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Old 03-21-2008, 08:52 PM
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Melling M155HV Oil pump?

Hey all, got some goodies today. I ordered my oil pump along with a pickup for a sbc 383, and a Moroso 7 quart stroker clearanced oil pan (8.25 inches deep). My question is, although the box the pump came in says it's an M155HV on the label, the casting number on the actual pump says it's an M55HV. Melling has an M55HV pump, and it's slightly different, also being high volume though (different model). What is also weird is that on the pumps bottom half, the bolts that hold both halves together came with a metal 'tag' on one of them that has M155HV etched into it..totally confused by this. Has anyone had any experience with these pumps?

I'm also a bit worried on the clearance it will make on the bottom of the pump, being that with the pickup attached to the oil pump it's only 5.25 inches long, giving it about 3 inches of play...that just doesn't seem right. I could be wrong, and it could be the fact that it's the wrong pickup anyways. (.625 inch inlet, oil pump is 7.5, didn't bother to say that on the summit site..). If i've got all the wrong parts, what do you think would work with this pan i've gotten? What would you recommend? I can provide pictures if it helps you understand my confusion.

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Old 03-21-2008, 09:17 PM
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First see if moroso makes a 3/4 inch inlet pickup, for the pan you got.

The m55hv has a smaller inlet.



Quote:
Originally Posted by mrdreex
Hey all, got some goodies today. I ordered my oil pump along with a pickup for a sbc 383, and a Moroso 7 quart stroker clearanced oil pan (8.25 inches deep). My question is, although the box the pump came in says it's an M155HV on the label, the casting number on the actual pump says it's an M55HV. Melling has an M55HV pump, and it's slightly different, also being high volume though (different model). What is also weird is that on the pumps bottom half, the bolts that hold both halves together came with a metal 'tag' on one of them that has M155HV etched into it..totally confused by this. Has anyone had any experience with these pumps?

I'm also a bit worried on the clearance it will make on the bottom of the pump, being that with the pickup attached to the oil pump it's only 5.25 inches long, giving it about 3 inches of play...that just doesn't seem right. I could be wrong, and it could be the fact that it's the wrong pickup anyways. (.625 inch inlet, oil pump is 7.5, didn't bother to say that on the summit site..). If i've got all the wrong parts, what do you think would work with this pan i've gotten? What would you recommend? I can provide pictures if it helps you understand my confusion.
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Old 03-21-2008, 09:26 PM
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Quote:
Originally Posted by dgcantrellsr
First see if moroso makes a 3/4 inch inlet pickup, for the pan you got.

The m55hv has a smaller inlet.
the inlet on the pump I have now is .75 in., and the inlet on the pickup that I received is .625 in. I know it's the wrong pickup, and i'm going to be sending it back. Moroso does make a 3/4 in. inlet:
http://store.summitracing.com/partde...5&autoview=sku

I just wasn't aware of the inlet sizes when I was ordering, because they weren't presented =/ I called and made sure it would fit (summit) and the guy that answered was more than willing to say it would work..go figure. I won't dog on them all, just some of them are more interested in selling you stuff than actually helping you out.
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Old 06-19-2010, 08:58 AM
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Melling oil pump ID

I know this is probably old news but...
The Melling casting numbers on the pumps is not necessarily the part number. Melling somtimes uses their older casting mold designation when casting new oil pumps. .If the description says it is for a "SB Chevy" and nothing else, it is generally understood to have a 5/8" inlet. The numerical prefix "1" indicates the SB Chevy pump has a 3/4" inlet. Just because it is a "high volume" pump does not mean it will have a 3/4" inlet and just because it has a 3/4" inlet does not mean it is a high volume oil pump. The "high volume" oil pumps have spur gears that are longer than standard oil pumps and they have a 0.587" longer pump housing. The pumps that are "high pressure" are equipped with a stronger by-pass spring.
Caution: High volume and high pressure pumps in a engine with standard bearing clearances usually accelerate distributor and cam gear wear. Always machine, grind or file 0.030" wide x .030" deep oil groove from the bottom oil passage on the exterior of the distributor shaft housing to the distributor gear for improved oiling. Always replace the nylon sleeve type drive shaft with a ARP,Melling, Moroso, etc., aftermarket drives shaft that has a steel sleeve, whatever pump you choose.

Melling M55
Std. pump, std. pressure, 5/8" inlet.

Melling M55HV
High volume, high pressure, 5/8" inlet.

Melling M155
Std. pump, std. pressure, 3/4" inlet.

Melling M155HV
High volume, std. pressure, 3/4" inlet

You can increase the oil "pressure" by replacing the standard pressure by-pass spring with the "high pressure" relief spring that comes in the box with the pump or purchase one separately and replace the standard oil pressure by-pass spring. Doing that will allow the pump keep your engine oil under pressure at a higher RPM before it by-passes. (when I was a kid of 15, and could not afford a tachometer, I used the oil pressure guage to tell me when to shift ). High pressure pumps require more frequent oil changes because dirty oil and a high pressure pump is just like sandblasting the bearings when spinning the engine at high RPM. That is called "washing out" the bearings, not wiping out. .

The M155HV pump has longer spur gears for "high volume" which makes the housing 0.587" longer. Therefore you must use a deeper pan and an aftermarket longer pick-up screen assembly. You cannot use a Chevy high volume oil pump in a stock oil pan. That is because the stock oil pump pick-up assembly is as short as it can get due to the location of the oil pump. That is why a high volume oil pump CANNOT suck a stock oil pump dry! However, that is not the case for all engines. For example, Pontiac engines with their "high volume" oil pump CAN suck a stock depth oil pump dry because the Pontiac high volume and standard volume oil pump is the same length which permits the HV pump to be used in a stock Pontiac oil pan. Pontiac so-called "high volume" oil pumps merely use a stronger by-pass spring and a 3/4" inlet, and they are not true HV pumps. Usually high volume and high pressure oil pumps should only be used if yoiur engine has a remote oil filter and oil cooler or the bearing clearnces are loose (.003" or more) as is found in some race engines. It has been proven on the dyno that a high volume oil pump requires 3 to 7 HP to turn it (depending on the RPM) compared to a standard oil pump.

I went through this with my 1991 S10 Blazer 4X4 with a 4.3L engine. The pick-up screen/pump combinations are nearly endless when trying to achieve 0.375" to .500" oil pan to pick up screen clearance. The S10 Blazer 4X4 has a oil pan sump that is 9.250" deep and after several trial fits with a few different oil pump pick-up assemblies, I will use a M155HV pump with standard pressure by-pass spring and a Milodon 18201 extreme duty pick-up screen assembly that is designed for a 8.250" deep oil pan.
The math: (8.250" pick up + 0.587" longer oil pump) = 8.837" pick up depth. Then: 9.250" pan depth - 8.837 pick-up depth = 0.413" pan clearnce......dead nuts on. More than 0.500" clearance between the pick up screen and the oil pan will cause a vortex to form and the resulting cavitation will cause air to be drawn into the oil pump with a loss of oil pressure.

The Moroso and Milodon oil pump pick ups press-in the inlet hole and also have a strut that bolts to the bottom of the oil pump. Using Milodon or Moroso bolt on pick-ups is simple and is more secure than brazing the pick-up tube to the oil pump housing. Brazing is a weak weld to cast iron, especailly not done correctly. .Do not trust the the Melling Select bolt on oil pump pick up screen assemblies because the tube is merely bronze soldered into the inlet bolt plate and does not enter the pump at all. I feel like vibration can break it loose with disasterous results.

Be advised:
1.) Securing the oil pump pick-up in some manner is absolutely necessary if you have a deep pan with a extended oil pump pick-up screen assembly.
2.) You may want to use the more expensive Melling Select oil pumps because the regular production Melling oil pumps, made after 1990 are lighter and have weaker castings, thanks to the bean counters at GM. The new design of the standard production Melling oil pumps have been known to break off the main cap especially when using solid motor mounts. Melling gives that disclaimer with a note in the box. I found my pre-1990 new old stock Melling M155HV oil pump on e-bay, still in the original Melling unopened box.

Last edited by MouseFink; 06-19-2010 at 09:28 AM.
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Old 06-19-2010, 11:22 AM
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Quote:
You cannot use a Chevy high volume oil pump in a stock oil pan.
In that the pickup is adjustable as to the angle that it enters the pump housing, the slight difference between a HV and a regular oil pump can be easily accounted for.

Many, many thousands of stock oil pans contain HV pumps and p-u's.
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Old 06-19-2010, 12:40 PM
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Adjustablke?

Adjustable pick-up screen assembly? You got to be joking. The oil pump pick up tube must be installed in the oil pump in a manner that will make the pick-up screen parallel and within 3/8" to 1/2" from the botom of the oil pan. Therefore the pick up tube must enter the pump only one way. When you press or drive the tube into the pump, you must first mark the pump housing and the pick up tube in some manner so you can install the tube with the pick up screen oriented in a position that is parallel to the botom of the oil pan. With a stock oil pump, pick-up and oil pan, you do not have to be concerned about about the clearance from the bottom of the oil pan to the pick-up screen because the pump, screen and pan are designed in such a manner to make them fit correctly. The problem become apparent when you try to install a aftermarket high volume oil pump in a stock oil pan.

Since a HV small block Chevy oil pump is .587" longer than a stock volume pump, the pick up screen will not fit within the oil pan. In that case, an aftermarket deeper oil pan must be used with a aftermarket pick up screen assembly. . That is why Chevrolet does not sell a high volume oil pump.

High volume oil pumps and deeper oil pans are only available from aftermarket suppliers.

Do not confuse an aftermarket "high volume" oil pump for a SB Chevrolet with a Chevrolet high pressure oil pump. The latter is avaliable from any Chevrolet dealer and will fit any stock Chevrolet oil pan. Or you can buy the just the by-pass spring from Chevrolet dealer and replace the one in your stock low pressure oil pump. The Chevrolet high pressure oil pump is merely a standard oil pump with a high pressure by-pass spring.
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Old 06-19-2010, 01:45 PM
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Gotta agree with cobalt. Many, many stock pans with melling high volume pumps in them. I know of at least one for sure, the pump and stock pan on my 350.
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Old 06-19-2010, 01:48 PM
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I'm not going to bother any further. Obviously this guy has all the book learning to supply his own needs, my emperical knowledge is no match.
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Old 06-19-2010, 02:01 PM
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Well, cobalt, I couldn't agree more with you on that. So many hotshots that are just plain ignorant. Perhaps this guy is Ap72's brother. I posted a link so he can read that the pickup for the melling 55 highvolume pump does indeed fit a stock pan. How long before he posts the obligatory flame where he tells us old farts to go pound sand, blah, blah like they all do when proven wrong?

http://www.summitracing.com/parts/MEL-55-S1/
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Old 06-19-2010, 02:16 PM
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Said I was done, but thought I might just add one more thing.

As to:
Quote:
That is why Chevrolet does not sell a high volume oil pump.
You might want to check THIS out.

I don't have a standard and a high volume pump handy to compare, but I recall someone recently saying the height difference in the spur gears is compensated for in the casting, making the pump pick up locations virtually the same between the two types of pumps.
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Old 06-19-2010, 02:51 PM
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The pickup tube location is different between the standard and HV pumps. But, for a street car, it doesnt matter much. The after market racing pans require different pickups for the various pump designs. Preferably, I use the new one piece pump-pickup units whenever possible as there is no chance of the pickup falling off.
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Old 06-19-2010, 02:55 PM
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Where is a reference to a high volume pump?

The Summit link shows a stock replacement SB Chevrolet 5/8" oil pump pick-up assembly. Don't you recognize one when you see it? Or, maybe you put in the wrong link by mistake. Nowhere in the description does it mention a high volume oil pump. Search again and show me a pick up assembly for a HIGH VOLUME volume oil pump pick-up that can be used with a stock oil pan.

If some street squirrels claims they have a aftermarket high volume oil pump and are using a stock Chevrolet oil pan, they are blowing smoke or they have been told they have a high volume pump by the crook who built their engine.
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Old 06-19-2010, 02:57 PM
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Quote:
Originally Posted by MouseFink
If some street squirrels claims they have a aftermarket high volume oil pump and are using a stock Chevrolet oil pan, they are blowing smoke or they have been told they have a high volume pump by the crook who built their engine.
You, my friend, are full of -ět.
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Old 06-19-2010, 03:01 PM
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Did a side-by-side comparison (not perfect-perfect, but colse enough).
Definitely longer gears/housing (as I recalled), but there is some difference
directly below the pump shaft. Possibly to compensate for the longer gears/housing?
But I remember there were physical-differences in height overall, but that slight
difference can be made-up by pickup tube adjustment.

P.S. Most of my engines ran stock pans, with HV oil pumps. No clearance problems.

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Old 06-19-2010, 03:39 PM
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Wow, Fink, you really are dense aren't you? The pickup in the link is for a Melling 55 HV small block high volume pump. THAT FITS A STOCK OIL PAN! Go look for yourself, know-it-all.
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