Low Oil Pressure Between Builds

[crashsvg]

ok guys. i had already made a post 'wide bearing clearance' but the guys started their own topic and bypassed my question

i have some new information and would like some builders advice....

i bought a rb26 moto that came with a damage oil pump.... i changed the oil pump and installed a new n1 crank also ....i also replaced the bearing with std acl ones .the builder said he checked the clearance and they were on target around .0015 ..on start up of that moto we got a average of 82 psi ....we dynoed the moto and at 300rwhp the rings cracked ..i noted that the oil pressure was a lil low on the dyno but i cant remember the exact number

when we took down the moto we saw that there were scratches on the cylinder walls and decided to use another block we had access to as we had already went ahead and bought forge std pistons..we basically switched the the block and the girdle only..we use the old oil pump ,water pump, crank ect....we measure the crank journals and it was in specs....we also noted some scores on the old bearing that suggested low oil pressure or clearance to close....the crank also had a lil score on the journals but the builder said his experience that damage was small and shouldn't be a problem

we measured the clearance in the new block and it was wide with std acl bearing....0025 of the max .0034 .. we consulted with some guys who build drag racing rb26 and they said it was a lil wide for a street car but they used similar specs on there drag cars that goes 8sec in the quarter..

now when we started the new moto we got back the same 80psi oil pressure... but the problem comes when the car gets up to temp i see only 60 psi at 5k and ad we go up to 6k it backs off to 52 psi as if the pump is running out of steam...

i then changed the oil pump and to a new n1 and replaced the gears with reimax gears for safety ..on start up the psi is the same and i still have the same low psi behaviour at high rpm.

i used 20-50 oil in both builds also..royal purple

i also changed the little o-ring by the oil filter on the block to ensure that pressure was not dropping off their ..i also looked at the pick up and it was clear ..but i also noted that the builder used silicone instead of the o-ring between the block and the pick up with a gasket

my question is why am i getting these strange oil pressure behaviour between builds with the .0015 clearance and .0025?? .am aware the wider clearance suffer from lil less oil pressure ,

also is the n1 pump capable of delivering enough oil with the wide clearance ,,,?? i know that i should be getting 100 psi at start up with the n1...

what else on the engine could be responsible for leaking or lowering the psi .? could the oring by the pick up cause this much difference?

am really out of answers and ideas ...please help....

Edited September 15, 2013 by crashsvg

[black bnr32]

tldr

[crashsvg]

tldr

??

[StevenCJR31]

??

Tldr means too long didnt read

[crashsvg]

well ..I Have to explain so I could get proper help..smh

[Gareth87]

@CrashSVG - It's a good idea that you do explain the issue as you did so people have all the facts to offer an opinion.

I don't know a great deal about RB's but it certainly sounds like you have an oil pump that's not keeping up with demand. In my experience, I have an external oil pump on my engine and I had a drama with the bypass at one point. I have 3 spring options on my pump and when I run the lightest spring it has a similar issue. Perhaps with the bearing clearance you may need to preload the spring a little more.

However, in saying that, pressure and flow are 2 different things and it sounds like when the RPM is higher, the flow can't keep up.

Just my ideas, but I would speak to someone that know's a thing or 2 about RB's.

G

[crashsvg]

thanks for your input gareth87.

but i dont believe its a spring issue simply because the spring acts likes a waste gate...for example a 10psi spring allows you to build 10psi of boost then the excess gas a dumped creating a stable boost.. the pressure relief valve does the same but stock relief is usually 100 psi...

if it was a case if not allowing more than 60 psi of oil pressure to build then i wouldn't be getting 80 psi on a cold start..

am leaning towards the pump cannot deliver the required volume to build the necessary oil pressure ...

but this only makes sense if the first builder lied when he said he plastic gauge the engine because the first time the engine went up it had close clearance of .0015

its basically a 400whp a tomi pump is over killed for the project...

[abr33]

Might be a silly idea, but the restrictors weren't removed to fit bigger ones and forgotten about? Would line up with the problems. Unlikely though

[crashsvg]

the stock restrictor was in the block

thanks still

[StevenCJR31]

thanks for your input gareth87.

but i dont believe its a spring issue simply because the spring acts likes a waste gate...for example a 10psi spring allows you to build 10psi

of boost then the excess gas a dumped creating a

stable boost.. the pressure relief valve does the

same but stock relief is usually 100 psi...

You are confusing volume with pressure

You can have a pump that moves a low volume of oil and still have good pressure and vice versa

if it was a case if not allowing more than 60 psi of oil pressure to build then i wouldn't be getting 80 psi on a cold start..

am leaning towards the pump cannot deliver the required volume to build the necessary oil pressure ...

but this only makes sense if the first builder lied when he said he plastic gauge the engine because the first time the engine went up it had close clearance of .0015

its basically a 400whp a tomi pump is over killed for the project...

[KiwiRS4T]

An N1 pump should certainly be adequate. Have you been using the same oil pressure gauge? Perhaps that is not reading correctly? You say the first engine suffered broken rings. Not sure if this can be attributed to low oil pressure - would have though that inadequate oil supply would have seen a bearing failure. Did you see for yourself the plastigauge results for the second build?

[portaz]

My 26 has over 100psi at cold idle and 35-40 at hot idle, n1 pump but 1.5 thou clearance and I have 3 oil pressure gauges just to be sure and a big arse oil cooler.

Scott

[dnegative]

am leaning towards the pump cannot deliver the required volume to build the necessary oil pressure ...

Its a fixed displacement gear pump, your not going to get higher oil pressure unless you make it bigger (as in, flow more at a given RPM) with the clearances you have.

Pumps create flow not pressure, if everybody else has good oil pressure with a OEM sized pump then your issue is excess clearance or something else not right in the system.

[crashsvg]

An N1 pump should certainly be adequate. Have you been using the same oil pressure gauge? Perhaps that is not reading correctly? You say the first engine suffered broken rings. Not sure if this can be attributed to low oil pressure - would have though that inadequate oil supply would have seen a bearing failure. Did you see for yourself the plastigauge results for the second build?

the gauge has been in the car for a while ..prob 10 years..am going to try a different one today and see .. and when the rings broke I installed the new pump after to ensure the old one was not damaged. but the result was the same ..

@kiwi i didn't see the results .but the measurements were checked with a bore gauge then checked again with the plastic gauge ..

maybe the gauge could be at fault. because both engine with tight and wide clearance had the same reading with the n1

[crashsvg]

ok .so just checked the oil pressure with another gauge and am getting around the same reading of 74-78 on cold start.......

think my best bet is getting some cosworth size 0 bearings .. to reduce the excess clearance

[datsun_1600]

You say you used the girdle (and therefore, main bearing caps) off another block - did you have it line bored afterwards ? If not, i'm just wondering if a misaligned set of mains could cause some sort of weird oil pressure issue you are seeing. Each block's mains/girdle are specific to the block they came out of.

Jeff

[crashsvg]

the block we used had its own girdle ...

we tried the old one just to see if the clearance would change in our favour but it did not fit correctly.

[datsun_1600]

the block we used had its own girdle ...

we tried the old one just to see if the clearance would change in our favour but it did not fit correctly.

MMMmmm Interesting, not sure hat it could be! I've seen air do funny things like this, but i'm guessing you have the oil pickup sealed correctly... bit hard to check I guess. Good luck :-)

[crashsvg]

the air pick up was sealed with a sealant and gasket ,,, it is questionable as we didn't get the proper o-ring to go there... the builder had a theory that it could be sucking up air after 5k why it showed the drop in pressure.... 2 of my close tuners keep telling me the clearance are to wide and they have all worked on builds exceeding 800whp ... so am gonna just go with what they say...

what i will do however, is that before i change the bearings i would take down the pick up and insert the proper seal put back in some oil and see what the pressure looks like .if it looks better i would leave the bearings as is

[NismoSTune]

Faulty gauges don't wipe out bearings, low oil pressure and bad clearances do...

I had the opposite problem as you. High oil pressure (8bar at 60000rpm) and crank walk shortly after (700 miles), tomei oil pump.

I wonder if you have an issue with the oil pump pressure release valve maybe? Your pressure drop Seems consistent. Was your pickup cleaned and inspected? You have head oil drain mods (in case of excess oil in the head), or orifice reducer?