Engine builder's warning - oil pumps

FYI to any GRMers building engines. Most of the major manufacturers of oil pumps, including Melling, Motorcraft, and AC Delco/GM have switched from steel gears to powdered metal gears. We just had a Melling M55 fail with the gears prematurely wearing in a 1,000 mile old GMC Syclone engine. The engine builder was lucky to have caught it before they shattered. Metal slag was found in the oil sump and there were large microfractures on both spur gears indicating impending doom, plus high and abnormal wear.

Please be aware that this is an industry-wide issue and if your build requires steel gears because it is an older oil pump design, a high-rpm, or high-HP application, make sure to buy a product where cast or forged steel is still in use. We tried four different vendors before we got a Milodon for this motor with steel gears in it.

What's a way to determine whether we need steel gears or if the powdered metal ones will be ok?

I still haven't found a PM gear worth a E36 M3.

rslifkin wrote: What's a way to determine whether we need steel gears or if the powdered metal ones will be ok?

Did the engine originally come with powdered gears? If so you can use those. Otherwise, steel gears...especially for anything you might call "high-revving."

GameboyRMH wrote:

rslifkin wrote: What's a way to determine whether we need steel gears or if the powdered metal ones will be ok?

Did the engine originally come with powdered gears? If so you can use those. Otherwise, steel gears...especially for anything you might call "high-revving."

Not a clue. But it's had a Melling M72 in it for a few months and around 6 - 7k miles (new enough that it's probably powdered gears). And I've spun it to 6000 - 6200 a few times (stock redline was 5300) without it exploding. So I'm assuming it's probably fine.

Do you have any noise coming from the oil pump or engine? Any metallic sludge on your drain plug magnet? If the answer is no to both, you should be okay.

Javelin wrote: Do you have any noise coming from the oil pump or engine? Any metallic sludge on your drain plug magnet? If the answer is no to both, you should be okay.

No funny noises, pressure is normal (and hasn't changed since this pump was installed). No magnet on the drain plug, but no glitter or metal sludge last time I changed the oil.

I'm guessing this is a case of higher risk of failure, not necessarily that they will always fail in some applications?

Here is a very well done engineering paper on PM versus steel gears on a test bench with hilarious results. The PM gear "shatters into several pieces" at load level 8, but is "not considered to have failed". Pretty sure a shattered gear is a failed one.

PDF

In reply to rslifkin:

Correct. In many stock applications it will be just fine. The problem is they are "backdating" PM "technology" into older PN's that require steel gears, and when they fail it is pretty catastrophic. Basically just a heads-up to check your parts before install, especially in any performance application.

How do you tell the difference?

Javelin wrote: FYI to any GRMers building engines. Most of the major manufacturers of oil pumps, including Melling, Motorcraft, and AC Delco/GM have switched from steel gears to powdered metal gears. We just had a Melling M55 fail with the gears prematurely wearing in a 1,000 mile old GMC Syclone engine. Please be aware that this is an industry-wide issue and if your build requires steel gears to buy a product where that is still in use. We tried four different vendors before we got a Milodon for this motor with steel gears in it.

I thought the M55 went BACK to steel gears after too many builders bitched about the powdered metal ones.

I went through that with my Disco.. the powdered gears died within a hundred miles. The replacement is still going strong

I only have half an engineering degree, but I can still figure that trying to haphazardly substitute powdered parts into an engine dating back to the 50s with all sorts of weird vibrations going on inside will not go well.

In reply to Knurled:

We tried 4 different M55's, and they were all powdered metal.

How do we know that a powdered metal gear is worse than a "steel" part? Aren't they both technically steel? How do you know the gears weren't defective?

Here's the point.. A blanket statement saying "powdered metal is bad" is idiotic. These gears were bad but they happen to be made of powdered metal. So.. either bad testing/specification or bad quality at manufacture.

In reply to Fueled by Caffeine:

Powdered steel, when it gets to a certain frequency shatters like glass does. Usually high revs or no harmonic balancer will destroy even factory oil pumps with powdered metal gears (ala miata). Normal steel (i hate using the word billet but thats what makes sense to most people) doesnt do that. So yes, in an oil pumps case, powdered steel gears are bad

Powdered metal is just that. Typically powdered metals have the consistency of talcum powder some are a bit coarser. The powder is compression molded into a die/mold usually a bit larger then the actual part. At this point the gears/parts are considered green. The compression molded parts are then put in a furnace at high temps and the powder is sintered which is supposed to melt the powder together. The sintering also shrinks the size of the part which is whay they are molded oversize. Sintered powdered have there place but never reach the tensile strengths of wrought or cast metals. They also tend to be somewhat brittle so are not real good when shock loaded. If I were building a performance engine I would certainly look for steel or the sometimes used cast iron gears.

In reply to Fueled by Caffeine:

PM is a completely different process and end result than cast steel with vastly different load and temperature ranges when completed. As mentioned, harmonics, vibrations, and shock loadings can cause PM to shatter, and older engines with wet-sump oil pumps are extremely bad for PM as a material as the pump is typically semi-suspended in the sump without much in the way of bracing and driven with torsional loads from the distributor drive. A more modern engine with a captive oil pump that basically just has gears within a casting that is actually a stressed member of the engine itself can typically get away with PM in standard situations. Simply put though, PM is cheaper, and that's why it's used more nowadays. A steel gear is superior in nearly every measurable way and circumstance in the intended application of dual-spur gear oil pumps inside engines.

Ranger50 wrote: I still haven't found a PM gear worth a E36 M3.

John Deere uses them in their Garden Tractors for part of the reduction gear train and the pump and motor blocks.

PM is like anything else, you put it in the wrong duty cycle or use and it will fail.

Shock loads are a PM's worst nightmare they aren't made for it. But they do very very well in compression and due to porosity work well as a lubricant wick.

As far as everyone talking about PM shattering at a certain frequency. Everything on the planet will do that.

I guarantee you guys are driving stuff with PM in it you have no clue is there.

My point is, this application may be bad, but don't knock an entire tech for a bad part.

It's all dependent on the shape and loadings, too. Mazda rotaries have powdered metal oil pumps and gear failure is extremely rare.

However, it's a gerotor type. (gearrotor? G-rotor? That thing)

American engine oil pumps tend to be a pair of spur gears that make a whole lot of "noise" and shock loading. Something like half the heat in the oil will come from the oil pump. They are not pleasant devices and they probably will only live with forgings.

Some OE powdered metal parts are "marginal", too. Take Audi inline five crank sprockets. They are PM, and the harmonic damper bolts to it, not the crank. They live fine at OE power levels. Crank it up a lot, run the engine at high boost and RPM for extended periods, the crank harmonics destroy the sprocket. The fix is a machined forged/billet gear at great expense.

Now. I see no reason, in 2016, why aftermarket oil pumps need to be spur gear, except for plain and simple design inertia. It should be easy to put a gerotor setup in a pump body the size of the spur gear one.

In reply to Javelin:

Ok, cost and lubrication retention, is steel superior to PM in those, as they are measurable? How about complex shapes? Inner core close tolerance blind geometry? Friction modification? Ease of alloying? Ability to change final material composition on a shot by shot run without remixing an entire batch? Ease of geometry change?

In reply to Knurled:

We did gearotor PM gears at Tuff Torq (gear train division of Yanmar diesel engines) with no problem for hydraulic pump and motors. the only time we had a gear failure was if the part was defective.

Flight Service wrote:

Ranger50 wrote: I still haven't found a PM gear worth a E36 M3.

As far as everyone talking about PM shattering at a certain frequency. Everything on the planet will do that. My point is, this application may be bad, but don't knock an entire tech for a bad part.

But a powdered metal oil pump gear can shatter at the frequencys the engines make at higher rpm/load as stated, a cold roll or whatever steel gear will shatter at a frequency yes but not at the frequency the engine can produce. Lots of issues with coyotes with revs turned up or supercharged.

No one here knocked powdered metal technology, they have their place and as we all know almost all cars these days have pm gears, but in an aftermarket oil pump that replaced steel with pm, thats not the place and thats the point of this thread.

Knurled, another reason you dont see gear failures in rotarys is because they dont vibrate like a piston engine

For any naysayers just google powedered metal oil pump gears and youll see, its not just heresay

Edit: again flighservice, no one is knocking pm technology, its amazing when its within its limits but as you know, a yanmar diesel isnt making a bunch of revs. We are talking performance/aftermarket oil pumps, not powedered metal technology, give me an address and ill mail you a panty detangler

chiodos wrote: No one here knocked powdered metal technology, they have their place and as we all know almost all cars these days have pm gears, but in an aftermarket oil pump that replaced steel with pm, that's not the place and that's the point of this thread.

Thank you!

Hell, many companies been using PM for connecting rods and other engine internals for quite some time now. It's not a new thing to have it internally in your motors. Like anything else, it's when you use it in the wrong application that it's bad.