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another regular NISSAN RB clearances question

General Engine Building Discussion

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Hello Andre,

I have read a lot of similar topics on the forum and first of all would like to thank you for such patient and detailed answers in every thread.

Planning my first build of the racing RB engine now and wonder if there are any advantages if its bearing clearances will be more than general .002/.0025?

How does it depend on the choice of rotating assembly components, oem/billet main caps, oil viscosity and oiling system type?

Thank you.

P.S.: availability of such huge amount of information regarding "building tricks" and "know-how`s" of RB engines in the Web causes one more question:

Do you generally advise 2.5/2 thou`s on main/big ends like the RB specific "rule of a thumb"?

How it would differ from your advice regarding the clearances of the high powered 4G63?

The clearance required is really driven first and foremost by the journal diameter. The old rule of thumb is that you want approximately 0.001" per inch of journal diameter, so a 2" journal would need 0.002" clearance more or less. This also changes when we're dealing with an alloy block as the alloy grows more as it heats up and you'll often start with tighter clearances cold due to this.

I'm not sure of your question though? Are you asking if there's an advantage being looser than 2/2.5 thou? If so then I'd say no. Those clearances are suitable for even extremely high power levels and very high rpm. There's no gain in going looser.

The clearances I use on a 4G63 and the RB26 are basically identical because the journal sizes are also very close. The mains measure 57 and 55 mm, while the big ends measure 45 and 42 mm respectively.

Thank you Andre.