How To: Set tappets on Brit twins

Most British twins have a 360° crank throw, which makes tappet setting easy. Here’s why...

 

1: Pistons go up and down together but fire alternately. So while one cylinder’s inlet (or exhaust) valve is wide open the other is fully closed, as you can see from this camshaft. This means...

Step 1.jpg

2: ... to set or check the tappets, turn the engine until one inlet valve is fully open; the other cylinder inlet is then fully closed, ready to check. There’s not always space for feeler blades.

Step 2.jpg

3: However, the pitch of the adjuster thread means that a quarter-turn adjusts the tappet by 10 thou, so by screwing the tappet lightly home you can back off the right amount for the correct clearance.

Step 3.jpg

4: OK, this is not a perfectly accurate method – but it’s good enough and more reliable than a blade when, as is often the case, there’s a misleading indent in the top of the valve stem.

Step 4.jpg