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How to Degree a Cam: Step 2: Find True TDC

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Step 2: Find True TDC

05.12

00:00 - In this step we're going to go through the process of fitting our degree wheel to our crankshaft and then we're going to fit a pointer and then zero everything on true top dead centre.
00:11 Now there are a couple of ways we can go about fitting our cam degree wheel depending again on what state our engine is in.
00:18 As we can see here we already have our Mazworx ATI damper fitted to the front of the engine and this gives us a convenient location to bolt the degree wheel down.
00:30 There is a three bolt pattern on the front of the ATI damper and we've drilled a matching set of holes in our Moroso degree wheel.
00:38 So it's really easy for us to bolt the degree wheel straight to the damper.
00:43 Alternatively though you can also fit the degree wheel directly to the snout of the crankshaft.
00:49 This will require you to space the degree wheel out with a few 16 millimetre washers, just in order to clear the pointer for TDC.
00:59 Either way though the process is essentially the same.
01:02 We're going to start now by bolting our degree wheel onto our damper.
01:22 Regardless how you've bolted the degree wheel to the snout of the crankshaft, it is essential once we've got that bolted just to make sure that it is going to clear any obstacles, it's not going to get hung up on anything.
01:33 With our degree wheel fitted we can now go ahead and fit a pointer.
01:36 In this instance I'm going to simply be using a piece of welding wire.
01:40 This is cheap, easily available and it's also easy to bend and manipulate the welding wire to point wherever we need it to.
01:48 What we want to do is make sure that we have a bolt hole on the engine block somewhere that we can locate the pointer.
01:55 In this case we're just going to use one of the bolt holes that holds the cylinder head down onto the front cover at the front there.
02:01 Let's go ahead and we'll fit our pointer.
02:25 OK so we've made our pointer there.
02:26 I've got it approximately aligned with TDC.
02:29 Although of course at this point we know that there's a chance that TDC isn't going to be super accurate.
02:35 So our next process we'll go through is finding true TDC.
02:38 It is important when we are making our pointer as well, to make sure that we can fit it as close to the degree wheel as we possibly can and this will reduce any chance of parallax error creeping in and affecting our results.
02:50 What we're going to do now is back the crankshaft off TDC by about 15 degrees and we'll wind our positive stop into our number one spark plug hole, and we're going to tighten that down until it just barely contacts the top of the piston.
03:06 So let's go through that process.
03:14 Alright I've just tightened the positive stop down onto the piston and then just backed it off very slightly.
03:19 What we're going to do is go through now, we'll bring the piston back up onto that positive stop, we'll take note of the marking on our degree wheel, and then we'll rotate the engine forward through 360 degrees until we come up on the positive stop from the other side and of course we're looking for the point directly in between where true TDC is, so let's do that now.
03:51 What we can see here is that on one side of our positive stop, we were at seven degrees and the other side gave us 8.5 degrees.
03:59 So we're actually pretty close.
04:01 What we're going to do now is find where we actually need to be using our calculator.
04:06 What we'll do is take our values, 8.5 and 7, and we'll add those together and then divide by 2.
04:14 What this shows us is that we want to be at 7.75 degrees on each side.
04:19 What we can do is simply now adjust our pointer to achieve exactly that.
04:29 Once we've adjusted our pointer, we're going to go through and just repeat the process and ensure that we do in fact get the same result on both sides, so we're gonna go through and bring our piston back up on our positive stop on both sides of TDC again.
04:51 As we can see there with our second confirmation, we have in fact ended up with 7.75 degrees on both sides of TDC.
04:58 So we know that our pointer is now in the correct place and we have found true TDC.