Summary

Why do we need to run a larger bearing clearance and thicker oil above certain engine power level or should we not? That's a really good question there Naden and I'm just gonna delve into that because there actually have been two directions of development recently and I wanna talk about those.

00:00 - Naden has asked, why do we need to run a larger bearing clearance and thicker oil above certain engine power level or should we not? That's a really good question there Naden and I'm just gonna delve into that because there actually have been two directions of development recently and I wanna talk about those.
00:15 Generally when we are dealing with OE production engines and we're modifying them, we're making more power and we are pushing them to higher rev ranges, then the theory has always been and still is that we want to generally build a slightly looser tolerance in our bearings than what the factory recommend.
00:35 The reason for this is that while all of our engine components may appear to be incredibly stiff and rigid when they're sitting here on the workbench, when we've got that engine running and it's producing very high power levels and it's also running to very high RPM, those components actually flex a considerable amount.
00:53 And what this means, particularly if we consider our crankshaft.
00:57 And we consider our crankshaft maybe flexing a bit like a piece of spaghetti at high RPM, this gives the ability for the journals to flex and move and if we don't have enough clearance we can end up with contact between the journal surface and the bearing.
01:11 So this is why we tend to go with a slightly looser clearance and this allows more movement before we end up with metal to metal contact.
01:19 This also allows us to use a thicker oil, provide a thicker stronger oil film, depending on the oil we're using, that's going to help protect those components.
01:28 So that's why the general trend is to build an engine with looser clearances.
01:33 If we look at professional motorsport though, they've actually move completely the opposite way.
01:36 And this doesn't mean that what they're doing applies to us.
01:38 But they're dealing with components that are designed specifically for the task so they've got very very expensive very rigid crankshafts and engine blocks.
01:49 These components don't flex anywhere near as much as our factory components.
01:53 And what they've tended to do is go to tighter clearances.
01:56 This allows them to use a thinner oil and this produces a lower frictional loss inside the engine.
02:02 So when they're chasing those last few horsepower, there can be advantages for them in going with a tighter clearance.
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