grand-illusion

Looking for ideas as to what caused the following. I have not started to do any trouble shooting yet:

The motor is a 1200HP, 600CI , w/1471 blower, dual dominators, wet sump configuration. Actual hours since major rebuild is unknown but believed to be around 75-100.

The motor ran fine the entire first day of boating for the season and started and ran fine the next day to the destination. Firing up the boat to go home...I start the port motor, it pops right off and settles back to 1000 rpm idle. I start cranking the center motor and the port motor literally explodes and stops running. I turn off all ignition switches and after the smoke clears form inside the hatch I raise it to find both valve covers blown totally off the port motor and excesive oil in the biluge.

Assuming there must have been fuel leaked into the CC from either a carb bowl or the fuel pump (gen IV style piston race pump), what would cause it to ignite? How would the spark get there. The boat had sat about 6 hours since running fine.

MOBILEMERCMAN

I had a guy working for me. He was working with a flooded motor. He said he saw a spark jump into the breather line to the valve cover and ducked away. I can only guess he apparently rested the flame arrester on or too close to the coil as he cranked it. It blew the valve cover off the motor. I was on the other side of the marina and heard the bang. As I looked out I saw Eric shaking his head and then saw a splash as the cover hit the water. If I wasn't there I wouldn't have believed it.

If yours has a breather hose going to intake or carb that could have been the source.

Strip Poker 388

Iv never heard of it.Can ya take a pick of the valve covers blown off? Curious

jeff1000man

I would love to see a picture of that.

Sorry to hear about the prob though.

Where is your coil mouted? Also, is there any metal close to the dist? I have seen sparks go through the boots on the MSD wires before.

I guess the first place to start is to figure out where the fuel came from.

Good luck.

grand-illusion

The coil is mounted on the rear of the head and I do have breather hoses hooked from the flame arrester to both valve covers...I'll hopefully know more when I tear into it.

Wally

I've seen an engine blow the distributor right out of the block and into a flourecent light fixture back when i was in shop class in highschool the kid that was working on the motor didnt put the dist hold down in place....the engines were all crap and had ring gaps the size of the grand canyon...and the carbs all leaked...plus if you try and give it a little gas when trying to start it, it shoots extra fuel in to the intake as well....so gas buildup in the crank case is very frequent

ezstriper

sounds like float/neadle & seat hung and pushed a lot of fuel in, must sat for a while to seep past the rings to get into the oil pan, then with fuel everywhere just took one to light it off, and with the blower forcing everything down, just made it worse, how long did it sit ? most of the time it will sit on top of the piston...Rob

grand-illusion

The boat sat about 4-6 hours since being ran. One other possible factor not mentioned is that I run 100LL av gas. The motor never rev'd high so boost should not have been much...where would a spark come from to ignite the vapors in the CC?

jeff1000man

Vapors were probably not only in the crankcase at that point. with the engine warming and oil circulating it would have been on thop of the heads. Fueal could have ignited anywhere in the oil circulating pattern.

Duing normal combustion you could have had some fuel between rings, or had some vapor ignite during the compresion stroke. Might not have had to come from a spark.

I am just dreaming up possibilities here.

mrhorsepower1

Exhaust rocker arm broken? and possible needle and seat leak. Engine obvious was loaded with fuel/vapors.