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Engine Building Fundamentals: How to Use Feeler Blades

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How to Use Feeler Blades


00:00 - In this module we're going to have a practical demonstration of how we can use feeler blades to measure clearances on engine components.
00:08 In front of me I have a standard set of feeler blades.
00:11 If we open the feeler blades up we can see that we have a range of hardened steel blades.
00:18 On each of the blades we have the measurement or thickness of that particular blade.
00:22 The measurements are listed in both metric as well as imperial units, depending on what you're happiest working in.
00:30 Now one of the problems when it comes to using feeler blades is a certain amount of feel is required as to what sort of resistance is expected.
00:40 If we use a feeler blade that is too thin for the clearance that we're measuring there's going to be no friction or resistance when we slide the feeler blade through the components we're measuring.
00:50 On the other hand if we choose a feeler blade that's just slightly too thick, we may be able to force it through the components we're measuring, but there'll be a lot of resistance.
01:00 So some of this requires some knowledge of what we're expecting.
01:04 Now a really good way of developing a bit of a feel for what is normal or correct when we're using feeler blades is to do a test with a couple of glossy magazines and a sheet of paper.
01:16 So I've got in front of me here two glossy magazines, I've got a normal sheet of A4 printer paper and what I'm going to do is put the sheet of A4 paper between the two glossy magazines.
01:25 I'm just gonna hold down on the corner of the magazine and I'm just going to gently pull the sheet of paper out.
01:31 Now it's going to give you a good guide as to what the normal amount of resistance should feel like.
01:37 Now if you go too large on your feeler blade there's going to be a lot more resistance, if you're too small on your feeler blade there's going to be minimal to no resistance.
01:46 Now we know what we're looking for, let's actually have a practical example, and we're going to measure the valve lash clearance on a Toyota 1FZ cylinder head.
01:55 So on this cylinder head what we're going to do for our demonstration is we're going to measure the exhaust valve clearance here on number one cylinder.
02:03 And what I'm going to be doing is sliding the feeler blades between the base circle of the camshaft lobe and the bucket that the camshaft lobe sits on.
02:12 It's relatively typical to expect somewhere in the region of about 0.010 inch clearance on this sort of mechanical valve mechanism when the engine or cylinder head is cold.
02:24 So let's grab our feeler blades and see what we actually have.
02:28 What I'm going to do here is start by using my 0.010 feeler blade and what I want to do is simply slip the feeler blade or the end of the feeler blade between the base circle of the camshaft and the top of the bucket or lifter.
02:43 So just going to push this through and now I can feel there's absolutely no resistance.
02:47 It's just sliding straight through the end, and this indicates straight away that 0.010 inch is too small in terms of our feeler blade.
02:56 So what we're going to do is jump up in size.
02:58 We're just going to open up our feeler blades and the next size I'll try here is our 0.012 inch blade.
03:06 So we're just going to do the same procedure there.
03:09 Now with my 0.012 inch blade, I can now feel a reasonable amount of resistance, so this indicates to me that I'm probably pretty much correct with the 0.012 feeler blade.
03:20 In order to just confirm this though, what I will do, is I'll try going a little bit wider, and we'll just open out our 0.013 feeler blade, and try pushing this between the cam and the bucket.
03:33 And in this case I cannot force, or I would need a reasonable amount of effort to force this feeler blade between the cam and the bucket.
03:43 So we'll go back and we know that in this case 0.012 is the correct clearance.
03:49 Like all of the tools we're looking at in this course, learning how to use feeler blades correctly is going to take a little bit of practise, but once you've used them a few times you're quickly going to get a feel for what sort of resistance you're looking for when you're trying different feeler blades to check your measurements.

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