No one I know has compression releases. I'm trying to understand why they are necessary and how they function, and the difference between manual and automatic releases. Anyone?

 

I don't have compression releases but they are use to make starting easier releasing compression to allow engine to spin over easier especially on hot starts. Higher compression engines or I have heard of guys with SE255 cams running them. Automatics are electronic and operate on their own, manuals you have to reach down by the spark plug and operate them.

 

The larger the displacement (and compression), the harder it is to start, especially when hot.

103's have automatic compression releases stock. Unless you're going a build above 96, you likely dont need them.

http://en.wikipedia.org/wiki/Compression_release

 

I had them installed when I went to a 103 from a 96 and the 255 cams. It was cheaper to do it at the time of conversion since the heads were off. Turns out I needed them. When the engine is hot, it doesn't start easily without them. I put the manuals in. No big deal to reach down and push the buttons. Have to be careful not to touch anything else. It's all hot.

 

The automatic releases are actually built into the cams.

 

No they are not. HD auto compression releases are in the heads and electronically controlled. S&S easy start cams are cam operated (hold the exhaust valve open) compression releases but their auto ones are electrically operated. Manual and auto ones open the combustion chamber to the atmosphere making lower compression for easier starting. They close when the engine starts.

 

I now have manual CR. Had them installed when I upgraded to 107, my 2nd upgrade. When I went from a 96 to 103 for my first upgrade with woods tw555 cams and no CR, I had trouble starting my bike when it was hot. The bendix drive in my starter paid the price. Now after upgrading to 107 with CR I have no trouble starting and my starter thanks me every time I use it.

 

A compression release is actually a small hole in the compression chamber that allows the engine to turn over more easily when cranking due to high compression pistons or a hot engine. Once the engine is started the releases close up allowing normal operation. There, that's it in a nutshell.

 

Old Hippie is correct. I stand corrected. Sorry for any confusion.

 

Lots of great responses here. Let's say I bump up an 88 to a 95 keeping but keep compression the same. Let's also say I send the heads out for a street port. Is the cost worth it?