Right Plugs For a Pan - Harley Forum

BaggerDad · #1 07-19-2008, 02:45 PM

A buddy is trying to fix up and get his Panhead running and isn't sure what the best sparkplugs are for it.

He has some old Harley plugs in it now, one is marked 3 and one is marked 4. How about Champion, Autolite or NGK recommendations?

If we get it running I get to ride it. Yipppeeeee!

evoKENevo · #2 07-19-2008, 03:20 PM

BaggerDad:
Check-out the July '08 issue of AIM page 42..there's a cross reference chart for HD spark plugs. It's a little vague on the #3 thru #5 plugs..but,this should be enough to get him/you going,incase you don't(?)have that issue

HD 3-4
Champion J12YC
Autolite 4275
NGK R5670-5
Screaming Eagle SH125
Accel Y2401P

P.S..........................Yippeee

!!!!!

frisco-rigid · #3 07-19-2008, 08:19 PM

Hey Bag

Brings back memories..

If I remember correct.. The 3 is hotter, meaning it retains combustion chamber heat slightly longer and the 4 is ever so cooler, transfering it's heat to the head a wee bit quicker..

We used to put the cooler plug in the front and the hotter plug in the rear.. The rear head/barrel was usually hotter already so the hotter plug retained it's heat and didn't transfer it to the head as fast..
Oh Yeah,, that was the theory anyway..

Just outa curiosity-- which plug was in which head.?
Been a very long time since my Panhead days, my memory is a wee cloudy..

We also used to use the J12YC, the thread reach is about half with these old plugs, stay with the correct reach..

evoKENevo · #4 07-19-2008, 10:06 PM

frisco:
Hmmmm...I'd have THUNK you'd want to put the COLDER plug in the HOTTER head/cyl. VISE-VERSA for the USUAL reasons...but am OPEN in THIS case...if YOU say so...

frisco-rigid · #5 07-20-2008, 02:49 AM

Remember how plug heat ranges work----
The plug itself is not Hot or Cold..
It just dissipates heat according to it's heat range..

A cold plug dissipates heat faster to the heads, that is why it can foul out easier than a Hot plug which retains heat longer in the plug itself burning off residue..

The theory was that a hotter plug would hold the heat longer and NOT transfer the heat to the already hotter rear head and the colder plug would not really make any diff at all in the cooler running front..

Interesting to note that in those days (many years ago) I was learning something new every other day,,,, and on those in-between days I was screwing something up..
When my Peers said "this or that" works I had to find out for myself.. Most of the time they were correct, um, but on this one, well, I gotta say, I followed this prevailing advice and heck, it seemed to work..

Like I said though,, today I'd prob use J12's and tune perfectly..
By golly I still have one of my old M74 Linkerts and an old Bendix I used on my pans back then.. Today I'd prob use a NEW Bendix or maybe an old 38mm Keihin.. Definately NOT an E..

evoKENevo · #6 07-20-2008, 09:00 AM

"OK'...on one hand I understand the THEORY of a hotter plug not dissipating as much heat into an already hot head..and that "many years ago" it SEEMED to work. But,unless I'm reading you wrong here,what you're clarifying now (in agreement) is that TODAY you'd be more concerned with the plug retaining too much heat at the risk of preignition/detonation,etc..and that you'd go with Perf-Tuning (carb,ign-timing,etc) to get the job done the RIGHT-WAY...along with the RIGHT-PLUGS of course..

All,of which,I'm following up on..not so much for OUR sakes..but for OTHERS reading this thread,who may already be a little "disoriented" on the subject..and possibley misinterpreting some if not all of the above...noting that even I was kinda/sorta bordering on accepting the OLD-THEORY (on YOUR word) to SOME degree in the case of the OLDER-HARLEYS and their somewhat MYSTICAL "complicated

simplicity"...whew !!

Thanks for "coming-thru"...as usual.
Geez...I could use a BEER now...is it NOON where you're at,yet ?

frisco-rigid · #7 07-20-2008, 05:04 PM

BINGO
You get the Gold Star..!

Just because we did it, and it's even recommended in the old OEM HD Manual, that doesn't necessarily mean it was really warranted even though it was the prevailing wisdom of the day..

AND, you got me thinking and remembering even more about it.. My cloudy memory dimly remembers something about the rear cylinder quite often being a bit richer so the hotter plug was a small benefit there also..

There's something else that, back then I was only slightly curious about but didn't really question-- why does the minute amount of heat transferred or NOT transferred to the head, via the plug, (compared to the actual combustion temps) seem to make any diff at all..??
Now you see why I still refer to it as theory..

Yeah, today I would try to figure it out better first rather than jump to a band-aid.. However I am having too much fun with my big inch Evo's now to give it much thought, except for this thread.. It is kinda fun to remember back though..

street bob · #8 09-18-2008, 12:09 AM

frisco- your sure right about that.
I always had the best lick using autolite 84 plugs. I had an old bendix on that pan at first, then changed to an S&S "E". Those autolites would run forever it seemed.
But....that was some years ago.