OLD Offy heads - 18 mm Spark Plugs hitting valves
 

I have been monkeying around with my "spare" flathead, preparing to fire it yesterday. It's a 59 block, with a 3 3/8" bore and 4" stroke, and a small lift cam of about .3125 lift. Wearing an OLD set of Offy 400 heads, with an 18mm thread size.

Bought a new set of Autolite 46 plugs, with a tapered seat and .46" reach, and when I cranked it over, 7 of the spark plugs are hitting the valves. (the 8th one was repaired probably 50 years ago and now uses a 14mm flat style plug.)

I'm at a loss, other than to have the 18mm holes converted to a 14mm flat style plug and am looking for suggestions.

Most appreciated.

Re: OLD Offy heads - 18 mm Spark Plugs hitting valves
 

Several alternatives here.
1- Buy a new set of heads.
2- Have the 18's plugged and re-threaded to 14.
3- Buy a set of screw in adapters that convert 18 to 14.

Re: OLD Offy heads - 18 mm Spark Plugs hitting valves
 

If the heads are OLD are you sure they take taper seat plugs?

Bob

Re: OLD Offy heads - 18 mm Spark Plugs hitting valves
 

That is what was in it. I looked at it, this afternoon, and think that I should be able to use some flat crush washer style. Still on the hunt for the right part number to compare with.

Re: OLD Offy heads - 18 mm Spark Plugs hitting valves
 

Hi Everyone,

bchrismer, I am certainly no expert on your subject, but... Wouldn't the spark plug hole be different for the crush gasket type plugs, vs. the tapered seat ones? Are they interchangeable?

Re: OLD Offy heads - 18 mm Spark Plugs hitting valves
 

Well...chalk that up for me not looking at the head and just taking the plug up to the store to get the same thing that was in it.

Come to find out, after looking at it, and comparing other plugs on Autolite's website, I ran up to O'Reilly and picked up a set of 386 plugs, with the crush washer.

Sorry for being an idiot and trusting that what was in it was right. Cost me another $20 in plugs. LOL

https://www.youtube.com/watch?v=7qtpL6QmP9A

Re: OLD Offy heads - 18 mm Spark Plugs hitting valves
 

Any "learning experience" under $100 is great.

Re: OLD Offy heads - 18 mm Spark Plugs hitting valves
 

bchrismer . Does these heads have steel inserts for the 18mm plugs or are they threaded in the aluminum heads? Most of the Offy heads I've used 400 and 425 have 14mm and have 3/4 reach plugs. I just installed a set of Offy 375 heads and they had 1/2 reach 14mm plugs. Walt

Re: OLD Offy heads - 18 mm Spark Plugs hitting valves
 

Before Helicoils the fix for stripped spark plug threads was to thread the item to the next larger size.

Re: OLD Offy heads - 18 mm Spark Plugs hitting valves
 

Walt,

There's only one with steel insert. It's "#2. The others are threads in the aluminum heads.

The biggest issue that I had with the "new" plugs is that that I don't own a 7/8" long well socket or spark plug wrench. I snugged them down finger tight, then used a short socket and a channel lock to tighten them up about 1/8 of a turn.

Chap, the good news is that I had bought an "extra" starter solenoid, so I returned it and took the refund in spark plugs and a $3 and change credit back into my bank account.

Re: OLD Offy heads - 18 mm Spark Plugs hitting valves
 

>>>The biggest issue that I had with the "new" plugs is that that I don't own a 7/8" long well socket>>>

Well, geez! Hurry up and go get one! 8^)

http://www.homedepot.com/p/Husky-1-2...DP78/202934346

Jack E/NJ