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Old 07-24-2011, 03:41 PM
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Oil Pump Clearance Test

This is just a little tidbit of info that I find interesting. I recently had my oil pan off and decided to mix and match parts in my oil pump to see what would happen.

As you can see from the chart below, I went from a loose tolerance pump (#1) and went to a tighter tolerance pump (#2) by using different gerotor parts, but the same housing and relief valve.

Also, Pump 1 had some scratches and scuffing on the lobes of the rotors. Pump 2 did not.

I did a test drive, and once the oil was up to temp, I checked the oil pressure at idle, at 2000 rpm and at max pressure. In all cases, the oil pressure was exactly the same with Pump 2 as it was with Pump 1.

My conclusion is an oil pump can wear a bit, or even get minor scratches from debris, yet still provide oil pressure as usual.

Actually, provide oil flow. For the most part, the pressure appears dependant on bearing clearances.


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Old 07-30-2011, 05:47 PM
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relief valve

some kind of pressure relief system on it? same spring pressure same oil pressure.
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Old 07-30-2011, 06:06 PM
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Yes, same pump housing, same relief spring, etc. And once the relief valve opens, yes, the presssure is expected to be the same. However I was interested in what was going on prior to that. My engine yields the following (hot) oil pressures with either pump:

800 rpm idle 13 psi

2000 rpm 43 psi

max pressure when relief valve opens 85 psi

My experiment was to see if I could reduce the little dip (red-line) that occurs at lower rpms in the chart below, thus raising the oil pressure at idle a little bit, but there was no change.



Sort of makes me wonder what good blueprinting an oil pump does, other than changing the relief spring. All that end play clearance adjustment and de-burring they do... perhaps the deburring helps keep the oil from becoming aerated, but so far, it seems spending money on a blue-printed pump isn't worthwhile.
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Old 07-30-2011, 06:19 PM
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[QUOTE=Argess]For the most part, the pressure appears dependant on bearing clearances.[QUOTE]

It's common knowledge oil pressure is directly related to bearing clearances. I would expect the same as you found, unless pump #1 had excessive rotor to housing clearance, which it didn't, and other clearances were only a couple thousandths apart, no huge differential.
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Old 07-31-2011, 06:16 AM
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pump it

When i worked on hot street and race pumps i polished the passage in the rear main cap, chebbies.Proper bearing clearance is everything.
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