Ha ha, I bet most of you thought this thread was dead (and maybe some wish it was).
But I wanted a little clarification on this subject and rather than begin a new thread I thought my questions would fit well here:
This may be a simple subject for most to grasp, and I think I’ve got it, but I want to put it in my own words to make sure I am understanding this correctly:
When speaking of TDC (top-dead-center), I understand this is the actual distance measured between the top of the piston (at its highest point - TDC) and the top of the liner (with or without shims). But for our pylon engines, when speaking of TDC, we are actually referring to the timing, or exhaust timing, or in actuality, the point at which the top of the piston eclipses the top of the exhaust port thereby sealing the combustion chamber. In other words, this TDC measurement is really "code" for how high or low the liner is in the case and the anticipated performance characteristics expected due to the "timing" or the closing of the exhaust port, right?
So, an engine with say, a .151” TDC will be “timed” lower than an engine with say, a .154” TDC, right? So again, TDC in this case is really used as a reference to the
timing, right?
Of course then too, we do need to know TDC (this time, the actual distance measurement between the top of the piston and the top of the liner) to calculate the head clearance between the top of the piston and the bottom of the head (or head button). (Isn’t this distance also referred to as the
squish band?)
Hey, hand me that squish band, will ya!? LOL
Again, I know this is basic, and I think I understand the premise, I’m just putting it in my own words:
When speaking of engine “setup,” we use the figures that describe TDC (referring to timing) and head clearance (a component of which is the TDC measurement).
So, for example, an engine that is set at .151/.015 is timed rather low (or, at least lower than an engine with a TDC of .154”). The .151" engine has its liner set lower in the case and could be said to be timed lower than the engine with TDC of .154”, yes?
Of course, raising or lowering the liner increases or decreases the head clearance (squish band?) accordingly.
I’m not asking how to set an engine, I’m just making sure my understanding and terminology is correct.
Once more to clarify, when we toss out figures such as “.151/.015” we’re speaking of the
timing and
head clearance.
Thanks!
Tim