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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.

Currently doing mains, soon to do rods. Ive miced and used a dial bore. Ive gotten a wide range of clearances, so i cant decide how to go with it... Ive got HX y and H shells on hand, ACL Race Series. I can either go all 0.0025" (ranging within 0.0002) or 0.002" (same as before), cant decide which way to go, this engine will have over 450hp, revved to 8k or maybe 7.5k to be safe. Purely a drift engine. First time going this deep into an RB, last time i got a stock engine refreshed with full HX, dont remember my clearance but it was loose, engine lasted a year until oil starvation got it. * Jun Oil Pump *RB25 Neo head *RB26 crank/Eagle rods/CP pistons in RB25 Neo Block.