How to Degree a Cam: Step 5: Measure and Adjust Exhaust Cam Timing
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Step 5: Measure and Adjust Exhaust Cam Timing
08.40
| 00:00 | - The next step of our process is to simply repeat what we've just completed in the last module, only this time we're going to be doing this on the exhaust cam, measuring our current valve opening and closing events, comparing those to our camshaft manufacturer's specifications and then making any adjustments as required. |
| 00:19 | Before we go into this step, I've already relocated our dial gauge across onto our exhaust cam and I've located the extension for the dial gauge on top of the retainer on one of the exhaust valves on number one cylinder. |
| 00:32 | I've also gone through and ensured that that dial gauge is free of movement as we go through a full engine cycle and that it's correctly zeroed when the valves are closed. |
| 00:44 | Before we go and make our first measurement we do need to know what our cam manufacturer's opening and closing points are. |
| 00:50 | Again we are looking at the opening and closing points at one millimetre exhaust valve lift and this time we're looking for the exhaust valve to open to one millimetre of lift 58 degrees before bottom dead centre and we're expecting to see the valve close back down to one millimetre of lift, eight degrees after top dead centre. |
| 01:12 | So with that in mind we're going to go through and mark our cam degree wheel and then we can take some measurements. |
| 01:19 | So our first point, our valve opening point is 58 degrees before bottom dead centre. |
| 01:25 | Now remembering that our engine is rotating anti clockwise, we have our BDC or bottom dead centre marker here, so we're looking at degrees before bottom dead centre and these are the black marks that we can see here. |
| 01:38 | I've already aligned our pointer at 58 degrees before bottom dead centre so I'm simply going to put a sharpie mark on that so we'll be able to easily reference it. |
| 01:48 | Now I'm going to rotate our crankshaft through and we're going to come just past top dead centre, the next point we're looking for is eight degrees after top dead centre. |
| 02:03 | So with our crankshaft rotated around there just so we can easily see that mark, again we're going to put a sharpie mark on our eight degree after TDC point. |
| 02:13 | Now this time, because we are looking at degrees after TDC, we are using the white marks this time. |
| 02:20 | OK so now that we've got our marks on our degree wheel we can go through and we can do our first measurement. |
| 02:26 | So remember what we're doing is rotating the crankshaft through until we reach one millimetre of lift, remember we're expecting to see that around 58 degrees before bottom dead centre. |
| 02:36 | So let's go through and do that now. |
| 02:47 | OK so we've just got the exhaust valve lifting off the seat now, coming through half a mil so I'm just going to smoothly and gradually open that up, again just applying a small amount of pressure on the strong arm so that we can very accurately come up to our one millimetre of lift point. |
| 03:04 | We're there right now and again I'm just going to hold a little bit of pressure on the strong arm so that I can make sure that the crankshaft isn't going to move while I check my degree reading. |
| 03:15 | So our exhaust valve opening point there is 61 degrees before bottom dead centre, remembering that our specification there was for 58 degrees. |
| 03:24 | So in this case our exhaust cam currently on our one measurement that we've made, is three degrees advanced. |
| 03:29 | We're gonna continue through though and we're going to check the valve closing point as well. |
| 03:43 | OK so we're just coming up on our valve closing point now. |
| 03:47 | Just again smoothly come up on that point, and we're on one millimetre of lift there. |
| 03:53 | So again just holding a smalll amount of pressure so that the crankshaft doesn't move and we can check our degree wheel. |
| 03:59 | So in this case our exhaust valve closing point is five degrees after top dead centre. |
| 04:04 | So remembering that our specification was eight degrees after top dead centre. |
| 04:08 | This again means that we are three degrees too advanced. |
| 04:13 | And again just like with our inlet cam, because the duration that we are measuring at one millimetre of lift matches the cam card, this again just double checks and confirms that our valve lash is correctly set. |
| 04:25 | So we can come back to top dead centre and we can actually make an adjustment there. |
| 04:34 | So we've found there that our exhaust cam currently is advanced by three degrees. |
| 04:39 | So in order to correct this obviously we're going to need to retard the exhaust cam by that same amount, three degrees. |
| 04:46 | Remembering again that because the camshaft rotates at half crankshaft speed, in order to make that adjustment of three degrees at the crankshaft, we're going to need to move the exhaust cam by 1.5 degrees, or in other words 1.5 marks on our Blox vernier adjustable cam gears. |
| 05:04 | So in order to do this, we're going to have to begin by loosening the locking nuts for our cam bolts. |
| 05:10 | We also need to consider which way we are going to be moving the exhaust cam relative to the crankshaft. |
| 05:16 | Remembering what we're trying to do here is retard the cam, in other words we want the valve opening and closing points to occur later in the engine cycle. |
| 05:25 | Because our Honda engine rotates anti clockwise, in order to retard the camshaft, relative to the crankshaft, we're going to need to turn it clockwise. |
| 05:35 | So now that we have a clear understanding of what changes we're going to make, we can go ahead and loosen those bolts and actually move the cam. |
| 05:48 | Alright so we've loosened the locking bolts there for our vernier adjustable cam gear and we're going to be turning the cam clockwise by 1.5 marks on our cam gear. |
| 06:02 | WIth our adjustment made we just need to tighten up the locking bolts again and we can go through and make a further measurement. |
| 06:19 | We can now go through and make another measurement and check that our valve opening and closing points do match our cam specification card. |
| 06:32 | So remembering here that we're looking for our exhaust valve to open one millimetre of lift at 58 degrees before bottom dead centre. |
| 06:39 | We're just coming up on our one millimetre of lift point now, I'm just very smoothly moving the strong arm and we're on our one millimetre of lift point now. |
| 06:50 | Now we can have a look at our degree wheel and see what our marking is. |
| 06:54 | In this case we can see that we are at 58.25 degrees. |
| 06:59 | So we're still a little bit too advanced, we're about a quarter of a degree too far advanced compared to our specification so that's our opening point, let's go through and we'll check our closing point. |
| 07:17 | OK we're just coming down on our one millimetre of lift point now, again just being really smooth with our strong arm so we can be as accurate as we can. |
| 07:27 | Sitting on our one millimetre of lift point now, so we'll hold the pressure on the strong arm and we can check our degree wheel. |
| 07:33 | So on our closing point there we're reading 7.75 degree after top dead centre. |
| 07:38 | Remembering that our specification in our cam sheet is eight degrees. |
| 07:43 | So again just like our valve opening point, we're a quarter of a degree too far advanced. |
| 07:49 | So at this point we've made one adjustment to our exhaust cam timing. |
| 07:52 | Now we know that we still have an error of a quarter of a degree there between our cam spec card and what we're measuring, however for the purposes of our demonstration I'm more than comfortable with that amount of error. |
| 08:03 | Really comes down to the individual engine builder, whether you want to chase this and try and get is absolutely perfect. |
| 08:10 | It does of course become increasingly more difficult as we're starting to make smaller and smaller adjustments because in order to correct an error of a quarter of a degree at the crankshaft, we're going to be trying to rotate the vernier adjustable cam gear by only half of that, so it's quite likely that we could actually end up making our cam timing worse while we're trying to get it better. |
| 08:34 | So at this point our exhaust cam timing is where we want it to be, we can now move on with the next step of the process. |
