Camshaft, chain and sprockets

1. Camshaft

a.   The cam lobe metal surface may have a blue discoloration due to excessive friction. The metal surface could also start to flake off or become pitted.

b.   If any of the above wear conditions are readily visible, the camshaft should be replaced.

c.   Even though the cam lobe surface appears to be in satisfactory condition, the lobes should be measured with a micrometer. Cam lobe wear can occur without scarring the surface. If this wear exceeds a pre-determined amount, valve timing and lift are affected. Replace the camshaft if wear exceeds the limits.

d. Install the camshaft on the cylinder head. Place a strip of Plastigage between camshaft and camshaft cap as illustrated (lengthwise along camshaft). Tighten the nuts with specified torque. Remove the camshaft cap and determine the clearance by measuring the width of the flattened Plastigage.

1. Plastigage

NOTE:
Do not turn camshaft when measuring clearance with Plastigage.

Camshaft-to-cap clearance:

Standard: 0.020 ~ 0.054 mm (0.0008-0.0021 in)

Maximum: 0.160 mm (0.006 in)

If the camshaft-to-cap clearance exceeds specification, measure camshaft bearing surface diameter.

Bearing surface diameter:

Standard: 24.967 ~ 24.980 mm (0.9830- 0.9835 in)

1)   If camshaft diameter is less than specification, causing excessive clearance, replace camshaft.

2)   If camshaft is within specification and camshaft-to-cap clearance is excessive, replace cylinder head.

2.    Cam chain

Except in cases of oil starvation, the cam chain wears very little. If the cam chain has stretched excessively and it is difficult to keep the proper cam chain tension, the chain should be replaced.

3.    Cam sprockets

Check cam sprockets for obvious wear.

4. Cam chain dampers and tensioner

Inspect the top cam chain damper (stopper guide) and two (2) vertical (slipper-type) dampers for excessive wear. Any that shows excessive wear should be replaced. Worn dampers may indicate an improperly adjusted or worn-out cam chain.

F. Cylinder

1.    Inspect the cylinder walls for scratches. If vertical scratches are evident, the cylinder wall should be rebored or the cylinder should be replaced.

2.    Measure cylinder wall wear as shown. If wear is excessive, compression pressure will decrease. Rebore the cylinder wall and replace the piston and piston rings. Cylinder wear should be measured at three depths with a cylinder bore gauge. (See illustration.)

Cap nut tightening torque: 1.0nvkg(7.2ft-ib)

If the cylinder wall is worn more than the wear limit, it should be rebored.