“All Model A engines leak a little oil – typically a few drops.” – FordBarn.com forum contributor

Baril Engine makes every effort to circumvent and prevent future oil leaks, but these engines have a known problem of oil leaks. Candidly, Model A Fords were built when dirt roads were more common than gravel, and oil drops were less of a big deal than today. Please continue reading for our initial troubleshooting guidelines, as the most common types of leaks are easy to solve.  

Overfilled Crank Case

While it may feel counterintuitive, many Model A engines will leak oil when the crankcase is topped off to the full line on the dipstick. This leak will resolve when the oil level has stabilized to the halfway mark between ADD and FULL. 

Bad Oil Filler Cap

Next up is to determine if you have a bad oil filler cap resulting in increased crankcase pressure. Remove your oil filler cap and verify there are no restrictions or blockages in the oil filler pipe. With the filler cap removed, take your car for a test drive to see if this resolves your leak. If this is successful, that indicates that the filler cap was seated too tightly, increasing crankcase pressure and forcing oil out of the rear main. This is one of the most overlooked yet easily fixed causes of oil leaks – solve your leak by buying a replacement labeled as a breather cap. 

Checking for Leak Location(s)

Now that you have eliminated the two most common causes, wipe down your engine assembly to better assess where the oil leak originates. Common locations to check include the cotter pin, cotter pin hole, oil pan, timing case cover, front seal, valve cover, and oil pump; the cotter pin is the most frequent place to spot drips. Please note that the probable leak source is different if the oil drips from the cotter pin hole rather than the cotter pin – noticing these small details will reduce your frustration in diagnosing the problem! 

Cotter Pin Hole 

If the oil is dripping from the cotter pin hole, you likely have a rear main leak. If you skipped checking your oil filler cap, do that now to eliminate the most frequent cause of elevated crankcase pressure.  

Next, check the oil filler pipe’s airflow volume: with the cap still off and the engine at high idle, hold a lightweight plastic bag around the oil filler pipe. The bag should flutter but not fill – filling with air signifies excessive blowby pressure in the crankcase, which causes oil to leak out the rear main or any other location not pressure sealed. Bad pistons, cylinders, rings, or valves & guides can cause this increase in crankcase pressure. Please give us a call to discuss service options. 

Not your oil filler cap or excessive crankcase pressure? Now it’s time to remove the inspection cover from your flywheel housing to check if the inside of the flywheel is wet with oil. If it is wet, this typically means the oil has leaked out either the rear main cap or the cap to the block. In a well-ventilated space, start your engine and watch closely to determine where the oil is seeping. 

  • Rear main cap on the right side of the engine – replace the gasket between your engine & flywheel housing. 
  • Rear main cap and block shims – check that the cap fits flat to the block; file if needed and add a fine layer of RTV to the shims. 
  • Rear main bolts – this is a less common leak source easily solved with a few drops of RTV on the threads & under the heads of the bolts. 
  • Rear main cap into the flywheel – remove the oil pan and verify the oil tube is not altered, broken, or missing, as this will cause elevated crankcase pressures creating blowby leaks. On the other end of the spectrum, having the oil pipe screwed in too far will restrict oil flow, also creating a rear main leak. If the tube is well sealed and the correct length, check your oil galley plug, Babbitt or bearings, and crankshaft shims.