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1jz building - Ring gaps and bearing clearances

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Hi guys, I've got a technical question,

Everything over 1mm I can deal with, but smaller than that and it gets confusing...

I'm building an engine and I'd like your input. 1jz vvti aiming at 650whp.

My questions are about ring gaps and bearing clearances,

1/ My understanding is that my 3.4 bore x 0.055 = 0.018-0.019inch (0.45-0.47mm) ring gap, i have slightly overground all top rings to around 0.020 (0.50-0.51mm) except n°4 which is 0.023 (0.60mm), do you think I need to reorder a set of rings for this specific one ? for all of them ?

All second rings were above 0.51mm when I tested them so I didn't grind them.

2/ I have been recommended STD-HX bearings, and apparently I need just STD bearings, no added oil clearance ? Bearings are already in, I'll try getting some plastigage but idk what's in the realm of acceptable oil clearances. My oil pump is a driftmotion modified one, so more oil flow apparently

Thank you very much !

Have a nice day !

Best regards,

Quentin

I wouldn't worry about the ring gap - most ring manufacturers suggest little, if any, significance until 40-50 thou' ring gap. It also gives a little more security against butting the rings which is a BIG no-no.

Bearings will depend on the condition, and wear, of the various journals - you may be perfectly fine with the stock diameter (I assume that's what you mean?) replacements, but you will need to accurately measure all of them to know. I can't comment on what the clearances should be, sorry.

For performance jz engine bearing clearances should be 0.05-0.06 mm providing that the crank shaft is not bent at all ( most of them are bent anywhere from 0.01 to 0.03 mm).

Hi Quentin, the ring gaps are a little looser than I'd choose but as Gord has mentioned it's unlikely to have a significant affect so no, I wouldn't suggest starting again with a new set. You 'may' find that the engine exhibits a little more blow-by than if they were gapped ideally but it will be minor. 650 whp is not exactly a massive stretch for a 1JZ and there's enough of these engines putting down these sort of numbers in completely stock configuration which should tell you enough about how suitable the manufacturer's stock clearances are. In general I'd be aiming on the looser side of the factory tolerance range and certainly the recommendations Shota has made above are in line with my experience. Ultimately you need ton know what you have now in order to decide if changes are necessary.

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