Spark plug hitting piston

[Early93Viper]

My Gen I was sputtering at around 1500 RPM after a spark plug change and we didn't know why. So we took the spark plugs out and found that the #1 Cylinder plug had absolutely no gap with the ground and was almost touching the electrode. So we put another spark plug in and sputtered the same way immediately. After taking off the spark plug we noticed the same thing was happening. We came to the conclusion that the piston was hitting the spark plug.

This is weird because the plugs we took out are gaped perfectly, it's the same Champion spark plug, and it wasn't over tightened. I also don't have any NOS or other power adders. And the way I track the car the way I do I probably shouldn't have much carbon build up.

We put another washer to raise the spark plug up a bit and it is working fine. Has this happened to anyone else? Anyone have any insite that might help us out? We are dumbfounded.

I am just praying it's not something big.

Please Help,
Dan

 

[carguy07]

Unmilled stock heads and stock plugs??

 

[SoCal Rebell]

Unmilled stock heads and stock plugs??

If it's only #1 maybe wrist pins, any knocking?

 

[grcforce327]

I am just praying it's not something big.
Dan

Don't know about the praying,but it's time to start some serious checking to be safe!

 

[PatentLaw]

Thread length the same on the ones taken out vs. the ones you put in? May be same electrode, etc, but what about the thread length. Check the easy things like this first.

Patentlaw

 

[Early93Viper]

If it's only #1 maybe wrist pins, any knocking?

No knocking or any other problems just missing at 1500 rpms.

We did mill the heads a bit when we changed head gaskets because it was slightly out of specs. That Could have contributed to this problem.

 

[Early93Viper]

Thread length the same on the ones taken out vs. the ones you put in? May be same electrode, etc, but what about the thread length. Check the easy things like this first.

Patentlaw

Good idea

 

[viperrt96]

No knocking or any other problems just missing at 1500 rpms.

We did mill the heads a bit when we changed head gaskets because it was slightly out of specs. That Could have contributed to this problem.

My heads are milled .060 No probelems here. I use NGK's now but I did have the stock champions in them. ?

 

[Purdue_Boiler_Viper]

You'd think that you would see the problem on all plugs if milling caused the problem. Anything unusual about the seat of #1 in the head? Damaged? Are you tightening the plug to the correct torque? (20 ftlb for GenII).

Assuming that you are using the right plug, tightened correctly, and that the plug seat is OK, I think something has to be wrong with the #1 piston or the valves in the head. The plug is right between the valves, so perhaps a valve is hitting the plug. I'd start with a compression check. Whatever the cause, I wouldn't start the engine until I got this figured out.

 

[Early93Viper]

Well we did a compression check and everthing checked out. Noticed the spark plug probably was overtorqued. The threads wouldn't let the plug go in easy so we put a spark plug chaser on it. We also noticed a small indention where the spark plugs where which again pointed to the plugs being overtorqued.

So we kept the extra spacer on the plug and went and dynoed it. The car dynoed 7 HP under the last run but it was a hot day and we think the carpet was under the gas peddle a bit not allowing for WOT. So we think just the overtorqued plugs along with my heads being milled, the new head gasket, along with bad luck caused the problem.

Hopefully the problem is gone for good. KNOCK ON WOOD

 

[Purdue_Boiler_Viper]

Interesting. My manual does say that overtorquing the plug can cause a change in the gap.

 

[X-Metal]

do you have your old plug, and can you post a pic of the old vs the new one. the thread etc is the same, but it sounds like you put in a extended reach plug, and thats the issue. you could mill .120" off the heads and not have an interference issue, and if there was a pin, or rod problem the noise alone would signify a serious issue--more of a problem than the plug!
i think you just have a plug problem, and champion plugs are horrible btw, run an NGK in her for better perfomance and consitancy.
pm me if you want the plug number for an NGK

 

[Madduc]

X-Metal, you don't have a PM contact...PM me bro!!

 

[X-Metal]

oh crap!!! they just set me up as a Vendor, so let me work on it!
how ya been man? my email is [email protected]

 

[Early93Viper]

do you have your old plug, and can you post a pic of the old vs the new one. the thread etc is the same, but it sounds like you put in a extended reach plug, and thats the issue. you could mill .120" off the heads and not have an interference issue, and if there was a pin, or rod problem the noise alone would signify a serious issue--more of a problem than the plug!
i think you just have a plug problem, and champion plugs are horrible btw, run an NGK in her for better perfomance and consitancy.
pm me if you want the plug number for an NGK

We messured the old and new plugs again and again (with instrument I believed to be called a trichometer) the new ones looked to us slightly longer. I don't have the new plug (well I do but it's in my engine) to take a picture with and you couldn't tell by looking at them anyways.

 

[X-Metal]

We messured the old and new plugs again and again (with instrument I believed to be called a trichometer) the new ones looked to us slightly longer. I don't have the new plug (well I do but it's in my engine) to take a picture with and you couldn't tell by looking at them anyways.

ok, welp if you need anything, let me know. the plugs reach, can be measured just by using a set of calipers from the plugs gasket surface to the ground electrode base, but it should be pretty obvious that the plug in question is too long, just from eyeballing it. in order for it to hit the piston it would have to be much longer. the other thing is if you chased the thread previously, a fragment could have came out into the combustion chmaber and that in turn hit the electrode when the engine turned over, smashing the gap closed.

 

[2000_Black_RT10]

If the plugs are too long there is an option of using index washers (spacers). These are for the extremists looking for power, that prefer the electrode hoop to be clocked in a position for ignition efficiency.. yet you can use them to reduce the spark plug length into the combustion chamber..

http://store.summitracing.com/egnsearch.asp?N=700+115+%2D113040&D=%2D113040

 

[PatentLaw]

I knew it was the problem. 2000 Black RT10 is correct on solution.

 

[X-Metal]

If the plugs are too long there is an option of using index washers (spacers). These are for the extremists looking for power, that prefer the electrode hoop to be clocked in a position for ignition efficiency.. yet you can use them to reduce the spark plug length into the combustion chamber..

http://store.summitracing.com/egnsearch.asp?N=700+115+-113040&D=-113040

sure you can do that, but why? just put the correct length plugs in and be done with it the right way

 

[2000_Black_RT10]

It's just an option / suggestion if the plugs aren't available in the specific length..

 

[Viper Specialty]

those plugs must be LONG. Viper pistons on a stock block sit an average of .030 in the hole, and off the top of my head, I would say there is easily .200 or more betwen an un-milled head's deck and the electrode in its "down most" orientation. That adds up to roughly ~.280 between a piston and plug tip. Not to mention, the plugs sits on an angle, so you would probably need a plug .300 or more longer to hit a piston top... there is NO WAY you could miss that by eye.

Are you sure there isnt something else going on here?

 

[99 R/T 10]

I agree with Final GTS, keep an open mind while looking for the problem. It just doesn't sound plausable.

 

[2000_Black_RT10]

Personally I would rig up a top dead center tool in the spark plug hole and compare the distance / depth measurement to the other pistons.

The spark plug seat in the head may be deeper, never know.. until it's measured, factory machining flaw or previous repair work on the head.

A friend told me a story of bad detonation, a run down the 1/4 mile closed the gaps on the plugs.. but it was a high c/r motor..

 

[X-Metal]

yep something isnt right. you would see a HUGE difference between the 2 plugs visualy

 

[mjorgensen Woodhouse]

I would borrow a borascope (sp) and look into the cylinder I bet you find your answer very quickly. We have seen this and there is usually something obvious in the top of the piston, like a top ringland broken off and bouncing into the plug and head. I would look before driving to prevent any more serious damage.

 

[Early93Viper]

It cannot be ringland broken off

Why Not:

1. Because I would hear it.

2. Because changing the plugs wouldn't cause the problem.

3. Because it Dynoed just 5 HP under normal (most likely because it was on a hot and humid day.

4. Because the compression test passed with flying colors (180)

5. Because it wouldn't be running perfectly.

6. Putting an extra spacer wouldn't have solved the problem.

And again the plug length is same trust me. It's the exact same plugs and everything. I have checked it literly 25-30 times.

 

[Early93Viper]

Well I had some time off today so I went to a shop and looked at it with a borascope. You could see small marks on the piston where it hit the spark plug. But THANK GOD! nothing else was wrong! Nice piece of mind since I will be tracking the car weds.

 

[mjorgensen Woodhouse]

I'm glad you at least took my advice and checked for yourself. Glad to hear it was nothing big! Good luck this weekend.

Mark J.