Oil Pump Replacement

[cleszkie]

My rear main seal is starting to leak, so I while repairing that I figured I would replace my oil pump as well since the oil pan will be down. My oil pressure has been slowly going down over the past 15 years due to normal wear and I was thinking about throwing a high pressure/high volume pump in there to help get the pressure back up. Went online to order one and found that there are a ton out there for the chevy small block with different inlet sizes and pressure controls. Does anyone have a recommendation for me on which pump to get, what pick-up I need if the stocker isn't reusable, and if I really need the oil pressure spring adjustment?

Also, what diameter is the stock oil pump inlet? Thanks.

[magicoolbus]

I think we might need some more info: 6cyl, small block, big block.

[cleszkie]

1972 SBC, about 100,000 miles on rebuild with stock Melling M55 oil pump. When warm at idle - about 10 to 15 psi. Warm at highway speed (2500 RPM) - about 25 psi. I know these pressures aren't bad for a worn engine, but I was wanting to bring them up with a high volume pump.

I did a search on the board for oil pumps and got a lot of good info, but want to see if there are any other opinions out there.

[SeventyOne]

I've heard sometimes that sometimes high-volume oil pumps will pump so much oil to the top end the bottom end is lacking oil.

Not sure how much of this is true but thought I'd pass it along.

May want to post in the engine/drivetrain section.

[mud.man.rj]

Same Melling part# with a HV behind it will do the job, have installed many.

[unclesalty]

heres my go round w/ a hvhp pump- mellings, I believe- the pumps body was taller than the the oem, and the oil pan wouldnt fit over it, it bottomed on the pump casting. (not the pick up). I didnt even know they made a hv/hp pump. Funny thing is, I dont recall asking for one, either. I think they sold me what they had on the shelf. A hi volume pump just comes with bigger diameter gears, same body as original, just machined to fit, where the hv/hp gets a larger diameter AND taller set of gears, so the casting is taller. My workbench is now graced w/ a super-duper hi-perf oil pump, as I didnt care to invest in an aftermarket oil pan ($), or give up the ground clearance. With the need to compensate for loss due to clearances, I would maybe lean towards more volume, a hi volume pump. Couldnt you shim the relief valve spring a bit for a little more pressure, if you needed it? I always thought the sbc had a great oiling system, one of its many great features. Its easy to get into trouble running too much pressure, like punching through the filter element on a cold day cold start up. I think the hv/hp pumps are for turbos or something crazy like that. I think the one piece pan gasket was well worth the money it cost, wouldnt do it again with out one. good luck.

[unclesalty]

I had to buy the pump pick up separate, it costs about $10 more. Whoever you buy from should be able to match you up. If I had it to do over, I would look for a pump/pick up that has the brace that gets bolted on, uses one of the gear cover bolts.The others are all press fit, your supposed to tack weld em, idk, the bolt up looks better to me. The after market deep pan gives you an extra quart of oil, also. I just dont care to lose the ground clearance, we have some killer pot holes in the roads up here.

[Ole Beater]

To replace the rear seal you have to pull the number 5 main cap.

[DANTES JIMMY]

hi volume is cool high pressure is ok for high perf stuff but not nec for a driver occasional wheeling and as far as pumping all of the oil to the top end that only happens when you have a sludge or blockage in the lifter valley to keep it from running back into the oil pan
any oil pressure is good high pressure not always a good thing i would do a hi volume on a worn engine

[k5xjfiles]

Ive talked to a very smart man, and he warned me....

High Volume is OK......high pressure is a NO NO............unless its some sort of race engine etc.

[cleszkie]

Appreciate all of the input. I agree that a high volume/high pressure pump is not appropriate for a fresh rebuild. For clarification, I would be using the high volume oil pump on a high mileage engine with relatively large clearances.

[tdkosta]

I'm in the process of replacing the rear main seal also. Did you pull the engine? I was able to use an engine hoist to lift the engine high enough to unbolt the mounts from the cross member and then move the cross member forward enough for the oil pan to come off. I hope the rest isn't too much work and goes well.

Has anyone replaced the real seal this way and have any advice?

[TBONE1964]

The Melling M55-HV will be just fine for you. I would use a stock pick up and set it about 3/8 of an inch from the bottom of the pan. Also remember that any thing over 80 psi is not good and is hard on the oil pump drive rod. I have seen them twist and snap from too much oil pressure.

[cleszkie]

tdkosta - The last time I replaced the rear main seal I was able to unbolt the engine mounts and raise the engine enough to pull the pan without moving the cross member. However, this time around I have an HEI distributor and ramhorn exhaust manifolds. These two things prevented me from raising the engine enough before the base of the HEI and driver side ramhorn touched the firewall. I could have pulled the HEI and removed the ramhorn, but I chose to just unbolt the cross member and slide it forward since I already had the engine off the mounts. It really was not that hard to do by myself. It would have been really easy if I had someone else helping me though.

TBONE1964 - I did end up going with the M55-HV. I installed it with a new pickup for a stock pan and a hardened intermediate shaft with a connected steel colar. According to the paperwork, the pump is manufactured with a pink oil pressure spring that should result in an equilibrium oil pressure of 70 psi. I have not gotten the engine up to operating temperature and up to highway speed to check the pressure yet. I will let everyone know what it is when I find out.

[tdkosta]

I think the rear main seal is good. Got the pan off and the flywheel is completely dry. Plus I just had the transmission rebuilt and I had asked them to check the seal out. I'm pretty sure the oil pan gasket was the culprit. the oil dipstick tube isn't leaking, nor is the intake gasket, head gaskets, or manifold gasket.

Here's my question though-as I was cleaning out the oil pan wouldn't you know I find about a two inch section of a push rod. I remove the valve covers to inspect the push rods thinking I would be able to locate the broken rod. All 16 of the rods seem fine. Should my next step be to manually turn the crank to see if I am right or do I need to remove all the rockers and inspect all the push rods? I don't know if the prior owner broke a rod and didn't fish the whole thing out.

[Ole Beater]

Was there any metal deposits in the pan? The only way a pushrod could get down there is through a oil return hole at the end of the lifter valley. If i were you i would pull the lifters and check them for wear also. More than likely if a pushrod broke then the cam could have been damaged. Unless its been replaced since.

[tdkosta]

There were a few metal shavings that I gathered with a magnet. Not much. I don't have the history on the engine, so I am no sure what had been replaced.

[cleszkie]

tdkosta - If any of your pushrods was missing a chunk you would know it very quickly. There would be backfiring either out the exhaust or card, and the engine would run with a very noticeable miss. Probably leftover debris from a previous failure. Just my opinion, but you should replace the rear main seal while you have the pan down, even if it doesn't look to be leaking. Its a $10 seal, and you have already done 99% of the labor to swap it out. You will kick yourself if it starts to leak in a few months, and you have to drop the pan again.

[cleszkie]

OK, back to the main focus of this thread....my oil pump.

Here are the results of my installation of the Melling M55-HV:

At operating temp (190 degrees) my oil pressure at idle (600 RPM) is 30 psi. This corresponds to the middle tick on the stock oil pressure gauge. At operating temp my oil pressure at highway speed (2500 - 3000 RPM) tops out at 60 psi. This corresponds to the last tick on the high side of the stock gauge. Of course, at cold starts the idle pressure goes up to 70 to 80 psi, and the stock gauge is pegged. but this only lasts for a little while until the engine temp comes up a bit.

Overall, I am very pleased with the performance of the Melling M55-HV oil pump. It should allow me to extend the life of my older rebuild (100,000+ miles). While I had the oil pan down I did check the wear on some of my crank bearings and found it to be acceptable. No scoring, groves, or exposed brass, with even wear paterns.

[tdkosta]

Thanks for all the info and sorry for sidetracking the original thread.