Summary

Are there any other downsides to aluminium rods besides service life? OK yeah there are. So one of the issues with aluminium rods is that they do require additional piston to cylinder head clearance.

00:00 - Auto Addicts has asked, are there any other downsides to aluminium rods besides service life? OK yeah there are.
00:08 So one of the issues with aluminium rods is that they do require additional piston to cylinder head clearance.
00:16 I dunno if I'd really say that's a downside but it is something we do need to consider.
00:21 So one of the aspects there with the aluminium conrods is that when they are in operation, they're obviously going to heat up and aluminium has quite a high thermal expansion coefficient compared to a steel rod, so what this results in is that the rod essentially stretches or grows when it heats up so the clearance that we have when the engine is cold and being assembled in our workshop will be very different to what we have in operation.
00:47 Likewise we find that the same aspect occurs with the big end of the aluminium connecting rod and that will actually grow and our big end clearance will change.
00:57 And this has the effect of reducing the crush on our bearing shells.
01:02 I'll just see if I've got one here, yeah I have.
01:07 This is an aluminium rod from one of our 4G63 drag engines, and because of the loosening or the adjusting of our clearances in our big end, it's uncommon on our aluminium rod to have a little pin to locate the big end bearing shell.
01:25 So you're going to have to modify your big end bearing shells to take this locating pin, otherwise you're not going to be able to assemble the engine.
01:34 The other aspect as well with an aluminium conrod that is a downside in my opinion is because the material is weaker than steel, you can see the sort of thickness that we've got through the beam of the conrod compared to an equivalent steel rod.
01:52 And what this often will mean is that you're going to need to perform some clearancing on your engine block.
01:57 But then of course the biggest problem that you've already highlighted there is that aluminium conrods do have a fatigue life.
02:03 So particularly they're not that suited to a circuit car engine or a street car engine because they do need to be replaced at relatively frequent intervals.
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