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View Full Version : Melling oil pump: Question about pressure relief valve



CaifanSC
12-20-2005, 05:23 PM
Im about to install a new melling hi flo (later style) oil pump but is it required that I replace the pressure relief valve? IF so, is there any other way to get the old one out instead of drilling it out like the hayes manual sais? Thanx!

CaifanSC
12-21-2005, 11:19 AM
any help appreciated fellas.

Micahdogg
12-21-2005, 12:26 PM
I don't know why you would want to replace it. NOt to mention I don't know how to replace it. But I can tell you what happens if that valve is siezed and won't "relief." After about 4 seconds of running you'll blow the oil filter gasket and spray oil all over the place.

Micah

David Neibert
12-21-2005, 12:56 PM
any help appreciated fellas.

Leave the pressure relief valve alone.

David

edspringer
12-21-2005, 01:13 PM
I just had my oil pump off this past weekend thinking it was that real bad noise in the front of my motor that is probably a spun rod bearing. There is no need to change it unless the plunger is binding or the spring is broke. Like David says, leave it alone. If you want to check the pressure regulator to be sure the spring is good and the plunger is not binding, take a small screwdriver and move the plunger toward the plug holding the spring. BE CAREFUL not to scratch the bore where the plunger moves. Need I say more!

Ed Springer

94 Red SC Auto: 70mm TB, Fresh Air Intake, Stock 90 SC Pulley, Accel 36# injectors, Scorpian 1.73 Rockers, ARP Head Studs, 190 l/h fuel pump, 180 Stat, Raised SC Top, I/C Fan, Headers, Raven Muffler (no cats) with stock resonators, 3:73 Gears, 76 C&L MAF (Gold Tube), Magnacore Wires, NGK Iridium Plugs, MSD DIS-4 + Ignition Box, TRANSGO Shift Kit, Haydon Auxiliary Transmission Cooler, Pro-Torque 2500 TC, Tokico Struts & Shocks, Royal Purple Synthetic Lubricants, Optima Yellow Top Battery, American Racing 17 Sniper Wheels, Michelin Pilot Sport A/S, COMMANDO Alarm and Remote Starter and Autometer A/F Ratio and Transmission Oil Temperature Guages.

CaifanSC
12-21-2005, 01:45 PM
Thanx for the info guys...the reason I asked is bc the new pump came with the valve and I remember reading the section on the hayes manual about replacing it so I decided to ask. Im going to test the one in the timing cover to make sure its not stuck since its going into the rebuilt engine.

Whats the reason why it should be left alone? Is it bc its just risky putting the new one in CORRECTLY?

David Neibert
12-21-2005, 01:57 PM
Thanx for the info guys...the reason I asked is bc the new pump came with the valve and I remember reading the section on the hayes manual about replacing it so I decided to ask. Im going to test the one in the timing cover to make sure its not stuck since its going into the rebuilt engine.

Whats the reason why it should be left alone? Is it bc its just risky putting the new one in CORRECTLY?

It sould be left alone, because it's a pain in the azz to change and there probably isn't anything wrong with the one you have. I would be much more concerned with the condition of the timing cover.

If there are any grooves or noticable wear on the surface where the oil pump gears ride, it will have a negative impact on the amount of pressure and flow the new pump will supply. If there are grooves big enough you can feel with your fingernail, replace it with a new late model cover.

David

PS: New timing cover includes the oil pressure relief valve.

CaifanSC
12-22-2005, 12:21 AM
it's a pain in the azz to change

I figured thats what it was. I havent tested mine but i hope its ok. In any case ill at least have the other one as a back up.

I checked the surface of the timing cover where the gears touch and altho you cant feel any 'grooves' you can feel the surface a bit rougher than the rest of the mounting surface. Check the pix. What do you think? Dave...whats different on the later timing cover? Also, if mind serves correct wouldnt i need a different bracket too for the crank sensor?

ps...from looking at the pix, the scratches look much worst than what they really are

http://webpost.net/jo/JorgeCafrune/cover1.JPG


http://webpost.net/jo/JorgeCafrune/cover2.JPG

http://webpost.net/jo/JorgeCafrune/cover3.JPG

David Neibert
12-22-2005, 02:02 AM
I think it's borderline, but will probably be okay. Mine had slightly more wear and I replaced it. But I rev the crap out of mine and didn't want to take any chances.

The late model cover is all Ford sells now. It is the same as the early style but will accept either the late or early style crank sensor mount.

David

68COUGAR
12-22-2005, 02:44 AM
Ques. guys! What's the actual difference between early & late model oil pumps? Is the late model a HV, HP, or HV/HP pump? What advantage does the late model pump, over the early pump, if the relieve valve is the same? Is the early pump just MUCH weaker than the relieve spring?

My experience with oil pressure relieve valves comes from FE motors, & may not apply here. I guess it depends on the oil pressure at the valve, & the rating of the valve spring. If the relieve valve is constantly pouring oil back into the pan, then useing a HV or HP oil pump will only ensure that you have a constant oil pressure, regardless of rpm. Does anybody know the normal pressure at the valve, from idle to around 6500?

I used a HV/HP pump (stock relief valve) in a stock 390GT. Oil pressure wouldn't go above 110 psi, which must be what the spring is rated at. Would run 90 psi hot. So to run higher oil pres. than 110, shimming the spring, or changing to the pink (427) spring is required. This is done because oil is fed from the mail oil galley, to the cam bearings, & finally to the main bearings (center oiler).

I've never seen a diagram of the oiling system in an SC motor. Does anybody have that diagram?

68COUGAR

CaifanSC
12-22-2005, 10:18 AM
will probably be okay.

Awesome news! Just in case im going to check the timing cover on my other engine and see which one is better.

ONe question though, for example in the case of this one...could i take it to the machine shop and have them smooth the surface and still be able to use it? IF this is an option I might do it as i might have to pay a visit to the machine shop depending on how my roller rocker install goes.

Kurt K
12-22-2005, 10:39 AM
FWIW, some people have had the oil pump mating surface remachined to smooth up the grooves from the gears. You don't have to take off much at all. But if you don't have access to cheap machining, it might not be worth it.

Edit: Oops, this is what happens when work interupts my post typing :) You already mentioned it.

Micahdogg
12-22-2005, 12:31 PM
Why are the scratches bad again? We can use superchargers that are all gouged up but a some scratches in the oil pump mating surface is way bad?

Micah

XR7 Dave
12-22-2005, 02:21 PM
Why are the scratches bad again? We can use superchargers that are all gouged up but a some scratches in the oil pump mating surface is way bad?

Micah

Some people are driving around with really bad superchargers.

CaifanSC
12-27-2005, 02:47 PM
If you want to check the pressure regulator to be sure the spring is good and the plunger is not binding, take a small screwdriver and move the plunger toward the plug holding the spring.

Well i checked the other timing cover and it looks better than this one (except much dirtier!), so im going with the other one. I checked to make sure that the small plunger thing moves and it does, and the spring compresses freely with no binding in the bore so I guess we're good in that department. Thanx for the help fellows!