Hmmm....I blew the spark plug insulator right out of the thread jacket....

[San_Diego_SeaRay]

Boat: 27' 1993 Chaparral 270 w. a Gen V 7.4 carb'd engine w. a Bravo 1 drive


Last Friday I opened up the throttle in the Ocean and was humming along at 35+ MPH. Probably doing 4200 - 4500 RPM (My tach doesn't work...sigh). About 8 minutes into it I heard a loud "boom/bang" noise, then a super quick rhythmic "pffft pffft pffft pffft" exhaust leak type of noise. I thought the absolute worst must have happened and got towed 10 miles back to my marina ($1300 bill to my insurance company if you were wondering).

Today I investigate and find the #5 spark plug wire dangling. I look at the spark plug and don't see one. Then I realize the threads are still in the block. I finally find the insulator piece in the bilge. I did a compression test and 145 - 160 psi all the way around, including the #5 (It was 150).

Anything to be learned/gleaned here? Or is this a fluke? That bank of spark plugs were barely tight. I must have forgotten to tighten them properly last time I removed them. Other side was fine.

(The burning you see around the spark plug hole is just the paint I used which is not high temperature paint).

 

[San_Diego_SeaRay]

[No message]

 

[Scott Danforth]

If the plugs are not tight, then they cant transfer heat to the head. You melted the plug.

Replace them and go boating

I have both regular boat insurance and tow insurace thru boat us for tows

 

[San_Diego_SeaRay]

If the plugs are not tight, then they cant transfer heat to the head. You melted the plug.

Replace them and go boating

I have both regular boat insurance and tow insurace thru boat us for tows

Thanks! I was convinced the lack of tightening must have had something to do with it, but wasn't sure how. That makes perfect sense now.

I also have both insurances through BoatUS and was very happy w. my experience (they will be the ones paying the $1300 bill). I broke down right in the middle of the main channel of San Diego Bay. If an Aircraft Carrier or Submarine had come through it would have gotten even more interesting...

 

[Scott Danforth]

my first tow was 23 miles....... bill would have been a bit over $1100. however that $156/year for unlimited is priceless. notice I stated first tow....