blueprinting small block oil pump

-
turboking15

turboking15

Well-Known Member
Joined
May 8, 2013
Messages
343
Reaction score
403
Location
Columbus, Oh
Does anybody have a good write-up or how to on this? All ive been able to find is, tear down, sand sharp edges, put back together. Is this all thats needed or are there tolerances / clearances that need to be checked and modified aswell?

Thanks
 
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.
  1. No more than.0015" cover warpage from flat
  2. Inner and out rotor heights >.825" (see 5)
  3. Outer rotor to pump body clearance <.012"
  4. Minimum rotor to rotor clearance < .010"
  5. Rotors when in the housing should be no more than .004" below the level of the housing body opening
  6. Inspect relief valve and its hole for scoring. If smoothed use 400 grit sandpaper and do not smooth the sharp edges of the valve.
  7. Relief spring free length 2.032 to 2.047".
  • 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.
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.

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.
 
Last edited:
Agreed with the above, probably about all you can do. An oil pump is a fairly simple device, there really isn't a whole lot you can do to them. As stated above, FSM will have nominal clearances to verify against, making them consistent across all surfaces is the goal but easier said than done. Measuring for pump cavity concentricity, consistent depth and flatness of the cover may be worthwhile exercises.

If you only have one unit it may be wiser to leave it as-is, once you start messing with machined surfaces there's no turning back. Swapping components from other units may reveal better tolerances between parts but obviously you'd need to have more than one pump on hand to compare against.

There is a company called Precision Pumps that offers this service, I bought a SB pump from them a while back. They enlarge and smooth the cast passages, inspect/correct rotor/cavity/cover clearances and coat the internal parts with teflon. Expensive proposition, not sure if it was worth the cost.

Incidentally I ended up trashing the pump body during the install. One of the main studs was a hair too long and when I went to torque the pump down I didn't see it was cocked. It split right in half! I got another non-blueprinted pump and swapped in the teflon coated rotor and cover. I looked at how they smoothed the passages out on the cracked body and copied it. Worked out OK, no problems.
 
I raced in rallies a long time, where you can put a lot of sustained revs on engines, and once I learned, found that pumps could be restored to very good condition with new gears and new a cover, or a new body if it was worn. Nothing fancy needed, just go back to the new clearances. So I don't subscribe to the coated gears and such being necessary for most engine hot-rodding.

I eventually got to just replacing the pump at every rebuild; cheap insurance. Never had an oiling related issues once I adopted those basic practices, and bearings always looked good at a teardown. Running 1 HP per ci to 1.75 HP per ci turbo'd.
 
Clean it, make sure the relief valve operates freely, and put it together. No need for any more work.
 
turboking15 said:
Does anybody have a good write-up or how to on this? All ive been able to find is, tear down, sand sharp edges, put back together. Is this all thats needed or are there tolerances / clearances that need to be checked and modified aswell?

Thanks
Click to expand...
All you really need to check are 3 critical clearances. The gap between the inner and outer rotors and the cover end play and the gap between the outer rotor and the body. You can just use feeler gauges. The gap between the outer rotor and the body should be less
Than .014, between the inner and outer rotor .010 or less and the cover and rotor end play maximum .004. Literally this is a go and no go with feeler gauges and a straight edge across the pump body with the rotors in there, try to put the .004 under the straight edge. If it does not go you are good as long as the rotors turn freely with the cover tightened up. IMHO.
 
nm9stheham said:
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.
  1. No more than.015" cover warpage from flat
  2. Inner and out rotor heights >.825" (see 5)
  3. Outer rotor to pump body clearance <.012"
  4. Minimum rotor to rotor clearance < .010"
  5. Rotors when in the housing should be no more than .004" below the level of the housing body opening
  6. Inspect relief valve and its hole for scoring. If smoothed use 400 grit sandpaper and do not smooth the sharp edges of the valve.
  7. Relief spring free length 2.032 to 2.047".
  • 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.
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.

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.
Click to expand...

.015 cover warpage lol are you sure that's not a typo?
.004 end play with a .015 warped cover is pointless.
 
turboking15 said:
Does anybody have a good write-up or how to on this? All ive been able to find is, tear down, sand sharp edges, put back together. Is this all thats needed or are there tolerances / clearances that need to be checked and modified aswell?

Thanks
Click to expand...
I should add that if you want to port your pump body to improve flow then I would refer you to Guitar Jones excellent oiling mods thread which has some good photos to go with it.
 
I plan on doing the port work as laid out by guitar, just wanted to make sure there was nothing else i needed to do while i was in there before it all goes back together.

Thanks for all the info guys!
 
Duane said:
.015 cover warpage lol are you sure that's not a typo?
.004 end play with a .015 warped cover is pointless.
Click to expand...
Good question, Duane...... I 100% agree..... and you are spot-on.. typo! I have corrected the original; many thanks for catching that.

I was giving these numbers to the OP so he could see what is measured and important. I'll emphasize again.... these are 'service limits' which tend to be tolerance limits for not replacing or repairing something that can be used in general service. Service limits are not always what you want to build to for anything performance.... For example, the service limit on timing chain slack for a /6 is such as to give you 3-4 degrees of timing retard.... not what you would want to do for a hot rod LOL
 
You must log in or register to reply here.
-

Back
Top