David Jenkins
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| posted on 17/4/04 at 07:32 PM |
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Broken plugs - any ideas?
I was having a furkle around with my distributor today, trying to sort out the engine's misfire (it looks like the sliding plate was stuck,
BTW). I took all the plugs out to allow me to turn the engine over for timing purposes, and noticed that two of the plugs were cracked - which
wouldn't have helped the engine to run properly!
However, I was wondering why they cracked in the first place, as they were new when the engine was rebuilt. I can think of a number of possible
reasons:
1. Ham-fisted fitting at some time (always possible, but I do have a proper plug socket with a rubber insert to prevent this sort of damage)
2. Accidental damage, e.g. when fitting the engine (also possible, but I don't remember banging them at any time. Always possible that I may
have dropped them though)
3. Cracked when bought (unlikely)
4. Cracked when the engine ran (unlikely, as the engine hasn't run much and it hasn't run hot at any time)
Anyone else got any bright ideas?
rgds,
David
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CairB
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| posted on 17/4/04 at 07:44 PM |
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David,
I've had plugs go like this and worse, requiring the head removing to get it out on a pinto. In this instance I ended up smashing the plug and
'graunching' an allen key down the plugs bore to remove it.
Sockets can put a lot of side loading on if levered from one side resulting in this type of damage, even with the rubber insert, as in the case with a
ratchet. IMHO the best bet it to use a T handled lever to minimise the side loading.
Also using copper ease or similar on the threads when fitting helps reduce the 'umpty' needed to remove.
Cheers,
Colin
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jollygreengiant
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| posted on 18/4/04 at 09:42 AM |
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Choices are, over-heating due to misfireing due to ignition problems. or poor work man ship when fitting/removing. Most common plug for breaking is
Taper seat variety, as in (VERY COMMON) HCS Engined Fiesta's. Dead simple to remove. Remove old broken ceramic from nut section by cranking
engine. FillCentre of plug & 13mm drill bit flukes with grease. Drill (SLOWLY) out centre of old plug until taper seatsection releases from
threads, then simply unscrew thread section. SORTED. 4 broken plugs removed in 15 minutes.
Enjoy
& you were write that would not have helped misfire.
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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britishtrident
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| posted on 18/4/04 at 09:58 AM |
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Both failures are identical --- I have seen this before the classic cause is using a plug socket with a rubber grip insert --- first thing to do with
any plug socket is pull this bit of rubber out and throw over the wall.
With 16 valve engines with deeply recessed plugs to start the plug on the threads I use a long rubber tube that fits neatly on the electrode plugs
to lower the plug down the hole and turn the first few threads -- it also reduces the possibilty of wrong threading or closing up the plug gap.
Also I never use a plug socket with out an extension on the ratchet -- it gives more control.
[Edited on 18/4/04 by britishtrident]
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David Jenkins
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| posted on 18/4/04 at 12:04 PM |
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Thanks to all - I reckon that it was option 1 - ham-fisted tightening! 
I've adopted the various suggestions - the rubber insert's gone, and I'm using a T-bar to tighten - which does feel more
'balanced' and secure.
As for starting the plugs - I was always taught to use my fingers to spin them in as far as I could, then finish them off with the socket.
My main concern was that there may have been something wrong with the engine that may have done it - but 'heavy-handed' fits the bill
(never ascribe anything to mysterious causes where stupidity will do!  )
rgds,
David
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britishtrident
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| posted on 18/4/04 at 02:30 PM |
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Very easy to do -- done it myself a couple times after buying a new plug socket -- those rubber inserts are pretty useless for normal use.
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