Why are both hot and cold valve clearances given for most radial engines?

Why are both hot and cold valve clearances given for most radial engines?

• A. The hot clearance is used for valve timing; after timing is set, adjust all valves to cold clearance.
• B. Hot clearance and cold clearance are used for different engines.
• C. Cold clearance is measured only during cold start.
• D. They are provided for redundancy; hot equals cold.

Answer: (A)

Valve clearance changes with temperature because metal expands when hot. In radial engines, the lash you set when the engine is cold isn’t the same as the lash the valve train has when the engine is running hot. The hot clearance is the clearance needed to accurately time the valve events at operating temperature, since the cam, lifter, and valve stem have expanded. Once timing is set using that hot clearance, you then adjust all valves to the cold clearance so the engine has the correct lash when it’s cold and during starting. This dual reference lets valve timing be correct at operating temperature while still providing a safe, proper clearance reference for cold conditions. The other options don’t fit because clearances aren’t engine-specific, cold clearance isn’t only for cold starts, and hot does not equal cold.

Valve clearance changes with temperature because metal expands when hot. In radial engines, the lash you set when the engine is cold isn’t the same as the lash the valve train has when the engine is running hot. The hot clearance is the clearance needed to accurately time the valve events at operating temperature, since the cam, lifter, and valve stem have expanded. Once timing is set using that hot clearance, you then adjust all valves to the cold clearance so the engine has the correct lash when it’s cold and during starting. This dual reference lets valve timing be correct at operating temperature while still providing a safe, proper clearance reference for cold conditions. The other options don’t fit because clearances aren’t engine-specific, cold clearance isn’t only for cold starts, and hot does not equal cold.