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Old 02-05-2013, 12:58 PM
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Melling M55 oil pump

I had heard some years ago about horror stories with oil pump breakage on Melling M55 pumps for sbc after melling redesigned them making them thinner.
I was reading up on more of it a little while ago and found a article that said Melling recommended it be replaced with the Melling select oil pump. I looked into those and they want $75 for it which I think is rediculous, especially considering the original M55 before the design was changed you could abuse it every which way and never have a problem and it only cost $20 bucks.
It seems I had heard that melling went back and improved the durability of the M55 after getting so many complaints but I can't seem to find out for sure. If anyone knows if they improved it or not I'd appreciate it As we plan to use one on a sbc were building to go in a 89 Ford Ranger 4x4 and we don't want to run into any surprises. Thanks for any info.

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Old 02-05-2013, 01:09 PM
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Do yourself a favor and run the M155 pump, its what all of the later model sbc's and lt engines ran- same basic pump but with a 3/4" pickup. I'd also port the housing and the cap it mounts to.

Also, I recommend a HV pump and cant see any reason to not use one in a street application but I wouldn't use it in a high rpm race application (not sure what you're doing here).

As for the pump breakage I have heard they fixed that as well and the select pumps are running billet gears instead of PM ones. IF you have clean assembly and keep crud out of your engine PM gears should be just fine though.
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Old 02-05-2013, 02:50 PM
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Yes, they improved the pump. But, there are thousands of the bad pumps out there as old stock in the parts warehouses. Of course the price went higher.
Luckily I bought all the original design pumps my warehouse could get back when the problem started. My left turn guys insist on them.
NEVER run a hi-vol pump in a street engine. The pump will cause excessive dist gear/cam drive wear in many applications. I have been seeing a lot of this since the oils we are forced to use came about. Plus most of that hi-volume oil just blows by the pressure by pass and is wasted.
My left turn customers are known for using an engine up. Amazes me how much a rules built engine can put out, and they all use std volume pumps with a spring replaced. Or M55-A
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Old 02-05-2013, 03:46 PM
How fast is fast enough?
 
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Quote:
Originally Posted by BOBCRMAN@aol.com View Post
Yes, they improved the pump. But, there are thousands of the bad pumps out there as old stock in the parts warehouses. Of course the price went higher.
Luckily I bought all the original design pumps my warehouse could get back when the problem started. My left turn guys insist on them.
NEVER run a hi-vol pump in a street engine. The pump will cause excessive dist gear/cam drive wear in many applications. I have been seeing a lot of this since the oils we are forced to use came about. Plus most of that hi-volume oil just blows by the pressure by pass and is wasted.
My left turn customers are known for using an engine up. Amazes me how much a rules built engine can put out, and they all use std volume pumps with a spring replaced. Or M55-A
The bypass will open up once your operating pressure is reached, most of the time in the mid RPM range (2-3k RPM) when that happens the only additional stress it can put on the cam drive gear is the force it takes to pump oil through the bypass (not much). In fact a high pressure spring will cause a lot more stress than a high volume pump.

There really is little to no truth about additional stress at high RPM, BUT it will put more load on the cam gear at low RPM, while also providing more oil pressure and flow throughout the engine (hence why I recommend it for the street and not racing).

One draw back it will have at high RPM is circulating a lot of oil through the bypass, causing cavitation and foaming. Porting the pumps passageways will help, as will using a good oil, as will increasing the bypass pressure (though that adds more stress to the cam gear again).

On the street where you'll see low rpms fairly often it can help a lot (if you run an OD, low gears, big tires, etc), BUT if you are almost always over about 2500 RPM or so (where the bypass opens up) then you won't see any advantage and actually create problems at high RPM.

SO for a street car that is usually at 2500 RPM or less its a good idea, if you're over that then it starts becoming unnecessary and if you're at HIGH RPM (5,000+) then it can become a problem.

Also, if you can always run the largest diameter pickup you can and port all the oil passageways you can to reduce dynamic pressure loss and cavitation- improving flow and quality of oil.

There are also pumps that are designed to deliver better pressure, volume, and quality of oil, but they're more expensive- these are the typical pumps that you'll get for $50 or less and are common to rebuild kits.
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Old 02-05-2013, 08:18 PM
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Sorry but I can't help it.

I just LOVE to hear no-nothing-from-hands-on-experience, never-built-a-real-engine, wanna-be's lecture REAL engine pros. Makes me laugh, but not in a good way.
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Old 02-06-2013, 07:59 AM
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Not for nuttin, but I've never had an M55 "fail" at the housing. That includes streeters, stockers, lower-level circle track engines and reasonable drag cars.

The "Select" pumps ARE stronger, it's true. Whether or not they're "worth it" can only be determined by the buyer.

The ONLY small blocks we use a HV pump in have 2.650" main journals (400). Even then, for circle track, we stick to the standard pump. Continuous high RPM operation WILL suck the pan "dry" and starve it for oil. Higher capacity pans help some.

be sure to install the "sleeved" drive shaft (Melling IS-55E).

FWIW

Jim
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Old 02-06-2013, 08:01 AM
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Only thing I'll add is if you get a pump and wonder if it has the billet or Powdered Metal (PM) gears; put a mark on it with a felt-tip pen. If the mark fades away, its Powdered Metal. Nothing wrong with PM in the correct application, however if you put any trash through the pump, it can break the gears, where a billet gear will probably chip a tooth and pass it through.

I haven't seen a PM one in awhile but, it sure is nice of companies being forced to upsell you if you question their old stock having the PM gears or not. I understand that there are rising costs of manufacture; but I also know that investing in the powdered metal dies is NOT cheap at all and takes tens of thousands of pieces to amortize the cost in a reasonable timeframe
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Old 02-06-2013, 08:33 AM
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The only one that is improved is the M-55-A pump not the M-55
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Old 02-06-2013, 08:59 AM
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No one mentioned the shear on the oil, as it is forced through the bypass. Causes a lot of heat generation, and kills the additive package in the oils. It is the same effect that kills power steering pumps when people repeatedly hold the wheel on the lcoks.
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Old 02-06-2013, 09:59 AM
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Quote:
Originally Posted by AutoGear View Post
Only thing I'll add is if you get a pump and wonder if it has the billet or Powdered Metal (PM) gears; put a mark on it with a felt-tip pen. If the mark fades away, its Powdered Metal. Nothing wrong with PM in the correct application, however if you put any trash through the pump, it can break the gears, where a billet gear will probably chip a tooth and pass it through.

I haven't seen a PM one in awhile but, it sure is nice of companies being forced to upsell you if you question their old stock having the PM gears or not. I understand that there are rising costs of manufacture; but I also know that investing in the powdered metal dies is NOT cheap at all and takes tens of thousands of pieces to amortize the cost in a reasonable timeframe
That's good to know, thanks.

Also FWIW, I had occasion to tear down a '97 Vortec engine w/a thrown rod. It wasn't pretty- the rod was in about 8 pieces (no exaggeration)- and it looked to have shattered (reminded me of a failed hypereutetic piston) instead of bending/breaking like a normal forged steel rod tends to do.

I still have the pieces if anyone's interested in seeing them all, here's one of the bigger ones:



I don't know the exact mode of failure, the crank's rod journal was badly worn, so it might have been driven in desperation long after it started knocking. That could have overheated it, although there's no discernible bluing of the metal. The rod bolts were still nutted and were holding onto pieces of the cap and rod (in two separate pieces) and hadn't broken although they may have stretched.

Until seeing this I believed the PM rods were at least as good if not better than the forged steel rods before them. The finish is much better on the PM rods, that much is known. But this does raise a little doubt, although one case does not mean that much either way.

Last edited by cobalt327; 02-06-2013 at 10:04 AM.
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Old 02-06-2013, 12:03 PM
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Quote:
Originally Posted by AutoGear View Post
Only thing I'll add is if you get a pump and wonder if it has the billet or Powdered Metal (PM) gears; put a mark on it with a felt-tip pen. If the mark fades away, its Powdered Metal. Nothing wrong with PM in the correct application, however if you put any trash through the pump, it can break the gears, where a billet gear will probably chip a tooth and pass it through.

I haven't seen a PM one in awhile but, it sure is nice of companies being forced to upsell you if you question their old stock having the PM gears or not. I understand that there are rising costs of manufacture; but I also know that investing in the powdered metal dies is NOT cheap at all and takes tens of thousands of pieces to amortize the cost in a reasonable timeframe
The more expensive Melling Select oil pumps have 8620 carburized billet steel spur gears. Carburizing of steel is a form of case hardening similar to austempering of cast iron. Steel billet camshafts are carburized.

Select austempering is the case hardening process used on cast iron hydraulic roller camshafts. Select austempering retains the malleable cast iron core.
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Old 02-06-2013, 06:43 PM
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I can't help it either, I get tired of biting my tongue

Quote:
Originally Posted by cobalt327 View Post
Sorry but I can't help it.

I just LOVE to hear no-nothing-from-hands-on-experience, never-built-a-real-engine, wanna-be's lecture REAL engine pros. Makes me laugh, but not in a good way.
Dis is da injunearin jenyus sayvant that can't even make a one cylinder engine run. Click dat link ;

small engine question
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Old 02-06-2013, 06:52 PM
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Amazing what three years of internet ejukashun will getcha!

What I see is just argument for arguments sake. On another thread it was said that the way to pick a Roots blower was to use flow charts and such, not the manufacturers recommendations, etc. Then goes on to provide a flow chart for a positive displacement blower IIRC as "proof".

But here, apparently it's perfectly acceptable to go on "what if's", "just in case", and "maybe's" when choosing an oil pump.

I would- again- suggest that the OP's problem be addressed. Sure- make corrections to info as needed- but make sure the OP's problem is dealt with, not just flapping jaw to start something.

Last edited by cobalt327; 02-06-2013 at 07:00 PM.
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Old 02-06-2013, 07:43 PM
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I have known some so-called "engine pros" that could not find their butt with both hands. LOL
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Old 02-06-2013, 08:32 PM
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Thanks for the info. I think this one I'm putting together now is the 11th small block I've built and I've always used the standard volume M55.
When the bearing clearances are correct there's no need for anything else, not on a mild rodded street engine anyways. However this build is a mild performance build to go in my nephews 89 Ford Ranger 4x4. This truck will see some street plus will be hanging out at the local mud park.
The only time I would use a high volume pump would be as a band aid for excessive bearing clearances in a engine I was trying to keep alive for a little while longer. I don't care much for HV pumps as they require up to 20 horses to drive.
It's pretty basic 350. Ported 305 heads, .224 duration cam, headers, KB 12cc D dish pistons, Weiand Action plus intake, Quadrajet carb, windage tray, comp double roller timing set and comp push rods. TH400 tranny, 2800 stall, NP241 transfer case, 3.73 gears and sitting on 36 inch tall Gateway Buckshot Mudders. In a light Ford Ranger it should be lots of fun.
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