November 2010 Chevy High Performance Q&A - Performance Q&A

Kevin McClelland Oct 12, 2010 0 Comment(s)
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A: Now you've got us confused! Reference plane from the tangent from the vertical axis? The easiest way to put valve angle into perspective, at zero angle, the head of the valve is flat to the piston head (or deck surface of the block or head). As you roll the valve toward the intake side of the engine, you are increasing the angle of the valve in relation to the piston head or deck. A 23-degree valve angle head will have the valve head angled from the piston head 23 degrees toward the intake. Now, let's shift gears for a moment. A big-block head has two angles based on the intake and exhaust and the amount of canted angle off on the crankshaft centerline. For instance, the intake valve on a Edelbrock RPM Xtreme big-block cylinder head has the intake valve rolled to the intake side 24.5 degrees, and is 4.4 degrees off of the crankshaft centerline. The exhaust valve is rolled 15.5 degrees toward the intake side, and 4.2 degrees off crankshaft centerline. These canted valve angles allow for larger valves in a smaller bore size than a standard wedge head.

Hope this clears up your questions about valve angles. We find the easiest way to keep the valve angles straight is to go off the head of the piston. Keep this in mind when referencing valve angles.

Lash Games
Q: A few years ago there was an article written on how to simply adjust valves on a newly rebuilt engine. It started with the No. 1 cylinder and it had you work your way around by rotating the engine manually a few degrees to set the valves on the different cylinders. I have lost the magazine so my first thought was you-can you help me? Thanks and keep up the good work.
Fred Evenson
Bakersfield, CA

A: Adjusting the valves has been covered by every magazine at some point. Also, every camshaft manufacturer lists a procedure on its website. Let's take a look at my favorite method and maybe a couple of tricks to ensure that you don't have those valve covers back off your fresh, clean engine.

There are many methods for adjusting the valves with hydraulic lifters. In some manuals, you will find that you can set the engine to top dead center on cylinder No. 1 and adjust four of the cylinders. Then you rotate the engine 180 degrees and adjust all the other cylinders. This method will work on a totally stock camshaft with very little duration. The bottom line is that you want to adjust the valves of any given engine when the tappet is on the base circle of the camshaft, preferably when it's directly opposite the nose of the lobe. The best method we know of to achieve this is the Intake Opening/Exhaust Closing method. What this means is that on any given cylinder you will adjust the exhaust valve lash when the intake is just starting to open on that cylinder. Then you would adjust the intake valve lash when the exhaust valve is just closing. Of course, this is with you turning the engine in its natural rotation.


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