Low Oil Pressure On Newly Rebuilt Engine:(

[youask]

Hello

Got some major headache here

I've rebuilt an rb26 after oil-pump failure

But when i start it up with 10-40w oil (20'c oiltemp) i got oil pressure of 2.5bar/1200rpm that drops to 1.5bar/1200rpm after 2mins. After 2mins i tried 3000rpm = 3bar
This seems way to low for me.

I've measured the pressure with a mechanical and one electrical gauge, not the dash-gauge.

I've done the rebuild myself (lot of expereince with 4g63, non with rb26)

Oil pump is a good used condition stock case with NEW reimax gears.
Main bearing clearences is 0.07mm
Rod bearings cleaences is 0.07mm
Oil squirters is torqued to spec.
Tomei 1.5mm oil restrickor to head.
Grex/Trust oil filter relocation and oil cooler kit (hoses connected the right way)
Crank is a R33 with good oil pump drive (modded to 0.2mm clearance)

I don't really know what it can be

[Ben C34]

That's not too low.

10 psi per 1000 rpm is considered typical.

[Hadouken]

Pressure sounds right to me. I think even the manual stipulates 3 bar at 3000 rpm

[89CAL]

+1

I was told 10psi per 1000rpm as well

Edited June 7, 2014 by 89CAL

[KiwiRS4T]

Stop idling give it some stick!

[abr33]

Should see about 60-80 psi @ 5k-redline

[Ben C34]

Should see about 60-80 psi @ 5k-redline

Where is that figure from?

factory manual?

[abr33]

no, what I was told by reputable engine machinist. Max pressure should be at the point of max torque, so give or take a bit.

[GTRPSI]

I see your issue its in your specs however you do have enough pressure for a street engine, 10 PSI per 1000 is right however your idle pressure should be a little higher, on the RPM side your OK.

When running around.003" clearances this is typical, those clearances are for all out race engines.

We have just built our bottom end with similar clearances, however.....

You want to be running at minimum a 50 weight of oil, if not 60 weight ideally, those clearances are far too loose for a 40 weight of oil, we will be running straight 60 weight (not multi grade) oil on .003" clearances.

Second part is in your oil pump, a stocky with reimax gears, in our case we used a Tomie pump, reason being was the external oil pressure adjustability for pressure control combined with more volume.

Start testing with a thicker oil and report back......try a 25-50 oil for starter if its a streeter with those clearances.

Im also assuming the clearances were checked properly with a mike and not plastigauges......

[KiwiRS4T]

I see your issue its in your specs however you do have enough pressure for a street engine, 10 PSI per 1000 is right however your idle pressure should be a little higher, on the RPM side your OK.

When running around.003" clearances this is typical, those clearances are for all out race engines.

We have just built our bottom end with similar clearances, however.....

You want to be running at minimum a 50 weight of oil, if not 60 weight ideally, those clearances are far too loose for a 40 weight of oil, we will be running straight 60 weight (not multi grade) oil on .003" clearances.

Second part is in your oil pump, a stocky with reimax gears, in our case we used a Tomie pump, reason being was the external oil pressure adjustability for pressure control combined with more volume.

Start testing with a thicker oil and report back......try a 25-50 oil for starter if its a streeter with those clearances.

Im also assuming the clearances were checked properly with a mike and not plastigauges......

Funny I was just thinking the opposite - being old school I like to check with plasti- gauge after establishing the clearances by measurement. Using an N1 pump my basically stock RB30 was running at well over 100psi from cold at 5000rev/min. The OP's pressures should be adequate with your suggestion of a heavier oil and maybe less oil control issues will present themselves!

[GTRPSI]

Funny I was just thinking the opposite - being old school I like to check with plasti- gauge after establishing the clearances by measurement. Using an N1 pump my basically stock RB30 was running at well over 100psi from cold at 5000rev/min. The OP's pressures should be adequate with your suggestion of a heavier oil and maybe less oil control issues will present themselves!

Im also old school and only use plastigauge for double checking, its a guide only and not accurate, i also use a bore gauge but i also back it up on mockup stage with a plastigauge to double check myself, much like yourself, you can never check enough, it only takes a small error of not having the bore gauge setup correctly to get it wrong, thats where platigauge is a good secondary measure but remember its not accurate and a guide only.

We had our machinist set up my clearances while the block and crank were in to my specs, got it home and started a few mock assemblies, used a platsigauge to double check clearances and found the rods at .002" when i specified .003".

Got my bore gauge out, yep he was off, had to go out and get some X stamped ACL bearings and mix and match them with the stock sized ones while checking with my mike for accuracy, finally double checked one more time with plastigauges.

Turned out he had the apprentice set up my clearances after going over to let them know it was wrong...... the apprentice didnt know how to properly zero a bore gauge.....

So plastigauges can be good for the obvious, but they are not accurate enough for fine detail, great for catching obvious error though.

Edited June 7, 2014 by GTRPSI

[youask]

clearensen both checked with plastigauge and bore gauge.

i'll try a 20-50w oil

remember that the values i've given was after only a few minutes so i guess the pressure will be even lower when the oil is warmer

i come from the 4g63 world and we have like cold-idle @8bar oil pressure with 10w-40

This is my old car

https://www.youtube.com/watch?v=Wu-mbkUcIRM

9.33/quar mile, 750whp mitsubishi mirage

[GTRPSI]

If your doing like in the clip above your clearances are OK, your issue is in the oil weight used and pump setup you selected.

Hopefully just the oil weight will sort you out to something a bit better.

Did you shim up the oil pressure relief valve for a bit more pressure before you closed the engine?

[youask]

problem solved

was missing all hex bolts on the crankshaft to the rodbearings,

6bar cold idle and 2.5bar hot now

Edited June 18, 2014 by youask

[GTSBoy]

Define "missing".

My definition of missing would mean that the rods were not bolted to the crank at all, which would have resulted in zero oil pressure and internal carnage.

[Ben C34]

Yeah. I'm confused!

[GTRPSI]

Or the crank grub screws were not put in.....hows the rod bearings?

[89CAL]

This sounds really odd.............

You can't be missing the rod bolts and be complaining about oil pressure. You'd have much more to complain about.......

ALL hex bolts sounds impossible. The thing would have fallen apart during installation when turning the engine over. Something in the description must be off, but I can't work out what else it could be.

[Ben C34]

EXPLAIN YOURSELF OP!

[jiffo]

Same thread appears on GTROC forum.

Apparently crank was cleaned and grub screwed but not all grub screws were installed ??????

Did well to survive at all.