Technical My favor with the spark plug gods has run out.

I somehow managed to put together a high compression engine, and run it, with no issues, until now.

Sunday was time for its first spark plug change, and this time, I was not so lucky. Several plugs were closed up nearly all the way, by making contact with the pistons.

Do I need to break down and by a bulk pack of plugs, and keep swapping them until I get lucky, or, do conical seat 18mm spark plug indexing washers exist?

My search says they either no longer exist, or never did.

Do I adapt out to 14mm? That's a thing that I have seen done. The adapters are $6ea. They, alone, might be enough to fix this. My question then would be, what plug, at 14mm conical, is the equivalent of an Autolite 46?

Anyone have any insights on this?

 

My son runs 2 washers under the plugs on his blown flathead due to the high-lift cam and the relationship of plug and valve, not due to a plug/piston thing. I'm not a flathead person so don't know if they are 18 or 14mm, I could check out one of his engines in my shed but someone else may be able to give you the answer before I make the trip over the yard. I do know that he will only use NGK plugs on all his engines.

 

It is the plug seat that is the problem. Mine are tapered, or conical, and would require a conical washer.

Many 18mm plugs have flat washer seats. Those folks are lucky, as they only need a ground parallel flat washer, or two.

 

What engine ? Since the plugs are hitting you can try a shorter plug but if they are to far into the pocket your engine is not going to run great. I have known racers that were fanatical about indexing plugs but you are going to have to do some testing. Maybe google different plug makers to see what length they have on threads . Two things . Do other foreign makers use different plugs thread lengths then say U.S. / Canada. Now if you use an adaptor you could modify with work , to get the plug in far enough if you don’t hit it out of the gate. If your indexing your plugs with an adaptor you may get a few more gray hairs indexing the adaptors to.

 

Is it possible to find a shorter plug which is equivalent to the Autolite 46 and is suitable for your engine/application. You may have to buy just one 18/14 adapter and check out your plug, piston relationship. Do you have a spare head that you could use? If it works then $48 is a cheap fix. Here in Oz plugs alone are over $6 each. Best of luck.

 

Did you check with Jegs or Summit for indexing washers ?

 

Plugs are $2.79 USD here.

 

Yup, 14mm, only.

 

It is a healthy Ford 200 inline 6.

The current plugs have only 0.438" of threads. It is hard to imagine shorter than that. I don't need to index them, per se, I just need the elbow on the ground turned a little. The adapters have a hex on the top, so that makes the threads deeper. There are a whole lot more choices in 14mm plugs. I might stand a better chance in that arena, in terms of getting a good depth, and position.

 

I think your right if the plugs are the short ones . I like that you built a in liner. What type are your pistons ?

 

Tried a little Googling - Moroso has your answer:

SPARK PLUG INDEXING WASHERS, 14MM TAPERED SEAT

Spark Plug Indexing Washers, Tapered Seat, .010", .021", .032"
Out of stock
Part #
71900
$22.74

https://www.moroso.com/spark-plug-indexing-washers71900/

Summit appears to have them in stock, should be a quick ship to your location

https://www.summitracing.com/search...atch&SortOrder=Ascending&keyword=Moroso 71900

 

I need 18mm ones.

 

They are Silvolites.

 

OOPS - Reading is fundamental...

 

Might be out of luck on the washers. How about trimming into side electrode?

 

How hard would it be to make some out of dead-soft copper sheet?

 

What about 18mm copper O rings?

 

Is it possible to trim the electrode and move the gap to the side .

 

I just looked up the Autolite 46 and noticed it’s a projected tip plug. Could you use a non projected tip plug?


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These folks may have an answer for you.....https://cliffordperformance.net/
Inline six is their thing.

 

buy these...and however more NORS ones you can find.

https://www.ebay.com/itm/292293692580?

It's the non extended nose version of the 46 plug.

 

Last ditch effort, pull the head and carve a slight dimple in the pistons...

 

https://aaok.com/index.php/electrical/spark-plugs/solid-copper-spacing-washer.html

I think these are flat but they may work.

 

The elegant solution. . . If you can pull it off.

 

@gimpyshotrods This is the direction I was going to send you. These copper washers will crush into a taper. Anneal them if you want them to be softer.

These guys can also probably make them in any thickness you want:
https://www.phoenixspecialty.com/pr...MIyJ7Ey7-s6wIVXSCtBh0L8g5qEAAYAiAAEgJCHfD_BwE

 

Check Mc Master and other sources for plain copper washers. I have used them as crush seals on tapered fittings and sealed leaks. This should be no different. I know extended tip give more power depending on the application but 90% of the 50’s engines did not use them. In my racing since I have custom pistons made to get very high compression I too must make sure plugs are not hitting.
I’m sure there are available copper washers in different thickness to help with this problem. Spark plugs will work with 3/8” of thread.. SBC’s were originally that way and so were the stove bolt 6’s. Cast iron head is very forgiving...Good luck.

 

Often a spark plug that indexes to between 10 and 2 o’clock in one hole will be incorrect in another hole. It’s standard fare in north east big block modified racing circles to buy 2 boxes of plugs, put a sharpie mark on the outside indicating the ground electrode and swap them around until you get everyone happy!

 

Do you have a domed piston? Lippy

 

I'll try that first, since I accidentally proved it works, with the first set of plugs.