A camshaft only works if the valves stay out of the pistons. That means the first job is measuring real valve-to-piston clearance at top dead center, where the exhaust is closing and the intake is opening. Using a cutaway head with setup springs, we can move the valves by hand and see exactly how much room the L5P valvetrain gives us. In this check, there was about .050-inch on the intake side and .065-inch on the exhaust. That clearance is the window we have to work with when shaping the cam profile. Use too much of it and the valve hits the piston. Measure it correctly and you know how far the cam can go.
The segment uses a cutaway cylinder head to provide a direct view of the valvetrain. With the combustion chamber exposed, both the intake and exhaust valves can be observed as the team checks valve-to-piston clearance during camshaft development.
Lightweight setup springs are installed in place of the normal valve springs. These allow the valves to be pushed open by hand while the piston is positioned near top dead center.
This makes it possible to physically measure how much room remains between each valve and the piston during critical portions of the engine cycle.
At top dead center, the demonstration shows approximately 0.050 inch of intake-valve clearance and 0.065 inch of exhaust-valve clearance.
These measurements establish the available physical space between the valves and piston before the final camshaft profile is determined.
The clearance check occurs around the overlap period near top dead center, when the exhaust valve is closing and the intake valve is opening.
This is a critical region for piston-to-valve interference because the piston is near the top of its travel while both valves are transitioning through their respective timing events.
The measurements establish how aggressive the camshaft profile can safely become.
Cam design determines when the valves open and close, how far they lift, and how their motion relates to piston position. Without sufficient clearance, an aggressive profile could allow a valve to contact the piston and cause serious engine damage.
The measured clearance becomes part of the design envelope for the new camshaft.
According to the demonstration, some of the available 0.050-inch intake and 0.065-inch exhaust clearance will intentionally be used by the new cam profile. The objective is to maximize the desired valve motion and timing while maintaining enough margin to prevent piston-to-valve contact.
