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Spark Plug Gap
Posted by: dingo50 ()
Date: August 07, 2017 10:37AM

I found this on the internet. I have a 1964 110 HP engine, it lists the gap at .030. Everywhere else lists the gap at .035. Does anyone have knowledge of this discrepancy?

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Re: Spark Plug Gap
Posted by: RobertC ()
Date: August 07, 2017 01:08PM

Your data sheet matches the specs in the GM shop manuals - for the standard point distributors.

The "low" hp (80 / 95) engines were specified AC 46 FF plug with a gap of .035

The "high" hp (110 / 140 / 180) engines were specified AC 44FF plug with a gap of .030

You will probably get varying opinions on point gap.

I have gapped my plugs at .030 for the past 40+ years with no issues 110 / 140hp engines).

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Re: Spark Plug Gap
Posted by: cepak ()
Date: August 07, 2017 01:34PM

When I had the Pertronix Ignitor II with Flamethrower II coil installed on my 102hp engine, I was able to open the spark plug gap to .045 and got a wee bit
better gas mileage.


Tom Cepak
Fort Worth, TX

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Re: Spark Plug Gap
Posted by: dingo50 ()
Date: August 07, 2017 01:39PM

The engine has AC R44FF plugs as you say, No points, Flame Thrower II ignition. The .030 plug gap seems to be an obscure setting, not well documented but it makes sense that the higher compression engines might use a different gap. Other charts list .035 gap for all Corvair engines. I am going to try .030 gap just for fun.

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Re: Spark Plug Gap
Posted by: curt ()
Date: August 07, 2017 01:41PM

46FF---Hoter plug than 44FF
42FF cooler yet

These are AC plugs

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Re: Spark Plug Gap
Posted by: Frank DuVal ()
Date: August 07, 2017 02:18PM

Obscure? It is in all the shop and owners manuals I have read for the 164 cu in engine. 110 and up HP gets .030" gap.

145 cu in owners stick with .035 for all HP. Well, that's what the shop manual says, I see the chart above sticks with all high HP engines get .030". OK, now it is confusing.eye popping smiley I'll stick with GM charts for now.

Higher voltage will fire through a larger gap. This is why "they" went to HEI and gaps of .045" to .060". This also fires leaner mixtures.

Frank DuVal

Fredericksburg, VA

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Re: Spark Plug Gap
Posted by: RobertC ()
Date: August 07, 2017 02:18PM

dingo50 Wrote:
-------------------------------------------------------
> The .030 plug gap seems to be an obscure setting, not well
> documented

Obscure LOL... It (.030 gap) is in the GM Shop Manuals.

You need to do more through research.

For an Igniter, you can use .035, maybe even .040 - I do not know what the specs are for an Iigniter.



Edited 1 time(s). Last edit at 08/07/2017 02:22PM by RobertC.

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Re: Spark Plug Gap
Posted by: jjohnsonjo ()
Date: August 07, 2017 03:00PM

Over .035 may be OK for a NA engine, if you go more than that with a turbo and a stock distributor cap it will cross fire inside the cap.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa

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Re: Spark Plug Gap
Posted by: dingo50 ()
Date: August 07, 2017 10:55PM

Truer words were never spoken.thumbs up

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Re: Spark Plug Gap
Posted by: BobV66Vair ()
Date: August 08, 2017 10:10AM

I recently bought a set of AC 44F plugs for my 140. I noticed that the thread length on the plugs I removed (installed by PO) were much longer than the new plugs. I am now concerned that either the old plugs were extending into the combustion chamber, possibly causing ignition to the piston, OR the new plugs will leave some of the heads threads uncovered, leading to damage.

Anyone seen this before? The old plugs were Autolite.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Spark Plug Gap
Posted by: MattNall ()
Date: August 08, 2017 10:22AM

Corvair and Aircooled VW / Porsche use 1/2" of threads...

One type of AC F or FF have 1/2" reach.... but are missing one thread...

You just use a thread chaser to clean the hole before going to full threads...

Most common mistake is the use of 3/4" reach plugs for later model Chevy inline 6's.... will lock up engine ...

Always was good to buy a locked engine and only have to change plugs!





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Spark Plug Gap
Posted by: MattNall ()
Date: August 08, 2017 10:22AM

Corvair and Aircooled VW / Porsche use 1/2" of threads...

One type of AC F or FF have 1/2" reach.... but are missing one thread...

You just use a thread chaser to clean the hole before going to full threads...

Most common mistake is the use of 3/4" reach plugs for later model Chevy inline 6's.... will lock up engine ...

Always was good to buy a locked engine and only have to change plugs!





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Spark Plug Gap
Posted by: Frank DuVal ()
Date: August 08, 2017 11:47AM

FF Fully Threaded
F Missing first thread
Both 1/2" length

Avoid any with an S suffix for extended tip. Also avoid the Champion (don't know P/N) with extended tip.

Frank DuVal

Fredericksburg, VA

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Re: Spark Plug Gap
Posted by: dingo50 ()
Date: August 08, 2017 11:14PM

The right bank of the engine developed a slight misfire here and there. It sounded like a spark plug miss. That is why I have been researching spark plugs and gaps. I finally broke down and bought a set of NGK B5HS. They were gaped at .028, I set the gap at .035 and the engine smoothed right out.

The AC plugs that were in the engine looked fine, good burn color but apparently they had issues.

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Re: Spark Plug Gap
Posted by: JimBrandberg ()
Date: August 09, 2017 06:16AM

Matt has good advice that bears repeating!
Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Spark Plug Gap
Posted by: phill66 ()
Date: August 13, 2017 06:01AM

Per Frank DuVal:
>Avoid any with an S suffix for extended tip.

I've used the NGK B6HS gapped at 0.030 in my '68 110hp for thousands of miles
with no issues. If you perform a search of "spark plugs" on the Forum, I believe
you'll find it is one of the recommended spark plugs.

Am I doing something wrong?

Here's what the NGK technical info states for spark plug gap:

The electrode gap of a spark plug dictates the spark magnitude. An incorrect
electrode gap may affect engine performance as the spark magnitude may be
insufficient to ensure complete combustion of the air­fuel mixture. Modified
engines with higher compression or forced induction will typically require
smaller electrode gap settings
(to ensure ignitability in these denser air/fuel
mixtures) as the voltage requirement at the electrode gap is increased due to
higher combustion pressures. As a rule, the more power you are making, the
smaller the gap you will need.


If I remember correctly, per the shop manual, the 110hp engine has an OEM
compression ratio of 9 to 1 and .030 spark plug gap. I think that is a fairly high
compression ratio. Therefore, the above tech info that higher compression will
typically require a smaller electrode gap setting applies.

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Re: Spark Plug Gap
Posted by: cnicol ()
Date: August 13, 2017 06:17AM

phill66 Wrote:
-------------------------------------------------------
> Per Frank DuVal:
> >Avoid any with an S suffix for extended tip.
>
> I've used the NGK B6HS gapped at 0.030 in my '68

Craig replies:
Frank's comment related to AC-Delco spark plug numbering only.

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later

+17 Tons of parts

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Re: Spark Plug Gap
Posted by: phill66 ()
Date: August 13, 2017 06:50AM

Thanks for clarifying cnicol. Look's like I'm not
damaging my engine after all.

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Re: Spark Plug Gap
Posted by: jjohnsonjo ()
Date: August 13, 2017 11:11AM

The extended tip in NGK is "P" as in NGK BP5HS for projected tip.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa

Image and video hosting by TinyPic

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Re: Spark Plug Gap
Posted by: phill66 ()
Date: August 13, 2017 11:22AM

Thanks for the detail tech info on NGK plugs jjohnsonjo. I'll stick with the B5HS.

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