Flathead Motor Startup

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Use good safety procedures to protect people and property


This article may miss a couple things, but the following are the some of the usual recommendations:

1) Check oil for clean appearance. If very low, add to full. If overfull, drain out the excess. If it’s very thin or otherwise nasty looking/smelling, drain and refill with new 10/30W. If oil looks dark but ok, leave it for now.

2) Loosen the generator/fan assembly to allow lots of slack in the belt (or belts if a two-belt system). Try to turn the water pump pulleys by hand. Repeat this test on the generator pulley and the fan assy. If all parts turn easily, reset the tension in the belts by snugging them back up. If any of these rotating parts will not turn easily, leave the belt(s) loose. You will not need them to operate for a brief  motor start-up test and they would just restrict the motor from turning over, possibly burning up a belt if it starts.

3) Pull the spark plug wire from the middle of the distributor to the coil.

4) Check and clean up any battery terminal connections. This includes the ground strap from the firewall or frame to the block. Use a new or good, fully charged-up battery.

5) Make sure all primary ignition wires are in place and that there are no bare un-insulated wires. If you suspect the wiring is not correctly hooked up, stop here and refer to the wiring schematics at www.vanpeltsales.com.

6) Remove all spark plugs. Have a look at each. Clean and re-gap, or replace as necessary. Most Ford & Mercury flathead V8’s originally specified the Champion H-10 plug, but here are alternatives if so desired. The gap should be between .025 and .030”. Complete tune-up information can be found on the FlatheadV8.com website as well.

7) Disconnect the fuel line from the fuel tank at the fuel pump for now. This steel line ends at the firewall and makes the final connection to the fuel pump through a short length of flexible fuel line. Disconnect either end of the flex line. This will prevent the fuel pump from pulling the old gas up into the motor.

8) Make sure all rags, hands, tools, etc are clear of the motor fan, and use the ignition starter switch to turn over the engine. If the starter hits but won't turn the motor over, don’t keep trying. Place a socket and large breaker bar on the front pulley nut and try to turn the motor over manually, turning clockwise. If still stuck, you will have to try using some Marvel Mystery Oil in the cylinders to help loosen things up. If the starter turns things over ok, let it spin about 3 or 4 times, for about five seconds each time. This will help circulate some oil back through the oil galleys and bearings in the motor.

9) If motor spins ok, put the spark plugs back in place and tighten them. Reconnect all spark plug wires including the distributor-to-coil wire.

10) You do NOT want to try to run old, dirty, gummy gasoline into the motor from the car's gas tank if it has been there for more than a year. Rig up a portable marine gas tank... a one or two gallon tank (with fresh gasoline) with a gravity hose connection and shut-off valve. Connect it to the carb's inlet fitting with a length of neoprene gas hose. You may have to make a hose barb fitting or something similar for a temporary connection. Set the tank up on the cowl and secure it to make sure it can't fall. It's a good idea to remove the hood for easy access and safety. Be sure to have a fire extinguisher handy and do the start-up out in the open. Do NOT attempt the start-up inside your garage, barn, or other structure. Have a helper remain with you.

11) Open the valve in your marine gas tank and let gas flow into the carb. If you see any raw gas leaking out anywhere, find the problem and fix it BEFORE you try to start the motor. It may also help to have a can of spray starting ether to help kick things off.

12) Make sure the car is in NEUTRAL and wheels blocked and parking brake set .

13) Try to start the motor. Don't be surprised if it doesn’t run smoothly. If you have squirted any oil into the cylinders, you can expect a big cloud of blue smoke when it starts. Any old gas in the carb may prevent it from doing its job properly. A carburetor rebuild would be in order anyway. Also, you can have one or more stuck engine valves (stuck open that is) which will cause rough running and popping. You can address these problems one at a time. A valve that is stuck closed could possible damage a stock lifter (poking a hole in the top).

14) If the motor starts and runs ok, just let it go long enough to warm up the oil. If you hear any drastic, horrible sounds (something banging or clanging or loud screeching) stop the engine immediately and try to locate the problem. If it runs ok, stop the engine, drain the old oil, and replace it (unless you have already done this procedure). Use a good, detergent type oil, but consider using a non-detergent oil on an old used motor (to prevent the loosening and flushing of old sludge particles that may block up an oil passage somewhere else). If your motor has the accessory oil filter cannister, replace the filter element inside. After the oil change, you can start it up again to let it warm up the rest of the way. You should watch for other problems such as leaking coolant , leaking motor oil, overheating, etc.

Things to watch for:

Gasoline leaks, antifreeze leaks, sparking/shorting wires. You should figure on pulling the gas tank later and having it professionally boiled out and resealed. Don’t skimp on the steel fuel lines either. Chances are, they are as old as the car and certainly can have rust internally as well, so replace them also. Add an in-line fuel filter before the fuel pump. Replace the fuel pump and the little flexible fuel line on the firewall also. They both have gas resistant rubberized components that do fail with age. Get the carb rebuilt. Consider putting new ignition points and condenser in. Perhaps the coil as well.

If you have a strong battery and the starter won’t spin, check the starting relay. As a brief test, you can connect 6 or 12 volts directly to the starter to check to see if it will turn. Be sure to use heavy 00 cables. The original Ford starters ran on 6 volts (positive ground) but will still spin correctly if the ground is reversed. They will also handle 12 volts…. they just spin faster.

Although it is difficult to detect, mice can get into the exhaust pipe and camp out way up toward the motor. This can cause the motor to stall out, run hot, or run poorly. A stuck-closed heat riser damper valve, if equipped on your vehicle, (located between the exhaust manifold and the exhaust drop pipe) will do the same thing. When the motor starts, have a helper check the exhaust pipe outlet for the feel of exhaust gases pushing out. You may have some exhaust system work to do!

Things to Replace:

§         Flexible Fuel Line between the fuel pump and steel fuel line. (Old flex lines can have cracks, preventing the suction of fuel up from the tank to the fuel pump).

§         Fuel Pump (rebuild if you know how and have the parts, otherwise replace. Old pumps often have cracked diaphragms, which might still pump gas, but could let some gas leak down into the crankcase, diluting the oil).

§         Engine oil. (Want to do it right ? Pull the pan and scoop out the old oil sludge, especially the inlet screen of the oil pump. You can unbolt the pickup tube & screen and soak it, blow it out, etc). Replace the pan gasket .

§         Vehicle wiring with stiff or cracked insulation. (Old car wiring is a fire waiting to happen. Even if your vehicle still fires up and runs, if the wiring is more than 20 years old or has obviously been tampered with or altered, replace it).

§         Ignition system (plugs, wires, points, condenser, coil, cap, and rotor. Beware of cheap replacement ignition parts…. they are well known to have defects right out of the box. Caps, coils, and condensers are particularly suspect ). The old points may be ok, but just need cleaning of the contact surfaces.

If you get the motor running, don't be tempted to drive the car around until you've had a chance to check the brakes. If the motor turns over but won’t start, you will have to begin a standard  troubleshooting procedure (often found in old MOTOR MANUALS or CHILTONS REPAIR MANUALS) to locate the problem. In general, try not to make assumptions about the state of your motor, or slapping on replacement parts everywhere, hoping to solve the problem. Don’t use the “dartboard” approach to troubleshooting.

Gas engines can be checked for some issues very easily. Two common basic problems are lack of fuel and lack of ignition (or badly timed ignition). Assuming these are ok, you need to check for compression. Many owners don’t seem to locate the answers to the FUEL and IGNITION questions very easily. Here are a couple tips for each:


Always start by checking for gas in the tank. Then if you know there is gas in the tank, continue on with removing the air filter, looking down the carb, working the throttle linkage, and watching for small sprays of gas down into the throats of the carbs, If I see the squirts of gas, I know the carb has fuel in the bowl. This means the fuel pump and fuel lines have delivered gas to the carb. It’s NOT a complete test of the fuel delivery system, but is enough to show that there is enough gas to fire off an engine. A sniff of gas in the carb is another tell-tale.

If the carb does not show any gas, it may not have any in the bowl. Removing the top screws on the carb body will reveal the float chamber and float assembly. If it’s full of gas, the accelerator pump mechanism (the gas “squirter”) may be worn out . If the bowl is empty but the float is stuck in the UP position, the needle valve on the inlet will prevent gas from coming into the bowl. Try to free up the float, replace the top cover and see if gas will flow in the carb. A sunk float is no good either as it will allow the fuel pump to over-deliver gasoline into the carb, causing flooding and rich operation. If the gas is still liquid but smells like old varnish, remove the carb, drain the old gas, and replace with fresh gas. Gummy old gasoline in the bowl means there will be more of the same in the tiny passages of the carb. A carburetor rebuild is in order.

The fuel pump may not be working but that is why I recommend using a temporary fuel tank that is connected directly to the carb. The motor might run from this temporary set up, but not run when connected to the vehicle’s fuel system. Rusted tanks, clogged pickup tubes, cracked flexible fuel line, plugged filters (if so equipped) and defective fuel pumps can all be at fault …..individually or collectively. Going back to my earlier notes, you should replace the old system components rather than guessing which is bad and allowing dirt to make it up to your carburetor.


A quick review of your car’s basic ignition wiring system is not a bad idea. With the diagram in hand, you can observe the various wires to see if they are connected to their proper locations. Spark plug wiring should be checked for correct firing order. The diagrams below shows the 1949-53 set up. Refer to the FLATHEADV8.COM website for the 1932 to 48 diagrams.

Note that ALL Ford and Mercury flat head V8 engines (from 1932 to 53) had the same firing order (1-5-4-8-6-3-7-2) as shown above. All were 6 volt positive ground systems. Many have been converted to 12 volt negative ground. This meant a reversing of the leads to the coil. If incorrectly wired, the coil will still produce voltage but it won’t be at full strength.

After you have pulled all spark plugs and cleaned and re-gapped them (or replaced them) you can perform a simple spark test . Remove any plug (I generally use the #1 since I also want to check the distributor for matching up the rotor to the #1). It’s best to try this in a well shaded or dark area. With the wire fully connected, grasp the spark plug with insulated pliers (I use gloves as well). Hold the plug’s metal base against the block or manifold, and crank over the engine. You should see a spark at the plug gap. A good strong spark will easily jump the gap and be multi-colored. If you have no spark, you will have to work your way back through the ignition system to find the problem. Do you have voltage to the coil? Are the distributor points clean and burr-free? Are all wires properly connected and insulated? A bad coil or bad condenser are easy to replace with known quality units for test purposes. If the points are suspect, replace and adjust the new ones to spec. Is the cap cracked or does it have heavy carbon track inside the top? Is the rotor busted or burnt at its contacts?

You may have good spark but if the motor is out of time, it won’t be delivered at the right moment for proper detonation of the fuel. This will require checking the timing. There were three different basic distributors used for flathead V8’s over the years. You can find tune-up info on these on the website as well.

If the motor has very poor compression in all cylinders it will be hard to start. However, many flatheads were known to start and run with very low compression. A new motor or fresh rebuild should show around 105 to 110 lbs of compression on a crank test . An obvious thing to look for is loose head bolts (or studs) from a previous attempt to remove the heads. Tighten the heads with the correct torque and sequence (see website). Remove all the spark plugs. Check compression with a proper gauge, one cylinder at a time. Prop open the carb throttle when cranking the engine over to determine the pressure for each cylinder. Record these readings by cylinder number for future reference.  

With the motor running, you can also use a vacuum gauge to diagnose many engine problems. The chart for vacuum gauge readings is linked below. Refer to the chart for specific tests.

Vacuum Gauge Readings


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