Spark plug reach in Aluminum Heads

[qmdv]

Offy heads

First pic is 3/4 inch reach


Second pic is 1/2 inch reach


Not sure what to do cus I think the 3/4 is too long and the 1/2 is a bit short. Never heard of 5/8 reach plug

tim

[19Fordy]

Would it be possible to shorten the reach of the 3/4 in. reach plug by using more washers or index washers?
http://www.summitracing.com/parts/stf-30500/overview/

[tubman]

What brand of heads? Gaskets on the plugs?

A little anecdote : Back in the early 60's I had a pair of Edelbrock heads, and the H-10's were obviously too short. Luckily, a friends dad was a rep for International-Harvester, and had access to all of the Champion books extant. We looked up "Alllard", some of which came with flatheads with aluminum heads. The book called out (I think) Champion L-5's for engines with aluminum heads (which rules out the Cadillacs, Chryslers, and Lincolns). I ordered a set and they fit perfectly. I thought they were 3/4 reach, but from your pictures, I don't know. Have you tried the test plug in all of the plug holes?

[4dFord/SC]

Not sure of the reach, but I use Autolite 437's in my Offy heads.

[GOSFAST]

Hi Tim, I have a few sets of the Offy's in stock here, they all use the conventional 3/4" reach-gasketed plugs. These are all new still in the original boxes!

I'll place some shots below here with this specific plug installed in one of these heads!

If you can't resolve the issue you have one other option, have a decent machine shop put a chamfer on the plug holes and run a 5/8" long tapered seat plug like we presently use many of Darts race aluminum heads. This isn't new, it's been around for some years now!

This would be an easy fix IF the 5/8" plug is at the correct depth. This is checked real easy! Just put one in by hand and see how it fits before the chamfer!

Thanks, Gary in N.Y.

P.S. Here's a couple shots of the Offy's I have here, one with the plug in place! It is a 3/4" reach (5/8" hex) with the gasket! If you need another photo let me know. The spark plugs shown are the ones we use with almost all our aluminum head pump-gas builds. We refer to them as "the black pump-gas plugs". They work really well.

[qmdv]

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Originally Posted by 4dFord/SC

Not sure of the reach, but I use Autolite 437's in my Offy heads.

They are only 1/2 in reach. What is a good number for 3/4 reach

Tim

[Ol' Ron]

I use a 45 degree counter sink and take off the 3 or 4 threads necessary. then use a power tip plug YF12 ?? I think this will clear the exhaust valve, but you better check to make sure.

[qmdv]

Originally Posted by Ol' Ron

I use a 45 degree counter sink and take off the 3 or 4 threads necessary. then use a power tip plug YF12 ?? I think this will clear the exhaust valve, but you better check to make sure.

So you counter sink the combustion chamber side?

tim

[qmdv]

Just did a Google search on power tip yf 12 and my post came up

tim

[JWL]

I have a few sets of Offy heads and none of them are suitable for 3/4" reach. They are all similar to the original posted picture. Just like Ron said, use a chamfer tool(countersink cutter) to remove the excess threads. It can be done with care and a hand drill.

[estout81]

I used Autolite 4093 plugs and chamfered the holes as been said. Here's a picture.

[estout81]

I screwed up! Maybe this time!

[Ronnieroadster]

The original Offy heads used the same length plugs as a flathead Ford the plug thread length is 3/8 of an inch. Theres no need to use 1/2 or 3/4 inch reach plugs or chamfer the head for any of the other plugs mentioned above. You can use standard Autolite 216 plugs or the best choice by far for a plug is the NGK B4L or B6L any of these plugs are easy to get at any good auto parts supplier and even on Ebay.

[estout81]

I don't know the vintage of my Offy heads but, Autolite 216 plugs were too short. 3/4" reach plugs were too long. Tried the Autolite 4093 and it was about two threads too short. That's why I chamfered the holes. Didn't hurt anything and it runs SUPER!

[BillM]

Here is an attached drawing of my Offy heads and some different plug choices. The measurements are for my engine and may or may not be the same for yours so careful measurements of your situation are in order.http://www.fordbarn.com/forum/attach...8&d=1333564954

[estout81]

Thanks BillM. Your drawing shows what I found when working on my engine. The Autolite 4093 plugs are 1/2" reach which left about two threads hence chamfering. My cam doesn't have .350" lift. If I remember right I think it is .325" so I have even more clearance electrode to ex. valve.

[Ol' Ron]

About 10-15 years ago Offy changed their patterns to give more room in the heads for higher lift cams, and that's the reason for the thicker spark plug hole. I enjoyed these heads because I could carve my own combustion chamber.

[qmdv]

Originally Posted by Ol' Ron

About 10-15 years ago Offy changed their patterns to give more room in the heads for higher lift cams, and that's the reason for the thicker spark plug hole. I enjoyed these heads because I could carve my own combustion chamber.

The heads in question were picked up used in 1976

Tim

[Ol' Ron]

Now, that's interesting. Never seen anything like that.

[Fairlane500]

I use NGK B5HS plugs in my Offys works fine no modifications. Have also run the B6L and B6HS previously