PS Magazine - FEBRUARY 1984
PS, The Preventative Maintenance Monthly
ISSUE 375
FEBRUARY 1984
1·
Anything with moving parTs has a
speed lIt. ±f the parTs are pushed
beyond the limit, things start faLng
aparT.
I
²ke a diesel or multiFel enGne, ³r
example.
±ts speed
is
´
meµsured in
revolutions per minute (RPM) on a
tµchometer or tacho¶aph. And each
en·e hµs an RPM limit. ¸hat's not a
lEvEl you try to rEach-it's onE you
avoid.
See what the RPM danger zone ³r
your ¹uck
i
º yoUr »10
T.
¼t's a good
idea to mark it along thE tµchomEter or
tachograph
with
red
paint
or
a
D½N¾¿R decal, NSN 7690ÀÁÂ924Â
4318. Appendà A, C¸A 50Ä970is your
authority ³r thE decal.
.
16
±f you slip up and lEt the RPM get
out of control, your enGne
c
wind up
with bent push rods, brokEn connÅtºg
rods or holes punched thru the tops of
pistons by "ÆoatingÇ valves ÈÈÈ not to
mention a bustedÉup Æywheel or clutch
pressure plµte.
±f thE enGne's not completely ruºed,
the repair bill will be out of sight.
FEB 8
What's the Cause?
ÊnGne oveËspeediÌg ÍsuÎlly happenÏ in downhiÐl travel, whEn yoÍr tËuck's
hauÐing a heavy load ÑÌ low gear. YoÍ tHnk the engine will work ÐÑke a bËaKe
and hoÐd your speed down. But that's not the casE.
¼nstead, the speed buÑlds Íp untiÐ it's too lateÒthe brakeÏ can't hoÐd yoÍË tËuck
back. Êngine speed Ëeaches the D½N¾ÊR zone, and things stÓt happeningÔ
al
baÕ.
Maybe yoÍ're lÍcky and a good enoÍgh driver to avoid aÌ accident. But you
tEar up a Ö×ghty expEnsivE engine.
And The Cure?
Be a smart driver. ½lways tËavel doWØ in the same gEµË you used to go
uphill. And keep an eye on the tachometer.
DoN±² ³ow´SHif² ²o Slow
vEHiclE µFER yoU S²µ¶·
³owNHill .¸.
Ùse thE brakes to hold the engine RPM well below the DAN¾¿R area. Don't
ride the Úrake pEdal, tho, or you'll burn up the brakes. Just apply the brakes
often enough to control your speed.
Some trUcks-like the M91
L,
M915ÀseÛes and Ü746Ýhave a retardEr to help
keep RPM undEr control. Ùse it along with the Úrakes. Þour operator's ¸M tell
you how.
·
FEB 8
17
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