Quote:
Originally Posted by Croustibat
I did not explain myself correctly:
Basically, if you are running your engine at high/ very high rpms, you need very tight clearances. but you need them everywhere: rod and crank bearings, rings, bore to piston and so on. It will also require a lot of maintenance, because these clearances must be kept tight.
If you are not trying to get the maximum power an engine can do, you can use looser clearances. Not saying that you should, but as long as you are in the manufacturer recommanded clearance, its ok.
Now there is another reason that you dont need to use nissans bearing: if another manufacturer bearing gives you exactly the clearance you need.
If you know your engine has never been reground, then you can use nissans marks on the engine block, crank and rods to get the correct part number. If you dont know, plastigauge is your new best friend.
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I would politely disagree. I'd say clearances have far more to do with piston and connecting rod material, power level, and oil pump capability.
Running tight clearances will be absolutely disastrous if the oil pump can't handle pushing the correct weight oil into those passages at high-rpm. Too much power with too tight of clearances will beat up the rod bearings pretty badly.
Opening up the clearances requires higher weight oil, but can provide more of a cushion of oil film, and can allow the pump to flow more volume vs having a higher pressure.
Moving to a dry sump usually solves a lot of oiling issues and allows tighter clearances or more power to be made.
Also, our aluminum rod 4G63 engines run much larger clearances than their steel rod counterparts, but we rev them to 10,000rpm. This is due to aluminum's higher expansion.
Also, plastigauge is quite inaccurate. It's far better to mic everything.