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
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.
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
and lifters are in and the bottom end is ready to go together.
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