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
04.29
| 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. |
| 04:23 | We can now move onto the last step of our process. |
