[AT] Rationale for firing orders

[Larry D. Goss]

Dudley does a good job of describing what's going on in the engine, Rog.
When it comes to 1-2-4-3 vs. 1-3-4-2 firing order, I remember being told
by the professor in the Internal Combustion Engine course that used to
be part of the mechanical engineering curriculum at Purdue, that
designers tried to even out the stresses in the crank and camshaft by
spacing the firing along the line of cylinders as far apart as possible.
The firing order probably doesn't make much difference on an in-line
four, but it does make a difference when you get into 6-, 8-, and larger
engines.

This information and 50 cents will buy you a cup of senior coffee at
your local McDonalds.  :-)

Larry 

-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com] On Behalf Of Dudley Rupert
Sent: Monday, March 22, 2004 4:22 PM
To: Antique tractor email discussion group
Subject: RE: [AT] Rationale for firing orders

Roger:

You ask "why is the firing order 1-2-4-3 and not 1-2-3-4.
I think the answer is in the way the crank is laid out -

If the cranks in the AC's are like those in the Farmall M then
1)  Pistons 1 & 4 are always in the same position in their respective
cylinders and likewise for pistons 2 & 3 and
2)  Pistons 1 & 4 are 180 degrees out of phase with respect to pistons 2
&
3.
    Said another way, when pistons 1&4 are all the way up 2&3 are all
the
way down.

This means then that when 1&4 are at TDC 2&3 are at BDC - so let's say
#1
fires this time.
180 degrees later 2&3 are at TDC while 1&4 are now at BDC - so let's say
#2
fires this time.
180 degrees later 1&4 are back at TDC while 2&3 are back at BDC - so,
since
#1 has already fired, we're left with #4
180 degrees later 2&3 are back at TDC while 1&4 are back at BDC - so,
since
#2 has already fired, we're left with #3.

FWIW The firing order for the Farmall M is 1-3-4-2.  This simply means
that
in the second firing step above AC fires #2 while Farmall fires #3.  I
am
not aware of any advantage of firing one way or the other -

Dudley
Snohomish, Washington

-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com]On Behalf Of Robinson
Sent: Monday, March 22, 2004 10:48 AM
To: Antique tractor email discussion group
Subject: Re: [AT] Rationale for firing orders


Roger Welsch wrote:

> Can someone help me with a brief and simple explanation of why a
motor's
> firing order wouldn't always be one-two-three-four?  My Allis WCs are
> one-two-four-three but I have no idea why....  I love to kid my
in-laws
that
> they've always prefered John Deere Bs because they can remember the
firing
> order.....
>
> Roger
>



	I don't know about that Rog, I am not sure if the firing order
on my
1948 A is 1-2 or 2-1.    ;-)


--



"farmer"

Just when I was getting used to yesterday, along came today.


Francis Robinson
Central Indiana USA
robinson at svs.net


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