Re: Dashpots, Aeration

[n9ads@domain.elided (Howard R Pletcher)]

On Wed, 4 Mar 1998 18:39:24 -0700 (MST) kemp <tkemp@domain.elided>
writes:
>	The function of the Dashpot Assembly on the carb is to slowly
>reduce engine Rpm's in the event of rapid deceleration. It may well be
>that it functions as an emission device but It was explained to me as
>being more of a safety device; ensuring that the vehicle doesn't die in
>the event of an emergency deceleration.  Consequently, I'd think twice
>about removing it. Unless the carb is being used with a manual
>transmission.

SLF-73-22 lists the dashpot as one of the carb mods for the 1974
emissions regs.  I think it has to do with the engine producing a burst
of "bad" stuff when the throttle suddenly closes although I'm not quite
sure why this happens.

>	On another topic can anybody think of another reason for oil
>Aeration besides a faulty pump or pickup? I've replaced these and still
>have little bubbles in my oil. -Thanks in advance.
>		
>
Tiny bubbles.  Wasn't there a pop song about them many years ago?

There was some problem with aeration to the point of dropping oil
pressure and getting lifter noise while running at high speed.  Part of
the problem was all the oil was getting pumped up to the upper parts of
the engine and not draining back fast enough.  

Another part of the problem related to the double sump oil pan used with
the Scout.  What follows is taken from an Engine Lab Report that is NOT
dated April First, although one might expect that while reading it. 
Investigating low pressure and lifter noise problems, they put plexiglass
windows in an oil pan and observed oil levels and turbulence in the pan
while the engine was running.		

"The initial test, made with the standard Scout II double sump oil pan
and the external bypass oil pump, revealed that at engine speeds above
3600 RPM, nearly all of the oil is pumped from the rear sump and bypassed
into the front sump.  The crankshaft windage, blowing down on the axle
clearance hump, is sufficient to prevent most of the oil from returning
to the rear sump."

Various baffles, changing the height of the axle hump in the pan,
increasing the engine angle, and an internal bypass oil pump were tested
to improve the situation. 
The internal bypass oil pump, 448 662 C91, was judged to reduce the loss
of pressure enough to eliminate most of the complaints, although it
appears that aeration and even pressure loss could still occur with
sustained high speed driving. I believe 448 662 C91 was put into
production as it is the oil pump listed in the MT-130 parts book, so if
you replaced the pump, you should have the internal bypass pump.  I don't
know that any other changes were made to fix the problem.

Beyond this, reducing the height of the axle hump in the pan by 3/4"
(probably practical only if you have lifted your Scout) and brazing a
piece of tubing from the front sump to the rear to act as a siphon
increased the oil return.  One of the field fixes used when the problem
was occurring was to overfill the crankcase by 1 quart so there was more
oil to draw from.

Howard Pletcher
Howteron Products Scout Parts

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