[Farmall] O-12 fixin'

[olmstead at ridgenet.net]

It was cold and windy here today; perfect for working in the shop.  Fired
up the wood stove and let things warm up for an hour or so while I worked
out in the yard.

I bought a '34 O-12 a month or so ago.  It has nice paint, but doesn't run
smoothly.  The right fender was wobbly.  Tightened up the bolts and fixed
that.  The rocker arm cover was leaking a lot of oil.  Removed it and
examined the gasket.  It looks OK.  Rocker arm covers tend to get crushed
around the bolt holes, so I pounded the dents out.  As long as I had the
cover off, I decided to adjust the rocker arms.  As I thought about it, I
decided that the head bolts might need re-torqueing.  The engine looks
like it had some work done as part of the restoration, and I suspect that
head bolts weren't re-torqued after it had run a bit.  I used 80 lb-ft. as
my goal, and sure enough, the head bolts (nuts) needed tightening.  Had to
pull the rocker arm assemblies in order to do that; the rocker arms block
access to the head nuts.  I know that you're supposed to adjust the valve
lash while the engine is hot, but that was impossible in this case.

Re-installed the rocker arm assemblies and set valve lash.  Thanks to the
big sparkplug holes, it is easy to find TDC on F-12 engines.  After
finding the compression stroke by turning the engine over with my thumb
over the spark plug hole, I use a flashlight to watch the piston rise to
top dead center.  The cylinder bores look fairly rusty, so I'm guessing
that the engine work consisted of a hone job and maybe new rings.  Good
enough, I guess; the engine runs and doesn't blow blue smoke.

Had to remove the carburetor in order to get to one of the head nuts, so I
set the carb on my workbench to take a look at later.  The engine has been
running VERY rich.  Reinstalled the rocker arm cover.  Checked the oil
level and reinstalled the air cleaner.  I had taken it off to make room
for valve adjustment.  I hate working in cramped quarters.

Took the top off the carburetor and removed the throttle butterfly.  The
throttle shaft was seriously worn and jets didn't want to come out, so I
decided to install a carb that I rebuilt a few years ago.  I've taken to
writing notes on carbs with a Sharpie.  This one said that the carb had
the large venturi, idled very well, but accelerated poorly.

Every F-12, O-12, etc. needs the same repairs.  The carburetor, fuel pump,
radiator fan and magneto are always in terrible shape.  I've found it
worthwhile to rebuild these items in batches of three to five and set them
on the shelf.  It's always more efficient to rebuild a batch, because I'm
more familiar with procedures and have more parts available when I do a
bunch of the same item.  The payoff comes when I start on a project like
this O-12.  Instead of piddling away a month or so rebuilding major parts,
I just grab rebuilt stuff off the shelf and bolt it onto the tractor.  One
of these days I'm going to do what Roger Welsch recommends and set up a
known good engine just to test rebuilt components like carburetors and
mags.

With the carb installed and the top fuel line back in place, I started the
engine.  Since the carb was bone dry, I squirted carb cleaner down the
inlet to get things going.  Worked well; engine started on second pull.  I
installed the air pipe between air cleaner and carb, opened the shop's
roll-up door and turned on the big ventilation blower.  Yes, I should have
turned the blower on before I started the tractor.  I usually do.

Tinkered with the magneto timing.  The rebuilt carb and freshly adjusted
valves didn't solve the missing/surging problem, but retarding the mag as
far as it would go without shutting down seemed to smooth things out.  I
shut the tractor down.

Pulled the magneto, one of my rebuilt ones, and retarded the magneto drive
by two bolt holes.  I have discovered a number of loose things on this
tractor, including the spark plugs (just finger tight), and the head
bolts, so it was not a big surprise to find the bolts which hold the
magneto drive dogs very loose.  I added lock washers and snugged the bolts
up a bit when I reinstalled them.

The engine wouldn't start until I removed the intake air pipe and squirted
more carb cleaner into the carburetor.  Then it fired right up.  Replaced
the pipe and drove the tractor around until the engine was hot.  It was
immediately obvious that the engine was running better.  After warmup, I
adjusted the carb main jet and idle jet, and drove the O-12 some more.  It
has no muffler, so you can hear every misfire clearly.  It really sounds
good now.  The exhaust is usually colorless; it used to be be visibly
black, and the plugs indicated that the fuel/air mixture was too rich.

I think that the rocker arm cover oil leak has stopped, too.  So I think
we're making progress.  This should be a wonderful parade tractor, and I'm
trying to get it running like it should.  This is probably the first time
I've had two good-running O-12s in my possession, so I'm quite pleased. 
One ugly one, one pretty.

Guess I'll have to switch back to component rebuilding.  I'm out of
rebuilt F4 magnetos, so that'd be a good place to start.  Also carbs and
fuel pumps.  Then there's the O-12 restoration I'm picking away at.  All
the steering and front axle parts are as good as new.  Time to start
putting it back together.  I've promised myself that I won't start on the
engine until the rest of the tractor is done.  Engines are fun.  The rest
of the tractor is less fun.

-Karl