Spark Plug Protrusion into Head?

[Ol' Ron]

B & S, that's an impressive engine. I had a set of Grancoe with a similar combustion chamber, However the plug was in the stock location, theu were also a pop up design , so I used a 3 3.4 stroke piston on a 4" crank. This was my Bville engine, wonder what happened to it/ Last known location was Yuba city CA/

 

[GOSFAST]

Read an older thread w a lot of concern on spark plugs & aluminum heads, here’s a pic w spark plug in head from chamber side as I’ve got the right head off. For protrusion look ok? I’m using Auto lite 437 spark plugs & here’s a pic of protrusion into aluminum Offy Head.

Hi Anthony, plug lengths are really considered a "non-issue" here anymore, simply choose the plug you want to use, take the heads to a "decent" machine shop and tell him to "make it happen", this is one procedure we've been doing for years now, we check EVERY head we build with for the proper depths, every one! (See the photo below)

I don't understand why the aftermarket doesn't move the plug to the center of the transfer area and be done with it. This has allot of benefits, besides running into the exhaust valve. Run a power tip plug shorter flame front and shorter advance . economy and more. The original position over the exhaust valve was to keep the plug clean (burn off the carbon) . But the number of flathead cylinder heads sold is avery small percentage of the bottom line/ A wedge style combustion chamber and a corisponding wedge piston could give 9/10 compression in a 239 engine tha would still run on 87 oct. I tried to have EGGe make a set for me 20 years ago, but 600 bucks for the set was way beyond my means. But a few years they showed up at Bville. Sour grapes I know. but???

Hi Ron, hope all's well by you, go back up here and see where we evaulated those "new" Navarro heads, those things had so many issues we wouldn't have used them if we got them for "free", back when were checking them out (if you recall the Edelbrocks were still on a nationwide back-order) I had said to my customer here (Joe V.) that I wish the Chinese would go into production for these heads! After all, not any parts in them like guides, seats, valves, etc. Not even a simple helicoil, basically a casting with some machining that just needs to hold water??

We've tried for a long time speaking to Tay (Offenhauser) and Vince to effect some changes in the Offy heads, just another dead-end. They STILL haven't gotten around to making any new castings lately! Recently offered to put 10 heads on the shelf if they had any??

Good luck getting ANYONE to make a "change", we'll more than likely never see it happen.

Thanks, Gary in N.Y.

P.S. Here's a shot taken today showing 4 different plugs, different brands and different lengths, there's not a single plug here going to work in these new Offy heads without some modification, regardless of the "flycutting" fact that you see. Hard to see but there are plugs in all 4 holes!

 

[tubman]

Hi Anthony, plug lengths are really considered a "non-issue" here anymore, simply choose the plug you want to use, take the heads to a "decent" machine shop and tell him to "make it happen",

If you can't find an exact fit, I would at least try to find the longest plugs that I could. Sometimes the installation may need to be modified to fit exactly, but to modify (someone earlier mentioned "chamfer") the heads to use a, say, stock H10 or equivalent would be a mistake in my book, Threads in cast iron are stronger than those in aluminum. The original designers knew this, which is why most after market aluminum heads call for deeper than stock plugs. Most used heads I see have one or several Helicoils in them. I believe this is the result of installing H10's with a breaker bar by over enthusiast amateurs. Back when I raced snowmobiles (with aluminum heads), we always used the wimpy little stock spark plug wrench to avoid stripping the plug threads.

 

[AnthonyG]

Been looking for 14mm thread .625 reach plugs. I have only been able to find .625 reach in 12mm thread. Lots of 14mm w .750 reach. I think that will be too long & interfere w valve. I’m think I’m understanding GOFAST’s spacer now. Would be a .125 spacer ring on the spark plug thread to let the .750 reach fit at the desired protrusion of the .625 reach?

 

[Bored&Stroked]

B & S, that's an impressive engine. I had a set of Grancoe with a similar combustion chamber, However the plug was in the stock location, theu were also a pop up design , so I used a 3 3.4 stroke piston on a 4" crank. This was my Bville engine, wonder what happened to it/ Last known location was Yuba city CA/

Thanks Ron - coming from you that makes my day!

Here is a picture of the chambers in our FlatCad head - with ceramic coatings applied:

 

[tubman]

"AnthonyG", what kind (brand) of heads do you have? I don't think I've ever seen any that required a 5/8" reach plug.

 

[frnkeore]

In reviewing the spark plug links, I couldn't find a 5/8 reach plug, either. So,to get the plug to fit right, I think you should go with GOSFAST spacers, as your thinking.

 

[AnthonyG]

Offy’s as supplied by builder w the .437 reach w extended gap anvil plugs that r 3.5 threads short of flush to the inside surface

 

[AnthonyG]

The arc pedistal is flush to inside surface + .03 gap + thickness of anvil makes total penatration at approx .09

 

[Bored&Stroked]

Given that these heads have short-reach plugs (not like the new Edelbrocks with .750 reach plugs), I like to use all the threads in the head that I can - as this helps prevent wearing out the threads and stripping them (like when your plugs are too short).

On older/vintage heads, sometimes I just go ahead and put in steel Timeserts in all 8 - to give me a lot stronger threads (in steel). This is especially true if the plug threads are worn and maybe already not in prime condition.

 

[AnthonyG]

I think a .750 reach will work for the thread but might be too long for penetration but possibly w a non extended arc anvil it might work. I’ll bring head to the performance shop I deal w & true the fit on a few to see.

 

[Ol' Ron]

I used Offy heads to make my iwn combustion chamber, they are thicker than the Edelbrock's I mill the area over the valves at a 5 deg angle towards the top of the block, and the transfer area ar an 8 deg angle towards the cylinder. Using a 14 mm powertip plug and counter boring out the unused threads. This was all done by hand, The depth of the valve relief depended on cak lift/ These were all street engines (276ci). This way I could get the most compression. At one time I took a junk head and made a different trans fer angle on the cylinders and found that a 12 deg angle was best. However there isn't enough material in the head to do this and it lowers the CR. At 8 Degs you have less material removed flow is still very good and the CR is about ad high ad=s you can get it without adding material to the sides of the transfer aera. Another thing releve the angle at the end of the transfer area as well to 69* or better, This allows the AF to flow freely into the cylinder

I now have my tongue all tangled up, so I can't see what I'm sayin. Now I'll go look for some pics

 

[AnthonyG]

Put a NGK BPR7ES .750 reach has same extension from end of thread to full extension of anvil as the Autolite, 7/32”. The space to the heads gasket surface of .437 reach is .26”. The space to the heads gasket surface for the .750 reach is less than 1/32”. Pretty sure valve would smack the .750 reach.

 

[AnthonyG]

First pic in last Post is .750 reach almost no clearance 2nd pic here is .437 w .25 plus spacing.

 

[GOSFAST]

Hi Anthony, one more time, the Offy head in the photo on the left has two .060" plug-washers installed on a .750" reach plug (shown lying on the head). Looks good to go?

The Edelbrock head in the photo on the right has no shims with the .750" reach plug, only the "thin" conventional plug gasket. But we did "chamfer" all the plug holes in these heads.

The "double" copper gaskets will pose no adverse effect in the overall picture! And it may just be your easiest way out right now??

No matter what method you choose you want the plugs as "flush" as possible to the chamber, no plug "overhang" and no overly exposed threads into the chambers. Plug threads hanging into the chambers is the worst of the two.

Thanks, Gary in N.Y.

P.S. This isn't a "new" issue for us here, it's something we've watched closely for as far back as I can recall. I firmly believe that many builders/rebuilders pay little to no attention to this issue. It is something that is extremely important, could mean the difference between "stripped" plug holes or not later!

 

[mfirth]

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

 

[GOSFAST]

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

Just to keep the numbers straight here, we stock the 216 Autolite's, the thread length isn't .437", it actually measures .406" w/o the supplied washer and .343" with the washer in place! Obviously not counting the "tip" here.

Because of this spark plug issue with the Offy heads we try to avoid building with them when possible, but when we do we have the ability to make the necessary modification to make them work. many of our builds get new spark plug "repair-inserts" from the get-go. We know when they will be required.

Thanks, Gary in N.Y.

P.S. Anthony, the copper washers (.060") run about a 1.00/ea. With the heads in my photo we would need 16 pieces to make it happen. Before we do that when we need these heads on a build I would set them up for no washers. Not a big deal over here.

 

[AnthonyG]

Gary I’m in Stroudsburg Pa. where r u & if I get the heads to u what’s the cost to set up in ur shop?

 

[Mart]

I run Autolite 216s in my Offenhauser 8BA type heads. I chamfered a few threads off the bottom to unshroud the plugs. I guess I did it wrong. But I haven't encountered a problem thus far and it does run really well.

 

[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.

No offense intended, but all of this talk about "chamfers" and "spacers" should not be necessary. The engineers that designed these heads were not incompetent and would not have completely screwed up the spark plug holes on an otherwise successful design. It just makes no sense at all.