Proper installation

Question:

For that timing gear Your column in the November 2014 Auto Restorer (referenced in the above question) brought to mind a problem I’m having with my 230 cid Chevelle Six. At about 90,000 miles this engine was rebuilt with hardened valve seats, bored .030 over, etc. Now there is a noticeable whirring sound from the new timing gear. The rebuilder tells me that this sometimes occurs with these rebuilds. Is this so, and will this noise eventually go away? I was expecting a much quieter motor.

Answer:

Originally, your 230 inline six came with a fiber timing gear to drive the cam. Chevrolet used these for decades because they were reasonably long-lived and most importantly, quiet. However, many of us, including me, switch to an aluminum cam drive gear when we rebuild or performance-tune a Chevy in-liner because they are tougher and longer-lasting. Problem is, they do make a little bit of a whirring noise, sort of like a supercharger whine. This noise should be minimal, but will not diminish over time.

But perhaps your mechanic installed the timing gear cold, and that can ruin it. What happens when you do that is the timing gear gets metal shaved off of it when you pound it onto the end of the cam, and then it loosens when it heats up. Then it starts walking back and forth inside the timing case. This can damage other components over time as well.

Aluminum timing gears should be heated to where they cannot be handled except with welding gloves, and then pressed onto a cold cam. That way, as the cam warms up and expands during operation, it will hold the gear firmly in place. This is called a press fit.