Here is A video that explains the misconception about pistons slapping spark plugs out the cylinder heads
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Spark plug injection myth
- Thread starter xsellr8
- Start date
Seems like OP can't live that one thread down.
Nice video!
Nice video!
Fake video is fake, Terminators don't blow up. Mods please delete and permaban.
Why are you rebuilding an 03 SVT Cobra? They last forever even when making 5000 horsepower
The car leaned out from a bad alternator + a few back to back pulls (friend's car, not mine). Melted a piston. Here is the series if you want to follow along
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So glad to see you're still following me around.
Maybe we can be friends someday?
This is a pretty good video if you've watched it.
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Good video, don't get discouraged....... but...
On the 03s and early 04s with only 4 spark plug threads in the heads, that have blown plugs out of the head, who in the world actually thinks that is was caused by the piston coming up and hitting the plug? That would have to be a very non-gear head, non-car guy type of person. Naive comes to mind.
When those few threads fail, it is simply the pressure in the cylinder that blows the plug out. It does not have to be the greater pressure caused by detonation. Additionally the ground strap is typically not hammered closed by the detonation event, it is hammered closed by the on going up and down slamming the plug is subjected to in the plug well of the head as the cylinder alternates between vacuum and compression. The plug is held captive by the coil boot and the coil covers, so it just keeps slamming up and down till the engine is shut off.
On the 03s and early 04s with only 4 spark plug threads in the heads, that have blown plugs out of the head, who in the world actually thinks that is was caused by the piston coming up and hitting the plug? That would have to be a very non-gear head, non-car guy type of person. Naive comes to mind.
When those few threads fail, it is simply the pressure in the cylinder that blows the plug out. It does not have to be the greater pressure caused by detonation. Additionally the ground strap is typically not hammered closed by the detonation event, it is hammered closed by the on going up and down slamming the plug is subjected to in the plug well of the head as the cylinder alternates between vacuum and compression. The plug is held captive by the coil boot and the coil covers, so it just keeps slamming up and down till the engine is shut off.
Jimmy, while most of know this I have seen/heard more than a few people say the piston hit the plug/could have hit the plug
Good point.
Yeah I guess I should not assume that most people understand compression height, deck height or piston dish depth. These days there truly are way less people who are even interested in internal combustion engines any more.
Yeah, that's a good point. My friend's Mach 1 (actually a 9 thread 04) spat the plug out when he started the car a few weeks after changing the plugs. My Mach 1 still hasn't had an issue with 4 thread heads but you have to be more careful for sure.
Now that I think about it, I wonder if anyone has forced a plug so far into the head that it made contact with the piston...or if once threads have been stripped the plug has fallen in deep enough to make contact. Who knows. There is a way for it to happen, but under regular circumstances the piston won't make contact with the plug. Just wanted to show that in the video since I had the parts out
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I have seen pistons contact spark plugs in blown motor forensic examinations.
However they were typically push rod V8s with old school wedge combustion chambers, not pentroof hemi 4 valve chambers like our cars. On those other types of blown motors, sometimes the rod bolts break and the rod cap lets go and the piston comes all the way up and hits the head. Valves, spark plug and all. Other times I have seen cast pistons shatter from detonation and the piston chunks will fly up and mash the end of the spark plug, as well as bending and breaking valves. Blown up engines are actually very interesting, I always try to determine what the initial failure was, which is not always that easy.
However they were typically push rod V8s with old school wedge combustion chambers, not pentroof hemi 4 valve chambers like our cars. On those other types of blown motors, sometimes the rod bolts break and the rod cap lets go and the piston comes all the way up and hits the head. Valves, spark plug and all. Other times I have seen cast pistons shatter from detonation and the piston chunks will fly up and mash the end of the spark plug, as well as bending and breaking valves. Blown up engines are actually very interesting, I always try to determine what the initial failure was, which is not always that easy.
The sad thing is that with all the photos easily available online all one has to do it look at pics of the various parts to realize that's not the failure mode.
Like Jimmysidecarr said wedge head pushrod motors can have a problem with this. I had a few friends that used to build 14.5:1 nitrous SB chevy. They had to add washers to the spark plugs to degree the ground strap. They also talked about it helping direct the burn towards the center of the cylinder, the ground strap was orientated towards the cylinder wall.
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