Changing Oil Pump on a Big Block
 

I bought a Melling MEL-M77HV high-volume pump (I'm doing this for good reason) and MEL-IS-77 shaft for my '69 L36. I'm hoping (praying) the swap can be done with the engine in the car. I just read a great thread, "Changing Oil Pump" submitted by frytex on 4/3/2019, that indicates this can be done with relative ease, but his car is a small block. So before I get too excited, can the pump be done in mine, and just follow the same procedures as with the SBC? Thank you.

Why are you changing it? Oil pressure trouble? I seriously advise against the HV pump unless you have no other options.

Yes the pump can be changed in the car........you will have to drop the drag link down......

Jebby

Can of corn, very straight forward. Melling makes a good pump. I have the melling select with an 8 qt milodon pan. But it's a small block. Still much the same job. Good luck.

Process is the same...easy to do on big block also.

JIM

Thanks guys, and whooo, I'm glad to hear the pump can be changed with engine in. I'll get it up in the air and do so. Jebbysan, the reason I'm installing the HV pump is due to lowered oil pressure once the engine has fully warmed up. I performed a complete rebuild last year. The crank main, pins, and block mic'd perfectly. The oil clearances on the mains with the new bearings were between 0.0021"-0.0025" which is near the service limit, but I attribute the reduced pressure to that. I have 15W-50 synthetic, and after a full warm-up, pressure is about 7-10psig at idle as measured with a remote gauge. Normal driving pressure is down too. I'm certainly open to comments.

what were clearances on the rods? are the rods and mains standard? https://www.ebay.com/itm/Enginetech-...4AAOSwFnFV8tA2 FM clevite king can all be found in .001. and you can make .0005 by using 1 side standard and other .001. go on ebay. search .001 bbc or 454 rod or main bearings.

How did you determine clearances? There's nothing wrong with those main clearances, may even be a bit tight, those are what I generally use for rods with mains a bit looser, up to .003 on the rear main since it feeds the thrust surfaces as well.
I think you need to look elsewhere for your pressure problem. What are the rod clearances?

maybe something interfering pump's piston movement? ... also, maybe spring may be weak?

if old pump was reused (nothing wrong with that) ... maybe gears are chipped/worn? ... maybe gear cavity is scored/worn etc?

A couple of things:

.001 per inch is acceptable clearance....you are on the tight side.

10 psi per 1000 rpm is acceptable pressure....how does it sweep? Nice rise and fall on the gauge? What gauge are you checking pressure with and have you compared it to another gauge?

HV pump is not the fix here and I advise against using it because it pushes way too much oil to the top end if not using restrictors....

Jebby

Thanks to all of you. The main and pin journals are not stock; they've been ground down 0.010", and they mic out according to spec. By that, I mean I mic'd the main and pins (front/back, 0 deg and 90 deg), added 0.010" then compared to the shop manual specs. Everything checks.

I measured oil clearances on the mains using Plastigage. The main clearances, as I earlier mentioned, are between 0.021"-0.025". This is within the shop manual specs with 0.025" being at the max spec. As for the connecting rod clearance, I have 0.029" on #2 which is barely over the shop spec range of 0.0009"-0.0025". I can't find records of the other rod clearances which might means I was likely lazy! But the pins all mic'd out as I said.

Here's what I have for materials (all brand new):

Melling stock oil pump: MEL-M77
Main bearings: Clevite P-Series CLE-MS829P10
Rod bearings: Clevite P-Series CLE-CB743P10

I do get a nice pressure-build sweep using a remote pressure gauge I bought from Auto Zone a few years back
Mobil 1 synthetic 15W-50.

So when cold, I read right at 52 psi maximum at about 3000 rpm and the pressure doesn't go up from there so I'm thinking that's the pump pressure recirc spring limit. It idles at a nice 25 psig. But after the engine gets properly warm, max pressure is at 45 psig and idle is down to about 10 psig or less. It just doesn't give me a warm fuzzy feeling, and, it's lower than before I rebuilt the engine with the old pump. What I mean is that when cold, it's the same as the pre-rebuild, but when it full warms, pressure drops. Maybe I'm fussing over nothing, but don't want any long-term damage of course.

I don't get it. The car is up in the air so maybe I should pop the rod caps and plastigage since it doesn't appear that I did all of them like I should have (lazy mechanic!). For what it's worth, I did examine the stamp on each and every bearing half to make sure they were all for a 0.010" grind.

Oh, and I did have the block magafluxed and that checked out.
Thanks!

Pull pump and inspect....something is amiss there....an M77 and those clearances should be well over 60 cold and 30-35 at idle....15-20 hot at idle or just slightly better....
The HV simply moves too much oil for everyday use.

Jebby

Don't worry. I put new rod bearings in an .010 engine to tighten it up a bit. Idiot at Pep Boys sold me 4 standard bearings. Idiot me just put em in. Didn't last an hour with .012 oil clearance.

Were the cam bearings replaced when you rebuilt it? Were the rods resized?
If the pump supplies adequate pressure when cold, it's working fine - it's not slowing down or pushing less oil when it's warmed up. Pressure is the oil's resistance to being pushed through the system. Something is hemorrhaging oil in the system and as usual, it's worse when the oil is thinner. If you're going to plastigage the rods, you'll have to clean all the oil off of the cap, rod big end and bearings, otherwise your readings won't be accurate.
I'm with you regarding the pressure drop, it sure wouldn't give me a warm fuzzy feeling either.

There are also .011 rods and mains. Not saying you should use them, but the option is there. And I don't think plastigauge is inaccurate on an oily bearing.

I don’t think it’s the rods but is your oil pressure gauge mech or electrical? I had an electrical oil gauge one time that acted like you described. Turned out to be a resistance problem (electrical) and I didn’t figure it out till I tore a good engine apart! :cry

Thank for the responses guys. Here are some key points:

- I now agree that with the given clearances, a stock Melling M77 should have no problem building and maintaining pressure when hot.
- I will thoroughly examine the pump, relief spring, and screen. I will also measure screen-to-pan clearance.
- The cam bearings were replaced anew.
- The crank mains and pins were already ground down 0.010" when I got the long block so I can't say what was done to the rods. I assume they are correct. Before engine assembly, I mic'd the ID of the rod bearings on #2 with the caps torqued, and measured 2.1928". The #2 pin journal was mic'd at 2.1899" (perfect per the shop manual when adding the 0.010" back in), so that's an oil clearance of 0.0029". Of course with me being lazy, this was the only rod I measured.
- As for possible hemorrhaging, I have no clue what could be doing so, but it's a very plausible idea. That sounds scary! Idea here?
- When Plastigaging the rod clearances, removing oil off of all surface makes perfect sense. Wiping off the cap end will be simple, but the journal and big end of the rod? Ugh. I guess I should remove spark plugs then CAREFULLY push the buggers up the cylinder. I have surgical tubing I can shove over the rod studs. I'm a little nervous about this. But what derekderek is suggesting is the when the caps are torqued down on the plastigage, any oil will be squished out thus the reading will be accurate. I want to do this right. Laziness gone!
- Another diagnostic idea I just read from Melling is to pressurize the oil system after removing the pump. I assume they mean to connect (compressed air?) a source to the oil pump mounting platform on the rear main. They don't describe anything much nor give what it is you're supposed to look for. Has anyone ever done this?
- The remote oil pressure gauge is like stock dash unit - it's mechanical. I can see how an electric one could act up as resistance changes!
- derekderek, sorry to hear about your misfortune!

I'll get to work on this weekend if not before. The car is on stands with oil drained.

Thanks!

I put the HV pump in my BB build two years ago per shop that did machine work and put the bottom end together for me. He said I could do either safely and that a lot of the guys that he builds for (primarily Drag Cars) demand it cause they don't like seeing 10PSI hot pressure. The original pump in the L71 was around 10 psi hot.

I now wish I had gone non-HV, the cold pressure with 10-30 dino oil pegs the factory Mech. gauge but is fine (25-30psi idle) when the oil warms up (I'm in MN and October can be 30 degrees in the morning when you leave for a car show).

I would go with non-HV as others have suggested,

I found the pan clearance to be over 1/2" with the Melling HV and the melling pickup (Corvette deep pan), I had to cut and weld in a tube extension to get down to 3/8" (I may have overthought it but, it was near 3/4")

I have a standard pump in my 454 and oil pressure at hot idle with 10W-30 is just over 30 PSI.

I will be interested in your plastigauge check, my theory is that the plasti will squeeze most of the oil out. If plasti falls off after torque I'm not sure I'd trust it. Maybe some one here knows the physics of this, the plasti is a solid and it should displace the oil. I just can't see how it would throw off the squish.

Needs testing, maybe when I clean up the garage in the next couple weeks I'll try it on my original L-71 Rods, Crank and Bearings for fun (wet and dry) I never checked mine before moving up to 460ci.

Plastiguage is supposed to be used dry to read as intended. It is oil soluble as well.

I would verify the pressure gauge with a known good mechanical gauge first. If the gauge checks out OK then you need to dig deeper.

The pump could be acting up. The pressure regulating spring/piston could be stuck. Just need to get in there and see what is up.

Putting in a HV pump is not the answer when you have no modifications to the oiling system that require additional volume. You need to find the real problem. Something has changed.