Tuesday, March 8, 2011

What is the differences between OHC and OHV?

Ok, so its been a while since I posted a blog. I apologize for that but I will try to get back into the habit of blogging more often.

In the last few blog posts we discussed what OHV is, the advantages of OHV (versus an L-head design) and the meaning of OHC and the different types of OHC. Today we are going to tackle the question of "What is the differences between OHC and OHV?"

The answer is pretty basic. OHV means "Over Head Valve" while OHC means "Over Head Camshaft". Now, OHC is always OHV but OHV is not always OHC. Simply put, OHC engines still have their valves positioned in the cylinder head versus in the block. For a better explanation of what this means, please refer to my previous posts.

Where the difference comes in is where the cam shaft is located. As you can see in the following photo, one of them has a camshaft below the valves and the other has the camshaft above the valves.

In the photo, the engine on the left is referred to as having "push rod valve gear". This is referring to the fact that it has its camshaft below the valves and thus requires a mechanism (i.e. in this case, push rods) to operate the valves. This type of camshaft typically has a gear that meshes with another gear on the crankshaft. Though, sometimes it has a "timing chain" to drive the camshaft.

The overhead camshaft (OHC) engine has the camshaft positioned "overhead", meaning it is positioned over the top of the head, along with the valves. Typically the OHC engines will have a timing chain or timing belt driving the camshaft. The overhead valve engine only has the valves positioned over the top of the head.

Keep your engines running and tuned! Next time we will be back discussing of the benefits and disadvantages of OHC vs. OHV.  We may even compare these 2 to the L-head design if we have the space.

Gentleman, start your engines!