AERA Cylinder Head Rebuilding & Valve Train 1 — Questions and Answers
Question 1: When measuring valve guide inside diameter, what is the maximum acceptable clearance between the valve stem and guide for a typical intake valve on a passenger car engine?
- 0.0010–0.0027 in (0.025–0.069 mm) (Correct answer)
- 0.0050–0.0080 in (0.127–0.203 mm)
- 0.0030–0.0045 in (0.076–0.114 mm)
- 0.0001–0.0005 in (0.003–0.013 mm)
Correct answer: 0.0010–0.0027 in (0.025–0.069 mm)
Typical intake valve stem-to-guide clearance for passenger car engines falls in the 0.0010–0.0027 in range; excessive clearance causes oil consumption and poor valve sealing.
Question 2: What is the primary purpose of cutting a three-angle valve seat?
- To narrow the contact band for better sealing and heat transfer (Correct answer)
- To widen the contact band for increased flow area
- To increase the valve face-to-seat interference fit
- To reduce the need for valve lapping compound
Correct answer: To narrow the contact band for better sealing and heat transfer
A three-angle valve seat narrows the seating contact band, which concentrates sealing pressure and improves heat transfer from the valve face to the seat.
Question 3: When checking cylinder head flatness with a precision straightedge and feeler gauge, what is a commonly accepted maximum warpage limit for an aluminum head?
- 0.002 in (0.05 mm) per 6 inches (Correct answer)
- 0.010 in (0.25 mm) per 6 inches
- 0.025 in (0.64 mm) per 6 inches
- 0.001 in (0.025 mm) per 6 inches
Correct answer: 0.002 in (0.05 mm) per 6 inches
Most specifications allow no more than 0.002 in (0.05 mm) warpage per 6 inches on aluminum heads, as aluminum is more prone to distortion and must be resurfaced if this limit is exceeded.
Question 4: Valve spring installed height directly affects which critical valve train parameter?
- Spring seat pressure and open pressure (Correct answer)
- Rocker arm geometry and pushrod angle
- Valve face-to-seat contact width
- Lifter preload on hydraulic systems
Correct answer: Spring seat pressure and open pressure
Installed height determines how much the spring is compressed, setting both the closed (seat) pressure and the open pressure when the valve is fully lifted.
Question 5: What condition is indicated when the valve margin (the edge between the valve face and the top of the valve head) is less than the manufacturer's minimum specification after valve face grinding?
- The valve must be replaced to prevent burning or breakage (Correct answer)
- The valve can be reused if the seat angle is corrected
- Additional lapping will restore adequate margin thickness
- The valve stem seal must be upgraded to compensate
Correct answer: The valve must be replaced to prevent burning or breakage
A valve margin below minimum spec creates a knife-edge condition that is prone to overheating and burning, requiring valve replacement rather than reuse.
Question 6: Which method is used to verify that rocker arm geometry is correct after a cylinder head has been resurfaced?
- Check that the rocker arm tip contacts the center of the valve stem tip at mid-lift (Correct answer)
- Measure the rocker arm ratio with a dial indicator at the valve tip and pushrod cup
- Verify that the pushrod is parallel to the cylinder bore centerline
- Confirm that all rocker arms are torqued to the same specification
Correct answer: Check that the rocker arm tip contacts the center of the valve stem tip at mid-lift
Correct rocker arm geometry requires the rocker tip to contact the valve stem tip near the center of its sweep at mid-lift, preventing side loading that accelerates wear.
Question 7: When installing new valve stem seals, what is the correct procedure to prevent damage during installation on an assembled head?
- Use a proper seal driver and lightly lubricate the seal lip; protect the seal over the valve stem keeper grooves with a sleeve or tape (Correct answer)
- Press the seal on dry to avoid contaminating the sealing surface with lubricants
- Heat the seal with a heat gun before installation to soften the rubber
- Install the seal after the valve spring and retainer are in place to hold it in position
Correct answer: Use a proper seal driver and lightly lubricate the seal lip; protect the seal over the valve stem keeper grooves with a sleeve or tape
A plastic installation sleeve or tape protects the seal lip from being cut by the sharp keeper grooves on the valve stem, and light lubrication reduces installation force without compromising sealing.
AERA Cylinder Head Rebuilding & Valve Train 1
When measuring valve guide inside diameter, what is the maximum acceptable clearance between the valve stem and guide for a typical intake valve on a passenger car engine?