keep on breaking spark plugs why?

[thesoundofspeed]

I am working with a '90 Toyota tercel 1.5L sohc 4cyl.
and for reasons unknown to me, every month or so, the #1cyl
spark plug needs changing due to broken porcelin surrounding the electrode which in turn causes the #1cyl. to miss-fire. I undrestand that carbon build-up could eventually reach a spark plug with the piston at tdc; but I dont think that is the case since I have not been fighting any pining problems or dieseling.
The plug comes out displaying a color that looks good to me so I dont think it's burning lean iether.

 

[MikeHalloran]

You're using a torque wrench and a cushioned socket to install the replacements.. right?



Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

and you can get a good angle on the wrench, and you are holding the head of the wrench not just whaling on the tail? That's why I prefer a speedbrace to be honest...



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[dicer]

What brand spark plugs?
Does it screw in easy?
What torque?
Compression check?
Coolant loss?

 

[CoryPad]

Thermal expansion or contraction of the parts (past or present) may be stressing the plug excessively. This is an 18 year old engine...

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evelrod]

Well---I've installed a couple plugs over the years and I've only seen a couple that just 'broke'---I mean, without help from me. One was on a Briggs-Stratten 4hp when a rod broke and the piston slapped the plug...sorta like a bullet it was.

I'm with Mike and Greg on this one.

Rod

 

[BobM3]

Is the broken porcelin on the side of the plug inside the combustion chamber or outside the combustion chamber? I assumed it was on the inside. If so, how would sloppy installation procedure break the inside porcelin (and not the outside)?

 

[evelrod]

The plug comes out displaying a color that looks good to me so I dont think it's burning lean iether.

I'm thinking it's the outside porcelain.

Rod

 

[patprimmer]

We have a saying here that RIR or Rod is right.

The OP says no detonation and good mixture or words to that effect, so that means the OP was wrong in his description or the damage is physical.

Physical damage in the chamber is the piston hitting the electrode which is not mentioned.

That leaves physical damage outside the chamber which all the respected long term members have already suggested with various emphasis on how and why.



Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[romke]

i have come across a similar phenomenon a couple of years ago with an Audi. If it is not physical damage due to a not so suitable wrench you might try to change the lead between distributor and spak plug. in the above mentioned case that cured the problem, although on an oscilloscope nothing unusual showed.

 

[thesoundofspeed]

Hey guys, The crack shows up on the inside. Although I will try swapping out the injectors to ensure the cyliners are all getting the same ammount of fuel.

 

[evelrod]

Starting to sound like a detonation problem. Your PCM may not "hear" destructive detonation.

Keep in mind that the "porcelain" is one piece and it is conceivable that a crack could be started from improper installation, I have not seen that except in one extreme case where the jerk used an impact wrench on a Ford taper seat.

You stated that "the plug comes out displaying a color---etc."???
How can you see a "normal" plug if there is enough detonation to "crack the porcelain"?

As you seem to already know, it's time for some basic diagnostics. Something is definitely NOT "normal"!

Rod

 

[thesoundofspeed]

Amy one see this happen in less humid weather???

 

[patprimmer]

If the porcelain cracks in the chamber always on the one cylinder but the ground strap has never been bent from impact, it is detonation.

If the leads are the wrong way around on a 4 banger, it means that 2 cylinders are at least 180 deg out and the misfire will be obvious, and most likely spectacular with great flames erupting from the induction or exhaust and less than 50% power output if it runs at all.

The cylinder in doubt has higher compression, gets a higher charge density, has more advanced timing, has a built in glow plug or is running leaner than the rest.

The reasons for one or more of the above can be one or more from a large and varied list, from faulty ignition system to faulty fuel system to worn camshaft.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[patprimmer]

Also wrong reach plug, poorly repaired plug thread, overhanging gasket, carbon build up, blocked waterwayetc etc etc etc etc.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[thesoundofspeed]

Would you suggest I change to a lower temp plug all accross the head? I should prob. pull the v.cover off and have a peek.
I wish I could convince the wife that it would be easyer to build a new sub-frame,shave the bottom of the passenger side shock tower and fab an adapter plate to mate a Supra twin-cam 6cyl to the stupid thing and call er' a day. hehehe
PS; thanks all y'all for your input.

 

[evelrod]

Changing the plug to a different type, mfgr or, range may help, but I doubt it. If detonation has reached the point of fracturing the plug...Gotta be something more severe than heat range.

Based on what you post here---I don't mean to pick on you, but do you know how to read a plug? Truly, most mechanics (even if they claim all sorts of book lernin') DO NOT!

Here is something 'just for those in the know'...My crew chief's wife burned up, for lack of oil, the bottom end of his MGB on the way back from Vegas..."But, the light never came on", says she! I can't post here what he said. ;-)


Rod

 

[patprimmer]

Rod

My brothers wife did something like that to two cars in a row

First was a VW Super Beetle with a 1918 cc forged piston bore kit, fully counter weighted crank, 40 DCN Webber big valves etc for 130 HP at rear wheels. It had an eternal oil filter and a big oil cooler up front fitted in line after the filter. On a cold start she popped the oil filter canister as it peaked out at over 200 psi oil pressure if reved before it had 10 or 15 seconds warm up time. She claimed that the oil pressure gauge read OK and the light did not come on as she drove it about 15 miles with no oil and drove it to a stall at full throttle in low gear on a level road. We saved inlet with carby, fuel pump, dissy, exhaust, generator, oil line, remote canister and some tinware.

Next car for her was more conservative (read idiot proof) It was a Holden Torana with a later model 3.3 litre straight 6 pushrod typical Chevy/Vauxhall inline 6 style engine. It had full CW crank and 12 port head with a 285 deg hydraulic cam and Rhodes lifters an 3 X 1.5" SUs. It Pulled good from 1000 pm in top gear all the way through to 6000 rpm where it ran out of power due to the small carbies. Once again gauges and lights. She burst a radiator hose. She claims the gauge was normal, the light never came on, no steam was visible (even though there were rusty water marks all over the windscreen) and she again drove it to a stall in low gear, WOT on a flat road. We saved the inlet with carbies, exhaust, alternator, distributor and flywheel oh and the fuel pump.

At that stage we considered a tank for her. Settled for a new SUV and replaced it every time the warranty was up.

We considered a system where a warning sound came into effect along with the idiot lights. The plan was for it to scream out real loud "HELP MURDER STOP RIGHT NOW ARRRRRRR"

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[RossABQ]

Pat, what does "saved the inlet" mean?

For the subject Toyota, I have no specific knowledge of that model, but the #1 cylinder on most engines gets the coolest water and cylinder wear is typically worst there. It is possible that cylinder has built up a bunch of carbon, but is still burning relatively clean.