Cause of oil pump gear failure discussion

[yoshimitsuspeed]

I have been wondering what causes oil pump gears to fail. It doesn't seem like the forces or loads would be all that likely to cause failure.
If the tolerances are right there shouldn't be any harmonics that would cause failure although I would put this as my second most likely guess.
I have been wondering if it's possible that cavitation could be the cause and if so then how much could be done to mitigate the problem. I know high RPM motor builders already port the pump to minimize this but could any more be done and if so would it help?
Most people don't think of cavitation as a destructive force but if it's extreme enough it definitely can be.




http://www.engineeringtoolbox.com/cavitation-d_407.html

I have been thinking about trying one of my dry film ceramic coatings on pump gears but I would need a controlled environment to test it in. Even then it would take a number of comparative tests to get any useful data. It would tighten tolerances, lower friction and give it better protection.

[yoshimitsuspeed]

It seems as though smoother surfaces tend to reduce cavitation damage. The oem pump gears are assumed to be sintered. Sintered metal tends to have a more porous surface than other forms of steel. Perhaps this increases cavitation and it's damage.
The ceramic coating I use have a very smooth low friction surface, especially the dry film. I have also been thinking after coating it could be lapped in place with a diamond compound to open up and even out oil clearances. A very fine grit compound could do a final polish on the surface.
http://cedb.asce.org/cgi/WWWdisplay.cgi?126742

http://www.repairengineering.com/cavitation.html

Improve surface finish

A smooth surface finish on a part has a lower likelihood of originating gas bubbles.

[oldeskewltoy]

Not sure it is cavitation(not sure it isn't either)... the old square tooth style pumps had issues, TRD offered a hardened gear set (long ago discontinued).


My own take (assumption): the pumps are getting hammered by the crank as the driver is pegged @ full throttle.. the ECU cut out drops and raises the rpms somewhat suddenly. Now add in the real possibility of pumping the sump dry.... and the first thing without oil is the pump gears.....

[yoshimitsuspeed]

Not sure it is cavitation(not sure it isn't either)... the old square tooth style pumps had issues, TRD offered a hardened gear set (long ago discontinued).


My own take (assumption): the pumps are getting hammered by the crank as the driver is pegged @ full throttle.. the ECU cut out drops and raises the rpms somewhat suddenly. Now add in the real possibility of pumping the sump dry.... and the first thing without oil is the pump gears.....

Each time a piston fires there is a sharp sudden impact going through the crank, I doubt the force of cutout would be greater than that. The rods, wristpins and pistons take much greater forces all day long.
Not saying you are wrong because I really don't know but it doesn't seem like that should be a big issue to me.

I looked at the stock pump gear today and it is very rough with big deep pits likely due to the sintering process.

[oldeskewltoy]

I looked at the stock pump gear today and it is very rough with big deep pits likely due to the sintering process.

You sure it is Toyota??? I've seen the Aisin pumps have more pores, and thinner internals - http://www.toymods.org.au/forums/showthread.php?t=64289&p=1497088&viewfull=1#post1497088

[jondee86]

Don't know much about the cause, but this appears to be the solution...

TODA 4AG (5 valve) Heavy Duty Oil Pump
These heavy duty oil pump gears are designed to replace the oil pump gears found in later model 4AG AE92 (16V), and 4AG 20 valve engines found in the AE101 (Silver head cover) and the AE111 (Black head cover).

Made from high spec material and machined by CNC, to give you improved high-revolution reliability. Standard oil pumps are made from sintered alloy, this is fine for standard use, but reliability is questionable in high performance application. (Pump capacity is the same as the standard)

Cheers... jondee86

[yoshimitsuspeed]

You sure it is Toyota??? I've seen the Aisin pumps have more pores, and thinner internals - http://www.toymods.org.au/forums/showthread.php?t=64289&p=1497088&viewfull=1#post1497088

The 4AGE pump I have is Aisin and it is more porous than the Toyota 7AFE gear but that one is far from perfect either.

Like I said, from the research I have done I believe that Toyota had at least three big pump revisions and I believe Aisin would have too. I expect the new OPT-036 pumps should have the thicker gear. I will be checking once I get my next batch in. If it is not thicker I will be looking into it further.

[yoshimitsuspeed]

Don't know much about the cause, but this appears to be the solution...


Cheers... jondee86

Yes this is a very good solution. Also not a cheap one.

[yoshimitsuspeed]

If anyone has a failed pump especially one that seems related to high RPM driving I would love to get my hands on it for inspection.

[oldeskewltoy]

Don't know much about the cause, but this appears to be the solution...

The Toda gears are better than stock... and for "only" $400 it is a lower cost alternative to a dry sump system... But if you are spending any time up around/over 9000... the dry sump is a far superior solution






BUT solutions to high rpm oiling wasn't yoshi's point... his was WHY do the stock ones fail.....

[jondee86]

I also ported/chamfered the openings on the oil pump so it is less restrictive.

I know this does not seem like much but in the past I have broken oil pumps with big revs but after this little trick I have not had any more broken pump gears. Here is a picture of an oil pump that I broke about 4 years back.

Copied from here... http://www.rollaclub.com/board/topic/40731-20v-blacktop/page__st__105#entry518435

Looking at the pics I would say that the initial point of failure was the root of the tooth
immediately above the driving face of the internal dog. The dogs appear to have an inclined
face, so the more power you feed to the pump, the higher the load on the face of the dog,
and the higher the resultant force trying to burst the gear. Add centrifugal forces from high
rpm, and if there is a weak point, those stresses are going to find it !!

Cheers... jondee86

[yoshimitsuspeed]

Good find. That is what I have been referring to as the rev1 design with the square cut gears. It makes you wonder if the redesign had more to do with efficiency, effectiveness, longevity or if this was a common enough failure in the design to warrant a redesign.
The round gear seems like it should be superior in most if not all the above ways.


It appears to me as though there is more overall surface area between the inside bore and the valley in the teeth. There appears to be more contact over more teeth as well as smoother transitions between teeth. It also eliminates the stress riser corner where each square tooth meets the bottom of the valley.

So another question would be does the rev2 design fail in the same way as the rev1?
And still what is the exact cause.

If porting was in fact what cured the issue then was it due to reducing cavitation? Or perhaps just reducing the pressure differential and strain?
It would be awesome to do a close inspection on a pump gear for signs of cavitation.

[jondee86]

Very cool picture of a Viper oil pump with the inner gear neatly expanded
into the outer gear



Read the thread here...
http://forums.viperclub.org/threads/667258-SRT10-Oil-Pump-Failure-%28Gen-3%29-w-Photos
And the Nissan thread linked in the above...
http://www.skylife4ever.com/2011/01/real-problem-with-rb26-oil-pump.html

Due to not paying attention in class, I previously just took it for granted that the
inner gear was driven by some kind of lug that fitted in the space between the two
lugs/dogs I now realise that the lugs are the drive surfaces that sit on the
flats either side of the crankshaft nose. From an engineering point of view, this is
even worse in terms of generating bursting stresses.

Anyone who has used a Cresent spanner to try and undo a rusted hex nut will know
how easy it is round off the corners. That same mechanism allows the flats on the
crankshaft to generate radial forces in the gear.

Looking at the later version Toyota inner gear, changing from 11 teeth to 10 teeth
allows the drive lugs to be better located, and for sure the rounded tooth shape will
pretty much eliminate stress risers on the outer surface. However, looking at the
other examples of similar rotor designs, it seems that the cutaway between the
drive lugs is now the likely point of origin.

Porting the outlet is an interesting question, as if the oil cannot exit the pumping
chamber quicly enough, the exit port becomes a restriction, and the pressure inside
the pump will be higher due to that restriction. So it would be interesting to tap a
pressure gauge into the the pumping chamber and see if porting actually reduces
the chamber pressure.

Cheers... jondee86

[Rogue-AE95]

I think I've posted these pics before in an oil pump topic here. Anyways here are a couple of oil pump gears I have sitting around:







^ The last pic shows wear on the inner gear (drive gear?) where it contacts the crankshaft. I'm wondering if it's possible to safely reinstall that gear "backwards" if reusing the pump, so that the crank will contact a fresh surface instead of the surface it had previously contacted (and wore down).

[oldeskewltoy]

Porting the outlet is an interesting question, as if the oil cannot exit the pumping
chamber quicly enough, the exit port becomes a restriction, and the pressure inside
the pump will be higher due to that restriction. So it would be interesting to tap a
pressure gauge into the the pumping chamber and see if porting actually reduces
the chamber pressure.

Cheers... jondee86

http://www.mr2oc.com/showthread.php?t=459412 -

[jondee86]

I'm wondering if it's possible to safely reinstall that gear "backwards" if reusing the pump,
so that the crank will contact a fresh surface instead of the surface it had previously
contacted (and wore down).

Theoretically, if the tooth profile is symettrical (and it appears to be), you could
reverse the rotor. However, as it appears to have a collar on one side, there may
not be any practical way of reversing the rotor. Plus, once the two gears have
"bedded" to each other and to the housing, you could find that reversing them
might lead to accelerated wear, as they go thru a new bedding in cycle.

The markings on the wear face are interesting. I have read that with sintered
gears, the pore structure of the material leads to micro pitting, and then failure
due to cracking between the pits. Kind of like joining the dots So if those marks
can be felt when you run the end of a scriber over the surface, that would be
spalling, where small flakes of material have broken away from the surface.

Cheers... jondee86

[jondee86]

@ oldeskewltoy
Yes, I have seen your work on porting the old pump housing (with excellent
pictures as usual). The focus of porting usually seems to be on improving flow
rather than reducing pressure drop, and for operation within the manufacturers
factory rev limit, that is reasonable.

But when an engine is run above the manufacturers redline, unexpected issues
can arise. And I am wondering if excessive pressure in the pumping chamber
due to pressure drop in the outlet might be one of them ? When the pressure
relief valve is having to pass high volumes of oil, does the relief valve itself
become a restriction to flow, thus raising pressure inside the pump ?The engine
oil pressure gauge only tells you the pressure downstream of the relief valve,
and that does not reflect the pressure being developed inside the pump housing.

Just speculating on possible causes of failure

Cheers... jondee86

[allencr]

That inner gearoter drive musta had some assembly trash in it, not deburred or forced onto the crank with a hammer. I'd look at its contact patch when new OR used to make sure it's uniform & file to fit if it isn't. Really doubt that it could be caused by crank flex and lack of a harmonic damper or RPM in a new range that isn't suppressed by the stock damper.
The under-capacity/obstructed relief valve would show up on the gauge.

I think there haven't been any signs of cavitation anywhere, that the boiling point of oil is so much higher then oil and that even though a gearoter pump isn't quite a 100% positive displacement pump, its slippage isn't anywhere close to what a boat's prop or a centrifugal pump's impeller do when creating a low pressure area that vaporizes.

[jondee86]

Cracked rotor from the Nissan forum linked above. Same design as the later Toyota
pump, but with only 11 teeth, so placing the driving face under the weakest part of
the gear. As the driving face erodes from repeated inpacts, the amount of "backlash"
between crankshaft and rotor increases, and the impacts become gradually heavier
due to the greater lash. At the line of impact erosion and/or pitting will lead to crack
propagation and eventual failure.

As mentioned above, light flywheels, removing the harmonic balancer and power
enhancing modifications can alter the torsional vibration characteristics of the
engine. It is not hard to imagine that it is possible to inadvertently create a critical
and harmful frequency within the engines operating range. When the engine runs at
that particular rpm the result is a severe "chattering" or extremely rapid forward and
back rotational movement of the rotor on the crank.

Resonant frequecies can break cranks, so breaking an oil pump would be easy

Cheers... jondee86

[yoshimitsuspeed]

That inner gearoter drive musta had some assembly trash in it, not deburred or forced onto the crank with a hammer. I'd look at its contact patch when new OR used to make sure it's uniform & file to fit if it isn't. Really doubt that it could be caused by crank flex and lack of a harmonic damper or RPM in a new range that isn't suppressed by the stock damper.
The under-capacity/obstructed relief valve would show up on the gauge.

I think there haven't been any signs of cavitation anywhere, that the boiling point of oil is so much higher then oil and that even though a gearoter pump isn't quite a 100% positive displacement pump, its slippage isn't anywhere close to what a boat's prop or a centrifugal pump's impeller do when creating a low pressure area that vaporizes.

While there isn't the technical slippage that you could see in a boat prop or turbine there could be areas of very low pressure.
There are a couple spots in particular that I have thought of. As the gears go from fully meshed to starting to open up it seems as though that could create a very low pressure zone. The faster it spins and the faster the inner and outer gear start to separate the greater this pressure drop could be.
The other thought that I have not seen addressed in any porting or similar discussion threads is in the divider between high pressure and low pressure sides. I should take pics to help clarify but I noticed that there is a gradual slope up to the divider but then there is a sharp edge where the cast sloped port rises straight up to the divider. You can see it in this pic of the rev1 style but the later round tooth pumps have a similar shape without the center gear divider.

As the pump gears pass this vertical shelf the oil between the gear teeth will be traveling with the gear at a very high rate of speed while the oil under the shelf will be brought to a rapid halt or spun in an eddy. It seems to me that this point of separation could also cause another low pressure zone between the layer of oil traveling with the gear and the layer of oil sheared off by the shelf. The same could apply to the outlet side where the oil being propelled by the gear meets much slower moving oil traveling in the channel. As far as cavitation goes though I would be much less concerned with the outlet side with higher pressure.
I am wondering if this is another area that could benefit from porting. I am wondering if porting that shelf into a gradual taper could help reduce this turbulent area. Even if cavitation isn't the problem this may improve efficiency and reduce load and if it is a point of cavitation it may reduce that too. Then again fluid dynamics are not my greatest strength. Perhaps the shelf and quick shear is actually a better thing.

[oldeskewltoy]

@ oldeskewltoy
Yes, I have seen your work on porting the old pump housing (with excellent
pictures as usual). The focus of porting usually seems to be on improving flow
rather than reducing pressure drop, and for operation within the manufacturers
factory rev limit, that is reasonable.

But when an engine is run above the manufacturers redline, unexpected issues
can arise. And I am wondering if excessive pressure in the pumping chamber
due to pressure drop in the outlet might be one of them ? When the pressure
relief valve is having to pass high volumes of oil, does the relief valve itself
become a restriction to flow, thus raising pressure inside the pump ?The engine
oil pressure gauge only tells you the pressure downstream of the relief valve,
and that does not reflect the pressure being developed inside the pump housing.

Just speculating on possible causes of failure

Cheers... jondee86

kind of agree... I'm not saying that there isn't any cavitation effect, but the pressure fluctuations caused by many things (operating outside typical range... etc.) I also believe is the larger of the problems.

A few areas I still wanted to work on when I was porting the pump....

1) "opening up" the bypass hole to accommodate more bypass volume. When I say opening it up... the hole would be larger, but the upper edge of the hole would not move up, the larger hole would be to keep the current top edge (pressure point), but open up below that to accommodate more volume if needed.

2) The oil outlet suffers past a 90 degree turn. I did part of the work in my porting thread, by working the short radius some, but a wedge shape fitted at the right point would reduce a great deal of turbulence

Getting back to cavitation... yoshi... the low side you mention is needed as suction to draw the oil from the pan,

as far as the older pie slice pumps sharp toothed pumps, the newer pumps appear to be better finished.

Comparing similar areas....




Old pump on left, newer on right. Some things were changed besides the gears... the orange arrow points to a different shaped chamber on the high pressure side. the red arrows show that the newer design shrank the gap between low pressure and high pressure sides. Finally, the newer style has more support - around the circumference - note the green arrow shows the shelf on the new, while the question mark shows the absence on the old





Now CnCing the entire housing from a single piece of billet might provide you with some cavitation drops

[yoshimitsuspeed]

So I took apart one of my new OPT-036 pumps today and it has the thicker less porus gears just like the Toyota pump of the latest revision. As far as I can tell it appears identical. It is 9.5mm thick as opposed to 7.5. The Sleeve on the inner gear that goes into the housing is the same thickness making the whole assembly 2mm thicker. This adds a good bit of material and has to add a good bit of strength.
This brings up a whole new question and that is how many failures have occurred on the thicker rev3 gear? Or were failures more common on the thinner round tooth rev 2 gear? Many people may not even realize there was a difference or that they were running the thinner gears when they failed.

[yoshimitsuspeed]

I just talked to Barry Mannon and he said that most of his experience is with the 9.5mm gear and that they tend to fail in circuit racing cars over time at around 8500.
He said the gears he has seen fail actually failed on the outside ring. He also said that the gears tend to start to wear and get bad pitting.
Pitting could be a sign of cavitation. Or it could be weak areas in the sintered metal or a combination of the two.
This could also mean that the different surface finish people have seen may not actually be from it being different material or different surface finish from the factory but perhaps the sign of wear and aging.
This makes me wonder if OST or anyone else has seen this rougher pitted surface in new Aisin pumps or just used ones or if the Toyota pumps get pitted over time as well. The OEM 7A pump I have still looks shiney but it also has a lower redline and probably didn't see nearly as rough a life as the pump that came out of my last motor that has the pitted Aisin pump.

[oldeskewltoy]

This makes me wonder if OST or anyone else has seen this rougher pitted surface in new Aisin pumps or just used ones or if the Toyota pumps get pitted over time as well.

As Andrew posted...



New OEM Toyota on left..... below, new Aisin below....




In my opinion... the Aisin shows far more pores, and flaws



Oh... one more thing no one has yet touched on... cover flex... oil weeping around the cover.... I wonder if a thin trail of FIPG red around the cover would eliminate that????

[burdickjp]

All other things being the same, a thicker pump gear also equates to a larger flow volume. Did we already mention that?

Unless stated otherwise, I'd have to assume Aisin pumps are Toyota pumps, as Aisin is an OEM supplier to Toyota, and 30% owned by Toyota.

[oldeskewltoy]

Unless stated otherwise, I'd have to ass-u-me Aisin pumps are Toyota pumps, as Aisin is an OEM supplier to Toyota, and 30% owned by Toyota.

I'd be careful.... it is ENTIRELY possible that some of the "Aisin" stuff is actually not Aisin, but a cheap ripoff... and so that might be what I got... but Toyota has/had a spec they need(needed too - past tense) to make sure the quality was up to new car warranty-grade, and then there are ways to lower the costs.... since it no longer needs to be new car warrant-grade... and with the "Toyota" smudged out, it can be any quality

[Tekkactus]

Hi, Bedding is for bedroom or bedding something about car?

[jondee86]

Hi, Bedding is for bedroom or bedding something about car?

When two surfaces of a machine rub together when the machine is working, the
two parts will develop a wear pattern. The pattern on one part will be the "negative"
of the pattern on the other part. This initial wearing of one part to conform with the
other is called "bedding in". Examples would be new brake pads wearing to match the
brake discs, piston rings to match the cylinder walls, or bearing shells wearing to
match the crankshaft journals.

So nothing to do with bedrooms... sorry about that

Cheers... jondee86