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Engine Building Fundamentals: How to Use Plastigauge

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How to Use Plastigauge


00:00 - As we've already discussed, plastigauge isn't the preferred option when it comes to measuring precision clearances, such as our oil clearances with our bearings, but since it is still used so widely, in this module we're going to have a lot at how to correctly use plastigauge.
00:17 Now here I've got two types of plastigauge.
00:21 I've got the green and the red variety.
00:23 There's also a blue variety available, and essentially we're going to choose the correct colour based on the range of measurement that we want to actually measure.
00:34 In this case, for engines that I'm dealing with, generally we're using the green scale plastigauge, which is capable of measuring between one and three thousandths of an inch, and this is going to cover the bearing clearances for both main bearings and connecting rod bearings that you're usually going to see.
00:52 So the actual plastigauge is a wax-like strip.
00:56 It looks a little bit like a thin piece of string.
01:00 We can see here we have the green and the red variants.
01:03 The process of using plastigauge starts by making sure that the crank shaft journal, as well as our bearing surface are both clean.
01:12 An easy way of doing this is to just use a spray-on brake clean product, and a clean rag.
01:18 This just allows you to remove any debris, as well as any oil contaminants on the surface of both the crank shaft journal as well as the bearing.
01:27 Once we've done this, we can now fit our section of plastigauge, and we're just going to lay the plastigauge across ways on the journal of the crank shaft.
01:36 What we really want to do here is cut a piece of plastigauge that extends the full width of the journal.
01:42 A tip before we actually instal and torque the bearing cap is to give the bearing surface a light spray of a silicon spray, and this will just stop the plastigauge from sticking to the bearing surface.
01:55 Now we're simply going to instal our bearing cap and we're going to torque this down to the manufacturer's recommendations.
02:11 Now that we have our bearing cap correctly torqued to manufacturer's specifications, we now simply want to remove the cap so that we can inspect the plastigauge and check our oil clearance.
02:26 A tip when it comes to removing the bearing cap is to make sure that the bearing cap is only pulled directly upwards.
02:34 This will prevent the plastigauge from being distorted and giving us a false reading.
02:39 Once we have removed the bearing cap, one of the first things we want to look at is whether or not our plastigauge has squashed down evenly.
02:47 Now this is one of the advantages, in my opinion, of plastigauge.
02:50 It makes it very easy to see if we have any taper in our journal.
02:54 And in this instance, we can actually see a minor taper, because this particular end of the plastigauge is very slightly thinner than this end.
03:03 Now, when the plastigauge is squashed out more, as we can see over here, this means that there is less clearance, because the plastigauge has been squashed tighter.
03:12 Now we can actually compare the plastigauge to the scale on our plastigauge packet.
03:18 And what we want to do here is match the plastigauge at the widest point and see what matches our plastigauge scale.
03:26 And we can see here that we're around about the 1.5 thou measurement, so this is where the width of our plastigauge matches the width of our scale.
03:36 So this means that we have a minimum clearance for this journal of 1.5 thou.
03:41 One of the limitations, when using plastigauge is the accuracy with which we can measure.
03:47 As you could see on the scale of our green plastigauge pack, we had divisions at 1, 1.5, 2 and 3 thousandths of an inch, so it's very difficult to be more accurate than that when we are actually comparing the squashed, flat plastigauge.
04:04 It is, however, useful to give us an indication of the available oil clearance.
04:09 In the case of the 2JZ that we're looking at for this example, the recommended manufacturer's oil clearance is a minimum of 1 thousandths of an inch and a maximum of 1.6 thousandths, we're within that scale so we could continue.
04:25 Of course, I'll reiterate again that plastigauge is not a replacement for using a micrometer and a bore gauge to get a more accurate idea of your actual bearing clearances.

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