Troy-Bilt TB4000 User Manual

23

9. If the clearance is not within specification:

a. Turn the adjusting nut using a 5/16 inch (8 mm)

wrench or nut driver (Fig. 6-19).

To increase clearance, turn the adjusting nut 
counterclockwise.

To decrease clearance, turn the adjusting nut 
clockwise.

b. Recheck both clearances, and adjust as neces-

sary. Clearance for both intake and exhaust is
.003–.006 inch (.076–.0152 mm)

10. Reinstall the rocker arm cover using a new gasket.

Torque the screw to 20–30 in•lb (2.2–3.4 N•m).

11. Reinstall the engine cover. Check alignment of the

cover before tightening the screws. Tighten screws.

12. Check the spark plug and reinstall. See Replacing

the Spark Plug. 

13. Replace the spark plug wire.

Use a Champion RDZ19H spark plug (or equivalent).
The correct air gap is 0.025 inch (0.655 mm). Remove
the plug after every 50 hours of operation and check its 
condition.

1. Stop the engine and allow it to cool. Grasp the plug

wire firmly and pull the cap from the spark plug.

2. Clean dirt from around the spark plug. Remove the

spark plug from the cylinder head by turning a 5/8
inch socket counterclockwise.

3. Replace cracked, fouled or dirty spark plug. Set the

air gap at 0.025 inch (0.655 mm) using a feeler
gauge (Fig. 6-20). 

4. Install a correctly gaped spark plug in the cylinder

head. Tighten by turning the 5/8 inch socket clock-
wise until snug. 

If using a torque wrench torque to; 

110-120 in.•lb. (12.3-13.5 N•m). 

Do not over tighten.