How to Deal With Oil Leaks Question

Oil leaks are a common frustration for Model A owners, often caused by small details overlooked during engine work. Prevention is far easier than repair.

Preventing Model A Oil Leaks

When building or servicing an engine, ensure the rear main cap fits perfectly flat against the block, the oil slinger housing is flush, and the oil return tube and gallery are correctly installed to prevent crankcase pressure from forcing oil out.

Rear main shims should fit closely to the crank, oil grooves must be correctly cut, and bearing clearance should be checked carefully.

During assembly, small amounts of RTV can help seal bearing caps, bolt threads, and other fasteners that may allow oil to escape. Pay special attention to areas where bolts protrude into the block, the flywheel housing gasket, and the oil pan and cam cover joints.

A smooth, undamaged crank pulley and flat gaskets are essential for preventing front seal leaks.

Diagnosing an Oil Leak

If a leak appears, proper diagnosis is critical. Clean the engine and observe where oil first appears. Many leaks mistaken for rear main problems originate from the oil pan, timing cover, valve cover, or oil lines.

Oil dripping from the flywheel housing cotter pin usually indicates a rear main issue, often related to crankcase pressure, poor cap fit, missing gallery plugs, or restricted oil return.

Careful inspection and correct assembly practices will keep oil inside the engine—and off the garage floor.

Check for Bearing Wear

One common cause of oil leaks is bearing wear. During the first 5,000 miles of operation, both the rod and main bearings often loosen enough that they should be readjusted to the correct oil clearance.

If this service is performed at that time, many future engine noises and problems can be avoided.

Inspect the Rear Main Oil Drain Tube

When the rear main cap is removed, take out the oil drain tube, even if it has been brazed or welded in place. This is necessary to ensure there is no blockage in the drain passage.

Check that the passage is clear by blowing through the tube in the direction of oil flow. Also verify how far the drain tube extends into the intersecting passage.

If it protrudes too far, grind or file it back enough to allow unobstructed oil flow. If the threads do not allow the pipe to fit tightly, it should be brazed in place so it cannot loosen or fall out.

Avoid U-Shaped Main Bearing Shims

Do not cut main bearing shims into a “U” shape to fit around the bolt, a practice sometimes used to simplify installation without fully removing the cap.