How to Degree a Cam: Introduction
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Introduction
12.13
| 00:00 | - In this worked example we're going to be going through the process of installing and degreeing a Kelford HS108D camshaft in the L98 engine fitted to our 2009 Holden Commodore SSV. |
| 00:13 | Now the L98 engine for all intents and purposes here is identical in most regards to the 6 litre LS2 and everything we're going to be going through here will generally be applicable to the wider range of LS engines. |
| 00:27 | If you live in a part of the world where you didn't get the Holden Commodore then again this doesn't really matter, we really are looking at this specifically as an LS cam degreeing worked example. |
| 00:39 | The camshaft we've chosen is getting on towards about the biggest cam we can fit in an otherwise stock standard engine while still retaining good clearance between the valves and the pistons. |
| 00:51 | Specifically, the valve lift is listed at 630 thou on the inlet and 610 thou on the exhaust. |
| 00:59 | The advertised duration with 6 thousandths of an inch lift is 284° on the inlet and 292° on the exhaust. |
| 01:10 | So this is getting on towards being a fairly large and fairly aggressive camshaft, it's designed for a naturally aspirated engine and we are going to expect that once this cam is installed and degreed correctly, we're going to have a fairly aggressive lumpy idle and we also do need to be mindful here as well, ideally this would be suited to a high stall converter however with the transmission tuning available on these late model automatic transmissions we can actually get good results or at least livable results with the stock converter. |
| 01:43 | The rest of the package of parts that go along with this camshaft include a set of Kelford beehive valve springs. |
| 01:51 | Now it's important when you are upgrading your cam to make sure that you do have all of the matching parts to go along with this particularly the valve spring does need to be matched to the camshaft in terms of the lift and duration that that cam provides. |
| 02:05 | Basically making sure that the valve spring is suited to actually control the valve motion with that more aggressive cam. |
| 02:12 | Likewise we also need to consider the cam timing set or cam chain and timing gears. |
| 02:19 | And in this instance there are a lot of aftermarket parts available for the LS range of engines. |
| 02:26 | The HS108D is on a point where it's aggressive enough that we wouldn't recommend running this with a single row factory style timing chain so we have moved to a Crow Cams double row timing chain and this is a vernier adjustable style timing set where rather than adjusting some locking screws and moving the cam relative to the cam gear, we actually need to disassemble the bottom pulley, remove that and there are a variety of timing marks or slots I should say for the keyway on the crankshaft and we can advance and retard the cam by selecting the correct relationship between the keyway slot that we've used and then the timing mark when we are actually timing the engine up. |
| 03:10 | A tip when you are selecting a timing set for an LS engine is that the majority of the LS engines include a cam position or synchronisation sensor that is mounted to the front timing cover and this picks up off some teeth that are machined onto the front face of the cam gear. |
| 03:29 | It's really important to make sure that the timing set that you purchase has exactly the same trigger pattern machined into the cam gear as your factory one and there are a few options here so it's always a good idea to make sure that once you've actually disassembled the engine, you check the trigger pattern and then you can order the correct timing set to suit your trigger pattern. |
| 03:51 | This can trip you up if you're not aware of this because you'll put everything back together after doing all of the hard work and unfortunately the engine won't start and run. |
| 04:00 | There are some pros and cons with the timing set we have chosen. |
| 04:03 | The method of vernier adjustment here means that every time we want to make an adjustment, we do need to essentially disassemble the front of the engine, removing our degree wheel, removing the cam wheel from our camshaft as well as the bottom sprocket from the crankshaft. |
| 04:20 | We can then make adjustments to the keyway position and put it all back together. |
| 04:24 | So this is a little bit fiddly, a little but cumbersome and a little bit time consuming, specifically we will have to find top dead centre again once we've made an adjustment and we've refitted our degree wheel. |
| 04:35 | The advantage of course is that there are no locking bolts to come loose like we may find with a more conventional vernier adjustable cam pulley. |
| 04:44 | So once we've got everything set and everything's installed for the final time, we can be confident that the cam timing can't move in operation. |
| 04:51 | One other aspect that is often complately overlooked when it comes to timing up the LS series engines is the way we go about degreeing the cam. |
| 05:03 | Now obviously you've come through the body of the course so you know the process that we do recommend here. |
| 05:08 | But this is a little bit tricky with the LS. |
| 05:11 | There are a few considerations here so I'm going to go through them. |
| 05:14 | First of all the LS in stock form uses a hydraulic lifter. |
| 05:18 | What this means is that we cannot degree the cam with the rocker gear installed because the pressure of the valve spring will mean that the hydraulic lifter will just bleed down. |
| 05:28 | This means regardless whether we are measuring valve lift or cam lift duration at those 2 points, we're not going to get a true indication of what the cam is actually producing because of that hydraulic lifter. |
| 05:40 | Usually, and as we've already talked about in the body of the course a way of getting around this would be to install a solid check lifter while we're going through the process of degreeing our cam. |
| 05:52 | Now yes we can do this in the LS but in reality it's not that practical. |
| 05:55 | To get to a point where we can change the lifter for a solid check lifter, we'd actually need to remove the cylinder head. |
| 06:03 | So maybe that'll work if we're building the engine on the bench but once we've got an engine installed in the car it's simply not a practical solution, it's going to take up way too much time and obviously we'll need to replace the head gasket. |
| 06:15 | So the cam specification sheet does give us information about the lift that the cam produces as well as the duration at the cam, meaning that we can ignore the valve lift and duration and focus directly on what the cam is offering. |
| 06:32 | In this way what we can do is leave the rocker gear off and we can instead locate our dial indicator, either directly on the lifter itself or alternatively we can place the push rod down the lifter bore and we can place our dial indicator on the end of the push rod. |
| 06:50 | Now there's pros and cons of either of these options and there are people who favour one option over the other. |
| 06:56 | I've used both to good effect and the reality is that provided you've got a good alignment between your dial indicator and either the push rod or the lifter itself, then either option will work. |
| 07:07 | Now this gives us a good solution to be able to measure cam lift and we can get our opening and closing points based on that. |
| 07:15 | However there is one other little tricky part that comes in here and this is the bit that people don't tend to talk about too much. |
| 07:22 | When we've installed our cam, we've put our push rod down the lifter bore, we're going to actually physically need to push that lifter back down the lifter bore so that it contacts the camshaft. |
| 07:34 | So that'll be fine, it'll roll along on the base circle of the cam and if we've got our dial indicator installed and zeroed, we'll be able to start seeing the cam lift as the cam starts pushing the lifter up the bore. |
| 07:47 | The problem however is once we go past peak lift, we're going to find that the lifter will actually stick at the top of the lifter bore and it's not going to naturally follow the camshaft back down on the closing ramp.. |
| 08:00 | So this means that with this method we can measure the opening point, the intake and exhaust valve opening points with our dial indicator but we're not going to be able to easily measure the closing point. |
| 08:13 | There are again various techniques talked about of pushing the lifter back down the bore, my own opinion on this and my own experimentation finds that when we're trying to accurately degree a cam, there's just too much inaccuracy that is brought in using this method. |
| 08:31 | So what can we do about this? Well we do have 3 pieces of information that we can use to degree the cam. |
| 08:39 | On our cam specification sheet we have our intake valve opening point. |
| 08:44 | So this lists the point where the intake valve should reach 50 thousandths of an inch lift. |
| 08:51 | Actually the intake cam, this is cam lift just to be clear. |
| 08:54 | Likewise we have the intake valve closing point again listed in terms of duration at the cam or degrees at the cam. |
| 09:02 | We've got the same information for our exhaust. |
| 09:04 | We've also got the amount of lift we should see, cam lift here not valve lift, at top dead centre for both our intake and our exhaust. |
| 09:13 | So what can we do with this information? As I've already mentioned, we can easily measure the intake and the exhaust valve opening points to 50 thou. |
| 09:22 | So this gives us 2 data points. |
| 09:24 | Given that it is a single cam engine, this is a CNC machined cam profile as well so the accuracy of the cam should be fairly reliable but here at HPA our philosophy is always to trust but verify. |
| 09:37 | So we've got those 2 pieces of data there we can measure our intake valve opening point and our exhaust valve opening point. |
| 09:43 | Now if everything's working correctly, we should find that regardless if the cam is degreed correctly, advanced or retarded, we'll find that the intake valve and the exhaust valve opening points should coincide at the same point. |
| 09:56 | In other words, they should either match the specification sheet or be advanced or retarded by the same number of crankshaft degrees. |
| 10:03 | So this gives us a bit of a sanity check there. |
| 10:06 | We do have one more piece of information though which is our valve lift at top dead centre. |
| 10:10 | Now here again, a little bit tricky, we can measure our valve lift at top dead centre on the intake valve because as we move through the engine cycle, the intake valve is on the opening ramp so that's OK, we can measure that. |
| 10:24 | We've got information on the exhaust valve lift at top dead centre but for the same reason as I've just mentioned, we're not going to be able to use that piece of data because the exhaust valve as we go past top dead centre on overlap is on the closing side or the closing ramp of the cam, hence our lifter is going to be floating up the bore. |
| 10:42 | So we've got 3 pieces of data that we're going to use, we've got our intake valve opening, our exhaust valve opening point and we've got our lift at TDC. |
| 10:52 | Now I'll just talk about another solution that we could potentially use here and why this won't give us accurate data, we already know that the lift is only any good when it's going up the ramp on the camshaft. |
| 11:05 | So potentially what we could do is actually go past the point where the valve closes, intake valve for example, push the lifter back down the bore, zero our dial indicator back on the base circle and then actually turn the crankshaft anti clockwise so a reverse rotation so that as we get to our exhaust or intake valve closing point I should say, it's actually going up the ramp. |
| 11:28 | The problem with this is while in theory yes that should work and it gets around our lifter sticking in the bore, what we have an issue with here is that there's inevitably going to be some amount of back lash or slack in our cam chain, meaning that we're not going to get an accurate measurement there. |
| 11:45 | I tested this for the purposes of our worked example and we saw about a 3° variation so that's what we're going to do here, it's potentially not the only way but it is a technique that at least gives us a sufficient number of data points that we can be confident that our final camshaft installation is degreed as per the manufacturer's spec card. |
| 12:06 | Now that we know what we're doing, let's jump into the first step of our process. |
