Crankcase vapor explosion!
 

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.

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.

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

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.

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.

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 :D 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 :D

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

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?

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.

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

For clarification,do you have three engines ? If yes,does each engine have it's own battery and perko switch ? Where were the perko's set for each engine ?

The port engine was running and blew when battery draw was applied,starting the second engine ? Somehow, that seems relative to where the battery/perko switch's were set.

The port engine saw enough RPM to engage the rectifier,before returning to 1,000 rpm. Therefore,subject to further variables,the alternator on any of the engines may have participated in causing a huge transit surge. Conductors,coil(s),and etc. couldn't handle the load. External arcing may not have existed,however,internal fuel soak existed and ignited from some source.

Possibly,the fuel pump and or needle(s) were leaking for some time. Logically, a lot of fuel is required to have enough force to blow both valve covers off.

Good info sir.

I still want to see a pic.

I appreciate everyones input...

Yes it is a triple engine boat. There are 4 batteries and 4 Perko switches each set to all.

Some visualize the boat is split through the middle. Each part may be thought of as an individual boat. In your case,you have three parts or three boats. Each part/boat has a separate battery,engine,gauges and etc.

Therefore,boat #1,#2 and #3 all have their own individual Perko set on their own individual battery,which is battery selection #1.

You have 4 batteries and 4 Perko's, therefore,subject to the riggers schematic,the 4th battery is intended for optional loads. Those loads would include such items as stereo, A/C and etc.

The #4 perko would remain OFF until all engines were running OR all load switches were OFF. Then the #4 Perko would be switched to #2 in/on the corresponding part/boat.

Perhaps, some ignition,injection and other electrical problems can be attributed to all switch's being set on ALL.

Another relative item is battery cable. Subject to cable length,cable size required increases expotentialy. For example,4 o or otherwise known as 0000 is seldom seen. However,typical #2 is not intended to carry a big load very far. Therefore, it is not unusual to blame a battery for starting problems,while the cables were the problem.

Therefore, the reasonable solution becomes,switching all to ALL. When all are set to ALL the toroid effect starts and transient voltage may occur.

Incidently,"Ancore Battery Cable" is high end stuff that carries more amps than most. It is also very flexible.

Hopefully,all you'll have to do is fix the seals and everything else will be fine. Good Luck !

Never saw one blow up that bad but blew a breather off/out when I had messed a piston up and fuel went into the crankcase. For this to happen you have to have correct A/F ratio in crankcase and then a spark. I can see fuel leak past piston and possible causing correct A/F Ratio, but then a spark in crankcase?

My guess is piston with a hole in it. This would give crankcase both fuel and a spark.

Let us know when you tear motor down what you find.

set to all doesn't sound right to me?? my Hustler paper work says don't run in the all position


don't think that related though

[QUOTE=CcanDo;2572621]


Incidentally,"Ancore Battery Cable" is high end stuff that carries more amps than most. It is also very flexible.

QUOTE]


I believe it and marine cable is tin coated.


I added a extra bank for stereo and the wire and ends are just copper or gold plate, sofar no propbs

One thing I see...you need terminal covers on the right battery in your picture. Easy way to get a ticket.

I had forgotten the time it sat by the time I posted...crs....anyway don't the electrical system had anything to do with it...and you are saying no boost, but that is not correct, if you ever spun a blower over at even starting rpm, there is a good bit of pressure even at that slow speed, no actual "boost" in psi but enough to force a full charge in. what you experianced is simular what drag race blower cars suffer when they get a load of fuel past a piston, ends up in the pan, fumes everywhere, fires...boom...did it damage the oil pan ? how about the dipstick(if you had a std type) seen them launched !!! Rob

What kind of piston to wall clearance did you have?

Just reaching here.

Opinion seems to lean away from electrical and towards mechanical.

However,the port engine had run satisfactorily, 6 hours earlier, re-started and appeared to be idling normal. Simultaneous with starting the center engine (creating current draw) the then idling port engine experienced an explosion.

There is nothing to indicate a burned piston or other mechanical failure....Though some definite volume of fuel was in the crankcase,that was mechanical.

Hey BIG Daddy if theres a burned piston it would make sense how it happened :cool-smiley-011:

Merc computers don't like to run in ALL position. On my boat it will break down at about 3000 rpms if the switches are set to ALL. If he is running carbs it might not be an issue, but it is still better to run a sep battery for each engine.

I cant find any that fit them right

Do a compression check or leak down. You will find the cylinder with the problem. I am betting leakdown will show one blowing into the crankcase big time.

When you were running you may have had motor in detonation. The piston got fractured but did not let go until you had the engine running again.

Appreciate the input. Im hoping to get a compression test done tonight before I leave for a 4 day weekend. If I do, I'll post the results. If not I'll be doing it next Tuesday evening. Thanks.

OK...here's the compression test results:

Cylinder - PSI
1 - 104
2 - 105
3 - 106
4 - 109
5 - 110
6 - 111
7 - 111
8 - 110

No appearant mechanical failure...

Well BIG Daddy we can scratch the piston theory :cool-smiley-011:

Put the valve covers back on and see if it will blow the supercharger off the top of the engine next time. :evilb:

Just kidding. Hope you find the problem. I am out of suggestions.

My theory is that if you fix the fuel problem, the rest won't matter. :cool-smiley-011:

nevermind

whats the CR? Was the carb throttle blades wide open?

I think if the hole was big enough to let the fuel thru and the spark it would show up on the compression test if blades were open or closed.

This is kind of scary. What would have happen if someone was standing over the motor when this happened?

The #'s seemed low just overall to me

Does anyone know what caused the problem ?

Yes.
The problem was that fuel leaked into the the crankcase from the fuel pump. I run the mechanical "racepumps.com" pumps and the O-rings that prevent fuel from entering the CC wore to the point where they leaked. Normal blow-by or back-side piston temps ignited it. Fixed the leak, changed oil and replaced the bottoms on the eickert valve covers and it's been runnin' great ever since.

Until Next Time?
 

Seems like a real good reason to invest in some electric remote fuel pumps and regulators to me. Just a thought on those pumps as they may have seal failure again and do the same thing again with even more disasterous results!?

Regards,
Ray @ Raylar

I agree with Ray. In my search for a high volume unregulated pump we never did find any endurance users of the Race Pump. Do you know for sure what caused the seals to fail? Does Races Pump have a recommended rebuild at a specified number of hours? Re-rigging the fuel system for a twin 1200 HP is a big project but the next explosion could be you or your crews last.

Forgot all about this thread. Glad to see it resurface with a solution and yet more input from those who know about possible better solutions. This thread had a few pearls for me.:drink:
.

We have a limited amount of experience with the CV Products pump (resembles the carter and holley) and it operates as expected.

CV had originally created the pump for small block,reportedly at the request of Nascar.

We are using an electric holley in addition to the CV engine driven pump. The holley is controlled with a dash mounted toggle switch. The holley is turned on for the initial carb prime and turned to either off OR standby while starting. When the switch is in standby position the normally open circuit is then electronically closed when the engine reaches 3,000 rpm.

The reasoning for this design includes dual pumps without heat from relief regulation,priming at start,volume ILO pressure at higher RPM and lower pressure than often found with a straight high pressure electric pump. The lower pressure could be construed relative to line burst.

grand-illusion,thanks for the report,glad you found the cause and the solution was not more complicated.

hi