At 01:30 PM 9/16/03 -0700, Dave B. Hammond wrote:
>.... I've replaced the camshast timing gear, now I don't know how to time
>the camshaft; no timing marks. My manual says how to do it with timing
>marks, but not without . ....
First assuming this is a stock camshaft, .... .... when any cylinder is at
Top Dead Center the intake and exhaust cam lobes should be a (near) mirror
image of each other either side of straight up (or straight down) on the
cam. At TDC on the exhaust stroke both valves will be open at the same
time, and both open the same amount, with the exhaust valve closing and the
intake valve opening.
If the cylinder head and valve gear are in place, back off the rocker
adjuster screws to relieve spring pressure, rotate cam to allow each tappet
to go to rest at bottom of stroke, and move the rocker arm aside to be
clear of the pushrod. This unloads all of the valve springs so they do not
push on the cam, and you will be able to rotate the cam easily by
hand. You may if you wish remove the last six pushrods. You will need in
place the front two tappets and pushrods.
Rotate the crankshaft to position #1 piston at TDC. You can simply hold a
finger across the top between block and piston to feel the small motion,
then rock the crankshaft back and forth a bit to find the point of rotation
where the piston is motionless at top of stroke.
Rotate the cam until the front two tappets and pushrods are both partially
raised and about at the same height. Place a straightedge across the top
ends of the two pushrods. Rotate the cam as required to get both pushrods
the same height, so the straightedge will be sitting level and parallel to
the top of the block. The long straightedge is a convenient means to
amplify the motion to easily tell when the pushrods are exactly the same
height.
Position the crank and cam sprockets to align the sprocket keyways to the
shaft keys, install the timing chain on the sprockets, and install the
sprockets on the shafts. You may have to turn one of the shafts as much as
a few degrees one way or the other to get both keyways to align with the
keys at the same time, but this small rotation should be only a fraction of
the distance from one sprocket tooth to the next tooth.
When the chain and sprockets are installed in this manner, the end result
will have #1 cylinder at TDC on the exhaust stroke (#4 on the compression
stroke), and the camshaft will be in stock timing alignment. This will be
the same as the description and pictures in the shop manual. At this point
you can add the punch mark(s) to the sprocket(s) on the centerline running
between the shaft centers. Notice that neither one of these marks is
exactly in line with the apex of a sprocket tooth (but close), and the
nearest two sprocket teeth will not be exactly aligned.
If you are installing a special grind camshaft which will require special
cam timing setup, this same procedure and position is the starting point at
nominal zero TDC on the #1 exhaust stroke, before you start to make
adjustments for the special cam timing. Before aligning and installing the
distributor drive gear and distributor by the book, rotate the crankshaft
one full turn to bring #1 cylinder to TDC on the compression stroke.
Barney Gaylord
1958 MGA with an attitude
http://MGAguru.com
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