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Dismantling spark plugs
scudderfish - 25/6/13 at 01:46 PM

I'm experimenting with making some tools to find TDC with no existing crank marks. I want to remove the ceramic insulator from an old spark plug, but it is tough stuff! Is there a special way of doing it? A specific drilling technique or drill bit required?

Regards,
Dave

dhutch - 25/6/13 at 01:52 PM

I would be aiming to the two parts apart rather than machine the ceramic away.

Not something I have tried to do mind, but assuming you have some old ones spare (and there not expensive) I would try removing the ground electrode, putting the plug loosely in a vice, and drifting the ceramic out,...


Daniel

HowardB - 25/6/13 at 01:53 PM

Dave,

it might sound daft, but,... hammer,.... the ceramic is brittle,.. or if you have to drill it, a tungsten carbide tile drill?

If you are looking for tdc, how about a home made depth gauge,.. a cork and a drinking straw,.. drill a hole in the cork, and push that into the plug hole. slide the straw through, turn the engine over to a point of maximum straw visibility,... ?

just a thought

matt_gsxr - 25/6/13 at 01:58 PM

Dave,

I was trying the same thing the other day, and so far have failed.
Smacking the top chunk of ceramic off is easy, but the bit inside is way difficult.

I'd really like to hear from someone who has actually managed it.
I'm thinking it is probably easier to drill a bolt.

Matt

Slimy38 - 25/6/13 at 02:10 PM

quote:
Originally posted by matt_gsxr
I'm thinking it is probably easier to drill a bolt.


Or cut a thread on a tube?

ashg - 25/6/13 at 02:31 PM

for the outer bit crush it in a vice for the inner bit hold it in the vice and smack it with a drift.

whitestu - 25/6/13 at 02:42 PM

If you succeed you have more patience than I do!

I had the same idea but gave up after much hammering.

Stu

AndyW - 25/6/13 at 02:50 PM

I know this is locost builders but for the sake of £10 have a look at this ebay item, spark plug gauge

britishtrident - 25/6/13 at 03:27 PM

quote:
Originally posted by AndyW
I know this is locost builders but for the sake of £10 have a look at this ebay item, spark plug gauge



Good tool but access could be a bit problematic on the deeply buried plugs on modern engines. An extension adaptor for compression tester with a rod passed down the centre would do the job.

When timing up Rover K engines to be 100% sure the crankshaft is correctly position at mid stroke I stick 4 plastic rods cut (from plastic coat hangers) to exactly same same length down the plug holes. If all 4 rods are at equal height I can be 100% sure the crank hasn't moved from mid-stroke.

40inches - 25/6/13 at 04:04 PM

I made an adaptor for my compression tester from an old spark plug. I cut off the peened over part, on the top of the hexagon, with a hacksaw, then punched the centre out by knocking a bolt through from the electrode side. Can't remember it being that difficult.
Just popped into garage to do one, once you have cut off the peening, it just knocks apart from the bottom.
Description
Description

[Edited on 25-6-13 by 40inches]

jollygreengiant - 25/6/13 at 05:03 PM

All I ever did was to grind the the metal dome off above the nut, then as said, punch the ceramic out from underneath.

If you are using a pinto plug (for a pinto engine) then these are large enough that if you grind the metal earthing electrode off, then you can fit a long tyre valve into the plug body and use the creation for cylinder leak down testing.

rusty nuts - 25/6/13 at 06:51 PM

As 40 inches has pointed out just use a hacksaw and cut just above the hexagon, hacksaw cuts ceramic easily.

Peteff - 25/6/13 at 07:11 PM

I made one for the scooter with a spark plug and a 6mm bolt. Put the porcelain in the vice and just tighten it to crush it then the rest will fall out or firk out with something or put it on something solid and beat it with the hammer. None of the hacksaw blades I have will touch a plug ceramic.

rusty nuts - 25/6/13 at 08:06 PM

quote:
Originally posted by Peteff
I made one for the scooter with a spark plug and a 6mm bolt. Put the porcelain in the vice and just tighten it to crush it then the rest will fall out or firk out with something or put it on something solid and beat it with the hammer. None of the hacksaw blades I have will touch a plug ceramic.



I've cut loads of plugs over the years without any problems using any old blades doing it the way I've described. I've never tried to cut just the ceramic

Peteff - 26/6/13 at 08:47 AM

quote:
Originally posted by rusty nutsAs 40 inches has pointed out just use a hacksaw and cut just above the hexagon, hacksaw cuts ceramic easily.


I read this and thought of you

scudderfish - 30/6/13 at 11:09 AM

Thanks for the advice. I first crushed most of the ceramic in the vice. I then cut off the dome above the hexagon, turned it over and the rest the the plug core fell out with a tap.
I'm making a hydraulic TDC finder. I'd thought of using a probe, but as the plug is at an angle to the piston then the accuracy will suffer. I'm fixing a pipe through the plug and putting the other end in some fluid. On the compression stroke it'll blow a load of bubbles. As it passes TDC it will start to pull fluid up the pipe. If I mark the pipe (and crank) and then wind it back past TDC until the fluid reaches the mark on the pipe again, then TDC should be half way between the current crank mark and the previous one.

Regards,
Dave

Peteff - 30/6/13 at 08:02 PM

On the scooter you put a bolt in the plug remains and screw it in the plug hole so it locks the piston when you turn it one way. Angle gauge on the crank nut and mark where 0* is then turn it the other way till it locks and mark it again then split the difference and you have TDC.

40inches - 30/6/13 at 08:08 PM

quote:
Originally posted by Peteff
On the scooter you put a bolt in the plug remains and screw it in the plug hole so it locks the piston when you turn it one way. Angle gauge on the crank nut and mark where 0* is then turn it the other way till it locks and mark it again then split the difference and you have TDC.

Old school, can't beat it

coyoteboy - 2/7/13 at 06:56 PM

if you are only finding tdc then just drop a thin rod down the plug bore and watch for Max extension, no need for hydraulics or cutting off plugs, done it dozens of times. I used a screwdriver last time, that was pushing the boat out a bit but then I got given a dial gauge to confirm my "by eye" measurement.