I just installed a new cam in my small block Chevy. The engine runs great, but I’ve noticed that at idle and at some cruising speeds the engine makes a noise that sounds more like a mechanical lifter camshaft. I bought a hydraulic flat tappet camshaft but this one sounds more like a solid lifter engine. Did somebody sell me the wrong cam?
Jeff Smith: The quick answer to your question is that the camshaft you selected is, in fact a hydraulic camshaft so don’t tear it out just yet. What you are hearing is the effect of more aggressive techniques to deliver more performance from either a hydraulic flat or hydraulic roller cam. A stock camshaft lobe profile adds more duration between initial lifter movement and the 0.050-inch tappet lift numbers in order to keep the lifters quiet.
Performance camshaft designers long ago realized that if they could increase the rate of lift of the lobe profile, they could make more lift for the same number of degrees of duration. This helps make more horsepower, but it also generates more lifter noise and this noise can sound very much like the lash clearance on a mechanical lifter camshaft. I believe that is what you are hearing.
All hydraulic lifter engines are designed to accommodate the growth that occurs as the engine warms up. With mechanical cams, this is accomplished with lash or clearance. Hydraulic lifters use what is called lifter preload, which compresses the small piston inside the lifter a given distance. This preload compensates for growth so no lash is necessary. Stock factory preload specs are generally ¾ to 1 full turn of preload, which moves the small piston in the lifter roughly 0.050-inch. Some performance camshaft manufacturers specify far less preload of more like ¼ to ½ turn with the lifter on the base circle of the lobe which reduces the preload down to perhaps only 0.015- to 0.020-inch..
It might be a good idea to recheck your preload settings on all the lifters as it’s possible that you may have missed the spec on one or more lifters and they might be making enough noise to cause concern.
The simplest way to set preload is to use what I call the EO-IC method – or Exhaust Opening Intake Closing. I like to start with the Number One cylinder and run down each bank. I start by bumping the engine over until the exhaust valve just opens (EO). This puts the intake lifter on the base circle of the lobe so we can set the intake preload. With the intake preload set, now bump the engine until the intake valve is halfway closed (IC). Now you can set the preload on the exhaust. With the first cylinder finished, you can move to the adjacent cylinder and run through the process again.
When setting preload I’ve noticed that some hydraulic lifter pistons compress very easily. When setting preload, it is essential to find the exact point of zero lash. When the hydraulic piston in the lifter compresses really easily, zero lash can be difficult to determine. Sometimes spinning the pushrod until it gets tight doesn’t work. If you add excessive preload, the engine will run rough at idle. So finding the exact point of zero lash is critical. It demands a deft feel when you can’t see the lifter.
Hope this helps answer your question.