Originally Posted by 69a (Post 2454087)

The Navarro heads that I have, in an engine supplied by H&H have the spark plug area too thick in the casting, about 4 threads to thick. The entire plug including the electrode is up inside the thread. The plugs get fouled every 500 to 1,000 miles. You can't put a longer plug in because the valve is too close. If he hasn't corrected this with the casting you will need to get some material removed.

Originally Posted by tubman (Post 2454102)

"Shoebox", didn't you have a pair of Edmunds heads that needed some work? If you still have them, are they both unusable, or just one? In my never ending quest to find usable Edmunds heads, I have accumulated a couple of odd extras. I just bought a set with a good left (US driver) side and a cracked right head. If you still have them, perhaps we should discuss what we have and maybe we can come up with a solution to your problems. Best case, you come up with a good set of heads; worst case, I might buy yours to add to my pile of culls. I think it might be worth looking into, as I am convinced of the superiority of the design of the Edmunds units.

And "69a", that is troubling to hear about the Navarro heads. If true, it brings the quality of the entire design in question. I have never paid much attention to the idea that the Navarro's are "one of the best flowing heads" since with flatheads all of the ports and valves are in the block. In my book, getting the most compression without hurting the flow too much is is the main concern. This has more to do with quench and flame front travel than any esoteric contouring of the head surface. I would suggest trying to unshroud the plugs by using the longest plugs possible and some minor contouring of the heads around the plug. One other thing I might suggest is using the proper length "surface gap" plug. These are usually found in 2 cycle outboard motors. I had a 276 Merc with Offenhauser heads years ago that I couldn't get the proper reach plugs for. I ended up using surface gap plugs out of a 65 HP Johnson "Loop-Charged" triple that worked very well. That engine had a complete MSD ignition system, so I had enough oomph to fire the plugs. The only problem I had was that the spark was so hot that in a year's time, it burned through the coil wire tower, ruining the cap. Other than replacing the cap once a year, it turned out to be a great setup.

Originally Posted by KiWinUS (Post 2454127)

Question. So if H&H built this engine what did Mike say about fouling plugs so often?

Originally Posted by Shoebox (Post 2454148)

I asked Mike about this subject, his response below.

On Jun 3, 2026, at 9:23 AM, Mike Herman <[email protected]> wrote:

 The electrode is not supposed to hanging out in the valve pocket or it will hit the valve

Originally Posted by KiWinUS (Post 2454155)

True with many different brand flathead heads. But what did he say about fouling plugs?

Originally Posted by tubman (Post 2454157)

Edmunds is the one exception I know of; I believe it is a huge advantage.

H&H is now marketing the Navarro heads; is that correct?

Originally Posted by Shoebox (Post 2454148)

I asked Mike about this subject, his response below.

On Jun 3, 2026, at 9:23 AM, Mike Herman <[email protected]> wrote:

 The electrode is not supposed to hanging out in the valve pocket or it will hit the valve

Originally Posted by Tim Ayers (Post 2454160)

It shouldn't be "hanging out" but it also shouldn't be tuck deep inside the threads of the head. If they are off the engine, you can get spark plug spacers to help you select the correct one so you can use common 3/4" reach plugs.

Now that I say that, are you sure they weren't reworked for 3/4" plugs? New Edlebrocks are recast this way.

Originally Posted by Tim Ayers (Post 2454160)

It shouldn't be "hanging out" but it also shouldn't be tuck deep inside the threads of the head. If they are off the engine, you can get spark plug spacers to help you select the correct one so you can use common 3/4" reach plugs.

Now that I say that, are you sure they weren't reworked for 3/4" plugs? New Edlebrocks are recast this way.

Originally Posted by tubman (Post 2454164)

A minor point, but wasn't it the Offenhauser heads that have been recently changed to use the longer plugs? There was an extended discussion on this board several years ago that came to the conclusion that there was no proper length plug currently available for Offenhauser heads and spacers were needed. I have a set of never-been-installed Offenhauser 8BA heads I bought new in the mid-90's that confirm this. The first set of finned heads I ever bought was a set of Edelbrock's in 1961, and they took a Champion "N" series plug even back then. I just bought a set of used Edelbrock's on eBay, and they take 3/4" reach plugs. I know; I measured them yesterday to determine which Time-Sert set I need to fix a bad plug hole. Jeez, are those things (Time-Serts) expensive.

Originally Posted by tubman (Post 2454164)

A minor point, but wasn't it the Offenhauser heads that have been recently changed to use the longer plugs? There was an extended discussion on this board several years ago that came to the conclusion that there was no proper length plug currently available for Offenhauser heads and spacers were needed. I have a set of never-been-installed Offenhauser 8BA heads I bought new in the mid-90's that confirm this. The first set of finned heads I ever bought was a set of Edelbrock's in 1961, and they took a Champion "N" series plug even back then. I just bought a set of used Edelbrock's on eBay, and they take 3/4" reach plugs. I know; I measured them yesterday to determine which Time-Sert set I need to fix a bad plug hole. Jeez, are those things (Time-Serts) expensive.

Originally Posted by KiWinUS (Post 2454184)

The latest update version of Edelbrock have fully CNC machined chambers.

Originally Posted by Tim Ayers (Post 2454186)

Yep

Originally Posted by KiWinUS (Post 2454187)

I have used several set.

Originally Posted by KiWinUS (Post 2454187)

I have used several set.