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July 2,2014

Exhaust Manifold

[Click the pics for a better view]

To finish up the engine attachments, I hauled the exhaust manifold up to the bench.

The 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.




After 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.




I 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.  

While 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.




Setting 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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