Re: Two Questions: Tires and Break-In Period
- From: "." <RhiannonX@xxxxxxxxx>
- Date: Fri, 7 Mar 2008 08:28:51 -0800 (PST)
On Mar 6, 8:07 pm, "David T. Ashley" <d...@xxxxxxxx> wrote:
Why would RPM _changes_ affect the piston rings? They would affectthe
crankshaft, but from the point of view of an individual piston, it is still
moving up and down, and the acceleration in changing direction far exceeds
changing RPM (which the piston itself doesn't really see).
I have discussed piston acceleration and the evolution of thinner and
thinner piston rings until I'm bored with the subject and won't spend
any more time on it, other than to say that modern 600cc sportbikes
use 0.5 millimeter thick compression rings and the piston acceleration
at 15000 RPM nears 4200 g's.
I've been using these ultra thin piston rings for over 40 years now,
and, while I personally dislike having to constantly shift gears with
high RPM engines that have narrow power bands, if I want to experience
that level of power, I have to operate them according to the way the
technology was intended to work.
If I want a good piston ring seal, I have to use a lot of throttle. If
I don't mind oil consumption, I can use less throttle.
I never rode my FZR1000 fast during break in, and it uses half a quart
of oil between 4000 mile interval oil changes.
It has so much power, it's hard to find enough room to really open it
up, so it loads up
during touring and when I do find a place to twist the throttle, it
blows black smoke and carbon out the exhaust.
Besides ultra-thin piston rings, it also has 5 valves per cylinder,
and that means three valve stem oil seals to leak oil into the
cylinders. Such is the price we pay for performance.
When a speed tuner tells you to "vary the engine RPM" during break in,
what he's *really* telling you is to vary the amount of *throttle*
continuously.
A piston ring doesn't rely upon its own inherent spring tension to
seal the combustion gasses, it is pressurized from the backside by
those gasses.
If you roll the throttle on and off, you allow the rings to expand and
retract and theoretically, engine oil gets sucked up onto the cylinder
walls as you roll the throttle off.
With nikasil cylinder walls becoming increasingly popular, engine
break in periods are sharply reduced. The piston ring is made of soft
cast iron and wears to match the cylinder wall rapidly.
Yamaha used to recommend a 20 minute ring break in period on their
nikasil cylinders. I had to keep my 250cc engine above 8000 RPM all
the time to get good power, but it would rev up to 14000 and survive.
I also am not sure that pistons "see" running the bike hard. I'm not sure
that the stresses on the piston change more than 20% or so beyond the
changes imposed by RPM.
If you double the RPM, mechanical stress increases by a factor of
four.
Half of the discussion at the web page looks questionable.
There are lots of sportbike racers who believe, "Fast break in, fast
bike. Slow break in, slow bike."
It's all about getting the piston rings to seal by getting pressure
behind them to resist to pressure on top of them.
Speed tuners will drill a circle of tiny gas pressure ports in the
piston crown to pressurize the compression ring...
The pressure ports will not get blocked with carbon because the engine
will never be run slow enough to carbon up...
.
- References:
- Two Questions: Tires and Break-In Period
- From: Remember My Name
- Re: Two Questions: Tires and Break-In Period
- From: Tim Kreitz
- Re: Two Questions: Tires and Break-In Period
- From: David T. Ashley
- Two Questions: Tires and Break-In Period
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