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4g63 HX bearing clearances

Practical Engine Building

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Hi im aiming for

0.0025-.0026 on the rods

0.0022-0.0025 on the mains

ill be aiming for around 900 bhp on race fuel

im using carrillo pro H rods with carr bolts

ill be using the kings p-cote max bearings for that extra protection

i use a norris drysump kit so i can dial in the oil pressure and have good pressure with a big clearances ill be using amsoil 15-50 oil or motul 300v

my question if using half HX bearings and half std bearing on the same journal is it better to have the hx bearing on the greater thrust side to allow a bigger oil film and more cousining from deflection etc

Personally I think your target clearance on the big ends is a little large. With our drag engines that were in the 900+ hp vicinity I was aiming for 0.002" on the BE and 0.0025" on the mains. I haven't used the amsoil myself but we used Motul 300V 15w-50 on all our engines with great success. If you're mixing and matching different bearing grades on the same journal in order to achieve your desired clearance then it doesn't specifically matter which side you fit which bearing to. the reason is that the oil film dictates the clearance when the components are under load and the crankshaft floats in the journal. You should consider that mixing and matching bearing shells for the likes of a conrod will have a very small affect on the deck clearance of the piston depending which side the thicker bearing is fitted, however the difference is going to be incredibly small and unlikely to be a real concern.

hi thanks for the reply.

i always thought you went looser on the rods compared to the mains.

im going to measure up and maybe bring the clearances down abit

ill let you know what i get cheers Andre

The rule of thumb is 0.001" per inch of journal diameter and the mains are larger in diameter than the rod journals.