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4G63 Rod and Main clearance

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Hey guys,

For a 400bhp street car revving to a max of 7500rpm, what do you think of 2.1-2.3 thou on the big ends and 2.3-2.5 thou on the mains for oil clearance?

Thank you

I generally aim for 0.002" on the big ends and 0.0025" on the mains

Regards Ross

actually, if you check in the search this question has come up multiple times

Regards Ross

I understand, read through them all several times. My issue is that my machine shop "overpolished" the crank and that's why my clearances are a tad on the loose side. What i wanted to know is if there's any risk running with those clearances? My main concern in the big end clearance.

Thanks for the response Ross

your not that loose that its likely to cause a problem.

you can likely run a thicker oil with out too much issue.

as long as you have oil pressure at idle you should be fine.

https://blog.k1technologies.com/bearing-clearance-and-oil-viscosity-explained

There are also several bearing companies that offer 0.001" undesized shells, if you used half (one shell) in the rod you'd close it up a little, or both if you want the full closing up of the clearance.

Thank you Joshua, that's exactly the information i needed.

Gord, actually i'm already running a .025mm oversize bearing so the next size available is a .25mm and that would require me to further grind the crankshaft. I'm avoiding going that route, that's the reason i wanted to know whether I can get away running between 2.1-2.3 thou on the big ends.

Thank you guys for the advice, much appreciated!

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