Deepening a spark plug

[ELS]

When I install a regular long sized spark plug in my cylinder head, it is 2-3 threads bellow the surface of the combustion chamber, I could swap the crush washer for a copper hydraulic washer probably but it wont leave me any room for indexing the plugs.
Is there a way I can deepen the spark plug hole without going to a machine shop? it's an aluminum head.

[HQM383]

When I install a regular long sized spark plug in my cylinder head, it is 2-3 threads bellow the surface of the combustion chamber, I could swap the crush washer for a copper hydraulic washer probably but it wont leave me any room for indexing the plugs.
Is there a way I can deepen the spark plug hole without going to a machine shop? it's an aluminum head.

Is it the head manufacturer recommended plug?

[ELS]

When I install a regular long sized spark plug in my cylinder head, it is 2-3 threads bellow the surface of the combustion chamber, I could swap the crush washer for a copper hydraulic washer probably but it wont leave me any room for indexing the plugs.
Is there a way I can deepen the spark plug hole without going to a machine shop? it's an aluminum head.

Is it the head manufacturer recommended plug?

what does that matter for? I said it was the long style plug, I've never seen a longer plug than those regular long plugs, and the recommended plug isn't made anymore and is even a bit shorter still.

[mag2555]

Can you post up a picture of what's taking place?

[ELS]

Can you post up a picture of what's taking place?

torqued down, no indexing washers ofc.

spark plug.jpg

I don't want to grind out the combustion chamber because I'm already struggling to get descent CR as it is, though maybe it'd be possible to deepen the spark plug mounting surface.

oh and the spark plugs are angled to the same side on all the cylinders, meaning that on cylinders 1 and 3 they are angled towards the exhaust and have a good chance of having the spark inside the combustion chamber, but on cylinders 2 and 4 they are angled towards the intake but have the intake side obstructed
in the picture cylinder #3 is shown

[ELS]

I'll perhaps try to weld and harden some screw drivers (because that's the highest carbon content steel I have around) into a cutter, then hollow out an old plug and install it from the combustion chamber as a guide.
hopefully the coolant jacket isn't closer to the threads deeper in the plug hole

[rp930]

Maybe just me but I don’t see a lot of hp gain.

[David Redszus]

When I install a regular long sized spark plug in my cylinder head, it is 2-3 threads bellow the surface of the combustion chamber, I could swap the crush washer for a copper hydraulic washer probably but it wont leave me any room for indexing the plugs.
Is there a way I can deepen the spark plug hole without going to a machine shop? it's an aluminum head.

Is it the head manufacturer recommended plug?

what does that matter for? I said it was the long style plug, I've never seen a longer plug than those regular long plugs, and the recommended plug isn't made anymore and is even a bit shorter still.

Most plugs are .750" in length. Bosch makes a plug (suffix H0) that is .840". Or, many extended tip plugs might work even
with standard length.

[jake197000]

put the plug in a lathe and machine it down

[ELS]

Is it the head manufacturer recommended plug?

what does that matter for? I said it was the long style plug, I've never seen a longer plug than those regular long plugs, and the recommended plug isn't made anymore and is even a bit shorter still.

Most plugs are .750" in length. Bosch makes a plug (suffix H0) that is .840". Or, many extended tip plugs might work even
with standard length.

I'll look into them, but I'd prefer using the regular 3/4' size, since all my favorite plugs are in that

about the cutter thing I said I was gonna do, well it turned out successful, until it broke... didn't bother to reduce it's hardness and it bit me in the ass

spark plug cutter.png

spark plug guide.png

cut spark plug hole.png

aftermath.png

spark plug installed.png

made it from a gutted out plug for the guide, an 8mm rod from a screwdriver, a 3/16" file iirc for the cutter bit.
tried drilling trough the cutter, but couldn't even when I annealed it, it was too hard for my crappy 1.5mm drill.
it sunk the plug down maybe like .7mm,
although I used it on the 2nd cylinder instead of the 3rd which I compared it to... precision analysis!

[Geoff2]

There are some plugs that have a longer projected tip than what was considered normal. Check with NGK to see if available in your thread size.

[ELS]

There are some plugs that have a longer projected tip than what was considered normal. Check with NGK to see if available in your thread size.

well I specifically want to deepen the spark plug bore instead of using more uncommon plugs, but I think I have that figured out, just have to make a new cutter and I'll probably solder the cutter blade in the shaft so it doesnt move this time. or weld it but I dont have a lot of space for that

[mag2555]

Just note that if you go to a extended tip plug that you may want to start off one heat range cooler until you see what there color change over point looks like after a few long full throttle runs.

[ELS]

well I made another cutter, this time using a 14mm steel bar and turning it down to 8mm at the end for the guide.
fit is terrible because the drill I used to 'lathe it' had the chuck slightly crooked, but I centered the blade as close as I could before soldering it so it's fine.

after 15 minutes of cutting I didn't even get the spark plug 180 degrees deepened (this time I used it on the #3 cylinder for a proper comparison).
I wanted to use a drill but I'll have to rig up some 'loose' connection between the cutter and drill, so the cutter doesnt get moved laterally by the drill.

cutter 2.jpg

spark plug installed 2.jpg

oh and btw if you're interested, the spark plug thread size is M14x1.25

[ELS]

update: using a drill, that cutter cuts like butter. too fast even, 1 second too much and it cuts a milimeter too deep.
and the soldered blade holds up fine, so no welding needed

photo of the finished cutter and guide

cutter finished.png