Re: head machining

["pcsolutions" <pcsolutions@mindspring.com>]

From: randy@taylor.infi.net To: jag-lovers@sn.no
Subject: Re: head machining
Date: Monday, February 03, 1997 7:02 PM

While everyone is still reading this ;)   Can anyone direct me to a
MG list?  I have a friend who would just love to bug the crap (i.e.
pick the brains)  out of some MG aficionados

> Since you said "heads", I have to assume a V-12. I'm very curious
about
> how the dealer arrived at this conclusion. the implication here is
one
> head was machined a lot more than the other, raising the
compression on
> that bank. How can they tell, and if this is the case, how would it
effect
> the idle? The V-12 operates as two six cylinder engines
intertwined. You
> could totally shut down one bank, reset the idle speed, and the
engine
> will idle well.
> If there was a mistake during head work that would have an effect
on 
> the idle, the most likely point would be cam timing.
> BTW, with the Mays head design, you would have to mill a very large
> amount off the bottom to have an impact on the compression.

I would also imagine that if the head in question was machined to a
such an extent to affect compression ration that drastically, it
would be impossible to adjust the timing chain slack.

> Modern cars (80-90's) have a sufficient ignition system to prevent
misfire.
> they have to in order to meet smog requirements. There is *very*
little
> to be gained by upgrading to a hotter spark or multi-spark
ignition, if 
> the rest of the engine is untouched and operating under normal
street 
> conditions.

I agree totally.  The electronic ignition systems on Jags are totally
up to the job.

Have you ever worked on american make cars?  General motors has a DIS
system that works extremely well.  One coil supplys the spark for two
clyinders, the center electrode of one plug is the cathode and it's
companion plug's center electrode in an anode. Which is to say the
spark crosses the gaps in opposite directions across companion plugs.
 This system develops more energy than any aftermarket system I know
of. 
 
> I have used Accel, MSD, and Electromotive ignitions on hot street
and race 
> engines. On the street engines, there really isn't much improvement
until
> you get into really high RPMs. I have never used Jacobs equipment
simply
> because I have been totally unimpressed with their techno-babble
hype
> passed off as an engineering desertation. 

Agreed, Jacobs techno-hype is a bit much.  For aftermarket ignition
components I like Mallory the best.  Their Chevy components I like
alot.  It's still hard to beat the HEI though.  The old coil in cap
HEI distributors are really reliable and fire all but the nastiest
plugs.

Tim

---

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• Re: head machining
• From: "Kirbert" <palmk@mailer.gadcomm.net>

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