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Re: tune up questions

To: RDWILLI@VM.SC.EDU
Subject: Re: tune up questions
From: Bill Schooler <schooler@erols.com>
Date: Tue, 24 Jun 1997 07:46:18 -0700
RDWILLI@VM.SC.EDU wrote:
> 
> Replaced the points, (gapped @ .015), condensor, cap, rotor, etc.  upon
> trying to crank, all i got was a hellacious backfire.  set the front
> piston to TDC with the crank pulley, pulled the distributor to check for
> any strange damage, and upon finding none, put it back in.  problem:
> had to re-route the wires to the cap in order for rotor placement to be
> at the first cylinder.  one is now where four was, three where two, four
> where one, and two where three.  does the drive dog only go in one way,
> or should i be able to turn the rotor 180deg. to put "one" back where it
> originally was?
> 
> the car runs now, with no backfire, but it seems quite odd to me that a
> tune-up would cause a 180deg. shift in the firing order as it was
> prior to the tune-up.  any help would be greatly appreciated.  i have
> yet to try to set the timing, as i'm not sure of what i should do
> concerning the rest.  please pardon if this is a stupid question, but
> this 73 B is my first experience with anything other than electronic
> ignition.  BTW, the car sat for 2-3 years prior to my purchase of it,
> and ran surprisingly well before my attempted tune up.  its running again
> after my attempted tune-up, just in a slightly different order...
> suggestions?...i'd really like to set the timing in the next couple of
> days, but would like any opinions/suggestions/etc. prior to doing so.
> 
> thanks in advance,
> robert williford
> '73 mgb

Robert,

A couple of other folks have pointed you in the right direction, but I 
thought I'd chime in and expand the explanation.  What you need to 
remember is that the crankshaft rotates TWICE for each complete firing 
cycle, i.e., each cylinder fires once.  What that means is that the crank 
pulley lines up at TDC twice for each cycle.  Once, when the No. 1 
cylinder is at TDC and once when the No. 4 cylinder is in that position. 
If you think this through, visualizing a one-cylinder 4-cycle engine, 
you'll understand better.  The piston in that one-banger is at TDC twice 
in each cycle, once at the end of the compression stroke, and once at the 
end of the exhaust stroke.  What happened to you is that you had your 
engine exactly 180 degrees out of time, and you corrected it by rerouting 
the spark plug wires.  

-- 
*Bill Schooler      *Check the MGCC Wash DC Centre Web Page
*Woodbridge, VA     *http://members.aol.com/mgccwdcc/
*schooler@erols.com *Editor of The Spark
*69 B/GT, 53 TD     *Web Page Coordinator

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