Balance Shaft: Service and Repair

Crankshaft, Intermediate & Balance Shaft Assemblies:

Some engines are equipped with two balance shafts installed in a carrier attached to the lower crankcase.
The shafts are interconnected through gears to rotate in opposite directions. These gears are driven by a short chain from the crankshaft and rotate at twice crankshaft speed. This counterbalances certain engine reciprocating masses.
1. Replace shaft as follows:
a. Remove oil pan, oil pickup, timing belt cover, belt, crankshaft belt sprocket and front crankshaft oil seal retainer.

Chain Cover, Guide & Tensioner Removal:

b. Remove chain cover, guide and tensioner.

Drive Chain & Sprocket Removal:

c. Remove balance shaft gear and chain sprocket retaining screws and crankshaft chain sprocket Torx screws, then the chain and sprocket assembly.
d. Remove double-ended gear cover retaining stud, then the cover and balance shaft gears.
e. Remove carrier rear cover and balance shafts.
f. Remove six carrier to crankshaft attaching bolts to separate carrier.
g. Reverse procedure to install, then adjust crankshaft to balance shaft gear timing as outlined in subsequent steps.
2. It is possible to replace carrier assembly with gear cover, gears, balance shafts and rear cover intact. Replace carrier assembly as follows:
a. Remove chain cover and driven balance shaft chain sprocket screw.
b. Loosen tensioner pivot and adjusting screws, then move driven balance shaft inboard (through) driven chain sprocket. Sprocket will hang in lower chain loop.
c. Remove carrier to crankshaft attaching bolts, then the carrier.
d. Reverse procedure to install, then adjust crankshaft to balance shaft timing as outlined in subsequent steps.
3. Balance shaft gear timing should be adjusted as follows:
a. With balance shafts installed in carrier, position carrier on crankshaft and install six attaching bolts, tightening to specifications.

Gear Timing Set:

b. Rotate balance shafts until both shaft keyways are parallel to vertical centerline of engine, then install short hub drive gear on sprocket driven shaft. After installation, gear and balance shaft keyways must face up with gear timing marks meshed as shown.
c. Install gear cover and tighten double ended stud/washer fastener to specifications.
d. Install crankshaft sprocket and tighten socket head Torx screws to specifications.

Balance Shaft Timing Set:

e. Rotate crankshaft until number one cylinder is at top dead center (TDC). The timing marks on chain sprocket should line up with parting line on left side of number one main bearing cap.
f. Place chain over crankshaft sprocket so nickel plated link of chain is over timing mark on crankshaft sprocket.
g. Place balance shaft sprocket into timing chain so timing mark on sprocket (yellow dot) mates with yellow painted or nickel plated link on chain.
h. With balance shaft keyways at 12 o'clock, slide balance shaft sprocket onto nose of balance shaft. Balance shaft may have to be pushed in slightly to allow for clearance. Balance shaft timing is correct if the timing mark on sprocket, painted link and arrow on side of gear cover are aligned.
i. If sprockets are timed correctly, install balance shaft bolts, tightening to specifications. A wood block placed between crankcase and crankshaft counterbalance will prevent gear rotation.
4. Chain tension should be adjusted as follows:
a. Install chain tensioner loosely assembled.

Chain Tension Adjustment:

b. Place adjustment shim tool No. C-4916, or equivalent, between tensioner and chain. Push tensioner and shim up against chain, then apply firm pressure directly behind adjustment slot to take up all slack. Chain must have shoe radius contact as shown.
c. With load applied, tighten top tensioner bolt first, then the bottom pivot bolt, to specifications. Remove shim.
d. Position guide on double ended stud, ensuring tab on guide fits into slot on gear cover, then install nut and washer assembly and tighten to specifications.
e. Install carrier covers and tighten screws to specifications.