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How to Degree a Cam: Step 4: Measure and Adjust Exhaust Cam Timing

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Step 4: Measure and Adjust Exhaust Cam Timing

06.41

00:01 - In this step we're going to take some measurements and find out where our valve opening and closing points are for our exhaust valves.
00:07 We're going to compare these to our cam spec card and then make any adjustments necessary.
00:13 We'll note here that our cam spec card suggests that our exhaust valve should be opening 59 degrees before bottom dead centre and it should be closing 7 degrees after top dead centre.
00:24 Both of these measurements are made at 1 millimetre of valve lift.
00:28 So now that we know what we're looking for, let's go through and we'll take some measurements.
00:39 And we know that we should be reaching around about 1 millimetre of lift at 59 degrees before bottom dead centre.
00:47 So we know we don't have too far to go and we're going to watch our dial indicator and see when we come up on that 1 millimetre of lift point.
01:11 Alright so we've got our 1 millimetre of lift, our exhaust valve is open, so we'll take a look at our cam timing.
01:24 What we can see here is that our valve is open 61.5 degrees before bottom dead centre so we're a little bit earlier than our cam spec card would suggest.
01:35 We'll make a mark here so we know where our valve opening is, and we'll check our closing point as well.
01:49 Alright we'll continue turning our engine through its cycle until we come back on that 1 millimetre closing point.
01:55 Remembering that this should be 7 degrees after top dead centre.
01:59 We're expecting that considering our opening point is a little bit advanced, our closing point should probably be about the same amount advanced too.
02:17 Alright so we've got our valve closing point, we can see that that's measuring at 4.5 degrees after top dead centre.
02:25 So again we're a little bit advanced there.
02:27 So let's make a note of that and we'll discuss our results.
02:35 With our first round of measurements completed there we found that our exhaust valve was opening to 1 millimetre of lift, 61.5 degrees before bottom dead centre, and it was closing back down to 1 millimetre of lift 4.5 degrees after TDC.
02:52 Remember that according to our spec card we should be achieving 1 millimetre of opening, 59 degrees before bottom dead centre and we should be closing back down to 1 millimetre of lift 7 degrees after top dead centre.
03:05 So in this case in both examples our opening and closing point, our cam is adanced by 2.5 degrees.
03:12 So we're not actually too far away from the mark, we've got our sanity check there because we know that both our valve opening and our valve closing points are both exactly the same amount advanced.
03:24 If there was a difference there, this would suggest that perhaps our valve lash was incorrectly set.
03:29 Now that we know what we're trying to do, we want to retard our camshaft 2.5 degrees there, we can loosen off our cam lock nuts and we can make that adjustment.
03:40 I've just rotated the camshafts around so that we can access the locking nut on our cam wheel and we can also see the degree markings on the cam wheel.
03:50 What we need to understand there is that one mark on that cam wheel is the equivalent of 2 degrees at the crankshaft.
03:57 So essentially what we're trying to do here is move the cam or retard the cam by just a touch over one of those marks.
04:04 Let's go ahead and make that adjustment now.
04:37 With our first round of adjustments made there on our exhaust cam, we're going to go through and take another measurement of our 1 millimetre opening and closing points and see if we're on our target from our cam spec card.
04:49 Let's go through that process now.
05:00 So we've just come up on our 1 millimetre valve lift opening point.
05:03 We can see that we're almost right on our target there.
05:06 59 degrees was our target and we're just about 59.25 degrees.
05:11 So we're very very close there.
05:13 Let's make a mark there and we'll check our closing point.
05:34 Looking at our valve closing point, we can see that we're sitting at 6.75 of a degree.
05:41 So again we're just very slightly advanced from our target.
05:43 We'll make a mark there and we'll discuss our results.
05:52 So what we can see there is we've made one round of adjustments there, and we started out with our cam advanced by 2.5 degrees.
06:00 We're now a quarter of a degree advanced from our cam spec card.
06:04 Now what we can do here is really dependent on exactly how fussy you intend to be.
06:09 We can go through and make another round of adjustments.
06:12 Understandably though when our error is that small, it becomes increasingly difficult to make such small adjustments to our cam position.
06:21 In this case I'm more than comfortable with an error of a quarter of a degree.
06:25 And we'll also in inevitably be further adjusting these cams once we hit the dyno.