the longest which use aluminum
> > heads and iron blocks.  Other engines have shorter heads, which
minimizes
> > cumulative end to end differential expansion or head warping.  Most 7M
> > gasket problems happen at the sixth cylinder, apparently due to
cumulative
> > differential expansion.  My JDM engine showed deep grooving in the head
> > and block around the stock gasket crimped rings, especially at the ends,
> > presumably from tendencies of the block and head to "walk" with respect
to
> > each other due to thermal cycling.
> >
> > I do not want to add fuel to a flame war here.  I just want to know what
> > the consensus is regarding life to be obtained from a 7M with a Cometic
> > gasket (mine was special ordered as 2 mm thick).  I'll be running 14 PSI
> > boost and ARP head studs.  I'd like to be able to get 150K miles with
> > periodic retorquing if needed.  Got that from the stock head gasket with
> > 72 Lb-Ft. retorquing at 8 PSI.
> >
> > Just out of curiousity, what did Toyota do in the 1J and 2J engines to
> > eliminate the problem?
> >
> > Thanks.
> >
> >        BernieK
> > _______________________________________________
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> > Supras at supras.com
> > http://supras.com/mailman/listinfo/supras_supras.com
>
>
>