How to Degree a Cam: Step 1: Set Base Cam Timing
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Step 1: Set Base Cam Timing
10.52
| 00:00 | - Before we can actually start degreeing or dialling in our cams, the very first step of our process is to set our base cam timing. |
| 00:08 | Now with the SR20 engine there are a couple of ways you can go about this, depending on exactly what state your engine is. |
| 00:17 | For example if you're going through a complete new engine build, then you'll be starting by fitting the cam chain with the front cover and oil pump assembly removed from the engine. |
| 00:27 | This will give you access to the lower cam drive sprocket that fits to the crankshaft. |
| 00:32 | In this situation, we can use the coloured links on the cam chain to help guide us with setting our base cam timing. |
| 00:39 | What we'll find is that there are three coloured links on our cam chain. |
| 00:43 | The two upper links align with the match mark on our cam drive sprockets, and then the lower coloured link will align obviously with the match mark on our lower cam drive sprocket. |
| 00:55 | This makes it really easy to install our cam chain and the associated components and be confident that our cam timing is correct. |
| 01:04 | On the other hand, if you are swapping the cams on an engine that's already built, then this can be a little bit trickier. |
| 01:11 | Those coloured links aren't going to align correctly with the match marks on our cam drive sprockets, every time we turn the engine through a full engine cycle. |
| 01:21 | This means short of removing that front cover assembly, which in a built engine is quite a lot of work, we're not going to be able to rely on those match marks or coloured links. |
| 01:31 | That's OK though because if you are in this situation we've attached a PDF to this particular module of the course which will give you a graphical representation of where the match marks on the cam drive sprockets should be so you don't need to rely on those coloured links on the cam chain. |
| 01:49 | Using this technique, what we do is start by aligning our crank pulley on top dead centre and then we can simply count the number of teeth on each of the cam drive sprockets from the horizontal surfaces of our cylinder head. |
| 02:03 | And this will show us where the match marks on our cam drive sprockets need to be to have our base timing absolutely correct. |
| 02:10 | Of course all of this information is also presented in the Nissan SR20 factory workshop manual so you're welcome to use that as a reference guide. |
| 02:20 | In our particular example we're working through here, while we have got the front cover assembly already fitted, we are fitting and degreeing these cams as part of a complete start to finish engine build and at this point we have got our coloured link on our lower cam drive sprocket correctly aligned, this is going to allow us to use those coloured links to set our base timing. |
| 02:44 | We've also got our cams initially installed and everything's been torqued down or correctly tightened in terms of our cam caps. |
| 02:53 | It's important to note that when we are doing this, we want to start by having our exhaust cam dowel sitting at approximately 12 o'clock or directly straight up. |
| 03:03 | On the intake cam we want our dowels sitting at approximately 10 o'clock. |
| 03:07 | This is a good starting position, it's going to also ensure that when our pistons are at TDC on number one and four cylinder, we're not going to have any valve to piston contact. |
| 03:17 | At the same time it's also critical to make sure that we have got our crank pulley correctly aligned on top dead centre. |
| 03:25 | This is going to be our starting point. |
| 03:27 | Now right at this point, we've got our cam chain fitted and a little tip that I will share here is to fit a cable tie around the cam chain, and this allows you to just link that cable tie around a component on the outside of the engine, as we've done here to prevent the cam chain from disappearing down inside the front cover. |
| 03:48 | What I'm going to do is start by getting our exhaust cam drive sprocket. |
| 03:53 | And we're going to align that with the match mark on our cam chain and we'll guide that in over the dowel into location. |
| 03:59 | So let's do that now. |
| 04:09 | So we've located our coloured link there, I'll just guide that onto our cam drive sprocket in the correct location. |
| 04:19 | Once we've got our cam drive sprocket and our cam chain aligned we can now locate our cam drive sprocket over our dowel and bring it into location on our cam. |
| 04:43 | Now in our example there we noticed that the cam drive sprocket actually slotted quite nicely into place and aligned correctly with our cam. |
| 04:51 | In most instances you may find however that the cam is going to need to be rotated slightly in order to let the cam drive sprocket locate correctly. |
| 05:01 | We can do this by simply using a ring spanner on the hex that's cast into the camshaft. |
| 05:09 | Now a little tip with this though is that there isn't a lot of room for us to get an open end ring spanner down into the cam. |
| 05:16 | And while there's almost certainly going to be a special service tool specifically for this task, it's unlikely that most novice engine builders are going to have access to that. |
| 05:26 | It's OK though, we can simply take a conventional existing ring spanner, and by slightly grinding down the sides, we can narrow that down until it's going to nicely locate in our cam. |
| 05:39 | Alright with our exhaust cam sprocket fitted, we can now go through and we'll do exactly the same with our intake cam. |
| 05:46 | Of course we'll be cutting off that cable tie at this point as well. |
| 06:02 | Alright we've got both of our vernier adjustable cam sprockets now fitted. |
| 06:05 | What we're going to do now is go through and fit our pulley bolts and we're going to tighten those up. |
| 06:12 | In this case on the intake side I can fit this bolt and torque it up for a final time. |
| 06:17 | We're going to be using Nissan's torque recommendation of 130 newton metres, and a small amount of Loctite on the threads of that bolt. |
| 06:24 | On the exhaust cam on the other hand, we are using a special Mazworx trigger wheel that fits to the front of the cam pulley. |
| 06:33 | So at this point because this trigger disk actually blocks off some of the adjustment bolts on our cam drive sprocket, we're only going to be temporarily fitting this so I'm not going to be Loctiting that cam pulley bolt, of course it's essential that we come back and do this later on. |
| 06:49 | I've also taken the liberty of loosening off the catch screws that will be hidden behind our trigger disk. |
| 06:56 | So let's go through and fit our pulley bolts now. |
| 07:23 | Once we've got our cam pulley bolts fitted and tightened, the next step is to fit our tensioner. |
| 07:28 | Now this is another area that we are straying a little bit from Nissan factory components. |
| 07:33 | In stock form the cam tensioner is a hydraulic cam chain tensioner. |
| 07:37 | In our instance because we are building a high RPM engine that's only for race use, we've actually swapped across to a Mazworx mechanical tensioner. |
| 07:46 | This does require a little bit more maintenance work that the hydraulic tensioner but it does ensure that there's absolutely no chance of the cam chain tension backing off under high RPM operation. |
| 07:59 | What we want to do is now fit our cam chain tensioner and it locates through a hole in the side of our cylinder head. |
| 08:06 | It is essential when we are fitting the cam chain tensioner that we ensure that the slot or cut out in our tensioner does correctly align with our movable cam chain guide. |
| 08:17 | Let's go ahead and fit our tensioner now. |
| 08:47 | WIth our cam chain tensioner fitted, we now need to actually tension the cam chain. |
| 08:52 | What we can see at the moment is we've got a huge amount of slack in our cam chain. |
| 08:54 | And what we're going to do here is simply follow the instructions that Mazworx have provided. |
| 09:00 | Essentially what we're going to do is tighten our cam chain tensioner until we've got approximately six millimetres or a quarter of an inch of total play in our cam chain in between our two cam gears. |
| 09:12 | Now we've also installed this at the moment with our cam chain tensioner completely backed off and that's an important first step. |
| 09:19 | Let's go through and adjust our cam chain tension. |
| 09:40 | Once we're happy with the amount of tension on our cam chain, we're going to lock up our mechanical tensioner, and there is a locking nut on the tensioner, we're just going to apply a small amount of Loctite to the threads before we tighten that up. |
| 10:02 | Once we've got our cam chain tensioned correctly we can go ahead and turn our engine through a full engine cycle and just make sure that once we get back to top dead centre on our crank pulley that our cam timing is still correct, in other words our two cam sprockets are still in the correct location. |
| 10:17 | As we've already discussed in this module, we know that once we've turned the engine through one cycle, we're not going to be able to use our coloured links to help us, but that's where the attached PDF comes in, we can count our teeth and ensure that our cam timing is correct. |
| 10:32 | Let's go through and do that now. |
| 10:41 | Alright with our base cam timing now correctly set, adjusted and confirmed, we can move on with the next step of our process. |
