Timing is Everything

Last month, we looked over editor David LaChance's shoulder as he removed the timing chain and gears from the 1,500cc four-cylinder engine in his Triumph Spitfire.

This month, we'll follow along as he installs the new chain and gear set, finagles the chain tensioner back into place, and times and adjusts the valves.

It's worth noting that the replacement gears for these engines often have no prescribed timing marks, and the camshaft gear is designed so that it can be reversed for quarter-tooth adjustments or rotated 90 degrees to make half-tooth adjustments.

So, when installing one of these gears, it's important to perform a valve timing check to ensure that the camshaft is in the correct position relative to the piston's stroke. This procedure is outlined in most shop manuals and can seem a little confusing, but it isn't difficult.

First, assign the rocker arms and valves numbers one through eight, with one at the front and eight at the rear of the engine.

Now, imagine a line between the center two cylinders dividing the engine in half. On this engine, the action of the rockers and valves in the front half of the engine mirrors the action of the rockers and valves in the rear half. So, when valve number one is fully open, eight is closed. When valve two is open, seven is closed, etc.

To determine the position of the cam, install the cam gear (without the timing chain) and turn the camshaft until the number one rocker arm has fully compressed the valve spring. Then, set the gap between the number eight rocker and valve stem to .040. Next, repeat the procedure on valves two and seven.

Now, turn the cam gear slightly, until the number seven and eight rocker arms begin to rock, then, move the cam to the position where the space between the rockers and valve stems is equal. This is the correct location for the camshaft.

Now, you can rotate the crankshaft until pistons one and four are at TDC and install the new timing chain. Inverting and flipping the camshaft's gear allows adjustment of the gear in quarter-tooth increments. When everything's set, adjust all of the valves so that the clearance between the rockers and the valve stems is .010.

Once the camshaft is timed, installation of the gears and chain is fairly straightforward.