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Post by Beans on Feb 4, 2013 2:54:16 GMT -5
Well I’ll start with saying that is this is probably one of the most important aspects of making power out of a new/used performance cam. The write up is going to use a Honda engine, but the ideas are transferable to multiple DOHC engine platforms. Okay, so why degree a cam? What exactly is the point of this? Without going into too much deal about how VTEC or how a DOHC engine works, basically the engine has an intake camshaft and an exhaust camshaft. The point of camshafts are to open and close the intake and exhaust valves to let fuel and oxygen in, and exhaust gas out. Depending on the rpm of your engine, the farther down the camshafts push the intake and exhaust valves the more air and fuel can enter into the engine, and thus more power. Degreeing a cam is basically deciding when to open and close the engines valves to make the absolute most power. For illustrative and reference purposes, I will be using pictures from an h22 four cylinder engine. What you will need: • A degree wheel. This can be found online, or at Mopac in Edmonton.  • At least two dial indicators. Three is ideal.  • Adjustable cam gears!  • Your newly bought cams and an engine.  • The camshaft specification card that came with your cams (will come with cams).  • A clothes hanger with a sharp point. |
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Post by Beans on Feb 4, 2013 2:54:43 GMT -5
1. Install your adjustable cam gears on your camshafts, making sure that the intake and exhaust gears start at 0.  Next, assuming your block is assembled put the head on the block and torque it down fully! Although some people don’t use a head gasket (hg) at this step, I recommend you do, as the thickness of the hg will ever so slightly change the dial indicators readings as it impacts the tension on the timing belt.   Next, install only piston 1’s rocker arms. Since the camshaft should be identical for ever cylinder (same lift and duration) we only need to use cylinder 1 as a reference (you could choose any cylinder, but 1 is the easiest and also allows the engine to turn more freely). Make sure to lock the rocker arms in VTEC, by adding a wooden dowel as a spacer and pushing out the metal rods (this has to be done before you install the rockers). If your engine does not have some sort of variable valve timing set up, then ignore this step.    Now rotate the crank to TDC (should be a mark on the crank gear that lines up with the oil pump). TDC means that piston 1 (the closest one to the timing belt) and piston 4 should be at the top of the block (or the highest they will go on their stroke). Install your cams (making sure they are at TDC by matching up the cam gear marks), bolt down the cam caps, and put on the timing belt.  2. Double check that BOTH cam gears are at TDC and the crank gear is at TDC before you rotate the engine! While the engine is at TDC, set the valve lash to 0.00" by using a feeler gauge. This step not only makes the degreeing process more accurate, but ensures maximum lift and duration.   Once this is completed, slowly rotate the engine two full turns on the crank gear (make sure you have the rotation of your engine right! Some engines rotate clockwise, some rotate counter clockwise. Most Honda engines rotate counterclockwise!). If you have any SHARP resistance stop immediately! Basically what you are doing is making sure your valves are not touching the piston top or each other. Since the cams you just bought are more aggressive then stock and have not been degreed for your engine and made sure your piston to valve (p2v) clearance and valve to valve (v2v) is adequate, this is an important step. After two rotations of the crank gear and no sudden stops or resistance, you are good to go! Now you might be asking, why two rotations? Well this is because that’s a full combustion cycle. The piston starts at TDC, and moves down wards to bottom dead center (BDC) drawing in gas and fuel. The process of moving to BDC is a 90 degree turn on the cam gear and a 180 degree turn on the crank gear. Next, rotate the crank gear another 180 degrees or 90 degrees on the cam gear (piston is now at TDC). You have just taken the air and fuel and compressed it. Now rotate the crank gear another 180 degrees or 90 degrees on the cam gear (piston is at BDC). The spark has just combusted the air fuel mixture and sent the piston flying down at tremendous speeds. Now rotate the crank gear another 180 degrees or 90 degrees on the cam gear (piston is at TDC). The piston has now just pushed out all the exhaust gas and your back where we began! Confused? This should help. cms.skunk2.com/id/165/Skunk2-How-To-Four-Stroke-Engines/4/ |
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Post by Beans on Feb 4, 2013 2:55:10 GMT -5
3. We can start the degreeing process now. We will begin by bolting on the degree wheel to the crankshaft. It does not need to be bolted on with TDC facing a certain direction. Make sure the degree wheel is secure, and will not move! These pictures aren't the greatest but you should get the idea. I had to make a spacer for my degree wheel.    4. Now to the good stuff. First thing we want to do is find the true TDC of piston 1. The marks on the cam gears and crank shaft are close to the true TDC, but are NOT a good reading of true TDC. Finding the true TDC is critical, as all of the following measurements are going to be based upon this step. To start, we place a dial indicator though the cylinder 1’s spark plug hole, making sure the dial indicator is long enough to reach the piston (there are extension kits on the internet). Make sure the dial indicator is SECURE, and WILL NOT MOVE!  Next rotate the engine until you see the dial indicators needle max out, and deflect backwards. Basically the needle will continue to rise until it hits TDC, and then it will start to lower. The point between the rising and falling of the dial indicator needle is the true TDC of the engine. We now take our clothes hanger that we have sharpened a point on and fasten one end to a secure location on the block, and the other to mark where TDC on the degree wheel is.  It is critical to note that you cannot rotate the engine backwards if you rotated the crank too far, as this throws off the tension of the timing belt and gives an inaccurate TDC reading. So suck it up and rotate the block TWO more times and start over. Remember, not just once, as this is not a complete combustion cycle. |
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Post by Beans on Feb 4, 2013 2:55:28 GMT -5
5. Congratulations, you have found TDC! Make sure not to bump the clothes hanger or else the entire rest of this process will be destroyed, and you will have to start again. We now need to grab the cam card supplied to us by the manufacturer and set up a dial indicator on the exhaust or intake side (doesn't matter which we do first). When installing the dial indicator, you have to make sure it is parallel with the valve and resting on the intake retainer (doesn't matter which intake retainer you choose). Rotate the engine over two turns to make sure the dial indicator does not move and is firmly fastened. Now it's time to go over some lingo. - BTDC means before top dead center
- ATDC means after top dead center
- BBTD means before bottom dead center
- ABDC means adfter bottom dead center
Okay now this is where it can get tricky, but basically the process should be the same across almost all DOHC engines. The cam shaft card will give a number of measurements about your cam such as duration, peak lift, what the lash should be set for, ect. One of these measurements will say what the peak lift is for the intake cam and the exhaust cam. For example, my cam card said 97 degrees ATDC for the intake cam and 113 degrees BTDC which will be the numbers I will be using for the rest of this illustration. Our job is to rotate the engine to these positions and then find the peak lift. So let's start with the engine at TDC on the intake side. The dial indicator should be firmly set on the intake retainer, and the clothes hanger point should be exactly on 0 or TDC on the degree wheel.  Rotate the crank counter clockwise a full 360 degrees (only 180 degrees on the cam gears) so you are starting the intake stroke (the degree wheel just made a full rotation and now is back at 0 degrees or TDC Rotate the engine counter clockwise 97 more degrees on the degree wheel to be ATDC. This is where the peak lift happens on my intake camshaft. Next, loosen the small little bolts on the cam gear and put a socket on the camshaft. The outside of the cam gear will be held stationary by the timing belt, and the inside should move with the cam. With the socket on the cam, rotate the cam back and forth while watching the dial indicator. Just like how we found TDC, were are looking for the point where the dial indicator needle increases and then starts decreasing. You will find that the needle will increase and then stay steady for a few degrees on the CAM GEAR before declining. This is called dwell, which is basically the peak lift of a cam and lasts for only a small duration. For my engine, I found dwell to be from 0 to +2 degrees on my cam gear so I set the intake camshaft at +1 degree. In other words, take how many degrees you have dwell for and divide it by two. If I had dwell from +1 to +3, I would set the cam in the middle at +2.  You are now done the intake cam, and only have the exhaust cam left! 6. Switch the dial indicator over to the exhaust side and set up the dial indicator just like you did on the intake side. Time to do the exhaust cam. While switching the dial indicator over to the exhaust retainer I did not rotate the engine at all, so the degree wheel should still read 97 degrees ATDC. Rotate the engine a full 360 degrees to 97 degrees ATDC again, and then another 150 degrees to at 113 degrees BTDC (or the exhaust stroke). I then loosened my cam bolts and found peak lift once again. This time it was at +2.5.  Tighten your exhaust cam and you are done! Congratulations, you have now optimized your camshafts for your engine! There is no other position that you your camshafts could be in that would make more power then the two positions that you just found. Keep in mind that you now have to check your valve to valve clearance and piston to valve clearance to see if you have enough clearance with the new cam settings. Just because the engine rotates freely does NOT mean there is adequate clearance! |
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Post by Beans on Feb 4, 2013 2:57:19 GMT -5
This is basically finished. If you find something confusing or wrong send me a PM and I'll change it!
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Post by bouckaroo on Feb 4, 2013 10:20:45 GMT -5
Awesome job chris!!
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Post by prudz on Feb 4, 2013 10:38:07 GMT -5
This is what people NEED to know! Looks great so far.
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Post by Beans on Feb 4, 2013 18:57:48 GMT -5
Hopes this helps guys!
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