Navarro heads and spark plugs

[hombres ruin]

Hey guys I am about to put a set of Navarro aluminum heads on my 41 ford(stock cam) I run NGK 6BL plugs at the moment , does anyone know if that plug has the correct reach? If not what are you guys using?

[Ken/Alabama]

I’ve got Autolite 216 in mine for the last 25 years.

[tubman]

I'm not familiar with Navarro heads, but if they're like all of the other brands of aluminum heads I have seen, I'll bet they require a longer than stock reach plug. Aluminum simply is not as strong as cast iron and needs more threads.

It's pretty simple to get a couple of different reach plugs and screw them into the head and look at the bottom side of the head. It should be obvious which are too short or too long. It would also be a good idea to check for plug/piston interference when doing final installation of the heads. Just screwing in a set of stock reach plugs and assuming they are correct would not be a good idea. Hopefully they are not like Offenhauser heads that don't have a commonly available plug that fit them and require the use of spacers.

[aussie merc]

ok tubman you raised the question what plugs do offenhauser say their heads require [ie thread x reach ]

[hombres ruin]

I agree Tubman. Checking for clearance is a definite . The Navarro heads aren’t as think as the Offenhauser and I know the Navarro are nearly identical to the stock. How much reach is enough so as not to cause interference?

[tubman]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by aussie merc

ok tubman you raised the question what plugs do offenhauser say their heads require [ie thread x reach ]

See this thread for a complete (and lengthy) discussion of the problems with Offenhauser heads : https://www.fordbarn.com/forum/showt...ht=offenhauser.

The final conclusion is that the heads require a 5/8 reach plug which is not made in 14 MM and that a 3/4" reach plug with a spacer approximately .2" thick and an extra washer would be correct. Check the thread, though.

[tubman]

Originally Posted by hombres ruin

I agree Tubman. Checking for clearance is a definite . The Navarro heads aren’t as think as the Offenhauser and I know the Navarro are nearly identical to the stock. How much reach is enough so as not to cause interference?

Since I don't have access to any Navarro heads, I don't really know. If "think" in your post should be "thick", then I would guess 1/2" reach plugs, or perhaps 7/16". (I may also be way off base and stock reach plugs may be correct.) Put various reach plugs in, torque 'em down and check the bottom of the head. It should look like this :

[hombres ruin]

Originally Posted by tubman

Since I don't have access to any Navarro heads, I don't really know. If "think" in your post should be "thick", then I would guess 1/2" reach plugs, or perhaps 7/16". (I may also be way off base and stock reach plugs may be correct.) Put various reach plugs in, torque 'em down and check the bottom of the head. It should look like this :

Thanks Tubman.. yep it was thick I meant to say . I will do as you advised and see what I get. Thanks for the pic appreciate it.

[tubman]

Let us know what you find out. From the amount of responses to your thread, I believe that it will be new, needed knowledge..

[HIGHTOWER611]

I emailed Mike Herman about this a few years back and he said, "I use autolite 216"

[tubman]

Pardon my ignorance, but who is Mike Herman?

[Bored&Stroked]

Mike Herman is one of the owners of H&H flatheads.

I run original Navarro center outlet heads on my 32 Cabriolet engine (they're new - have not been milled). I have a cam that lifts .420 - and am running .050 thick head gaskets. There is no interference with the valves and plugs that I run - which are NGK B6L - with a reach of 7/16.

I did have to rework the top of the combustion chambers - the 'eyebrow area' - to obtain a bit more valve to head clearance - about .060. Keep in mind that the valves are canted on Ford Flatheads, they are angled toward the bore . . . giving you more valve to head clearance the closer to the bore you get (on most heads). For additional valve clearance, if "fly cutting" is done, it really should be done at the valve angle - and not parallel to the deck surface.

Some Fun Info: Back in the day, Edelbrock (and probably others) shaped the chamber areas above the valves to follow the valve angle - and even had a left vs right head (as the angles are different). I liked their older chambers a lot more than I like their newer chambers (too much volume / CCs today).

Now Days: Edelbrock changed their chambers (above the valves) quite a few years ago - they are no longer cast like they were and there is really more chamber volume around the valves than is needed. They also increased the depth over the valves - probably to reduce the number of calls related to "my valves are hitting my heads".

[hombres ruin]

I used Autolite 216 plugs in aluminum Navarro heads and the used NGK 6BL in the same heads and this is why I got. The NGK had more reach . Is this enough ? Or do I need more protrusion? First pic is Autolite the second pic is NGK

[51 MERC-CT]

Originally Posted by hombres ruin

I used Autolite 216 plugs in aluminum Navarro heads and the used NGK 6BL in the same heads and this is why I got. The NGK had more reach . Is this enough ? Or do I need more protrusion? First pic is Autolite the second pic is NGK

This is what stock reach (7/16 ") plugs look like in stock heads.
Most aftermarket aluminum heads use a plug with much longer reach.
Unless running shrouded plugs is some new magical way to go.

[hombres ruin]

Originally Posted by 51 MERC-CT

This is what stock reach (7/16 ") plugs look like in stock heads.
Most aftermarket aluminum heads use a plug with much longer reach.
Unless running shrouded plugs is some new magical way to go.

That’s what I need .. more reach . I will find a plug with longer reach. Shrouded isn’t the way to go

[Bored&Stroked]

Keep in mind that my Navarro heads were original ones from Barney. Who knows how H&H is doing the machine work and how deep the plug threads are today?

You'll have to measure the thread depth and determine the best plug. You really don't want the plug "down in the hole" and shrouded, so I'd run a longer reach plug. There are some 1/2" reach plugs - and a TON of 3/4" reach plugs. You may find that you need some thick copper washers/gaskets to use the 3/4 plugs - so they don't protrude too much. You don't want spark plug threads out in the chamber - can create hot-spots and detonation issues - and potentially get "whacked" by your valves (depending on cam, etc.).

Also, contact H&H and see if they modified the patterns and machining for 3/4" plugs (like Barney did on his High-Dome versions).

[tubman]

Let me get this straight : This Mike Hermann of H & H flatheads recommended plugs that are obviously incorrect (Autolite 216's) for their own heads?

There has to be a misunderstanding someplace.

[tubman]

Be careful; there seems to be a problem in this area with the new Navarro heads from H & H. At least Gary ("GOSFAST") thought so. Although he is no longer with us, he was a well respected engine builder in his day.

Check this post out : https://www.fordbarn.com/forum/showt...ro#post1818558.

[hombres ruin]

Originally Posted by tubman

Be careful; there seems to be a problem in this area with the new Navarro heads from H & H. At least Gary ("GOSFAST") thought so. Although he is no longer with us, he was a well respected engine builder in his day.

Check this post out : https://www.fordbarn.com/forum/showt...ro#post1818558.

The heads now from H & H are cast better and are machined in a new shop, they look pretty nice and clean. No rough spots, bad machine work. I think he took notice and cleaned it up a lot.

[tubman]

Originally Posted by hombres ruin

The heads now from H & H are cast better and are machined in a new shop, they look pretty nice and clean. No rough spots, bad machine work. I think he took notice and cleaned it up a lot.

Gary's problem was with plug reach, the very thing you are asking about, so I felt a "heads up" was in order. I sure hope that they have cleaned up their act; "GOSFAST" seemed to be quite disappointed. Have you tried a 1/2" reach plugs? Champion "L" series or equivalent. If they're not long enough the next step up is 3/4" reach; Champion "N" series or equivalent.