Listers,
It appears that there is some interest in Degreeing a cam so I thought I
would pop in my thoughts.
The process is generally to index the cam to the Crank to ensure that the
cam is oriented in such a way as to ensure that when the crank has the #X
position piston at TDC the cam is where the cam manufacturer intended it to
be. As others have indicated there can be some significant variance if you
use no name stuff or low quality parts. While several Listers indicated that
they observed weird results I thought it would be good to quickly go
thorough the process, Please bear with me if you already know or do not
care.
Tools needed:
Dial Indicator and Magnetic Base ($50)
Piston stop (I use a bar with a hole drilled through one end that can be
bolted over the Cylinder bore)($10)
Timing pointer (Coat hanger all bent up and sharpened to a point) (Last dry
cleaning Bill)
Degree Wheel ($30???) Been a while since I had to buy one
Cam Card (Should be in Cam box in a plastic bag)
Steps to achieve:
1) Find Crank TDC
Assembly engine short Block to a point where the cam is installed but you
will have access to the timing chain and the cylinder heads are not yet
bolted on. Bolt the piston stop to the top of the block through the hole in
the end. If the piston is a flat top and does not have a dome protruding,
weld a 3/8" thick piece to the underside to stop the piston part way down
the bore if you were to rotate the reciprocating assembly. Attach the
Balancer to the crank snout firmly and bolt timing wheel to the front of the
Balancer. Try to position the wheel as close top where you think TDC will be
based on the Balancer markings. Mount the pointer so that it points over the
front edge of the cam timing wheel and ensure that it is firm and not
contacting the wheel. then rotate the engine carefully until the engine is
stopped by the piston stop and take a reading on the wheel. Carefully mark
the reading with Tape or removable paint on the degree wheel. Then rotate
the engine in the opposite direction until the assembly stops rotating again
and mark this point on the wheel. You now have two reference points on the
wheel. If you measure the distance in degrees between them and divide it by
2 you will have the position of crank TDC. Remove the piston stop and rotate
the engine to Crank TDC. Remark the Balancer if necessary it most often is,
and relocate the TDC mark on the wheel by rotating it or move the pointer to
have it reference TDC on The wheel,...whatever is easiest.
2)Determine the Cam reference to the Crank
This is where you actually degree the cam. Some guys like to do it with the
heads on and measure Valve lift at the valve and some do the math and
measure off of the lifter assuming that the rocker really has the ratio that
the manufacturers state. I prefer to measure off of the valve / Valve
spring. Assemble the head for Number 1 cylinder and get lifters and pushrods
in place. I like to replace the heavy valve springs with light ones as it
makes it easier to rotate the engine. With the head affixed and the Pushrod
and rocker assembled with no lash (Some prefer the lash specified but I
think this is close enough)mount the dial indicator so that it is
perpendicular to the top of the valve spring (In line with the valve
travel)and oriented so that as the valve drops away from the indicator you
will be able to have enough travel to make your measurement. Zero the dial
indicator. Go get the manufacturers cam card or get the specs for the cam
from whatever source is necessary as you need this to proceed. Most cam
companies state the valve lift (0.050") at some measure of crank rotation
(230 degrees opening). You simply rotate the engine assembly until you reach
the valve opening amount as measured by the dial indicator. With the engine
at .050" valve lift read the degrees on the degree wheel at the pointer and
compare this to what the cam card states and determine whether you are
advanced, Retarded, or right on. If you are "spot on" I will be very
surprised as that has only happened once to me in about 20 engines and then
it was only too close to adjust but was not exactly right. Once you
determine which way you need to go use the appropriate advancing method
either the crank keyway approach or the offsetting dowel approach on the Cam
Sprocket. After You have done this adjustment remeasure the cam timing and
check whether you guessed advance/retard correctly.
3) Separate note:
You can use cam timing adjustments to move the "power band" up and down to a
small degree if you like the profile of a cam except for the RPM range. This
is why people will advance a cam 4 degrees to drop the power band a little.
This is different than advancing a cam to sync it to the Crank. So if you
needed to advance the cam 2 degrees to obtain the cam producers factory spec
and you wished to advance the profile 4 degrees then you would actually
advance "that cam" 6 degrees in "that engine".
If you wanted to verify the cam profile you can do this in the same manner
by noting degrees at different events such as Valve lift at .050", max lift
or lobe centre-line and lobe centre-line spacing intake to exhaust. Duration
is usually measured from .050" opening to .050" closing as it is difficult
to determine exactly when the valve is closed or when it starts to open.
Roller tappet profiles typically perform better as they can successfully use
more aggressive cam profiles without the consequences of poor idle.
Regards,
Tim Ronak
B382000680
PS: I will gladly contribute to keep the list up and running but this Fat
Chance Garage??? is this the guy that we need to pay?? I am pretty new to
the list and this is the first I heard of this guy. I need to trust input
from some of the names that I recognise
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