possible sticky cylinder heads 101

[zex97]

This could be a good sticky or maybe for FAQ section if there is one. Got this from another site several years ago and I can't remember the name of it. It might be shut down now but here you go.


I've been asked on several occasions to do something like what you're going to read here by more than one member or moderator of the SOHC Forum. And that is, do a monthly/bi-monthly tech article for the SOHC guys. Call it newbie information, call it guru enlightenment, call it me just talking out of my ass, or even call it something to read and think about. Just take what I say with a grain of salt, take what everyone else says with a grain of salt, and take your own grain of salt, and put them all into a shaker. A salt shaker only works when it's full of a lot of pieces. Now, with that said......

Here's Cylinder Head 101:

"What's a Head?"

Cylinder heads are easy to explain if you're a NASA scientist that plots Moon orbits for a living, it's something you'll understand in a few seconds. If you're not, then you'll have no idea what it is, what it does, or what to do to it until you THINK it's time to do something to your cylinder head. But everyone forgets to ask the first BIG question. WHAT IS IT? WHAT DOES IT DO?

Here it is in a nutshell. It's a piece of metal with holes in it that makes the engine breath.

When I say "breath", I mean that in a very articulate way. A cylinder head's job is to let the intake air and fuel charge into the engine, let exhaust gasses out, and give the gasses a place to burn as well as house the thing that makes the burn happen (called the combustion chamber/spark plug). That's IT. That's ALL it does. If you try to get more complicated than that, you're missing the point. The point is simple. Cylinder heads like to be treated like they're simple machines, not overcomplicated and not over thought. But at the same time, you need to remember that they are very PRECISE machines that need to be kept within tolerances. So... What have we LEARNED here?

We've learned that a cylinder head is a piece of metal with holes in it, that is a simple, precise machine that allows intake air and fuel into the engine, lets exhaust gasses out, and houses the combustion chamber and the spark plug.

"The Cam's Job"

Now this is where cylinder heads get really simple. The camshaft. What does the cam do? It times the valves opening and closing, and tells it how far to open. THAT'S IT!! All the cam does is "time" and "lift". The time we call "Duration" in degrees of rotation. 360 degrees of crank duration is equal to 1/2 of the cam's rotation. The reason for this, the crank has to make 2 trips around for the cam's 1 rotation. Thus, we have a "4 Stroke Engine". Up, Down, Up, Down. One Cam rotation. The lift we call "Lift" in inches or millimeters. We multiply the "Cam Lift" times the rocker ratio to get the "actual valve lift". I'll explain this later.

So far we've got...

A cylinder head is a piece of metal with holes in it, that is a simple, precise machine, that has a device in it that times the lift and the duration of the valves by rotating at 1/2 the speed of the crankshaft, that makes the engine breath the fuel and air charge in and let the exhaust gasses out, and also houses the spark plug and the combustion chamber.

See how easy these things are?

Wow, it's such a simple device that I think I'm ready to go ahead and grab a dremel tool and port and polish it, order up a replacement cam, put a new set of valves in it, and get some high dollar springs and retainers! I Know all there is to KNOW about cylinder heads now!!

They're just a piece of metal with holes in it, that is a simple, precise machine, that has a device in it that times the lift and the duration of the valves by rotationg at 1/2 the speed of the crankshaft, that makes the engine breath the fuel and air charge in and let the exhaust gasses out, and also houses the spark plug and the combustion chamber!

So what to do NOW?

Simple. If you so far understand what a head is, what a head does, and what a head's role in life as we know it is... Then you're NOT ready to go build one, you're JUST getting ready to start learing about them.

Stand by for the next installation of cylinder head tech... Heads 102.