Mercruiser 496 MPI (8.1 Litre) - Exhaust Water Causes Piston Rod Failure

candav

Recruit
Joined
Jul 19, 2004
Messages
1
After a day of running with 8 people on my Doral 360SE I came back to port. My guests retired from the vessel. I brought it to the fuel dock and filled it with fuel. When I went to start the engines the starboard engine did not start and then turn over with a mechanical "ticking" sound that accelerated with the throttle... It was two bent piston rods! Now if the problem is bad - it could mean a new "long block". <br /><br />The dealer is telling me "out of warranty from Mercruiser and "as is where is" from dealer" and likely caused by sudden stop underway and water being pushed back through the exhaust on the Bravo III over the Riser, past the manifold and into the cylinder. The solution , after many thousands of dollars, is, the dealer suggests, to put taller risers on in the hopes of avoiding the backwash and also modifyiong how I come off plane to prevent stern wave from washing up against transom (accelerating after coming off plane to keep pressure in the exhaust and avoid the sternwave at the same time). <br /><br />Am I crazy or does this seem like a 1:1,000,000 problem? I had come off plan nearly 25 minutes before docking (the harbour speed is 8 mph and it is a 25 minute trip in from open water). The problem only occured after the engine had been shut down for fueling and at that point no guests were onboard. The dealer believes that the weight of the guests (8 at 180 per on the stern seating area) followed by the weight o the fuel (125 gallons added at dock) may have casued the engine and risers to sit below the normal water line of the boat. This would be a design error for Doral and for Mercruiser in specing that level of riser.<br /><br />1. What can I do to avoid the Problem in the future?<br /><br />2. I just bought the boat(used 2 years old with 198 hours on the engines but no Mercruiser extended warranty) but no warranty from the dealer - can I recover from Doral or Mercruiser for the design flaw?<br /><br />3. This could be anywhere from $4000 (pull and rebuild engine) to $20,000 (new long block - at which point you might as well drop a new engine in)repair.<br /><br />Help!!!!!!
 

Sydmoe

Petty Officer 3rd Class
Joined
Dec 22, 2003
Messages
83
Re: Mercruiser 496 MPI (8.1 Litre) - Exhaust Water Causes Piston Rod Failure

I don't have any answers to your post only another question and that is I thought the exhaust flapper were suppose to prevent such things from happening? <br /><br />Do you know if you have flappers in your exhaust tubes?
 

Rickles

Petty Officer 2nd Class
Joined
Mar 24, 2004
Messages
101
Re: Mercruiser 496 MPI (8.1 Litre) - Exhaust Water Causes Piston Rod Failure

Flapper valves are supposed to prevent this from happeing but.....they do get stuck and do burn up from time to time.when was the last time you did a water pump impeller?If you pull the exhaust hoses you'll see what condition they're in.This will answer alot of questions of why it happened.As for the bent rods....an overhaul should fix it.Unless the motor gernaded rebuild it.
 

Sydmoe

Petty Officer 3rd Class
Joined
Dec 22, 2003
Messages
83
Re: Mercruiser 496 MPI (8.1 Litre) - Exhaust Water Causes Piston Rod Failure

DFWC, $20K seems a little steep! I would just have it rebuilt. Even if the block and heads are scrap a little searching I am sure will turn up so kinda donner motor you can probably have rebuilt.
 

mercrewser

Petty Officer 1st Class
Joined
Dec 4, 2003
Messages
367
Re: Mercruiser 496 MPI (8.1 Litre) - Exhaust Water Causes Piston Rod Failure

Call your insurance company. They may be more understanding than you think. Did the engine run on or diesel when you shut it off? This may cause water to run up the exhaust. Also if the idle is set to low on some engines it can do it as well. There are some techs on this board who can steer you in the right direction. Your dealers explanation sounds like a lot of crap to me.
 

mercrewser

Petty Officer 1st Class
Joined
Dec 4, 2003
Messages
367
Re: Mercruiser 496 MPI (8.1 Litre) - Exhaust Water Causes Piston Rod Failure

Also, how many other times have you taken the boat out? If you told the mechanics what you told us, they dont even believe there own answer.
 

floydff

Cadet
Joined
Jul 14, 2004
Messages
25
Re: Mercruiser 496 MPI (8.1 Litre) - Exhaust Water Causes Piston Rod Failure

Well, I can tell you the odds aren't 1:1,000,000. I recently bought a 25' Chaparral boat that had less than 10 hours on a rebuilt 5.7L Mercruiser engine, and it died after me having it for TWENTY MINUTES. The negative to the ignition module came loose (LOUSY connection to the painted block by the CERTIFIED Dealer) and the engine died while at 35 knots. I was able to turn it over after fixing the problem, but the engine backfired and then locked up from water under the plugs. The Dealer says "well, it doesn't matter if it was our negligence, it's been over 30 days". Plus, since they didn't replace the exhaust manifolds (they never mentioned the need to replace them), they say there is no engine warranty. Without even taking the engine apart, they say the engine is "full of water and locked up" and all they want to do is install ANOTHER engine with me paying the full cost. That's why I'm going out of the Country tomorrow to get away and try to relax until the previous owner gets back in town. I hope you have better luck with your experience!!
 

flashback

Rear Admiral
Joined
Jun 28, 2002
Messages
4,065
Re: Mercruiser 496 MPI (8.1 Litre) - Exhaust Water Causes Piston Rod Failure

what did your mech do to determine that the ticking sound was rods and not valves? most people describe rods as "knocking" and valves as "ticking". did he tear down the engine? and by the way I'll put new engines in your boat all day long for 20 thousand a pop...that,s insane....I think I would get a second opinion... ;)
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,308
Re: Mercruiser 496 MPI (8.1 Litre) - Exhaust Water Causes Piston Rod Failure

Sounds like you're Both being Taken for a He!! of an Expensive Ride..............
 
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