RB30 Oil Clearance Calc Help

[RB25Detonator]

Hi guys.

Feel free to delete this post if it's already been asked but I cannot find anything on google showing how people calculate the oil clearance without bearings installed. I have an idea of how to, but I just need someone to confirm my calculations for my bearing/oil clearances before I buy the bearings. This is my first ever build and first ever RB30/25. I've never done something like this and I'm trying to do as much labour as I can before I send it to the machinists to save $$, so bare with me.

I have measured the journals with a micrometer and mains + big end tunnels with a bore gauge (without bearings installed). I'm going to be using ACL Race bearings for mains and big ends. I need to know what bearings to choose for my desired oil clearance.

Now here's the thing. By looking at the ACL RB30 bearings spec page, the thickness of 1 standard big end bearing shell is 1.503mm. Am I correct?. And 1 main shell = 1.827mm.

So, if I were to go with a 0.025 oversized bearings, the thickness of one 0.025 big end bearing shell would be: 1.503 + (0.025/2) = 1.5155mm. Correct? Because it's adding 0.0125mm on each shell to make the diameter of the 2 shells 0.025mm bigger right? And thickness of one 0.025 main bearing shell would be 1.8395mm.

Ok, so calculating oil clearance would be tunnel OD minus the thickness of 2 bearing shells, then minus the crank shaft's ID to get oil clearance right?

So, for example my #1 main tunnel OD = 58.682mm.

If I used standard main bearing, the thickness of 1 shell is 1.827mm.

My #1 main crankshaft journal ID = 54.962mm.

So calculating the oil clearance would be 58.682 - (1.827x2) = 55.028 - 54.962 = 0.066mm of oil clearance which equals to about 2.5 thou.

If I were to use 0.025 oversized then I would calculate it like: 58.682 - (1.8395x2) = 55.003 - 54.962 = 0.041mm of oil clearance (1.6 thou).

So calculating all my oil clearances using standard bearings on the mains would be 0.057mm to 0.077mm (2.2thou to 3thou) of oil clearance.

Big ends oil clearance using standard bearings = 0.032mm to 0.053mm (1.2thou to 2thou) 

Calculating oil clearance using 0.025 oversized bearings: Mains = 0.032mm to 0.052mm (1.2thou to 2thou). Big ends = 0.007mm to 0.028mm (0.3thou to 1.1thou).

Calculating oil clearance on big ends using HX (thinner bearing shell thickness of 1.49mm) would be = 0.058mm to 0.079mm (2.3thou to 3.1thou).

 

Another question I have is what would be the best oil clearance for an RB30/25DET Neo that will only be used for street use with about 300kw (max) with a crank collar and RB25neo oil pump limiting the revs to 6500 or 7000rpm (with the correct oil restrictions in block). I might shim the oil pump spring to give it more pressure if needed. My goal is just a responsive and reliable streeter engine that will last years.

I've read somewhere that someone qouted Qubes saying that he recommends 2.5thou oil clearance on the mains and 2.2thou on the big ends for RB30s. Can someone confirm this?

So should I go with standard ACL Race bearings on the mains and standard on the big ends or HX on the big ends (3.1thou max though?). 

Thanks.

 

[Rusty Nuts]

I used clearances as stated by the factory (after all they built it first)

here is RB30 manual page

 

[Rusty Nuts]

I used genuine Nissan bearings figured out the correct size then installed and checked clearance with plastigage. also have nitto oil pump drive, N1 pump and great oil pressure.

Edited February 23, 2019 by Rusty Nuts

[Rusty Nuts]

BTW stick with metric measurements mixing in imperial conversions will do your head in (and mine)

[RB25Detonator]

Thanks for the feed back! I also have an R31 PDF manual that says the standard oil clearance is 0.02mm to 0.047mm for an RB30E and that the limit is 0.09mm, and standard big end/conrod oil clearance: 0.011mm to 0.035mm with a limit of 0.09mm. So if I were to "Blue print" an RB30E, I would stick with those standard clearances right? But I'm building a RB30 with a 25DET Neo head (about 8.3:1CR) , with highflow turbo, nistune, bigger injectors, fuel pump, FMIC, 3" exhaust blah blah blah... that's gonna demand more HP than stock which means bigger oil clearance right?  That's what I've read, or maybe I'm wrong. I also read somewhere a while ago that the rule of thumb is 1thou of oil clearance per inch of journal diameter?  I don't know! That's why I just wanna clarify to which oil clearances to run. I would totally go with genuine nissan but I heard their bearings are bi - metal instead of ACL's being tri - metal (plus ACL is reasonably priced). 

So, If I go with standard ACL bearings and get an oil clearance of about 0.066mm on the mains and go with HX ACL bearings on the big ends and get an oil clearance of about 0.079mm, it would still be all good? Nissan lists the oil clearance limit as 0.09mm.

But then the thing that I don't get is why ACL has a min and max on the tunnel and journal shaft sizes. If you calculate ACL's oil clearance using their max tunnel and min journal shaft using standard bearings for the mains, you get 0.053mm for the max oil clearance, and 0.044mm on the big ends.

Edited February 24, 2019 by RB25Detonator

[Rusty Nuts]

On 2/24/2019 at 6:09 PM, RB25Detonator said:

that's gonna demand more HP than stock which means bigger oil clearance right? 

Its not 1950 mate, this sort of logic went out with old flexible cast iron cranks, today's oil is thinner and far better, Fifty years ago, "loose is fast" was a common belief. A low-viscosity oil will be squeezed over a greater area of the bearing surface when there is a tighter clearance. I built my 30 with main clearance of 0.038 and conrods 0.025. I would not go any where near Nissans max oil clearance. I had my crank linished not ground so had less control over clearances.

[azzada1]

How much power are you making rusty? Reason i ask is ive been told to run up to 3 thou depending on application and overall power output, The person giving me this advice has made over 40 passes with his 1000+ HP Rb30.. Just looking to open the discussion is all

[Rusty Nuts]

290 RWKW last time dyno'ed in 2017.