spark plug reach
 

Anyone have list of spark plugs showing their reach ? The reach as I understand it is the length of the threads from the gasket seat to the end of shell. Thank you Fordbarners.

Re: spark plug reach
 

I did a search on prior posts, and came up with Autolite 216 with a 7/16 reach, or 0.437, and Autolite 4634 with a 1/2" reach or 0,500. If you subtract the 0.060 for the gasket, that is a 0.440 reach on the 4634. Any other options out there ? 0.750 reach or 3/4" is too long for the Navarro heads I am using. Thank you Fordbarners.

Re: spark plug reach
 

"The Autolite 216 has a 7/16 reach. The Autolite 4634 has a 1/2 reach"

The above was a Fordbarn post, 2018. I have looked on line and checked with Advance Auto & Rock Auto, and there is no current listing or crossover for an Autolite 4634. Any suggestions ? Looking for and Autolite 1/2" reach plug for the Navarro head.

Re: spark plug reach
 

Isn't Navarro now sold by H&H?? Try contacting them for a recommendation??
Paul in CT

Re: spark plug reach
 

Google: Spark Plug Reach"Be sure to get a clear understanding of what each plug manufacturer means by the tern "spark plug reach". Definition seems to vary.
For instance, NGK GR4 2635 plug has a 3/4 in. reach. On this plug the 3/4 in. reach is measured from the surface of the body of the plug where the gasket sits to the bottom of the metal housing encapsulating the ceramic tip.

https://www.jegs.com/i/NGK-Spark-Plugs/739/GR4/10002/-1

It's shown on the NGK Long Reach Plug in this link.

http://www.ngk-sparkplugs.jp/english...q13/index.html

Re: spark plug reach
 

Unfortunately, The exhaust valve prevents the use of power tip plugs in most heads. The location of the ex valve near the exhaust was there to keep the spark plug clean. Back min the day you had to clean your plugs every 5/10,oo0 miles. the Edmonds heads located the plug between the valves sso a mpower tip can be used. As you saw in JWL's book he just moved the plug into the transfer area where it does the most good.

Re: spark plug reach
 

It appears both NGK and Autolite use the same method for measuring "reach". It is likely standard across all mfgs. It is from the base where the gasket rests to the end of the shell, (the part that surrounds the insulator & electrode.
So the question is what plug has a 1/2", or .500. ?
I can live with the plug location over the exhaust valve, although it is not ideal.. With a 1007B cam, the exhaust valve lift at it's zenith is .345.. So from the top of the valve to the plug seat in the installed head is .610. he thread depth in the Navarro head is .500. So with a .065 gasket, the reach is.435, which exposes about 1 thread which I will chamfer out. That leaves about .055 ckearance between the valve and electrode tip. Thank you Fordbarners.

Re: spark plug reach
 

We have custom shims to adjust the height of the plugs into the chambers?

Thanks, Gary in N.Y.

P.S, I sure hope those Navarro heads are not "new" ones, do a search up here, we checked some out recently. Totally disappointed in their quality or lack of it. Had a long discussion with H&H about them and ended up refusing to do the build with them?

Re: spark plug reach
 

Spark plug indexing washers available in different thickness.

Re: spark plug reach
 

I bought these heads from Barney before he passed away. What plugs have a 1/2" reach is the question. Anyone have a direct answer to the question instead of going round and round with out answering it.

Re: spark plug reach
 

I think this was covered in a previous thread (may have been a question by Tubman) and as I recall they didn't come up with any (1/2 inch reach spark plugs). I could be wrong, but the thread was fairly long on the topic.

Re: spark plug reach
 

See if any of this is helpful.

Mfirth: What about NGK B6HS-7534 plugs? 1/2" reach compared to say an Autolite 216 with 7/16" reach, which Offy recomends.

Tubman: Everything I remember tells me that 1/2" reach plugs are the correct fit for Offenhauser heads. Champion "L" series plugs are 1/2" reach. I have a bunch of Champion "L" series plugs and a set of never been altered/never been installed Offenhauser 8BA heads at my shop. I will go up tomorrow with my camera and screw some 1/2" reach plugs into these heads and take some pictures and get to the bottom of this.

Mfirth: Thanks Denny [tubman]. Will be anxious to see those pics. I read on the H A M B, i think about guys using NGK B6HS- 7354 1/2 ' reach in Offys & like'n them. Mike


The Offenhauser references are not correct, but they are references to 1/2 reach spark plugs.

Re: spark plug reach
 

Thank you JSeery. That confirms what I found doing some lengthy research. The Champion L78C has a .500 reach. I will get one and see how far the electrode protrudes from the end of the shell. If it's like the Autolite AL-7, the electrode is .120, which will clear the exhaust valve.

Re: spark plug reach
 

Using a new set of the Offy heads here for a measurement, the spark plug threads measure exactly .540" deep. As seen in the photos below. The .750" long plug and a .125" spacer sets the plugs at the preferred height!

Sometimes it's not as easy to get the correct plugs to work no matter what the mfr recommends! Don't forget you need the correct lengths AND the correct heat range! Offy's have always been a problem with plug lengths, this is why we made the custom spacers I mentioned above!

Thanks, Gary in N.Y.

P.S. If you use the .540" measured thread length and use a .060" gasket the plugs would have to measure some .600" long? Much easier in my opinion to use shims. I recommended to Vince and Tay out at Offy to make the new heads for the more popular .750" reach plugs, this was a couple years ago already!

Re: spark plug reach
 

Gary,

I believe the Offy heads come in 2 or 3 chamber volumes as you are no doubt aware. Would that also affect the reach of the same plug in the various head cc options?

Mike

Re: spark plug reach
 

When you get the right reach plug for the head thread depth, the right electrode and correct heat range, that's 80% of the battle. Then, either shims, counter boring the top of the thread in the head, or chamfering a thread or 2 out of the combustion chamber to unshroud the plug and prevent pre-ignition is a combination of comprises given the flatheads plug location over the exhaust valve. Some research, especially here on the barn, some machine shop skills, and dial indicator and you can solve the problem