Ok...I need some help from you motor guys

I have a motor that runs with the NGK # 7 V groove plugs.
Dart Pro 1 heads.

What ill affects (if any) would running with shorter stem plugs have? AC Delco MR43T

all manner of things... none good. if the combustion chambers/head/piston tops are designed for that length plug then you will get lousy flame propagation , misfire at higher revs and maybe even detonation from the open edges of the spark lug hole/threads... can not imagine why you would want to do this.

I would never have done this.

these are the plugs that I pulled from my engine after I got my boat back from the mechanic. I now have oil coming out the exhaust from the # 5 cylinder.

Are you saying that the shorter plug was installed by accident during service? If so, that sucks

Spark plugs have two functions. First the obvious one is to fire off the air fuel mixture in the cylinder. Second one that every one forgets or has no idea about is that the plug is also there to remove the heat from the combustion chamber. With the shorter reach plug you have less contact with the head hence less area for the plug to dissipate heat to the head.
Mike

Absolutely.....but on the flip side....too long of a reach on the plug and you run the risk of piston contact. Theres also the issue with flame travel now as the flame has to travel around the threads and up instead of just to the sides and down.....

If those are the actual plugs. The one on the left is a typical plug for a iron head SBC with the taper seal. One one on the right is from your Dart heads. Cant believe that the delco plug would seal up and if it does it would probable damage some threads. I don't know what other damage could happen, but a compression test and a leak down test will tell the story.

Bruce,
The AC R43T is a .460" reach, tapered seat plug
The correct plug is a .750" reach, gasket seat
Do you know where exactly are you passing the oil on #5?
Bob

If those were the actual plugs that the mechanic had installed in the engine, I don't think I'd ever take it back there again.

hey guys ..I appreciate the feedback

yes..these are the plugs the mechanic installed on this engine. I know they are wrong. What he was thinking. I dont have a clue.
I have not pulled the motor apart yet. I just pulled it out of the boat.
Im looking for feedback and some education before I speak with him.

if you look closely, you can see some hardened buildup on the strap of the plug. None of the other plugs have this buildup. Which leads me to believe we detonated the # 5 piston. there is oil coming from the exhaust on the port side only and was smoking a bit when it was running.