I rest my case 
Spark Plug thread length
Thread Starter
Intermediate
Joined: Apr 2006
Posts: 37
Likes: 0
From: Gilbert AZ
Spark Plug thread length
Hey everyone,
I went to Napa today to get a new alternator and decided to get stuff for a tune up as well. They gave me AC Delco 41-629 plugs (they told me it was factory spec), however, when I removed one of the existing I found that the thread on the existing is much shorter than on the AC Delco. I couldn't find a brand or part number on the existing plug.
Which one is right?
My car is an 87 coupe w/auto.
Thanks.
Delco on the Left, exisiting on the right.
I went to Napa today to get a new alternator and decided to get stuff for a tune up as well. They gave me AC Delco 41-629 plugs (they told me it was factory spec), however, when I removed one of the existing I found that the thread on the existing is much shorter than on the AC Delco. I couldn't find a brand or part number on the existing plug.
Which one is right?
My car is an 87 coupe w/auto.
Thanks.
Delco on the Left, exisiting on the right.
Team Owner
Joined: Jan 2003
Posts: 20,254
Likes: 221
From: Summerland B.C. Canada
The AC delco plugs they gave you are the correct length. It ran OK with those short plugs ??? 
I know for a fact that the length of the AC Delco plug is correct as i used them when i CC'ed my combustion chambers. They just reach the chamber.
I know for a fact that the length of the AC Delco plug is correct as i used them when i CC'ed my combustion chambers. They just reach the chamber.
Racer
Joined: Nov 2004
Posts: 445
Likes: 0
Originally Posted by vader86
The last set of Delco Rapidfires i bought had this problem, it cant be the right plug.
When I ordered them, I specifically asked for 87 al. head sp. plugs. These are what TLD sent me.
In fact, I bought 2 boxes of these R'fires and they are all long reach..
I only just took them out yesterday to check them, and must admit that the last couple of threads looked like they were protruding into the chamber....other than that, they looked fine..
Have I been lucky, or is this not going to be a problem...?
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
I'm running the 41-629 ACDelcos also, no problem. In fact you can go to the ACDelco website and verify these are the right plug, I did an they are. No problems. The plugs that were in the vette prior to this were Autolites, and they were much shorter.
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Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Oh yeah, one other thing, when I went to install I found one plug with a buggered thread, called the store and they had no more 41-629s, but they did have the ACDelco with the original plug number called out in the owners manual, so I took the plug with me and compared...they were the same length, just the old ACDelco number.