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How to Degree a Cam: Steps 4 & 5: Measure and Adjust Cam Timing

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Steps 4 & 5: Measure and Adjust Cam Timing


00:00 - Traditionally we'd separate step 4 and 5 out on a twin cam engine but of course the relationship between the intake and the exhaust valve timing is fixed on our single cam engine so we're completing both steps here together.
00:14 This will also give us the needed measurement points that we need to be confident of our cam timing.
00:19 Now that we've got our dial guage fitted and zeroed we can start by checking the intake valve opening.
00:25 From the cam spec sheet we can see that the intake valve opening point should be 6° before top dead centre and the exhaust valve opening point should be 53° before bottom dead centre so we can mark these on the degree wheel as a reference before we get started.
00:40 With the exhaust valve opening point, we need to count the 53° from bottom dead centre which of course is marked on our degree wheel as 180°.
00:50 Therefore we need to subtract 53 from 180 which gives us 127° which is where we want to make our mark.
00:59 Now we can rotate the crankshaft smoothly and slowly until we reach exactly 50 thou lift on the inlet.
01:06 We know that this should occur at 6° before top dead centre but we can see that we actually reach this lift at 10° before top dead centre which means that from our first check, the cam appears to be advanced by 4°.
01:19 Now that we've checked the intake opening point we can repeat this on the exhaust.
01:24 To do this, we'll start by fitting a push rod onto the exhaust lifter and refit the dial gauge and align it as we've already done on the intake push rod.
01:33 Once we've zeroed the dial gauge on the base circle of the cam, we can rotate the crankshaft until we reach 50 thou lift.
01:40 We can see that this occurs at 57° before bottom dead centre which is also 4° advanced from where it should be.
01:48 This means that the 2 measurements we've now taken do agree with each other and we can be confident that our cam is actually advanced by 4°.
01:57 Of course to correct this we need to retard the cam 4° so we need to remove the timing chain to make this change.
02:04 We can start by removing the degree wheel from the crankshaft and the 2 bolts from the chain guide.
02:09 Next we can remove the cam pulley bolts and remove the pulley, cam chain and chain guide from the engine.
02:16 In our case, because the crank pulley is a light press fit, we're using a puller to remove it.
02:22 Now we want to locate the -4° keyway location on the crank sprocket which will retard the cam by 4°.
02:30 We need to be mindful when using the -4 mark on the crank that we need to also use the -4 mark on the outside of the sprocket when aligning the cam sprocket as previously discussed.
02:40 Now it's simply a case of repeating the assembly process we've already covered.
02:45 It is useful here to rotate the crankshaft a little before we attempt to reinstall the cam chain so that the new -4 mark is pointing vertically up.
02:55 Once we have the cam chain back on and the timing confirmed, we can repeat the process of fitting the degree wheel and confirming TDC using our positive stop again.
03:05 This is unfortunately a bit of a tedious process given that we need to remove the degree wheel each time a change in cam timing is required but you will get pretty fast at reestablishing TDC.
03:17 It's now a case of repeating the measurement on the exhaust cam pushrod since we've already got the dial gauge positioned here from our last measurement.
03:25 This time we can see that we reach 50 thou lift at 53.5° before bottom dead centre which is half a degree off our spec.
03:34 Realistically we can't make an adjustment of 0.5° so we're about as close as we can hope to be.
03:41 Now we can reposition the dial indicator to the intake push rod, 0 it again on the base circle and we're ready to take another measurement.
03:49 Bringing the crankshaft through to 50 thou lift on our intake, we can see that this is actually right on our mark of 6° so we have about 0.5° discrepancy between our 2 readings so far which is totally acceptable.
04:02 We can perform our last check which is to continue rotating the crankshaft until we're on TDC and we can see that here we're measuring 70 thou lift which is 2 thousandths of an inch off our spec sheet.
04:15 Again, this is about as close to the spec sheet as we can expect and we now have 3 data points that back up our cam timing.