[Farmall] O-12 fixin'

[Robert L. Holtzer]

olmstead at ridgenet.net wrote:
> 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
>
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>   
Nice story, Karl!!  As usual!

Bob Holtzer