GasGas 4T trials motor...

If they do install it in a trail bike, I hope it doesn't have the disadvantages that the wikipedia paragraph described. Unless they have those problems figured out, it sounds great. It would be nice to see GasGas release a completely new 4 stroke design not copied from someone else. I like the current design but something brand new would really turn me on.
In that second photo...that guys hand was right in front of the cylinder...arrgh...:mad:
 
Side valve engines are very simple. A lot less moving parts. No timing chain, rocker arms, push rods..etc.
For trials applications, it is very attractive. The head is very compact and will fit better in a narrow trials frame.

The big disadvantage is, very poor volumetric efficiency. The combustion chamber has to be huge. The air/fuel mixture does not have a direct path into the combustion chamber.

Here's a side valve engine in action.
Scroll down to The sv engine

http://library.thinkquest.org/C006011/english/sites/ottomotor.php3?v=2
 
I have friend who did his PhD in internal combustion motors and I mentioned to him a few months ago that I thought the side valve would once again have its day. Perhaps it's arrived. My reasoning (with which he agreed) was that with DFI you can overcome the problems associated with the flamefront inherent in any side valve. However gasgasman i hadn't considered the volumetric efficiency.
 
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