Spark Plug Protrusion into Head?

[AnthonyG]

Thx for all the work on this tubman! Much appreciated!

[flatjack9]

On a set of Offy heads I used spacers with the N5C plug measuring a total of .210 consisting of spacers and a second spark plug gasket.
as noted by Tubman, plug depths will vary from cylinder to cylinder. Quality control is not the best.

[tubman]

Ya' know, after thinking this over, the "N" series Champions (or equivalent) may just be the correct plugs for these. Add and extra plug washer, and everything should fall into place, eliminating the need for spacers, etc. Don't really know if it's the optimum solution, but that's the first thing I'll try when I use these heads. I do know I want all of the threads engaged that I can with aluminum heads.

[flatjack9]

An extra plug washer won't be near enough. Read above.

[GOSFAST]

Originally Posted by flatjack9

An extra plug washer won't be near enough. Read above.

"Nailed" that one Jack, probably need a "hundred" or so! Don't have the time to figure the exact number out??

Thanks, Gary in N.Y.

P.S. I would think after 120+ replies and over 3200 views some sort of decision would have been made at this point??

[flatjack9]

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I've made my decision to use spacers and one extra plug washer totaling .210. Makes for a good fit.

[AnthonyG]

I had a friend make copper spacers for the 3/4” reach plugs. .19” thick plus the existing compression gasket works on mine. Used Autolite A3924 Spark Plugs dimensions for ref. Which r recommended for the Edelbrock heads. Reinstalling head & think all will work ok. Fingers crossed

[Bored&Stroked]

You will have no issues . . . should be a good solution

[AnthonyG]

Thought I’d show what the spark plug w .19” spacer plus supplied compression washer looked like installed in head. I like it. Thx all for good discussion & all the knowledge!

[Bored&Stroked]

Threads look great - just make sure that 'extended tip' doesn't hit the valve. I don't tend to run extended tip plugs (due to very high valve lifts) - just something for you to check!

On the other hand, if you're going to rev the heck out of it and don't have a tach - then run extended reach plugs. When you FLOAT the valves, they'll hit the plugs and close the gaps, which acts like a 'mechanical rev limiter' . . . ask me how I know these things! LOL

[AnthonyG]

Lol, got Bored&Stroked, should have added the plug is not the ones I’ll be using, just a 14mm 3/4 reach I had measured for depth of thread. I’ll be using the recommended Autolite 3924 used in the Edelbrock 8BA heads

[Bored&Stroked]

All good my friend . . . I think you are on a solid tract . . .

[Chopped29Tudor]

Originally Posted by GOSFAST

Hi Anthony, no good, needs to be addressed?

This has been an ongoing issue with ALL the different vendors with the aluminum heads. Some call for .437" reach, others .750", we find them all over the place?

How long is that plug from the gasket surface to the very first thread??

Thanks, Gary in N.Y.

P.S. This has been an ongoing issue with many of the aftermarket alum heads! We actually make our own "spacers" (photo below) to correct the plug depths!

Im just now figuring out this problem....Offy heads...cant get the right plugs. I see your spacers. If I need a 5/8 reach and I am using 3/4 plugs, it seems I need spacers that are .125. Is that what yours are? If so, how do I get a set? Thanks

[tubman]

Unfortunately, Gary (GOSFAST) is no longer with us. You are correct; Offenhauser heads are problematic, in that there seem to be no spark plugs that fit them correctly. I believe that "flatjack9" on this forum may have the spacers you need. Hopefully, he will chime in.

I have been thinking about this and you may consider having the head "spot-faced" on the exterior to allow the use of 1/2" reach plugs.

[Tim Ayers]

Of course, I didn't check this until after the motor was together. Ugh. Plug holes are .750". NGK BL-4's are way too short.

I'll figure out the spacer deal, but what is the NGK plug that works for this situation?

[Ronnieroadster]

The 3/4 inch reach NGK plug number is B4ES. If a spacer is needed I simply add another spark plug washer. Works perfectly for any high lift cam applications.
Ronnieroadster

[Tim Ayers]

Originally Posted by Ronnieroadster

The 3/4 inch reach NGK plug number is B4ES. If a spacer is needed I simply add another spark plug washer. Works perfectly for any high lift cam applications.
Ronnieroadster

Thanks Ronnie. Plugs on order and will do the washer trick.

Also found some ARP washers that are .120" thick. Will order those too, just to have a few options to index them correctly.

[Bored&Stroked]

Hey Tim - what heads are you running? Newer Edelbrocks, or?

I would think you'd not need any extra spacers on the modern versions of the Edelbrock heads - as they're designed for 3/4" reach plugs. Just use a very small amount of anti-seize on the threads.

[Tim Ayers]

Originally Posted by Bored&Stroked

Hey Tim - what heads are you running? Newer Edelbrocks, or?

I would think you'd not need any extra spacers on the modern versions of the Edelbrock heads - as they're designed for 3/4" reach plugs. Just use a very small amount of anti-seize on the threads.

No, repop Cyclones. The hole depth is +/-.625". I tired to post a pict, but the file was too large. I have a set of new block letter Edlebrocks on the shelf in case I need to swap.

For a number of reasons, I would not have used these Cyclones if I was to do it again. They have some porous areas and are weeping at the two casting nubs on each head. I'm going to run some silicon silicate to hopefully stop those weeps coming from the casting nubs.

I wanted pre-war heads and these were originally made just before the war.

[Bored&Stroked]

In NGKs, I don't like to run a heat range of '4' (a bit too hot for me) - much prefer a '6' for a performance street engine. NGK has a whole host of .750 reach plugs - with various electrode designs, heat ranges, different materials/cores, etc. You might checkout the NGK 7910 - which is a heat range of 6. Another number that I used to use is a B6ES . . . which can be cross-referenced to a lot of different plugs.

Another option is a R5671A-7 - which is a racing plug, but it is in a heat range of '7' - which is a bit cooler - though their racing plugs don't come much hotter than this (for obvious reasons).

Keep in mind the nomenclature for NGK is backwards from Champion (when it comes to heat range). The lower the number, the hotter for NGK.