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Engine Rebuild - Cam Set Up - Step 3

By Ryan Ballou

If one was to think of the crank and rods as the muscle behind an engine, then the cam would have to be the heart and lungs. It's the cam that dictates when and how much air-fuel mixture your engine will be breathing and igniting. Cam choice is probably one of the toughest decisions you will have to make when planning a new engine project, as the choices can seem endless. The best thing you can do to help narrow the field is to speak with as many people as possible about their engines and what cams they have run.

When it comes down to it, experience really pays off here. Generally speaking, more lift means more power across the board and more duration will move the power band up in RPMs. That is of course an over simplification yet for the most part it holds true. Short duration, high lift cams will make good power with lots of torque, but have steep ramps and require more valve spring pressure to control valve float. This added pressure along with the more aggressive cam profile will lead to premature wear and shorter tear down intervals. Depending on your application this may not be a concern. Long duration, low lift cams will still make good power, but you'll have to rev the engine to do so. Your valve train may last longer, but you'll stress other parts more from the excessive revving and likely require a close ratio tranny to make use of the power band. The key is finding a good balance that still provides the drive-ability characteristics that you'll be happy with, and that's where the advice of others can be invaluable.

For my build up, I chose the 2288 grind from CB Performance, featuring 308 degrees of advertised duration, 256 degrees of duration at .050" lift, and .529" of lift at the valve with 1.4:1 ratio rockers. For those in the know, this is roughly the equivalent of an Webcam 86b which I've used before, or an Engle FK-8. This is a cam requiring ratio rockers of either 1.4:1 or 1.5:1 to meet the cam grinders specification. This means that whatever the lift at the cam lobe measures out to, the valve will be lifted 1.4/1.5 times as much. Ratio rocker cams offer a trade off in reliability. They have gentler ramps since they rely on the rockers to gain more lift, but this in turn increases the spring pressure seen by the lifter through the mechanical advantage of the ratio rocker arm. The trade off tends to be for the best, allowing more lift with less duration, but avoiding steep ramps. With the milder grinds like I have chosen, you still don't need excessive spring pressure (Chevy springs) to control the valves and therefore can escape accelerated wear.

There is certainly more to cam choice than just this and I heartily recommend you schedule time to talk with some cam grinders and hear what they have to say. The people at Engle and Webcam are very knowledgeable about this stuff, and the people at CB Performance have first hand experience in the field of racing with their cam grinds.

Once you have chosen your cam, setting it up is a breeze if you know what you're doing. The first step is to make sure the end float of the cam is correct and ensure it spins freely in it's bearings. Cam end play is just like crank end play Lay the cam in the bearings in one case half without the crank installed. Install the other case half and bolt torque down the nuts on all the studs above and below the cam, be sure to do all six mains, not just the lower three. Use a dial indicator on the gear side of the cam and push/pull to measure how much end play you have. My preference is .002"-.003" with a factor spec of .0016"-.0051". 9 times out of 10, you'll be nearly at '0' with new parts. Use a micrometer or set of calipers to measure the width of the thrust bearing and record this as your starting point. To add clearance you need to flat sand the thrust surface of the bearing, but go slowly and measure often to avoid over shooting it. Try to do both sides evenly to prevent going to deep into the babbitt material. Once your end play is set you can check the radial play at the bearings. Factory spec here is .0008"-.002" (wear limit of .0047") with all surrounding studs properly torqued. A dial bore gauge is the most accurate way to measure this, but since the bearings are all a split design Plastigauge can be used in it's place. Barring a major machining error, you should be within spec here. The only potential hang-up would be runout in the center cam journal that would take up any clearance you have. Maximum runout on new parts is spec'd at .008", meaning that if your radial clearance on the center journal is .008" and you have .008" of runout, then you have an effective clearance of '0'. The symptom of this problem is a cam that does not spin freely with the case halves torqued together and nothing else installed, very similar to what we did in the last article with the crankshaft. If you only need to gain a very small amount of clearance, you can polish the appropriate cam bearings with some 600 grit sand paper. Finish with 1000 grit, then 2000 grit. However I wouldn't use this method if you need to pick up more than .0005" of clearance. Any more than that and you should either have it polished off the cam journals by your machine shop, or have the cam checked out and replaced if it's out of spec.

With the cam fitted to the case, it's time to dial it in. You will need an adjustable cam gear and you'll need to make up a special tool for checking lift in the shortblock phase. This tool is nothing more than an old lifter with half of a pushrod glued in with epoxy. Use a lifter that's in good condition and has no imperfections on the face and then cut an old pushrod in half making sure it's long enough to stick out the case. Ideally you want two of these so you can check an intake and exhaust lobe at the same time without having to split the case to swap. You may even want to make up four so you can check all the lobes against each other. Most of the time your local shop will have piles of this stuff in back that they'll let you have for a few bucks.

Install your lifter tool (or tools) at the #1 cylinder location. Install the crank, it's preferred to do this before installing the rods, but not necessary. You will also need a pulley with degree markings to check crankshaft rotation. Lay the camshaft in place making sure to align the marks on the cam gears for proper location. Bolt the case together and install your dial indicator so it rides on the tip of the pushrod sticking out of the case.

A common misconception is that you actually need your cam card to degree your cam, that's not true with symmetrical cams and most cams are symmetrical. Check with your cam grinder if you're unsure. The cam card just shows checking numbers so you can be sure the cam has been ground correctly. Ultimately, quality control is always your responsibility. If your cam in asymmetrical then you will need those checking numbers, but the job will be even easier. Just set up the cam so you get those numbers.

For the majority of cam grinds (symmetrical) you need to get 2 pieces of information each for the intake and exhaust lobes and then do a little math. With the dial indicator on the tip of the pushrod, turn the crank until the dial is at it's lowest reading and zero the dial. Now slowing spin the crank in the normal direction (clockwise at the pulley end), and watch the dial. Stop when it reads .050" and record the degree reading on your pulley. If you overshoot .050" back up at least a half turn on the crank and do it again. Do not back up to .050", the little bit of play in the cam gears will throw your reading off. Now continue turning the crank until you reach your max lift value, record this number for future use. Continue spinning the crank until the dial reads .050" from being fully closed. Record the degree reading on the pulley again. Take those two numbers, add them together, add 180 (this should be your duration @ .050" from the cam card) and divide by two, then subtract the intake opening event (smaller number), this is your lobe center. When doing the exhaust, still add the two numbers to 180 and divide by two, but this time subtract the exhaust closing event. If both numbers are the same, the cam is installed straight up (not advanced or retarded) and 99% of the time I'd call it good. Hypothetically, if your intake number is 105, but your exhaust number is 111, then you're advanced 3 degrees and you're cam was ground on 108 degree lobe centers. I.E. 111-3=108 and 105+3=108. Adjust the cam gear as needed until the cam is straight up and you're done. For reference, Engle and Webcam brand cams are almost always on 108 degree lobe centers unless otherwise specified. The same goes for CB Performance brand cams, except they are on 107 degree lobe centers.

With your cam setup for the bearings in the case and dialed in you only need to check the clearance between the cam bolts and your oil pump and you're done. Set the cam in a case half, then install the oil pump. Spin the cam by hand and check for interference between the cam gear bolts and oil pump body. It's almost certain they will hit. You can either grind a little off the pump body, or take a little off the head of each cam bolt. Either way, shoot for about .040" of clearance.
All that's left is to use a dab of red Loctite on each of the cam gear bolts and torque them down. Refer to the documentation that cam with your cam for proper torque values, most manufacturers recommend between 18 and 23 ft*lbs. We're now one step closer to the point where you can drive it like you stole it.

1-First thing's first. Some cams have sharp edges on the lobes leftover from the grinding process, some don't. If yours still has these sharp corners, use a file or a carbide burr and very carefully knock the corners off. Go as slow as you need to and DO NOT hit the face of the cam lobe. If you don't have a steady hand with power tools, use a hand file.

2-Cam end play is easily checked with a dial indicator. You can get a finger on both sides of the cam to push it back and forth to check the clearance.

3-A quick check with the dial shows my gear backlash is .002", exactly what the paper work from CE (Competition Engineering) says is should be. Not bad considering these have already seen 20k miles on my previous engine.

4-A little bit of scotch tape helped keep the lifter/pushrod from spinning as the engine was turned over while checking the cam. If the lifter spins, your measurements will be erratic unless you glued your pushrod in perfectly perpendicular to the lifter face, quite unlikely if you did it by hand like I did. Repeat the degree'ing process until you get identical results at least three times. Remember, the worst errors are made when we hurry.

5-Adjustments to the cam gear can be made with the case halve bolted together. Remove the cam gear bolts and use a screwdriver in the slot of the cam while holding the crank from spinning. Install the appropriate degree washers and re-tighten the bolts before checking again.

6-The cam bolts will most likely interfere with the boss for the lower oil pump gear shaft. If you think you're going to have to cut the bolt heads down by more than half there original thickness, then take some off the pump body to leave more meat on the bolts. It's a good idea to check the drive tang engagement of the oil pump to the cam slot now while you have a clear view. Make sure it's engaging the cam deep enough and not bottoming in the cam.
7-Cam gear is installed and the cam is set to straight up. Notice how little had to remove from the bolts, this was a best-case scenario. Now I just have to track down that 3rd washer that rolled off under the fridge. 8-Cam and lifters are in and the bottom end is ready to go together.  

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