Listers,
For those few who might be interested in my progress with the spark plug
problems, here's an update. Thnks to David Franchi and Dick Barker for
their input on this subject. David claims his mechanic has found Autolite
plugs in general to be no good and Dick passed me a tip regarding Autolite
124's he got from Dan Walters, a very knowledgeable Tiger
Owner/Mechanic/Racer here in S. Calif.
First, wrt Autolite, we old farts may be operating more on history than
facts in this matter. Time was when Autolite was considered a quality
product and plugs like the BF-32 were popular with Ford racers. On the
other hand, Champion plugs seemed not to be highly regarded in these same
circles. It has been my practice to change plugs in the Tiger pretty often,
and for the most part I have never had any problems with plugs, regardless
of the brand. I have heard stories, as maybe you have too, that a new set
of plugs is good for a substantial increase in power output on a dyno, but
I have no idea if this is really true, or just one of those many "urban
myths". But, like the interval between oil changes, better too often than
not often enough, right? It's hard to talk about the subject of plugs
without including the ignition system too, and I am a strong believer in my
MSD unit, or some kind of capacitive discharge high output system because
the stock coil setup just can't deliver enough energy above 5-6k rpm. Also,
plug gap is a related parameter, and bigger is better to a point (no pun
intended). In the 70s, the engines started using very large gaps to help
with ignition of the very lean mixtures they were trying to burn; 0.070" or
so gaps. Also, you can read volumes on the importance of combustion chamber
design and the best position of the spark plug for efficient burning; e.g.,
near the center, or closer to the exhaust valve. All of this gives one the
impression that there's more to it than just whether a spark fires or
doesn't. With my MSD, I set my plugs to 0.050" because it idles smoother
for one thing and bigger is better, right? And even with this size gap, the
MSD fires out to way beyond where I aught (thanks Dick) to be revving. On
the other hand, I am totally unbelieving of claims made by Splitfire, which
I place right alongside those of Prolong, etc. There are some fanatics who
index their plugs so the gap is oriented optimally in the chambers while
others twist the ground electrode away from the center to "unshroud" the
gap. I recall that one time I used a set of Mazda rotary plugs in my Tiger
because they are completely unshrouded with no separate ground electrode. I
believe some aircraft plugs are made this way too. At least there is no
electrode to fall off! These plugs seemed to work pretty well, although I
have not continued using them. Maybe I should reconsider in light of my
recent experience.
Getting to the update part of this posting, it turns out I had two - Yes
TWO! - bad plugs; number 1 and number 8 cylinders. Both were identical, no
center electrode visible and half the ground electrode apparently burned
away. I'm very surprised the engine wasn't running a lot worse than it was.
I guess the MSD was compensating for some of the problem - or perhaps part
of the problem? So what to put back in? Normally, I'd never use anything
that gave me this bad service again. But then again, this isn't exactly
normal service I'm subject them to either. And it is likely the MSD erodes
the electrodes faster than a normal ignition would, and maybe it was
running too lean, especially in #1 and #8, etc., etc. So what to do? In
response to my first post, Dick Barker reminded me of Dan Walters'
recommendation of the Autolite 124 plug, which may be nominally for a truck
application. So off to MM&J's for a set of these. Comparing them with the
45's I took out, the electrodes protrude at least 1/8" less into the
chamber. The center ceramic insulator ends about flush with the end of the
plug body and the ground electrode is correspondingly shorter. I assume
this plug is design for extended high load conditions; i.e., it's a cooler
running plug which is obviously the direction I need to go. I'm a little
concerned that it doesn't stick as far in though; farther in is better,
right? Oh well, I have a lot of respect for Dan's judgement and experience,
so in they go. Takes me all of about an hour to gap and replace them,
twenty minutes of which I spent trying to get that *&#@!! #6 screwed back
in. Wound up pushing some fuel line hose over the end of the plug and
screwing it in that way. Took a short little cruise last night and
everything seems A-OK; idles smooth, runs strong, etc. Haven't tried a
banzai run on the Interstate yet, er, I mean on that close circuit course.
Better check the fuel pump and filter first and put the #67 front jets in
first.
Well, TTFN,
Bob
PS:
In case you're interested, Autolite is part to the Consumer Products Group
of AlliedSignal. CPG is comprised of four major business enterprises; FRAM,
Autolite, Prestone and Holts. We've already seen FRAM filters trashed on
this List. Is it possible we need to add Autolite to the "Do Not Buy" list?
Don't want to unfairly accuse them, just asking for input.
Robert L. Palmer
Dept. of AMES, Univ. of Calif., San Diego
rpalmer@ames.ucsd.edu
rpalmer@cts.com
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