Monday, October 3, 2016

Carburetors I

I've been avoiding the big messy job that is the rear axle.  So, I took down everything else in the attic that needs cleaning.  It's not a big pile any more.  The first box I found had the carburetors in it, so in the spirit of avoidance I started cleaning them up.

They don't look too bad.  They're really dusty, of course.  The dashpots in the carbs still move.  I'll have to replace the jets, fuel lines, maybe floats, and float needles... but these were in good shape otherwise when I put them away.

I did start cleaning up some stuff...


From top left: The intake manifold, the PCV valve, and the heat shield.

The PCV valve is an interesting thing.  The engine only keeps oil in it when it's running by virtue of a scroll seal on the rear main crankshaft journal.  It needs some help to do that.  Hell, it needs all the help it can get... it's a 'seal' in name only.

Positive Crankcase Ventilation (PCV) draws a partial vacuum inside the engine block, which keeps combustion pressures that leak past the piston rings from pushing oil out of the crankcase through that so-called seal.  The vacuum is drawn from the intake manifold through the PCV valve.  It's a one-way valve so as to not allow outside air (from backfires and such) into the engine block.  The valve draws from the crankcase through a tube off the timing chain cover, which also has some steel wool to (try to) catch oil vapors.

It's simple and pretty effective, when the engine's running.  When the engine stops, there's no more vacuum and the little bit of oil in the "seal" leaks out, giving rise to the infamous drip under every British vehicle of the era.  There is an aftermarket kit that fits a proper rubber seal to the crankshaft, but it's expensive and I don't think I care enough to install it.  It's "character".

I have a little problem with the heat shield, though.  It's cracked.  Not easy to see it, but the crack is under the holes on the right side of the shield in the picture.  I have to at least spot weld it to keep it together, because I don't want to have to buy another one.  I also have to clean up the other side before I do that.

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