Mailing-List: contact type2-help_at_type2_dot_com; run by ezmlm
Date: Wed, 12 Nov 2003 07:22:29 -0500 (EST)
From: librarian <librarian_at_uulibrary_dot_com>
To: <type2_at_type2_dot_com>
In-Reply-To: <1438.216.254.214.81.1068596070.squirrel_at_webmail.primus_dot_ca>
Message-ID: <20031111223128.E21270-100000_at_quidpro.everybus_dot_com>
Subject: Re: [T2] Fitting Heat Exchangers to new heads?

On Tue, 11 Nov 2003, Jamie Rivers wrote:

> I dunno about best,, you be the judge, I like this article
>
> http://www.bostonengine_dot_com/articles/hbmanifold.htm

The article is excellent.  I agree with it entirely, but would like to add
a comment or two where I have found problems in the past.  See below.

> Installalation Tips
> (Or Why Does My Van Backfire Every Time I Let Off The Gas)
> by Bob Donalds
>    This is a tech tip for the heater boxes on the type two engines with
> the copper exhaust gasket used to seal the exhaust pipe to the head. There
> is very little space to work up inside the head and the sealing can be a
> hit or miss prosess. This problem lead to broken studs from over
> tightening or worse broken exhaust stud boss.

Despite its humble appearance, these are a very high precision joints.
The seal surfaces must be flat not only individually but both ends must be
co-planar.  In addition that plane must be perpendicular to the holes for
the studs.  Lastly, and little remarked, the flats on the collar through
which the studs pass must not hit the head before the seal surface hits
the seal.  While this distance on new exhaust manifolds has a generous
surplusage after the ends of the pipe have been filed for 20-30 years that
surplusage has often disappeared and the flats on the collar must be
reground to establish contact.

> When I prep exhaust manifolds I start by filing the manifold gasket
> surface flat with a long file doing both surfaces at the same time.
> With any luck the gasket surfaces on the head for the copper gaskets
> is close to paralel.

When I prep exhaust manifolds that are nearly new or in obviously good
condition this is the procedure I follow.  A couple of strokes of a
file that covers both openings is good if you have file that large.  If
you don't then a piece of wet/dry sandpaper mounted on a cut-off from an
old countertop will do the job.

If the engine has run with a leak for a significant amount of time or has
obvious erosion or a couple of strokes of the file reveals that it is
warped then it goes stright to the machinist.  Especially on the later
exhausts the exhaust supports are very important and running without them
can cause significant damage to the entire exhust system.  In time it can
torque and warp the headers present on these years.  If they are warped
then it will take special machining to bring it back into anything
resembling true.  Note that the weight will also warp the seal flanges
between the various parts of the system and they may also need to be
refaced to obtain an adequate seal.

> Next find a drill bit in your drill index that that fits in the
> exhaust stud opening in the manifolds and go up approximately two
> drill sizes then use this larger drill bit to open all 8 stud openings
> in both manifolds this gives you the chance to move the manifold
> around against the head. This allows you to get the flanges as flat as
> possible against the cooper gasket without the studs pulling the
> manifold in four directions at once.

When the head left the factory in Germany all the head studs were
parallel.  All the holes in the manifold were also parallel and lined up
with the studs.  Of course when the bus left the factory all four corners
of the exhaust system were supported and the head studs were supporting
NONE of the weight of the exhaust sytem.  Years down the road the supports
have often disappeared, the studs have been pulled out of line, have been
replaced with oversize step studs drilled in at an angle, and have
otherwise been seriously abused.

Drilling the holes to an oversize is often necessary these days.  I have
performed this by times but it should not be done lightly or as a matter
of course.  If the manifold is warped and the studs are bent then the
solution is to have the manifold aligned and the studs replaced, not to
compound the problem.

If you do choose to drill the holes oversize, at very least clamp the
manifold in a vise.  The metal in the collars is very hard and will "grab"
the bit and can injure you.  A drill press at low speed and machinists
vise are by far the preferred tools for this job.

> I also check the head to pipe clearance so the manifold does not hang
> up or bind at the stud bosses or the lip of the gasket surface. I have
> even gone so far as to take a file and shaped the flanges and manifold
> ends to get the job done.

This is a vital step!  Take a micrometer and measure the distance from the
step on the head to the copper gasket.  Measure the distance from the step
on the collar of the manifold to the seal surface. You should have an
interference of at least a couple thousandths of an inch.  Measure all the
ends and all the steps.

If the interferance is inadequate then the flanges will meet before a seal
is established.  More torque will only pull the studs out of the head or
break them.

> The gasket will leak and the engine will backfire unless the gasket
> makes a good even contact with the head and the manifold.

Exactly so.

> When I am satisfied with the fit I use a exhaust paste
> on both sides of the cooper gaskets. Never use silicone to seal the
> exhaust pipes at the head it can not take the heat. Then while holding
> the manifold against the head I install flat washers and new nuts
> tighten the nuts evenly so as not to prelude the manifold to one side
> or the other. This can be hard to get right because the age of the
> parts. The manifolds must be sealed at the head first and then finesse
> the other pipes into place next.

The other pipes AND THE SUPPORTS!

>
> As told to me by Gerg Malany of Gergs repair Natick Ma. Phone # 1 508 647
> 9749

                             OOK!

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