Rb 26 Bearing Wide Clearance

[crashsvg]

Hey ...am desperate for some professional advice on my rb26..

we assembled my moto with main and rod bearing at .0025 - 0028 ... we used standard bearing size and measured it properly. I know its wide but it still within in factory specs of max 0.0034..

I have a n1 pump with reimax gears fitted .on start up am getting 78psi ...when the moto is warm am getting 30psi at idle... at around 5k reving am getting between 68psi ans 72 psi and the pressure will stay there..

The service manual says at 6000rpm u should have on average 66psi. so while am within factory specs am a honda driver and am accustomed seeing 90psi and rev to 9500...

Am using 20-50 none synthetic oil ..still in break in period.... I have tried to locate bearings to bring the clearances to at least 0.002 but am having a hard time..

I know its not all about psi ... am not looking to race the moto just get it up to 400hp .. would the moto be ok with 70psi ??..not looking to rev pass stock limiter either..

Am trying hard to aviod a expensive jun or tomi pump... would a lil thicker oil help?

Edited September 12, 2013 by crashsvg

[GTRNUR]

_{20W50 will give you a thicker oil film and protect your journals and bearings more but it may not make all that much of a difference to oil pressure at the top end of the rev range. The relief valve is limiting your max pressure. You would need to shim the pump spring relief valve to gain more pressure. You could give royal purple 20w50 a go but don't expect more than a 5psi gain in pressure.}

_{Just an after thought, but you may want to consider switching to a Tomei pump anyway.}

_{Everyone is aware of the sketchy reliability of N1 oil pumps. When you factor in the wider clearances on your crank, you may be at much higher risk of pump failure. The splined drive in the 3 piece tomei pump will tolerate larger crank main bearing clearances.}

Edited September 12, 2013 by GTRNUR

[crashsvg]

so even with the reimax gears its still prone to break?

[GTRNUR]

Sorry I didn't read that part.... certainly a lot safer with a billet pump gear set. The pump will still take more of a flogging due to the increased clearances though.

[Shoota_77]

Aren't big ends supposed to be a fraction tighter than mains? I'd need to recheck the figures in the book but pretty sure they are...

[crashsvg]

yes I have on reimax gears..but am concerned about the oil pressure level... would a oil cooler help maintain that oil pressure. I noticed when driving tonight that when the car heated up my oil pressure went down more...and is 70psi sufficient?

[siksII]

You should calculate the oil pressure assuming normal oil temp.. What oil temp does it usually run once its hot?

The oil is much thicker when cold hence pressure it higher (and flow is less)

[GTSBoy]

And 70 psi is actually not a bad pressure. What you need really does depend on how much load the bearings are expected to be under.

And I echo the comment above that says your oil pressure is probably more a function of the relief valve setpoint.

[crashsvg]

I don't believe its pressure relief issuse. that's there to stop the oil pump from passing a set psi which in a n1 about 105 psi...if the valve was the limiting of 70psi I wouldn't be getting 80psi on cold start..

[GTRNUR]

Oil viscosity is affected by oil temp, and directly affects flow through the relief valve. This higher oil pressures when cold.

[T51B1]

This is just IMO, but I don't think oil pressure is the end all be all factor if your bearings are properly lubricated. Too many people worry themselves sick over their oil pressure figures.

Pressure is just a restriction to flow. Volume is the important factor. You also aren't going to build enough pressure to overcome the pressure the crank will be exerting.

If it was me, I would just run a synthetic 15w50 or 20w50 oil and keep the bearings you have.

[GTSBoy]

Not quite right. Main and rod bearings are hydrodynamic bearings. The metal bits on the outside don't touch the metal bits on the inside for only one reason. That reason is sufficient oil pressure in the bearing to float the inside bit off the outside bit against the machanical load applied. You cannot rely on the film strength of the oil itself to prevent metal touching metal. The pressure is absolutely the thing that makes the bearing work.

You can have an oil pump with twice as much flow capacity as any other pump, but if you run it against a set of bearings with incorrectly wide clearances, (or perhaps with too low a relief valve setting!) then you still won't necessarily get the pressure you need to float the bearing.

The sheer quantity of oil used in high volume pumps for high po engines is as much about pushing enough oil through the bearings to take the heat away and prevent the oil getting hot enough in its brief moment in the bearing to lose enough viscosity and hence lose film strength (which will kill your bearings even if you do have good enough pressure).

[KiwiRS4T]

My RB30 with just new bearings and a stock N1 pump has a good 100 psi at start up. I am using 10 - 40 fully synthetic Agip atm (will be using Motul 300 next). Did you use plastigauge to confirm your clearances? Its definitely not a matter of getting a more expensive pump.If you start caning your engine I suspect your oil pressure will drop even more. 10W 60 is considered too thick these days but maybe you should give it a try before you pull your engine down again.

[datsun_1600]

And to add a bit more to the fire, remember during the loading phase of the crank rotation (ie take for example the big end right after fuel ignition) the bearing separation comes from the pressure created hydraulically as the pressure from the conrod tries to force the oil film out of the bearing. If we were using just the oil pump to keep the big ends separated, we would need like 3000psi of oil pressure. Hence why big ends knock with incorrect bearing clearances, even though they may see 70psi of oil pressure.

Jeff

[crashsvg]

yes we plastic gauge all...am really not comfortable with the pressure now as it drop dangerously low when the oil heats up...now am getting a max of 4 bar after 5k and it slowly drops to 3.5 bar after that... so its park up time

i dont wana try to mask the problem with a big pump which may end up failing also .... am looking for some bearing to drop the clearance from .0025 to .0015 ...am from the caribbean and am getting a hard time finding a company who makes them, i checked for cosworth size 0 bearings but its been 3 weeks and no reply from them....

any help at all locating some bearings like those will be much appreciated

[T51B1]

Not quite right. Main and rod bearings are hydrodynamic bearings. The metal bits on the outside don't touch the metal bits on the inside for only one reason. That reason is sufficient oil pressure in the bearing to float the inside bit off the outside bit against the machanical load applied. You cannot rely on the film strength of the oil itself to prevent metal touching metal. The pressure is absolutely the thing that makes the bearing work.

You can have an oil pump with twice as much flow capacity as any other pump, but if you run it against a set of bearings with incorrectly wide clearances, (or perhaps with too low a relief valve setting!) then you still won't necessarily get the pressure you need to float the bearing.

The sheer quantity of oil used in high volume pumps for high po engines is as much about pushing enough oil through the bearings to take the heat away and prevent the oil getting hot enough in its brief moment in the bearing to lose enough viscosity and hence lose film strength (which will kill your bearings even if you do have good enough pressure).

100 psi oil pressure versus 5,000 psi the crank is/can be exerting?

Hydrodynamic pressure(what keeps the crank off the bearing surface) has no relationship to the engine oil pressure, except that if there is insufficient engine oil pressure to deliver the required volume of oil into the bearing, hydrodynamic lubrication will fail and the bearing will be destroyed.

[33GTRV]

Huh? You just explained the very thing you were arguing.....

Mind.......Blown.

[GTSBoy]

Yeah. There's a reason the oil is supplied to the bearing on the opposite side from the high pressure under load side.

[DCIEVE]

I think what he was correctly saying (along with a few others) is that a hydrodynamic bearing generates its own oil film. What you have described is a hydrostatic bearing.

[crashsvg]

sorry to say you guys are drifting from the topic about my psi issue