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Frequently Asked Questions

 

How do I degree a cam in?

 

Procedure for checking camshaft position.

 

1. Working on number one cylinder;

a. For hydraulic tappets, remove rocker and measure direct on pushrod.

b. For adjustable lifters set inlet and exhaust lash to exhaust clearance. Measure on valve.

 

2. Rotate engine to T.D.C. on number one cylinder (not on the firing stroke)

 

3. Read lift, valve lift or pushrod lift on inlet and exhaust.

 

4. Inlet lift should be the same as or up to 0.010" more than exhaust lift.

 

5.

a. If inlet lift is greater than 0.010" more than exhaust, retard camshaft timing.

b. If inlet lift is less than exhaust advance cam timing.

 

6. Recheck and move camshaft until the lift is the same or slightly more on the inlet.

 

NOTE. To move power band down the rev range advance cam timing. To move power band up the rev range retard cam timing. Six degrees is the maximum recommended advance or retard, (power band moves around 200rpm for six degrees).

 

If this is not sufficient you have the wrong cam in the engine.

 

How do I check valve train geometry ?

 

VALVE TRAIN GEOMETRY

 

Checking Geometry in Pushrod Engines

 

When building a modified pushrod engine the pushrod length should be checked as follows.

 

1. Paint the end of the valve with a felt tip pen.

 

2. Assemble pushrod and rocker with correct lash.

 

3. Rotate engine through two revolutions.

 

4. Check marking pattern on the end of the valve.

 

If the marking is not in the centre of the valve the pushrod length should be altered until the correct marking is achieved. Micrometer pushrod gauges are available from Crow Cams. You can make a simple adjustable pushrod by cutting a 202 and threading the inside to take a piece of threaded rod. Note Holden 202 and 308 pushrods are not hardened so they can be cut easily.

 

For mild camshafts changing rocker ratios can be a helpful tuning tool. For racing camshafts care should be taken as race cams are designed to suit specific rocker ratios.