460 Ford Forum banner

1 - 20 of 20 Posts

·
Registered
Joined
·
1 Posts
Discussion Starter #1
My spark plugs are kissing the top of the piston dome. I have a TF A460 head with pistons that were supposedly designed for that chamber. The plugs are hitting just to the point of pushing the ground strap to the center electrode. I had Autolite 3923 plugs installed. I am looking for a plug that doesn't have the porcelain sticking out of the plug, thus making the plug a bit shorter. I planned to try the NGK R5673-8 plug. From the photos it looks like it is a possible cure. If I cannot find anything shorter I will have to put a 14mm copper washer under the plugs. Does anyone have any recommendations?
 

·
Registered
Joined
·
89 Posts
Isnt the NGK -7 a heat match for the Autolite 3 since they use opposite heat scales? Or were you looking to go to a colder plug as well?

Edit: sparkplugs.com detailed say the Autolite is a gasket type and the NGK is a tapered seat, can you use tapered seat plugs? The NGK also has no resistor.
 

·
Premium Member
Joined
·
9,268 Posts
Autolite 3933 non extended tip plug.


SJ
used 2b RHP
 

·
Registered
Joined
·
48 Posts
Try indexing your spark plugs. Indexing you say? What? Shim the spark plug so that the ground electrode is in the upper 100 degrees of rotation. I'll even take the upper 160 degrees of rotation. You need to experiment with different thicknesses of shims. Only use one shim. You may have to try different spark plugs in each cyl but it's doable.

Phil
 

·
Registered
Joined
·
48 Posts
Or...modify the domes.
For $25 you can buy a pack of indexing washers or, pull the engine apart, new head gaskets, front cover/water pump, oil pan, intake gaskets. I think the indexing washers are the way to go here.
 

·
Registered
Joined
·
89 Posts
For $25 you can buy a pack of indexing washers or, pull the engine apart, new head gaskets, front cover/water pump, oil pan, intake gaskets. I think the indexing washers are the way to go here.
Missed @The Mad Porter 's alt plug option that the OP originally asked about?

Although that does not negate the reasons for indexing, however, many outside of racing do not grasp the value.

Personally, myself, I am unsure how indexing performs on recessed dome pistons and what the optimal orientation would be? Do you have a reference for that @Philm ? I am thinking it would vary on the number of valves with recessed.

Sent from my SM-N950W using Tapatalk
 

·
Registered
Joined
·
48 Posts
By indexing the spark plugs, you're rotating the ground strap to the upper portion of the combustion chamber and moving it away from the piston as it's rising up. it exposes the spark energy to the mixture in the chamber and allows additional clearance. A non-projected tip spark plug might also give you that clearance (see The Mad Porter's comments above to reference that part number).

I run the FOMOCO A-460 head with a domed piston, if I don't index, the piston dome will hit the ground strap every time. Ask me how I know...

Phil
 

·
Registered
Joined
·
89 Posts
By indexing the spark plugs, you're rotating the ground strap to the upper portion of the combustion chamber and moving it away from the piston as it's rising up. it exposes the spark energy to the mixture in the chamber and allows additional clearance. A non-projected tip spark plug might also give you that clearance (see The Mad Porter's comments above to reference that part number).

I run the FOMOCO A-460 head with a domed piston, if I don't index, the piston dome will hit the ground strap every time. Ask me how I know...

Phil
Hmm, and I do it for ignition burn and wash control thermodynamics, silly me.

Sent from my SM-N950W using Tapatalk
 

·
Registered
Joined
·
1,007 Posts
Indexing is nice for ultimate performance. We'd see about 3/4 - 2 hp on 200hp+ 800cc two strokes back in the day. For this issue, get the non-projected tip plugs Scott referenced. Easy, peasy, done, with no worries. Seems like if we're indexing just to make the piston not hit the ground strap, we've probably got the wrong plugs in.
 

·
Registered
Joined
·
948 Posts
For $25 you can buy a pack of indexing washers or, pull the engine apart, new head gaskets, front cover/water pump, oil pan, intake gaskets. I think the indexing washers are the way to go here.
Since we have no actual data, I don't know how much interference he has. Indexing might work....indexing might not.
 

·
Registered
Joined
·
89 Posts
Some people can complicate corn flakes.
Sometimes that is how new methods and innovations are found, many times money is thrown at a mediocre idea with little benefit, occasionally it just becomes an unpalatable mess that someone else gets when it is abandoned.

Is that really so bad?



Sent from my SM-N950W using Tapatalk
 

·
Registered
Joined
·
89 Posts
You figure that this is the place for a philosophical discussion?

KISS became an acronym for a reason.
Not really, nor for obvious trolling either.

However, as you, yourself already said: Maybe indexing will help, maybe both indexing and a shorter plug is required, or perhaps something else is required. We still have no information on the actual clearance.

Sent from my SM-N950W using Tapatalk
 

·
Registered
Joined
·
3,904 Posts
My spark plugs are kissing the top of the piston dome. I have a TF A460 head with pistons that were supposedly designed for that chamber. The plugs are hitting just to the point of pushing the ground strap to the center electrode. I had Autolite 3923 plugs installed. I am looking for a plug that doesn't have the porcelain sticking out of the plug, thus making the plug a bit shorter. I planned to try the NGK R5673-8 plug. From the photos it looks like it is a possible cure. If I cannot find anything shorter I will have to put a 14mm copper washer under the plugs. Does anyone have any recommendations?
B UY SOME INDEXING WASHERS, THEN NEXT TIME THE HEADS ARE OFF CLEARANCE THE PLUG AREA ON THE PISTON A LITTLE,
 
  • Like
Reactions: The Mad Porter
1 - 20 of 20 Posts
Top