D&B Lambert writes:
> All,
>
> I guess I'm confused/uneducated here, being unfamiliar with how the
> internals of an engine really act under extremely high revs. Doesn't the
> stroke of an engine remain constant during the entire RPM range? If so, the
> wouldn't the top ring to ridge distance always be the same no matter what
> the revs were? Or, do the internals (rods, and pistons, etc.) flex or
> distort enough during high revving to cause the piston to actually travel
> higher in the liner than "normal"?
At rest, yes, everything maintains the same dimensions. Under load, however,
the forces go up and parts stretch and compress according to the amount of
load. Those acceleration and deceleration loads are determined by the square
of the rpm. Faster it goes, more load, more stretch. As well, the rings are
not tightly bound in the piston ring lands, so they tend to float up and
down in the lands.
> Also, I think someone mentioned revving the engine to the ultimate max RPM
> occasionally during break-in to cause the ridge to form "high" enough to
> accept this ultimate stroke. Isn't the ridge formed by the very repetitive
> scraping action of the rings on the cylinder walls over a long period of
> time, so in order to change the ridge "height", wouldn't you have to rev the
> engine to the max on a regular basis during the entire life of the engine?
Yes, this is true, but I didn't want to overly complicate the answer.
*smile* Long periods within a set RPM limit will eventually develop a new
ridge below that formed during times of higher RPM use. And, more
specifically, I believe I said that the engine should be pushed near the
redline (the "ultimate max RPM" would be the point where the engine comes
apart catastrophically (!)), and that this should be done near the end of
the break-in period. That's important--I've seen engines go "bang" because
they were pushed too hard, too soon (including one very hopped-up 396 in
high-school, whose owner thought that starting it up from scratch and
immediately goosing it to 6000 rpm was a good idea--the engine didn't think
so, and showed its objection by first shooting a broken rod bolt through the
oil pan and then disassembling itself).
Taking it easy at first, with lots of rpm changes, is good. Pushing the
engine some when it's starting to break in well is also good.
Cheers.
|