motor is destroying my spark plugs

[absolum]

Hello guys I am really out of ideas and need your help.I am running a T3/T4 set up on a sr20det. I am currently running about 7 psi of boost, I have a wideband and monitor my air fuel whenever I hit boost.There is a strange issue that happened, My car is destroying my spark plugs.Doing some mild boost , The motor started to knock violently almost as if there was something loose in the motor itself. Description would be like having marbles inside a cylinder. The motor was also running on 3 cylinder. I pulled the park plugs and the spark plug #4 had the side electrode pressed in the center electrode ( yes you read right ) , there was no gap on that park plug, it almost looked like someone hit it with a hammer , Yes there were touching. These were bkr7.The safc knock was showing 35 recorded count of know, I though it knocked while in boost and detonation destroyed the plug so I bought a new set of spark plugs and upgraded to a 8 heat rating spark plugs. I even used a magnet and try to sweep the cylinder just in case. Nothing. The knocking diseapeared as soon as I changed the plugs , got home done a compression test and getting about 160 across consistent . Just for safe measure, I up the air fuel from 11.5 to 11.0 . I drove the car for 1 week in and out of boost and it happened again.This time while boosting heading home. Important * this time I was checking for knock while boosting and the knock started to register as I started running on 3 cylinder, The # 4 spark plug again had no gap , the electrode were pressed against each other.I pulled the valve cover and cranked the motor manually and the valve, retainers and rockers are all moving the way they should.Put everything back in and started the car, mad knock like you wouldn’t believe.I get in the car all pissed off and give it a good rev to about 5000 RPM , Noise is now gone and car is running 100% ok.

I am really scare of boosting this car now. What could be the problem?

What are the odds of it been the piston hitting the top of the spark plug while in boost? Could it be a stuck valve? What can do this to a spark plug. Notice that the destroyed spark plug is only originating from # 4.Are my rod bearings loose?

HELP , I am seriously running out of ideas

[absolum]

Forgot to add:

car has been running since march and been boosting ever since, July 19th was the 1st time that I needed to replace the spark plugs and july 23 is the 2nd time it happened again.

[Hijacker]

I take it you haven't touched the bottom end at all.

Only contact would cause the spark plug to get smooshed like that. I would pull your plugs, crank the motor to TDC and measure how tall the piston is sitting and compare it against another cylinder.

I can only guess maybe some carbon has built up in that cylinder, causing the plug to contact the piston under load.

[absolum]

that makes sense but arent there suppose to be dish on the top of the sr20det piston? SOmeone people done a sr20det rebuilt with some flat top piston and I bet they were not having this type if issues. ( unless I have some mad carbon deposit , which is very unlikely ).what are the odds of it been a loose bearing? I have also noticed that this is most likely to happen when I am boosting at high RPM ( close to 7000 rpm).

And the knocking noise? sounding like marble in the head. I would love to believe that it may be a rod knock but how come it's all gone now? I drove the car to work and boosted as far as 6000 RPM and all is well ,Car is still pulling insanely well and makes no noise at all.

[Hijacker]

Knock like that is typically ignition timing based. And it won't smash a plug tip. It'll fry a plug, it'll melt a plug, it'll discolor a plug, but it can't physically deform it like what you're describing.

Physical contact will smash the plug, which means something in your cylinder is doing it.

Loose bearings don't just magically go away. Once rod knock starts it keeps going. And their is no way to get rod knock confused with detonation. Rod knock is a very distinctive sound. And the rod would have to be thrown for it to be able to allow the piston to reach a plug.

Just look at the physical characteristics of the piston and combustion chamber design. You have a slightly dished piston moving to a domed combustion chamber with the plug sitting at the apex of the dome. the ONLY way the piston can make contact is with something filling in the space, such as a carbon deposit.

If you want to be totally certain as to what is causing the problem, pull the motor out and pull the head off. Since you have something making physical contact, that would be the course of action I would take in that situation. Mainly because I know something has gone madly wrong with the motor and I would check every moving component inside the block.

[FAST-DATSUN]

Are you running a extended plug??? The plug could be hit by the piston if so...

[absolum]

OK guys.

thank you very much for the information , these are giving me some ideas.

1- NGK BKR7 are not extended , as far as I know.

2- I am going to try to get a cooper spacer on the park plug in cylinder #4 since it seems to be the one that usually crush the plug. I will go do some 7500 RPM passes and see how it goes.

One thing I was wondering is that since SR20 are all used motors, will the constant removal and installation of the plug cause a wear thus making the plug closer to the pistons.I also noticed that when I installed the plugs , I did hand tight them , after 1 run I checked the plugs and I needed a rachet to pull them out ( must be the pressure or something).

[Hijacker]

you need the ratchet because the head is aluminum. Aluminum has this wonderful ability to "fuse" itself to threaded items once it's heated up. The expansion and cooling down is what causes it.

The only thing that could happen from wear and tear of the threads for the spark plug is that the threads will get more likely to pull out if over tightened. But that's really only likely if the plugs get impacted in with air tools or you tighten them repeatedly with a breaker bar.

[Sil80315]

your motor is toast..there is no strange reason for the spark plug to get touched unless there is some damage to the crank/rod/wrist pin..

Once you hear the sound of the marbles inside the motor..that pretty much all bad..

you change your plugs and it goes away but after a shor time it comes back..this is because the internals heat back up and they slowly start to stretch and its probably just hitting the sparkplug..

Time for a rebuild myfriend

[Hijacker]

Just out of curiousity, what gen SR20 is it?

Also, I should have asked this earlier. Did you change the headgasket out? Cause my SR guru friend is thinking it could be a headgasket issue.

[absolum]

the motor is a S13 blacktop.

I don't know much about motor and all but how can a headgasket be a problem? Compression are even , motor never overheat and issue does not happen all the time.

As far as comenting that the motor is toast, I am sure internal component will heat up after like a couple if hours of driving or couple of passes with boost, no weeks after.

I used a spacer on the spark plug and so far so good, i done over 10 passes shifting at 7000rpm and checked the plugs every 2 passes , So far so good. I even raise the boost to 10 psi for the last 4 passes and stilll good.As far as the internal noise, my friend told me that the only moving component that can cause such a noise could either be a bad chain tensioner or I may need to install a RAS,( if anyone selling, please let me know)

I will try these 2 and we will see how it goes.

Let's hope it stays that way.

[karmakaze]

if you don't want our advise then don't ask for it. and if you don't want to follow it, then do not come here complaining when your engine blows up.

you need to at least take your head off, not ghetto rig your spark plug.

[Hijacker]

The reason why I asked about the head gasket is that a friend of mine who has been working on Nissans for 35 years has encountered some of your symptoms in motors that partially blew their headgaskets out. A piece breaks off and rattles inside the combustion, but since it's not a blow out, the compression would still stay decent.

Also, as anyone on these boards will tell you, one of the first upgrades that shoudl be done in anticipation of a new turbo, especially a T3 hybrid of some kind, should be a metal headgasket. The stock paper headgasket doesn't hold up very well past where you max out the stock turbo and injectors.

[absolum]

The headgasket scenario makes the most sense.

thanks man.

karmakaze : I was just looking for some advise on what could be the problem, telling me that the head has to come off does not answer my question. I would love to have the replacement parts ready in case I am pulling the head off so I needed to know what I am up against.So far the head gasket scenario is the best explanation I have, that makes complete sense. This can also explain the fact that I wasnt able to pick up any debrit with the magnet. It could also have been that peice of debrit boucing around and hitting and closing the gap on the spark plug before exiting through the exhaust.

thanks tenkawa_akitoWe can put this thread to rest now.