|The MGA With An Attitude
VALVE LAYOUT In Cylinder Head, And Eyebrows - CM-203
This cylinder head valve layout can assist you in determining position of eyebrows if needed. Click on image for larger printable PDF file. (More information below).
This is a full scale drawing. Printed on 8-1/2 x 11 paper it should be 40% scale. You can print at 250% on ANSI D-size paper (22" x 34") for a full scale image. The illustration shows a big valve head ("16" or "18" but not "L") sitting on a 1500 block with standard 2.875 inch bore. The valve lift diagrams show standard lift and 0.064 inch additional lift as generated by my Crane Cams fast street cam. It is clear here why you need to add eyebrows in the block when increasing valve lift or shaving the head. For the 1500 block both intake and exhaust valves overlap on top of the block. For larger bores only the exhaust valve overlaps and needs the eyebrows.
All valves lie on centerline of the cylinders, and each combustion chamber and cylinder is a mirror image of the adjacent cylinder. I like to use the four studs on left side of the block for position reference, because these control location of the rocker pedestals and the rocker arms. You should note that the cylinder bores are offset 3/32-inch toward the intake ports. Also note the center between the two valve stems is offset 1/32" in the opposite direction. This makes center between the valves offset 1/8 inch from the cylinder bore. An odd result is that the valve stems are offset 1/32 inch from the rocker arms (which most people never notice).
The primary cylinder bore circle in red is for 1500 engine standard bore. The black crescent lines are for 1600 engine standard bore. Valve head circles in red are for standard size valves in the "15" head on 1500 and 1600 engines. Valve head circles in black are for standard size valves in the "16" head on 1600-MK-II (1622cc) engines, and the "18" head from early MGB 1800 engines.
1500 Std bore and Std valves, the intake valve is nominally flush with the cylinder bore.
1600 Std bore and Std valves, the intake valve falls 0.046" inside of the cylinder bore.
1500 Std bore and MK-II valves, the intake valve overlaps the cylinder bore by 0.031".
1600 Std bore and MK-II valves, the intake valve falls 0.015" inside of the cylinder bore.
You don't need the drawing to cut the eyebrows. Just measure distance between the two center exhaust valves, and place the eyebrows 1/16" closer together so they clear the valve heads by 1/32". Then measure distance between two intake valves, and place the eyebrows 1/16" closer together so they clear the valve heads by 1/32". The exhaust eyebrows at the ends will be a mirror image of the center ones, same overlap distance on top of block. All valves and eyebrows lie on the same centerline as the cylinder bores. Circle templates used need to be 1/16 inch larger than the valve heads.