How to Degree a Cam: Making Cam Timing Adjustments
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Making Cam Timing Adjustments
10.37
| 00:00 | - In this module, we're going to have a look at how we can physically make cam timing measurements. |
| 00:05 | We're going to be measuring the valve opening and closing points on our Honda B18C. |
| 00:09 | We're then going to be comparing those valve opening and closing events to the camshaft specification card for the Kelford cams we're using and then we're going to see how we can actually adjust our cam timing to correct any error. |
| 00:22 | Now to start with, we've already gone through and we've fitted our degree wheel, we've found true top dead centre and we've also fitted our dial indicator to our intake valve on number one cylinder and we've correctly zeroed it. |
| 00:35 | What we can do now is go through and make an initial measurement and find out what our valve opening and closing points are. |
| 00:42 | Before we do that though, we do need to understand or know what we're actually looking for. |
| 00:47 | So coming from our cam specification sheet, we know that we're going to be looking for points at one millimetre valve lift, so we're going to be looking at the point where the intake valve first opens to one millimetre of lift and then again where it closes to one millimetre of lift. |
| 01:03 | From that cam specification card, we know that we should be opening the valve to one millimetre lift 19 degrees before top dead centre and then it should be closing back down to one millimetre of lift 55 degrees after bottom dead centre. |
| 01:19 | So now that we know what we're looking for, let's go ahead, we'll make an initial measurement and see what we've got to start with. |
| 01:27 | Now when I'm rotating the crankshaft, I'm using just a long strong arm here. |
| 01:32 | And this just allows me to make very smooth and gently movement. |
| 01:36 | That's really important when we are trying to accurately reach a certain valve opening. |
| 01:41 | So I'm going to turn the crankshaft 'round now and we're going to come up on the point where the intake valve first starts to open. |
| 01:48 | So particularly as we start moving our crankshaft from TDC, intiially we're not going to have anything much happen. |
| 01:54 | So we've just started to have our valve lift now, we're just coming up on half a millimetre of lift. |
| 02:01 | And I'm just going to very smoothly apply pressure here on my strong arm until we come up on the point where we have one millimetre of lift, which is what we've got now. |
| 02:11 | Now the important point is that once we've got to that one millimetre of lift point, we still want to apply a small amount of pressure on that strong arm, and this is just going to prevent the crankshaft from snapping back and giving us a false reading on our degree wheel. |
| 02:26 | Now that we've got everything sitting there at one millimetre of lift, we can actually look at our degree wheel and we can check our marking. |
| 02:33 | In this case we can see that the point on the degree wheel is 9.25 degrees before top dead centre. |
| 02:40 | So in this case we know that we're already around about 10 degrees retarded from the camshaft specification sheet. |
| 02:46 | What we're going to do though is go through and we're also going to check our valve closing point. |
| 02:51 | So let's do that now. |
| 03:02 | Now when we're measuring our valve closing point, we are looking at degrees after bottom dead centre. |
| 03:08 | So what we're looking for here is our black marks which start increasing as we go past bottom dead centre so we can see that the black marks on bottom dead centre here read zero, and then as we continue to turn the crankshaft, these start incrementing. |
| 03:23 | So these are the marks that we're going to be using now as we close the valve back down. |
| 03:31 | OK so we're just coming up on one millimetre of lift again now. |
| 03:35 | Again we're just moving very very smoothly with our strong arm so we can be really accurate. |
| 03:41 | And we're right on that one millimetre of lift point now. |
| 03:44 | So again I'm just going to maintain a small amount of pressure on the strong arm so that the crankshaft doesn't move and we can check our degree marking. |
| 03:53 | In this case our valve closing point is 64.75 degrees after top dead centre. |
| 03:59 | So there's a couple of things we need to take note of there. |
| 04:02 | First of all we want to make sure that our valve opening point and closing point are both consistent, relative to our camshaft spec cards. |
| 04:11 | In this case our valve opening and closing points are both occurring 9.75 degrees after the point specified in our camshaft degree card. |
| 04:21 | So that means that our duration of our cam or valve opening event is correct, or matches what the camshaft specification card says. |
| 04:28 | What this also means is that we now know that our camshaft is retarded by 9.75 degrees or almost 10 degrees. |
| 04:36 | So what we're going to need to do now is make and adjustment to our vernier cam gear in order to adjust that. |
| 04:43 | Before we make any adjustments I'm just going to continue turning our crankshaft and we're just going to come back up onto top dead centre. |
| 04:50 | Now that we've got our crankshaft back onto top dead centre, we can loosen the locking bolts for our vernier cam gear and make the necessary adjustment. |
| 04:58 | Before we do that though we do need to understand what we're going to be trying to achieve, or what adjustment we're going to need to make to that vernier cam gear. |
| 05:08 | We've found out here that our cam timing or our valve timing events are retarded by 9.75 degrees compared to what's recommended in our camshaft specification card. |
| 05:19 | For this practical example though we're going to just round that and assume that our valve timing events are retarded by 10 degrees just purely for simplicity. |
| 05:28 | What we're going to need to do then is advance our intake cam by 10 degrees of crankshaft rotation. |
| 05:36 | Now the subtle aspect we need to keep in mind here is that because our camshaft rotates at half engine speed, in order to achieve a change of 10 degrees at the crankshaft, we only need to move the camshaft by five degrees. |
| 05:51 | So what we're going to be doing is moving the camshaft by five of the individual degree markings on the vernier cam gear. |
| 05:58 | So let's go ahead now and make that adjustment. |
| 06:01 | I'm going to start here just by loosening off these locking bolts. |
| 06:05 | So we just want to loosen them enough so that we can easily rotate our vernier cam gear and we're also going to be taking note of the current degree marking, so where we currently are sitting on our vernier cam gear. |
| 06:18 | An this is going to allow us to make really accurate changes to our cam timing. |
| 06:23 | With our locking bolts loosened off we can now actually move our camshaft. |
| 06:27 | What we need to always keep in mind is what direcion we need to rotate the camshaft. |
| 06:32 | You'll remember that our cam timing at the moment is retarded by approximately 10 degrees, this means that we need to advance the cam. |
| 06:40 | We need to understand what way we need to rotate the cam in order to advance it. |
| 06:45 | This is a little bit more complex on our B18C because it is one of the few engines that rotates anti clockwise. |
| 06:52 | In and engine that rotates anti clockwise, if we want to advance the cam events, we need to also rotate the camshaft anti clockwise. |
| 07:01 | Of course in a conventional rotation engine, if we needed to advance the cam, we would rotate the camshaft clockwise. |
| 07:07 | So in this case we want to move the camshaft by five marks on our cam wheel anti clockwise. |
| 07:13 | So let's go ahead and do that now. |
| 07:27 | OK so with our adjustment made to our cam gear there, we can now lock up those adjusting bolts again and we can go through and make a further measurement to our cam or valve timing events. |
| 08:00 | With our locking bolts now tightened on our cam wheel, we can go ahead and make another measurement. |
| 08:06 | So this is going to just be a repeat of the process that we've already looked at. |
| 08:09 | We're going to be turning the crankshaft around, looking for the point where our inlet valve first reaches one millimetre of lift. |
| 08:16 | So we'll continue rotating the crankshaft and we're just seeing that inlet valve start to open now. |
| 08:23 | Again just applying very gentle pressure until we come up on that one millimetre of lift point. |
| 08:28 | Once we get there, again just holding a small amount of pressure on our strong arm to prevent the crankshaft moving and we can have a look at our degree wheel. |
| 08:36 | In this case we have reached the manufacturer's recommendation, we're right on 19 degrees before top dead centre. |
| 08:43 | So so far so good, we're going to continue though and we'll have a look and see whether our closing point is also correct now. |
| 08:58 | Now remembering in this case we are now looking at the black markings on our degree wheel because we are moving past bottom dead centre. |
| 09:06 | Remember that the recommended specification is 55 degrees. |
| 09:10 | Just coming up on that point now and again just being very very smooth with our strong arm so we can be very very accurate here. |
| 09:18 | OK so we now have our valve closed to one millimetre of lift so again we can inspect our degree wheel and see what our marking is. |
| 09:26 | In this case we are again matching our manufacturer's cam card specification at 55 degrees after bottom dead centre. |
| 09:35 | So in this case, with one single adjustment to our vernier adjustable cam wheel, we've achieved the manufacturer's recommendation. |
| 09:42 | So this is the process we're going to go through when we are measuring and adjusting our cam timing. |
| 09:47 | Of course on a twin cam engine like our B18C, we'd then repeat that process on the exhaust cam. |
| 09:55 | Often the process is not going to go quite as easily as that, and often it does become an iterative process of making a measurement, adjusting our vernier cam timing and then measuring again. |
| 10:08 | Of course if we understand the procedure that we're going through and we understand the relationship between the degree markings on the vernier cam gear and the degrees of movement at the crankshaft, this does speed up the process and allows us to make much more accurate adjustments. |
| 10:24 | Once we are comfortable with our cam timing though, it's always a good idea to just go through and make one final check and confirm that you are getting repeatability with the numbers that you are measuring. |
