Nissan Skyline GTR Oil Pump problems

The Real Problem...
These Japanese super cars had a common problem that would often lead to the self-destruction of the motor. The Achilles Heel of the Skyline RB26 motor is the oil pump, I personally caught this issue on my own Second GTR (Build Story) leading me to replace it with a new one . This wasn't a problem on all Skylines, only the GTR's made between 1989 and 1991, after 1991 Nissan fixed the issue. Most people will tell you the problem is the width of the drive on the oil pump gears, they say the engagement area is too small, while that may be true (by appearance), it also isn't the 100% exactly correct answer...

The real problem is on the nose of the crank, the clearance between the nose of the crank and the part that drives the oil pump inner gear was too loose. The inner circumference of the oil pump inner drive gear was actually too much larger than the outer total circumference of the crank nose. The extra play had no effect on the motor at low RPM, but at high RPM the harmonic engine vibrations would often prove fatal for the oil pump, usually resulting in absolutely shattered pump gears. This was emphasized as the main problem further by the fact that the biggest risk of failure always came at high RPM and on the rev limiter, it was the full throttle pull followed by the ignition cut on the rev limiter that would result in the leading edge of the drive slamming into the top side of the pump gear, this repeated hammering (even though the swing length was only measurable in fractions of a millimeter) is what leads to the shattering of the gears. Early signs of this could sometimes rarely be seen by a vigilant driver with a keen eye on the oil pressure gauge.
The net effect of the hammering on the drive gears, was that, some of the Philip's head screws that hold the back-plate of the oil pump on, would back themselves out of their screw holes... to the point that oil would leak out of the pressurized part of the pump and right back into the sump, resulting in minimal oil flow through out the block. Over time this would cause engine failure too, just significantly slower then the instantaneous boom and seizure from oil starvation, usually caused by the broken drive gears. Although it was rare to catch this in time, an accurate oil pressure gauge can go a long way. Hard evidence of this is provided in the next following sections.
At the end of last summer I started to notice my oil pressure was low, meaning it would not go above 2.5 bar even at 7,000 rpm... so after doing my research I realized it was the classic sign of oil pump failure, the slow kind, that has the backing plate coming loose, not the usual catastrophic type. After removing the engine, my concerns were justified, and the issue surrounding oil pump failure was very clear.
What we discovered once the oil pump was out....

....its pretty clear what happened here... all the encrusted burnt on oil on the pump housing says a lot about the situation...

The reason for the oil leaking through and my horrendously low oil pressure... 2 of the screws on the backing plate had backed themselves out of their holes, and 2 other screws were merely finger tight...

A look inside the pump itself shows a rather worn out situation

Here's the reason those screws had come loose. The engagement area between the crank and the oil pump gear is only about 4mm, and there's a lot of play between the pump and the crank... so at high rpm these things are prone to explode, or in my case vibrate themselves apart. It's very obvious to see the the indentation on the engagement area, that small dent on the crank and gear are evidence of the aforementioned "hammering effect".

We then look to the crank and bearings to tell the other half of the story. When the crank does not receive enough oil to properly lubricate the journals, due to the fact that, the majority of the oil is being leaked before it can be pumped, the crank journals and bearings will wear out, and show signs of scratching, rough surfaces and heat marks. All of these symptoms can lead to bearing failure, which means the end of a running motor.

If we look closely at the individual journals, the # 1 rod journal shows score marks...

... and the # 6 rod journal showed major scratches and excessive heat. Attention now on the bearings themselves, the problem becomes even more apparent.

Heat and rough surfaces on a number of these shells, tells us that things were on their way to getting bad. There's a REALLY good write up on How to Assemble the RB26 Engine where they go into detail about bearing installation tips and tricks.

This one in particular showed some really excessive heat. It's clear that, the protective coating usually on each bearing has worn away. It wouldn't have been much longer before this bearing let go.

This outlines the real problem with the RB26 oil pump in a basic nutshell.
More Details now... First up, basic Specs: 
Stock: 47 L/min @ 6000 RPM
Nismo: Nismo claims comparable output to Stock but uses stronger gears.
HKS: 53 L/min @ 6000 RPM (Old Pump, Jun style)
HKS: ?? L/min @ 6000 RPM (New Pump, Tomei style)
Tomei: 57 L/min @ 6000 RPM
JUN: 59 L/min @ 6000 RPM (Calculated using Jun's Claim of +25% of OEM)
Trust: 59 L/min @ 6000 RPM
Reimax: 70 L/min @ 6000 RPM


(originally posted on GTR PWR: Post by Allan JD74)
As a result of many forum based discussions and many broken oil pumps from various manufacturers, the user: TryingToBeBest (GTRcanada) has put together a whole bunch of additional information gathered from all over the world, here is what he had to say about oil pumps:

Here is the pictures of my pump, its amazing how they crack even on the long sleeved crank collar!

I bought a used oil pump, order a crank collar (from Australia dealer) and a Reimax gearset directly from Japan!

Here is my findings:

#1 - Outside diameter of the N1 pump is ~77mm, the STD is ~81mm, they do looks like they made from very different materials! I do not have any dots on the used STD pump gears (like on the N1) that i bought from the guy on this forum! I would dream to have the gears already replaced with performance, but im still pretty shure they are stock!
N1 Has 11 tooth and the STD has 12!

#2 - The collar from australia, the guy is telling me that he copy the actual JUN collar and i do belive him. It looks like a very qality product, BUT it is very wobbly in the standard oil pump and even more wobbly in the REIMAX oil pump gearset. Here is some pics:

Side clearance on the standard pump is .013 one side and .010 on the other so ~.011 - .012, comes to a ~.006 each side. I think this is crazy large!

So if i measure clearance the same way on the Reimax gearset, this numbers are growin even higher! .018 and .016, so comes to a ~.008 each side. OMG.

Reimax gearset is ~81mm outside diameter but it similar to a profile of an N1 pump. I guess they make that to lower the cost of the product, the inside gear stays the same and the outside (internal gear) is slightly larger(STD) or smaller (N1) depending on the application! But Reimax gear looks very very nice!

#3 - And in the end I just would like to say what if Nissan production would rotate the oil pump gear half tooth eather way, than the common breaking point would be MUCH MUCH stronger. But this is just my personnal opinion, and it would probably worked only on STD pump gear with 12 teeth! (in RED - common breaking point)

I received a collar from Allen (jdms13rhd) and all i can say is that im very very pleased and impressed with quality, craftmenship and clearances of the collar!
I also received second STD oil pump to doble verify all of the findings!

Here is the beginning, you can see Caliber676's oil pump (he said around 60k km) and GTRBrian's pump (He stated around 80k km was on his)

Here is the first pump (~60k km), as you can see .0015" and .0025", so around 0.002" each side. Even though that Allen was promising ~.001 each side i think, by the feeling of collar going in and out of the pump inner gear, it almost feels like TOO LITTLE CLEARANCE!!! And when the collar is going to be pressed on, its going to stretch a little, making the clearances even more tighter!)

Here is the Reimax set! As i was saying before the gear is larger than stock so, here is the specs on it: 0.007" and 0.009" which comes roughly around .008; much much better than my stock R33 crank!

And in the end, here is another stock pump with ~80k km, as you can see clearances are very very tight! .002 and .0025" so ~ .002 each side which = very very good! 

If you guys can see there is a clear image of the old short collar, the part of the drive where tche collar was not touching is like new, so i can say that my measurmens are practically identical to the new pumps!

In the end I would like to thank Allan for doing his research on this problem, ask him to use even more stronger metal in the feauture, if it is possible of course (in order to be bulletproof on international market) andrecommend him to decrease inner diameter of the collar by .012 - .025". This, in my opinion will make collar a bit thicker and increase the thickness of the hard working flat spots of collar which make them a little bit stronger.
Thank you Allen

So here is another update withe the measurements of my ~R33 crank! They are not looking very good!
Firs is stock pump gear! .014 and .013 comes to an average ~ .006" on each side - even more than with australian collar! THIS IS CRAZY

Now with Reimax gears - .019 and .018 SO - ~.009 each side! No matter what metal this would be made of they will brake soon or later with this wobble!

In the end i would like to state my opinion, because i see sometimes people are saying that there should be a clearance, if Nissan engeneers did it so there should be one! I would like to say that Nissan almost missed the oil pump with theirs early short oil pump drives, and in the "upgraded" drive they only band aid this problem extending the drive, so no they didn't pay enough attention in that area and the clearances there should be much smaller than what we experiencing right here! 

Even GReddy pumps can explode:

Broken GReddy Oil Pump