Red's Engine Talk
Oil Pressure Woes Nov/Dec 2005
What are some of the problems that can cause no or low oil pressure? First of all, if you think that you have a problem, make sure that you have an oil pressure gauge that is indicating correctly. Especially if it is an electric sender with a wire to the dash gauge, check with a known good mechanical gauge.
If you truly have no oil pressure, these are some of the things to check:
• Engine has no oil.
• Engine has no oil pump
• Oil pump driven gear is not turning the oil pump shaft
• Engine has no oil pump pickup or it is loose on the pump
• Oil pump has one gear missing
• Oil pump cover is loose or missing
• Oil pump pressure relief valve is installed incorrectly or missing parts
• Engine has no oil pump idler gear
• Cam has no oil pump drive gear on the rear
• The oil pump drive gear on the cam is not turning consistently with the cam. Most cams, and oil pump drive gears, have a flat to prevent this. The gear without the flat is Part No. 18-6254-A, the gear with the flat is 18-6254-B.
• A dry oil pump – no prime. It can usually be primed through the ¼" NPT holes at the left rear of the block.
• Oil pump pickup gasket installed incorrectly.
Here is a list to check for the source of a very low oil pressure problem. If you have some, but very low, oil pressure you could check:
• Wrong undersize bearings for mains, rods or cam shaft. Due to wear, many Flathead Ford cams have been ground down on the journals. Cam bearings are available in -.010, -.020, and -.030". They are also available in +.010"ID and +.080" OD. Rod bearings are available in many undersizes for the journals. The full floating type used is the USA from 1932 – 1948, are also available in +.004 and +.008" OD. Main bearings are mostly straightforward but there are factory blocks that are line bored to +.015" on the OD. They require bearings to match. Measure journals and bearing housings to determine what undersize, and possibly oversize OD, bearings you need. Measure the bearings when you get them to make sure they are what you need. Check clearances to ensure that they are correct.
• Missing the screw in plug in the front of the block behind the timing gear.
• On 1932-1948, using a plug in the block behind the timing gear that does not have the built in restrictor.
• Oil pump pickup gasket installed incorrectly, or missing.
• Oil pump pickup flat against the bottom of the pan.
• On a bypass (factory) oil filter system, no restrictor fitting in the supply line.
• Engine oil temperature too hot for grade oil used.
Low oil pressure can, of course, also be caused by wear. This could be normal wear due to mileage or abnormal wear due to debris in the oil, using the engine without an oil filter or an air filter, low oil levels, high temperatures, or extra heavy loads.
It is also possible to get abnormal wear from clearances set either too small or too large when the engine is assembled.
If you have had oil pressure problems from other causes, let me know and I will add them to the lists. - Red.