|The MGA With An Attitude
CAM SPROCKET ALIGNMENT, Without Punch Marks -- CM-105A
Sprocket position for timing chain installation.
#1 piston is at TDC after exhaust stroke.
Sprocket position for distributor drive gear installation.
#1 piston is at TDC after compression stroke.
At 01:30 PM 9/16/03 -0700, Dave B. Hammond wrote:
"I've replaced the camshaft 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 read the prior article about standard installation of the timing chain and sprockets, paying particular attention to shimming of the crank sprocket.
Now 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 camshaft 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.