Summary

Where do I remove material from a piston? Yeah good question there, we've got a similar question there from Alexander, when you are balancing pistons, where do you remove the excessive weight and Matty has also asked, pretty much the same question, on rods. So let's deal with the pistons first.

00:00 - Where do I remove material from a piston? Yeah good question there, we've got a similar question there from Alexander, when you are balancing pistons, where do you remove the excessive weight and Matty has also asked, pretty much the same question, on rods.
00:15 So let's deal with the pistons first.
00:16 So it is going to be very dependent on the particular design of piston.
00:21 So a little bit of common sense needs to come into play here and really it's just a case of looking at the design of the piston and seeing where we can remove material without adversely affecting the strength.
00:32 First point, we're never going to be removing material from the top of the crown or the sides of the piston skirt or anything like that.
00:39 It's always going to be on the underside of the piston.
00:42 Our next point is, we don't want to be drilling into the underside of the crown, that's going to result in stress raises and it's also going to adversely affect the thickness of the crown which is a very big aspect of the piston's strength but let's get this under our overhead here and we'll have a look at this particular JE piston.
00:59 So what we can see is we've got our pin bosses here that the wrist pin sits in and we've got a little bit of material here and here, here and here which if I just turn the piston a little bit, we can see that at that point there's quite a lot of thickness before we get down to that wrist pin boss itself.
01:18 So we can actually use our die grinder and remove material from these 4 points without adversely affecting the piston's strength.
01:24 Likewise if we need to remove a little bit more, we can do exactly the same on the outside points.
01:29 We can usually also remove a little bit of material from these little struts that run out to the skirt.
01:35 Now the idea here when we are doing this is we want to remove as little material as possible from all of those points.
01:43 So we don't want to focus our die grinder on just removing material from one point, obviously that would result in us removing excessive material from that one place.
01:50 Instead, if we spread the amount of weight that we need to remove across all of those parts I just pointed out, that's going to result in us not needing to remove as much material, meaning that we retain as much strength as possible from that component.
02:03 Now for our second part, the connecting rod, so again a little bit of common sense comes into play here and it is a case of analysing the design of the rod.
02:12 This one here is an argo rod and it's pretty representative of a number of aftermarket I beam style rods.
02:21 Now what we can see here is on the cap of the rod, we've got these two little ribs or ridges.
02:27 Now I've actually seen quite a number of professional engine builders linish material off these ribs and on face value that seems like a nice simple place to remove material.
02:36 We do not want to do that though.
02:39 Those ribs are actually there for a very important reason.
02:42 What they do is they increase the rigidity or strength of that cap which means that under high load, high RPM, the cap is not going to flex as much so that's a big no no.
02:53 Instead what we want to do is actually remove material from the sides of the rod, this is for balancing the big end.
03:00 The sides of the rod beside where the bolts go through so let's just have a quick look at that under our overhead and we can see, this particular rod I actually have already balanced, so basically I've linished material down the side there and again what I've done is I've done this on all 4 of those edges meaning that we obviously have removed the minimal amount of material.
03:22 Now if we just look at this on a different angle, you can see by removing material here, again this was a sharp square edge, we're removing that material, we're not adversely affecting the wall thickness here so we're still retaining strength.
03:35 Now on the small end of the rod, again what we want to do is obviously retain as much wall thickness through that little end as possible for strength and what we're going to do is just linish smoothly around the outside edge of that, so just removing the material evenly from the entire circumference there and that's going to get us a good result without adversely affecting our rod strength.
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