Contributed by: RC Driver Magazine | Published: November 2004 | Views: 117897 |  Email this Article
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This
review appears courtesy of RC
Driver Magazine.
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Article
by:
Ed Bridges
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Photos
by: Walter
Sidas
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New
Engine Break-in
If you asked five different RC car drivers
how to break-in your engine properly, you would
probably get five different answers. Some say to
idle the engine on one tank of fuel; half throttle
on the second and full throttle on the third. Some
say to run it super-slobbering rich for a few tanks
and then lean out the needles. Some say heat cycle
with a race tune. Some say just to fuel it up, lean
it out, and go, go, go! Ive tried them all
and think that the best way incorporates a
little of each, with the exception of the last theory
(if I ever see the guy who told me that, Im
going to take his glow starter away from him). If
you follow the engine advice Im about to give
you, youll find that your new powerplant will
last longer and run more reliably.
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Heat
Cycle Break-in
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A
heat cycle involves getting the engine to an operating
temperature of 190 degrees. This temperature is
critical so that the metals that make up both the
piston and sleeve can expand and conform to the
proper size. For proper engine break-in, run your engine for
three minutes and a total of five times, letting
the engine cool between runs. I like to run
the engine rich, making sure the engine still gets
up to temp so its heat has cycled. Dont lean
it out to get the temps up, as valuable lubricants
in the fuel are essential during the break-in process.
The richer the better: Just make sure the engine
gets up to temp. You can use a temperature gauge
to check the temps. Quality units can be purchased
from Tempgun. com, OFNA, DuraTrax and other manufacturers.
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STEP
1:
By using aluminum foil, heat tape or header wrap
for full-size cars to block off cooling fins on
the heat sink, you can somewhat manipulate the engines
temperature so the engine can reach optimum temperature
faster. Of course, thats only if its
not warm enough outside to allow the engine to build
heat quickly enough.
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Warning: Engines
that have excessively tight pinch at top dead
center (TDC) can wear out a connecting rod
quickly, meaning youll have to invest
in a new piston and sleeve even sooner. Getting
the engine up to temperature properly will
help prevent this problem.
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STEP
2:
While the engine is idling and warming up, leave the
glow driver attached to the glow plug. This reduces
the chance the engine might flame out early. Avoid
revving the engine wide open to warm it up faster:
that will actually wear out the piston and sleeve
more quickly. You might see some of the guys at the
local track doing it but believe me; this does more
harm than good. You can give it some short moments
of 1/4 throttle to help build engine temp and to keep
the engine running while on the starter box. |
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ALTERNATE
Step 2:
Otherwise, a more fun method is to simply place it
on the ground and start running figure eight patterns
while driving smoothly at low throttle. Ease on and
off the throttle. Try not to blip the throttle too
much, as this puts a lot of extra stress on the rod
and crank pin.
Step
3:
While the engine cools between break-in runs, always,
I mean ALWAYS make sure the piston is bottom dead
center (BDC) when the engine is cooling.
Step
4:
After this first 15-minute break- in period, you
should then run the engine in three 5-minute
intervals. Again, make sure to let your engine cool
down sufficiently between runs. Run at no more
than half throttle with some short full-throttle
burst. Again, make sure the engine gets up to temp
and the piston is BDC (bottom dead center)
each time when cooling. When the break-in process
I described is finished, you will have a total of
30 minutes run time and break-in on the engine.
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Piston
and Sleeve Dynamics
Our nitro engines are a lapped piston and sleeve design.
This means that the bore becomes gradually smaller
as the piston reaches the top of the sleeve. This
gives you that pinch at TDC (Top Dead Center). The
pinch is required to keep the piston and sleeve sealed
when the engine gets up to temp. That is why its
important to get the engine up to 190 when breaking-in.
If you dont, the sleeve will never
expand and the piston will wear out faster. The piston
will end up wearing down as a result of friction,
tapering the head of the piston to match the size
of the sleeve. When the engine finally does get up
to temp and the sleeve expands, the piston is
now too small, allowing for blow by. That means the
cylinder pressure blows by the piston down to the
crankcase, and it will cause the engine to overheat
and stall. Unfortunately, the only way to remedy
this is a complete rebuild with new piston, sleeve
and connecting rod.
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CONCLUSION
Well, thats all there is to it: Your engine
is now properly broken-in. As you start tuning for
racing, just remember that running rich is better, but
the engine must get up to temp. Take your time
when breaking-in your engine. Dont rush
the break-in process. If you rush it, you will
only be rushing to the hobby shop to buy a new
engine. The better you treat your engine during
break-in, the better your engine will treat you.
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Tip |
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TIP
After each run, make sure the piston is BDC
(Bottom Dead Center) when the engine is cooling.
You can do this simply by putting a mark on
the back of the flywheel with a Sharpie or any
type of permanent marker. The easiest way is
to look through the exhaust (before you mount
the header) and spin the engine until the
piston is BDC. Then, mark the flywheel on the
back so a starter box wont wear off the
mark. It is always good practice to make sure the
piston is BDC after each run, and not just
after break-in. |
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This
article appears courtesy of RC Driver.
RC
Driver Magazine is published by Maplegate Media.
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