My 65 FSM has complete service measurement for all parts of the oil pump. Now those are service limits, which tend to be on the excessive side for hot rodding, but it is a basis for which measurements to make.
- No more than.015" cover warpage from flat
- Inner and out rotor heights >.825" (see 5)
- Outer rotor to pump body clearance <.012"
- Minimum rotor to rotor clearance < .010"
- Rotors when in the housing should be no more than .004" below the level of the housing body opening
- Inspect relief valve and its hole for scoring. If smoothed use 400 grit sandpaper and do not smooth the sharp edges of the valve.
- Relief spring free length 2.032 to 2.047".
How much to tighten up on the above numbers, I don't have a good sense. In most cases, the tighter, the better. However, scored/chewed surfaces on the rotors that face each other is a very good source of pressure loss. The same pressure loss happens with a lot of scoring or wear on the pump cover or on the gear ends, top or bottom.
- This length may be for the lower pressure relief spring; there are 2: one for 55 psi and another for 72 psi. There is a minute difference in spring wire thickness between the 2.
FWIW..... A new oil pump is one of the simple but quite good places to spend money. I prefer the HV types, which keep pressure up better at lower RPM's. New oil pumps like these do not cost a lot.
