Spark plugs & Gap

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bartz paul

New member
Dec 3, 1997
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Emory:

If you're using the HEI distributor, the recommended plug gap is 0.060.
Otherwise, I'm told you'll probably suffer distributor damage.

Early models had a none-HEI distributor and used the 0.080 plug gap.

Paul Bartz

From: EMERYSTORA [mailto:EMERYSTORA]
Sent: Tuesday, February 02, 1999 11:25 AM
Subject: GMC: Spark plugs & Gap

A few days ago someone posted a question regarding spark plugs for the GMC.
I have a 455 with the HEI ignition. The manual show a gap of .080 but I
have been told and read that I should use .060 and by others .045. Has
anyone tested different gaps and, if so, what have your results been?
 
Hmmm .080 spark plug gap for NON-HEI

shouldn't that be .040 spark plug gap
for NON-HEI ignition -- like my '73
Painted Desert



==
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. Home Phone- (904) 672-0571
.1973 GMC Painted Desert---She's old..but she sure is PRETTY
.1976 Aniversary Iron Head Harley Davidson M/C
.1979 280ZX Datsun (First Production Year - 1 of only 1000)
.
.Home Page> http://members.tripod.com/~mehawk_ii/index.html
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With JR Slaten's help, let me make a correction to the below information:

Page 6Y-44 of the X-7525A shop manual, which pertains to the none HEI
ignition system, calls for a plug gap of 0.040".

Page 6Y-33 of the X-7725 (77 & 78 supplement) shop manual lists a plug gap
of 0.080" for the 77 455 ci engine and the next page specifies a plug gap of
0.060" for the federal version of the 403 ci engine and 0.080" gap for the
California version of the 403 ci engine.

Word has it that a plug gap of 0.060" is recommended for both engines having
an HEI ignition system.

Sorry for the confusion.

Paul Bartz

- -----Original Message-----
From: Bartz, Paul
To: 'gmcmotorhome'
Sent: 2/2/99 11:31 AM
Subject: RE: GMC: Spark plugs & Gap

Emory:

If you're using the HEI distributor, the recommended plug gap is 0.060.
Otherwise, I'm told you'll probably suffer distributor damage.

Early models had a none-HEI distributor and used the 0.080 plug gap.

Paul Bartz

From: EMERYSTORA [mailto:EMERYSTORA]
Sent: Tuesday, February 02, 1999 11:25 AM
Subject: GMC: Spark plugs & Gap

A few days ago someone posted a question regarding spark plugs for the
GMC.
I have a 455 with the HEI ignition. The manual show a gap of .080 but I
have been told and read that I should use .060 and by others .045. Has
anyone tested different gaps and, if so, what have your results been?
 
With JR Slaten's help, let me make a correction to the below information:

Page 6Y-44 of the X-7525A shop manual, which pertains to the none HEI
ignition system, calls for a plug gap of 0.040".

Page 6Y-33 of the X-7725 (77 & 78 supplement) shop manual lists a plug gap
of 0.080" for the 77 455 ci engine and the next page specifies a plug gap of
0.060" for the federal version of the 403 ci engine and 0.080" gap for the
California version of the 403 ci engine.

Word has it that a plug gap of 0.060" is recommended for both engines having
an HEI ignition system.

Sorry for the confusion.

Paul Bartz

- -----Original Message-----
From: Bartz, Paul
To: 'gmcmotorhome'
Sent: 2/2/99 11:31 AM
Subject: RE: GMC: Spark plugs & Gap

Emory:

If you're using the HEI distributor, the recommended plug gap is 0.060.
Otherwise, I'm told you'll probably suffer distributor damage.

Early models had a none-HEI distributor and used the 0.080 plug gap.

Paul Bartz

From: EMERYSTORA [mailto:EMERYSTORA]
Sent: Tuesday, February 02, 1999 11:25 AM
Subject: GMC: Spark plugs & Gap

A few days ago someone posted a question regarding spark plugs for the
GMC.
I have a 455 with the HEI ignition. The manual show a gap of .080 but I
have been told and read that I should use .060 and by others .045. Has
anyone tested different gaps and, if so, what have your results been?
 
>HEI systems originally specified .080" plug gap, but it was found that
the
>voltage required to jump such a wide gap under load was so high it
tended to
>burn holes through the distributor rotor, plug wires, etc. Later GMC
products
>reduced the recommended...

Rick:

Last fall I installed new plugs, plug wires (fat ones), distributor cap,
rotor, coil (GMC O.E.), and MSD's multi-spark ignition. Not knowing any
better, I followed the specs in the owner's manual and set gaps at
0.080".

Do you think my rotor etc. will be OK until next regular plug change or
would you pull the plugs and regap now?

Richard
 
Richard,
The .080 was completely new to me as well. Actually another mark on the wall
for this list :-)
I've been running the .080 gap for 230+k.

However, I'm going to change to .060 before the next trip even though I
think it's hard to fathom that all will come crashing down in the next 5 or
10k.

It's just that once I know about a problem or potential problem I'm going to
fret over it every mile and every miss, cough or hiccup.

That means that even if the wheels fall off it'll be because I didn't
re-gap.

If you're not the frettin' type, flip a coin.

My pennies' worth

Heinz
'76 Transmode
www.bytedesigns.com/gmc



>Last fall I installed new plugs, plug wires (fat ones), distributor cap,
>rotor, coil (GMC O.E.), and MSD's multi-spark ignition. Not knowing any
>better, I followed the specs in the owner's manual and set gaps at
>0.080".
>
>Do you think my rotor etc. will be OK until next regular plug change or
>would you pull the plugs and regap now?
>
>Richard
>
>
 
>I've been running the .080 gap for 230+k.

230+? That's good enough for me. Guess I should be OK until the next
spark plug change then, shouldn't I, Heinz.

When I bought these plugs last August, the first store told me the plugs
listed in my owner's manual had been superseded by a new number - same
heat range but I noticed that they came gapped to .060".

Wanting to go "by the book," I went to the next parts store and was told
the same thing. But they had 8 of the old ones left, so I took them.

Richard

>Richard,
>The .080 was completely new to me as well. Actually another mark on the
wall
>for this list :-)
>
>However, I'm going to change to .060 before the next trip even though I
>think it's hard to fathom that all will come crashing down in the next
5 or
>10k.
>
>It's just that once I know about a problem or potential problem I'm
going to
>fret over it every mile and every miss, cough or hiccup.
>
>That means that even if the wheels fall off it'll be because I didn't
>re-gap.
>
>If you're not the frettin' type, flip a coin.
>
>My pennies' worth
>
>Heinz
>'76 Transmode
>www.bytedesigns.com/gmc
 
Plug itself... same number and just .060 or different plug/heat-range?

TIA - Heinz

>
>> Do you think my rotor etc. will be OK until next regular plug change or
>> would you pull the plugs and regap now?
>
>Richard,
> If your plug wires are top quality and in good shape, and since rotors
are
>cheap, I'd probably take a chance. (But I'd carry a spare rotor with me.)
It
>might be interesting to see whether you notice any performance difference
when
>the plug gap is changed.
> Failure symptons include misfire/bucking under HEAVY load.
> HTH.
>
>Rick Staples
>'75 Eleganza
>Louisville, CO
>
>
>
 
You can run .080" of gap IF you have very good 8mm wires and a premium cap
and rotor. It is still tough on the system however and .060" works as good
and doesn't put your ignition system at risk. I have seen what .080" gap
will do, opened up the engine compartment at night and it looks like
christmas lights going off as the high voltage jumped through the wires to
the valve covers or anything where else it could find a ground. Bet those
that are running .080" of spark plug gap are having more problems and
changing their wires, caps and rotors more often than those that run .060"
of gap.

When I got my coach the distributer cap had holes burned through it.

Fellows GM changed to the .060" gap for the GMC, but as Arch says its your
money and your choice if you want to use .080" of gap on the spark plugs.

>>I've been running the .080 gap for 230+k.
>
>230+? That's good enough for me. Guess I should be OK until the next
>spark plug change then, shouldn't I, Heinz.
>
>When I bought these plugs last August, the first store told me the plugs
>listed in my owner's manual had been superseded by a new number - same
>heat range but I noticed that they came gapped to .060".
>
>Wanting to go "by the book," I went to the next parts store and was told
>the same thing. But they had 8 of the old ones left, so I took them.
>
>Richard
>
>
>>Richard,
>>The .080 was completely new to me as well. Actually another mark on the
>wall
>>for this list :-)
>>
>>However, I'm going to change to .060 before the next trip even though I
>>think it's hard to fathom that all will come crashing down in the next
>5 or
>>10k.
>>
>>It's just that once I know about a problem or potential problem I'm
>going to
>>fret over it every mile and every miss, cough or hiccup.
>>
>>That means that even if the wheels fall off it'll be because I didn't
>>re-gap.
>>
>>If you're not the frettin' type, flip a coin.
>>
>>My pennies' worth
>>
>>Heinz
>>'76 Transmode
>>www.bytedesigns.com/gmc
>
>
>
>
Tom & Marg Warner
Vernon Center NY
1976 palmbeach
 
This clears up the whole issue for me. Thanks, Tom.

Richard

- -----Original Message-----
From: Thomas G. Warner
To: gmcmotorhome
Date: Thursday, February 04, 1999 6:06 AM
Subject: Re: GMC: Spark plugs & Gap

>You can run .080" of gap IF you have very good 8mm wires and a premium
cap
>and rotor. It is still tough on the system however and .060" works as
good
>and doesn't put your ignition system at risk. I have seen what .080"
gap
>will do, opened up the engine compartment at night and it looks like
>christmas lights going off as the high voltage jumped through the wires
to
>the valve covers or anything where else it could find a ground. Bet
those
>that are running .080" of spark plug gap are having more problems and
>changing their wires, caps and rotors more often than those that run
.060"
>of gap.
>
> When I got my coach the distributer cap had holes burned through it.
>
>Fellows GM changed to the .060" gap for the GMC, but as Arch says its
your
>money and your choice if you want to use .080" of gap on the spark
plugs.
>
>
 
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