Summary

00:00 - Alex has asked, how do you mitigate piston slap on forged pistons in the building process? Alright so this really comes down to what I've kind of touched on a few times already, there is unfortunately a bit of a requirement to have additional clearance on our forged pistons.
00:17 And what we find is that, again I've touched on this as well, a lot of machinists tend to be a little bit generous with our clearances on the piston to cylinder wall and this is what results in the knocking or piston slap.
00:32 These days with a high quality forged piston in a block that is machined to the piston manufacturer's specification, you should be looking at piston to cylinder wall clearances in the region of maybe 3500 to 4500 thou in most applications, somewhere around about that.
00:51 The engine should run very quietly.
00:54 There are also some developments, one of the piston sets we have, I don't have it here, but it is very similar to what we're looking at here, JE have produced what they call their perfect skirt finish.
01:07 So this is a coating that is applied to the piston skirt.
01:09 This one here is also coated, this is an anti friction coating but this is a fairly traditional coating.
01:15 The perfect skirt coating is slightly thicker and it is designed to essentially wear on the bore wall and allows the forged piston to be fitted up with very very tight clearances or tighter than you would conventionally run and this allows them to run very quietly.
01:32 So most of the problems that I see with piston slap with forged pistons really come down to those clearances being excessive or there's actually bad wear on the pistons and unfortunately when everything is really loose, this actually exasperates that problem because the pistons aren't well supported in the bore, they do tend to end up wearing more dramatically than if the clearance was set correctly.
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