Hello All,


     I have been in this hobby for about 4 1/2 or 5 years now. I am fascinated by all aspects of it and try to learn as much as possible about as much as possible all the time.

     I don't know to much about engines but want to learn it all 
Can some one tell me what a head shim is, Where does it get placed and what does it do performance wise?


     I also would like to know what one means when they say they have re-tunned the timing on an engine?


                                            T.I.A.
                                               -Steve

The only dumb question is the one unasked. 

Stunt folks have been messing with engines for years in order to get "a more perfect" engine run. Most engines are designed to produce maximum power for their size, but that's not necessarily good for our needs. We need controlled power, with possible changes at certain times (like when we pull the nose up for a loop or etc.).

Engines guys can change the timing of a two stroke engine several ways: 1. raise or lower the cylinder liner, 2. raise or lower the ports in the cylinder liner, 3. grind the leading or trailing edge of the bypass port on the crankshaft, or 4. use a combination of all the above.    What these tricks do is change the intake and/or exhaust behavior the engine. The timing of a two stroke engine is usually measured in degrees of crankshaft rotation and is stated as "n-degrees" BTDC (Before top dead center) or ATDC (After top dead center) of the piston.

You can raise the cylinder liner by inserting a shim (similar to a head gasket, but sized differently) between the liner and the crankcase. You can lower the liner by cutting material off the top of the crankcase, which lets the lip of the liner drop lower into the case. The other tricks are done by using a small grinder on the target ports.

If you know what you are doing, you can change the performance of an engine to match your desired outcome. If you don't know what you are doing, you can ruin the engine in a few seconds.  It's very easy to grind material off - it's very hard to put it back.

This is a very simplistic answer for a topic I spent a whole semester studying in college. I hope I've answered it well enough for you.

Ron

I have a question I should know and probably did once upon a time on a flying circle a long,long time ago....Ok...Some of the various Enya engines come with 2 heads..a standard and a high compression version...How does one detect which is which...seems like one has higher fins than the other..is this a clue....Inquiring minds want to know....!

Thanks to all for this forum.....very enjoyable, entertaining, and informative..