I've had a '59 F100 4x4 for about a year now, I drove it to it's parking spot, put it on blocks, and have been working on it on my lunch hours since then. The biggest project has been replacing the brakes.

During that time, I would start it usually 2-3 times a month, and it always started easily and ran great. Idled great. Today I started it after about a 3-month downtime and it started right up (on choke, as usual), but developed a stumbling miss, and nould NOT idle. Even when hot and holding it at around 1000 rpm, the "miss" was there, not a regular miss like a bad valve or bad plug, but something more intermittent. It does not seem like an ignition miss, although I haven't checked that.

What I DID find out was TINY BUBBLES bubbling up around the head gasket under the #3 and 4 plugs after I shut it down. I started it back up and ran it on choke and looked in the same area, and could not see the bubbles while running.

This may be an obvious question, but is my head gasket leaking? Would that account for the sudden roughness and no-idle?

Would a head gasket begin leaking after sitting for a while on an old truck?

Should I try to re-torque the head?

 

A head gasket usually doesn't start leaking all of a sudden just from running an engine on blocks. and they typically don't leak to the outside since that is the furthest distance from the combustion chamber. That doesn't mean it can't happen it's just not likely. After sitting for 3 months, the gas in the tank could have gone "stale" (the lighter more combustable components evaporate off) Varnish may have built up in the carb restricting passages or causing rubber seals or diaphrams to stick and tear, the carb gaskets may have shrunk allowing air or vacuum leaks. or a vacuum hose may have split or cracked. Sometimes plugs will rust and foul out or moisture may have found it's way into plug wires or distributor cap. Other causes of rough idle could be a hydraulic lifter or valve that is sticking.
There are 3 relatively inexpensive diagnostic tools that should be in every gearhead's tool box, they can tell you volumes about the health of an engine:
1. Compression gauge. by taking compression readings on all the cylinders you can gauge the health of the engine. All should be within a few percent of equal. If you have two adjacent cylinders that are both reading low while the rest are high suspect a blown head gasket between those cylinders. A single or random low cylinders can indicate worn rings or bad valve(s). Squirt a tablespoon of motor oil into the low cylinder and recheck. If the compression increases noticable think rings or scuffed cylinder walls, if it doesn't figure on a valve job is in the near future. All cylinders low? figure it's time for a rebuild. If one or more cylinders are reading higher than normal it could indicate extensive carbon build-up.
2. Vacuum gauge. (and a T fitting and rubber plug) T the gauge into the main vacuum hose and start the engine, the vacuum reading should quickly climb and hold fairly steady. If you quickly gun the engine the reading should drop and then immediately return. If the reading is low, or bouncing you likely have a vacuum leak or a stuck valve. Start wiggling and wrapping your hand around the hoses between the engine and the PB booster, the carb and vacuum advance on the distributor, and or any nipples or tubes around the base of the carb. If the engine starts running smoother or the reading smoothes out you have a leaking hose. If that doesn't produce any changes, disconnect one hose at a time at the engine end and plug the connection point (not the hose with the rubber plug or your finger. If the reading smoothes you've found the problem line. When checking the ine the gauge is hooked to just hook the gauge directly to the fitting instead. If it is the line going to the vacuum advance, disconnect the line at the carb. Now suck hard on the hose and you should see the arm on the advance diaphram move. Stick the end of your tongue over the end of the hose to hold the vacuum in the line. Does the arm stay advanced and the vacuum hold until you pull your tongue away? If not replace the rubber hose and try it again. If it still doesn't hold replace the diaphram.
3. Cylinder leakdown tester. You'll need a source of compressed air with this gauge as well. A more accurate and extensive way to test the health of each cylinder. It will pinpoint blown head gaskets, stuck or burned valves, worn or cracked rings, burned pistons, damaged cylinder walls, general health.

 

Thanks, AXracer, but what would cause the tiny bubbles to form along the head/block interface
after shutdown?

 

Worse case: cracked block. best case: moisture or condensation buildup that boiled when the engine got hot. In the middle: a loose sparkplug or exhaust manifold gasket leak, a plugged oil breather that's pressurizing the valve cover?
Try the old leak test: brush a solution of 50-50 dishwashing liquid and water over the area and watch for more bubbling. try to pinpoint the source of the air causing the bubbles. If it is between the head and the block, try turning the engine over by hand. When that cylinder comes up on compression the bubbles should reappear if it's a head gasket. Also open the radiator cap while the engine is cool. Make sure the coolant level is above the bottom of the tank and start the engine. A blown headgasket into the water jacket will make a continuous stream of bubbles in the coolant after the thermostat opens.

 

Have you had the head off?

 

Nope, haven't pulled the head yet. I forgot to clarify that the bubbling was on the distributor side, not the carb side.

It's right at the head gasket. I cleaned the area of the 40-odd years of oil and crud, so next time I start it I'll have a clear view of where/when/how it originates.

 

While we're at it, does anyone know what the torque value is for the head bolts?