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!

What does "OHC" mean?

In the last two blog posts we discussed OHV and the advantages of OHV.  Today we will discuss OHC, what OHC means, and what OHC can do for you.

Some of today's lawn mower engine manufacturers are coming out with OHC engines.  There are an increasing number of OHC engines hitting the power equipment market.  This is not all good and it definitely is not all bad.

What does OHC mean?
OHC simply means that the camshaft is positioned in the head rather than in the block.  As we discussed in the previous posts, the L-Head and OHV engines both have the camshaft positioned in the block.

Here are several designations you may see on engines and engine materials and what each one means:

1. OHC (Over Head Camshaft).  This means that the camshaft is positioned in the cylinder head rather than in the block.  If the only designation is "OHC", it generally means that the engine has only a single camshaft.
   
2. SOHC (Single Over Head Camshaft).  Once again, this means that the camshaft is positioned in the cylinder head rather than in the block.  The "S" part of the designation simply means that the engine has only a single camshaft.
3. DOHC (Dual Over Head Camshaft).  Once again, this means that the camshaft is positioned in the cylinder head rather than in the block.  The "D" part of the designation simply means that the engine has two or "dual" camshafts positioned in the cylinder head.

Next time we will discuss the differences between OHC and OHV.  For a discussion about this topic, visit the Superior Power Equipment Forum.

Until then, keep your engines running folks!

What are the advantages of an OHV engine versus its L-Head counterpart?

Last time we discussed the mechanical difference between OHV and L-Head engines.  Today we will discuss the advantages of the OHV engine when compared to its L-Head counterpart.

So what are the advantages of OHV engines versus L-Head engines? OHV engines are alleged to have the following benefits:

• Higher quality engine (better grade components),
  
• Higher torque,
• Better fuel effiency,
• Quieter operation,
• Cooler operation,
• Cleaner operation,
  
• Longer engine life,
• With the final result of requiring fewer major repairs than their L-Head counterparts,
• And allegedly, less expensive to operate.
  

Disadvantages of OHV versus its L-Head counterpart:

• Not as compact (bigger external size),
• More complex,
• More components (this can also mean there are more components to fail),
  
• Due to their complexity, typically are more expensive to purchase,
  

Summary: The advantages of OHV far outweigh its disadvantages.  When purchasing engines, and given the the option to purchase one with OHV or and L-Head engine, it is easily worth the extra initial cost to purchase the OHV rather than the L-Head engine.

Next: Next time we will discuss what "OHC" means.  Stay tuned while we rev our engines!

What is an Over Head Valve (OHV) engine?

 What is an Over Head Valve (OHV) engine?

In today's Power Equipment market you may see a machine advertised with an "Over Head Valve" or "OHV" engine.  What does that mean? First of all, let's understand that there are 2 basic valve configurations in today's engine.  These configurations are:

1. L-Head (commonly referred to as "flathead", "conventional head", "valve in block" or "side valve").  As some of these names imply, the L-Head engine has the valves positioned in the block, typically next to the piston/cylinder.
   
2. Over Head Valve (commonly referred to as OHV or "valve in head").  Again, as the name implies, the OHV engine has the valves positioned in the head of the engine, above the piston/cylinder.  The valves are also in an inverted position when compared to the L-Head engine.
   

So how are the L-head and OHV engine different from each other?  The L-head is the "old" design, with the valves in the block.  The valves normally are positioned along side the cylinder with the tops of the valves being even with the top of the cylinder.  Below is a diagram of a L Head or flathead engine, courtesy of howstuffworks.com.

The OHV engine, on the other hand, has the valves positioned in the head.  The valves are positioned directly above the piston, as shown in the photo below.

Next time we will discuss the advantages of the OHV engine versus its L-Head engine counterpart.