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To finish up the engine attachments, I hauled the exhaust manifold up to the bench.
manifold is a pretty standard iron casting. The
only possibly remarkable thing about it is that instead of dumping
all six exhaust ports into a single downpipe outlet, the fore and aft
sets of three ports each dump into a separate downpipe. With the
inlet manifold arranged the same way between the two carburettors, it
may be reasonable to think of the engine as two separate three cylinder
plants for some purposes. There is, however, an opening between
the two halves of the exhaust manifold just above the downpipe outlets.
I'm not sure of the purpose of this passage, but considering the
speed and inertia of the moving pulses of exhaust gas, it's doubtful it
has a large effect on exhaust flow.
My manifold was appropriately dirty and rusty.
All four of the downpipe studs sacrificed part of themselves on disassembly.
several rounds of penetrants, heat, and swearing, I eventually removed
two of them by welding a bar to them for additional torque.
Unfortunately, in a case of pure defiance, the other two decided
to mock me by simply breaking off inside the casting.
drilled out the two bad boys, but in the process managed to damage the
threads in one of the holes. This meant some kind of insert, and
I decided it wasn't much more work to just do them all.
waiting for the mail order Helicoils, I derusted the manifold to make
it more pleasant to work on. My derust tank isn't big enough to
do the whole manifold at once.
up the manifold on the mill was a challenge in work holding.
Luckily, the machined surface on the head end of the manifold is
at a right angle to the downpipe end, so I could just clamp the top end
to the front surface of the table to drill and tap for the inserts.
Since I already had the manifold mounted like this, it seemed
silly not to face off the rough pitted surface. The layout lines
were for a plan I had to install two bungs for oxygen sensors. I
ended up deciding to put them in the downpipe instead.
A coat of high temp manifold paint, and new stainless studs, installed with plenty of anti-sieze.
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