496 ho blown up
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496 ho blown up

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    Senior Member namba860's Avatar
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    Default 496 ho blown up

    I have gone threw 2 496 ho reman long blocks from mercury in the last 8 hours of operation. 2 pistons gernaded and laying in the oil pan. Any idea's whats going on?

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    Quote Originally Posted by namba860 View Post
    I have gone threw 2 496 ho reman long blocks from mercury in the last 8 hours of operation. 2 pistons gernaded and laying in the oil pan. Any idea's whats going on?
    hmmmmm...old pistons with new rings and bearings? ...motor reassembled on a monday or friday?
    tuning issues?
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    Senior Member namba860's Avatar
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    EDDIE I CAN TELL YOU THIS THE PCM WAS JUST REPLACED JUST BEFORE BOTH THESE ENGINES WERE INSTALLED

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    Quote Originally Posted by namba860 View Post
    EDDIE I CAN TELL YOU THIS THE PCM WAS JUST REPLACED JUST BEFORE BOTH THESE ENGINES WERE INSTALLED
    Shane, post some pics of the parts...
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    gn7
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    Quote Originally Posted by namba860 View Post
    I have gone threw 2 496 ho reman long blocks from mercury in the last 8 hours of operation. 2 pistons gernaded and laying in the oil pan. Any idea's whats going on?
    Stop trying to put 10lbs of boost on them

    Curious, what went wrong with the original engine.



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    Senior Member namba860's Avatar
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    This engine is in a 32 Advantage Victory with twin 496 HO's. the original engine was at a shop and the shop said the pcm was bad. The shop put a new pcm in it and a couple hours later he brought it to me to take a look at the stbd. engine. The stbd. engine broke #8 piston. Nothing left in the bore but the rod and wrist pin. I ordered a new reman long block from Merc. installed it and 2 hours later it was brought back to me with the #4 piston broke laying in the oil pan just like the first engine. I verified the pcm part number with the one that was replaced and it is correct number. No codes, alarms,guardian modes nothing.The owner of the boat noticed the coolant resivoir was empty. I checked the oil and it was way over full so the coolant went into the pan.Im assuming the wrist pin punched a hole in the cylinder wall and thats how the coolant enterd the oil pan.What sucks is both times there was not enough of the the piston to look at to see if it detinated or not. I have replaced at least 20 of these 496 long blocks over the years and have never had a problem like this with any of them. I'm just puting some feelers out there if anyone else has experienced this before.

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    Senior Member namba860's Avatar
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    GN7 there is no supercharger on these engines. The only upgrade is lightning exhaust headers which have been installed for 4 years now without any problems.

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    Quote Originally Posted by namba860 View Post
    GN7 there is no supercharger on these engines. The only upgrade is lightning exhaust headers which have been installed for 4 years now without any problems.
    I was just mess'n with you namba. Seems the biggest problem with those engines is when someone abuses one trying to make more power than they should. Hope you finds out something. I haven't of issues with them when left reasonably stock. In fact quite the opposite.



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    Bostick Racing Engines six-oh-nine's Avatar
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    Did you reuse the intake of the original engine after the piston failure? I have seen instances where guys attempt to clean the intake after chunks of piston and/or valves/valve seats went through the engine and end up in the intake. After this cleaning "attempt" the parts that were sticking around in the intake that were not able to be cleaned out come back out in the new engine after a little bit of use. I have seen it on quite a few of these style intakes... especially on the new Dodge Hemi's.

    Also... if they were both "remans", used the stock hyperspaztic pistons, and been honed up a bit... they may have had enough clearance in them to be banging around and bust the skirts off. They are kind of known for doing it on a brand new from GM engines with stock size bores... the skirts are short and they rattle around a bit before warming up.... now hone the thing a thou or so more and you really have some rocking around in the bores.

    Not saying any of this is your problem, but based on what you put out there, and what I've seen... here are two possibilities to check of your list of things to look for.
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    Senior Member namba860's Avatar
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    I do remember a bunch of debris up in the intake and spent about 2 hours cleaning it out. Maybe a piece was stuck in it and came loose? I'm going to replace the intake this time for sure!

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    did you pressure test the headers?

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    Senior Member EVILFORCE's Avatar
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    The first thing I thought of was debris in the old intake.
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    Quote Originally Posted by namba860 View Post
    I have gone threw 2 496 ho reman long blocks from mercury in the last 8 hours of operation. 2 pistons gernaded and laying in the oil pan. Any idea's whats going on?
    Check the injectors. I had an injector fail and grenaded piston..my experience.

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    Did it look like this? My 460 did this last friday. Seems like it might be contagious ...

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