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BUGGED11111
Samba Member
Joined: February 03, 2006
Posts: 1821
Location: Oregon
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 Posted: Thu May 13, 2021 5:36 pm Post subject: Spark plugs |
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I'm helping someone with their 73 bug. He has a newer VW of Mexico engine on it. This is the first time I've seen one and I notice he has longer 3/4 inch reach spark plugs on it as opposed to the standard 1/2 inch reach plugs.
Any one have any insight on this? Is there a change in the head design that requires a 3/4 inch reach plug?
Also interesting, there's no thermostat on it or way to mount one because there's no mounting hole in the case, but that's for another day. |
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Glenn 
Mr. 010
Joined: December 25, 2001
Posts: 76940
Location: Sneaking up behind you
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| Posted: Thu May 13, 2021 5:39 pm Post subject: Re: Spark plugs |
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Yes... newer Mexican heads use 3/4" plugs.
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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
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BUGGED11111
Samba Member
Joined: February 03, 2006
Posts: 1821
Location: Oregon
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| Posted: Thu May 13, 2021 5:50 pm Post subject: Re: Spark plugs |
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| Glenn wrote: |
| Yes... newer Mexican heads use 3/4" plugs. |
I'm just curious what design change happened that caused that change.
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Glenn
Mr. 010
Joined: December 25, 2001
Posts: 76940
Location: Sneaking up behind you
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| Posted: Thu May 13, 2021 5:58 pm Post subject: Re: Spark plugs |
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| BUGGED11111 wrote: |
| Glenn wrote: |
| Yes... newer Mexican heads use 3/4" plugs. |
I'm just curious what design change happened that caused that change.
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Updated design, longer plugs are less prone to getting blown out. Some aftermarket heads use a 12mm plug over the older 14mm. Again the heads are stronger int he spark plug area which tends to get cracks.
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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
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BUGGED11111
Samba Member
Joined: February 03, 2006
Posts: 1821
Location: Oregon
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| Posted: Thu May 13, 2021 6:06 pm Post subject: Re: Spark plugs |
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| Glenn wrote: |
| BUGGED11111 wrote: |
| Glenn wrote: |
| Yes... newer Mexican heads use 3/4" plugs. |
I'm just curious what design change happened that caused that change.
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Updated design, longer plugs are less prone to getting blown out. Some aftermarket heads use a 12mm plug over the older 14mm. Again the heads are stronger int he spark plug area which tends to get cracks. |
So hypothetically (as in not going to do it) if you put a 1/2" plug in, it would still function or is the head design different so they won't work?
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Glenn
Mr. 010
Joined: December 25, 2001
Posts: 76940
Location: Sneaking up behind you
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| Posted: Thu May 13, 2021 6:12 pm Post subject: Re: Spark plugs |
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The plug will be recessed 1/4" into the head.
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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
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Cusser
Samba Member
Joined: October 02, 2006
Posts: 31379
Location: Hot Arizona
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| Posted: Thu May 13, 2021 7:38 pm Post subject: Re: Spark plugs |
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| Glenn wrote: |
| The plug will be recessed 1/4" into the head. |
And the non-used threads could get buggered up and cause issue for someone later trying to use 3/4" plugs.
Use 3/4".
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297 |
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ashman40
Samba Member
Joined: February 16, 2007
Posts: 15987
Location: North Florida, USA
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| Posted: Thu May 13, 2021 11:09 pm Post subject: Re: Spark plugs |
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| BUGGED11111 wrote: |
| So hypothetically (as in not going to do it) if you put a 1/2" plug in, it would still function or is the head design different so they won't work? |
I know you said you were not going to do it... but don’t do it.
The above pic shows what happens when the wrong reach (length) spark plug is used.
Note the build up that forms inside the spark plug hole. At some future point when someone realizes the correct spark plug for the head is are 3/4” reach ones and they install it... when they hit the build up inside the threads of the plug hole they will either stop and think the plug is fully in when it isn’t resulting in a loose plug and low compression... or they will continue to tighten the plug and push thru the build up. If they are lucky they will break it free and the plug will seat fully. If they are not lucky, the inner edge of the hole will break off and fall into the cylinder. This will encourage the head to crack at the spark plug hole. Just use the correct spark plugs for your head to avoid future headache..
From the pic you can also guess that too long a spark plug is also bad. The build up tends to make spark plug removal very difficult. The spark plugs are made from steel. The heads are made from magnesium / aluminum. Which do you think will break first? 
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AshMan40
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'67 Beetle #1 {project car that never made it to the road  }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!} |
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Igpoe
Samba Member
Joined: February 24, 2019
Posts: 853
Location: South Boston, VA
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| Posted: Fri May 14, 2021 3:56 am Post subject: Re: Spark plugs |
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If his heads use 3/4" reach and 12mm diameter I recommend the plugs above unless he has a higher compression than normal. If he does have a fat motor he might need a cooler plug
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'73 super. |
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[email protected]
Samba Member
Joined: May 17, 2003
Posts: 4863
Location: Harmony, PA
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| Posted: Fri May 14, 2021 6:26 pm Post subject: Re: Spark plugs |
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| If it is an actual Volkswagen head, it should have a 14mm plug. A good 14mm 3/4 reach non-resistor plug would be an NGK BP6ES, or modern NGK number of 7333. |
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Glenn
Mr. 010
Joined: December 25, 2001
Posts: 76940
Location: Sneaking up behind you
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| Posted: Fri May 14, 2021 6:29 pm Post subject: Re: Spark plugs |
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| [email protected] wrote: |
| If it is an actual Volkswagen head, it should have a 14mm plug. A good 14mm 3/4 reach non-resistor plug would be an NGK BP6ES, or modern NGK number of 7333. |
BCP6ES (left) BP6ES (right)
The BCP6ES has a 5/8 hex heave vs the BP6ES 13/16
More clearance for large manifolds.
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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
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Igpoe
Samba Member
Joined: February 24, 2019
Posts: 853
Location: South Boston, VA
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| Posted: Sat May 15, 2021 3:52 am Post subject: Re: Spark plugs |
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| Glenn wrote: |
| [email protected] wrote: |
| If it is an actual Volkswagen head, it should have a 14mm plug. A good 14mm 3/4 reach non-resistor plug would be an NGK BP6ES, or modern NGK number of 7333. |
BCP6ES (left) BP6ES (right)
The BCP6ES has a 5/8 hex heave vs the BP6ES 13/16
More clearance for large manifolds. |
That's good info! Non-resistor plugs are becoming difficult and expensive to find.
Resistor plugs issue a weaker spark but you may need them in some of the high energy electronic ignitions. Your Bosch rotor under your OG distributor cap has resistance built-in.
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[email protected]
Samba Member
Joined: May 17, 2003
Posts: 4863
Location: Harmony, PA
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| Posted: Sat May 15, 2021 7:30 am Post subject: Re: Spark plugs |
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It’s been a while since I used a 14mm 3/4 reach plug, and I forgot all about the BCP6ES/4930!
The bakelite og plug wire ends also have resistors. I think that’s why VW spec’d non-resistor plugs. On the other hand, if you are using a modern set of plug wires without resistors, you may want to use plugs with them if you are having electrical noise issues. |
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