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496 ho blown up

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8K views 28 replies 11 participants last post by  gn7 
#1 ·
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?
 
#6 ·
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.
 
#8 ·
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.
 
#9 ·
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.
 
#18 ·
There's no mention of fuel pressure verification.....did you make sure you had at LEAST 43 psi KOEO? IF both motors went, maybe you have a fuel delivery problem and leaned out said motors? I've ran the hell out of mine for 300+ hours, in addition to the 140 that were on it when I bought it. No problems, other than a bad TPS one time.
 
#20 ·
Just when you thought....



It's amazing that a seemingly "un important", relatively inexpensive, and often overlooked part can create all that hate and discontent inside an engine.... When they wear out it's a pretty gradual loss in power/RPMs, but when they break it's usually catastrophic.. Seems to be a pretty common occurrence in the current NASCAR engines as well.... Those valve parts sure tear up the related parts when they start bouncing around in there....

Ray
 
#21 · (Edited)
True. The valvesprings in these motors, especially. I know I am on borrowed-time. They have like 75-85 lbs seat from factory. Basically C2500/3500 pickup springs.

I have CompCams conversion studs to make mine normal adjustable valvetrain and will eventually replace mine with Comp springs and some better rockers.

Valvespring at 7000 RPM - YouTube
 
#23 ·
I don't think there is anyone here that doesn't know it's just a truck big-block. Different cam and ECU.

What's a "ling"?
 
#25 ·
Valves and springs..

Valves and springs have to be the 9th wonder of the world.... @6000 RPMs, each valve is opening, AND closing, 50 times a SECOND..... Think about that, each valve opens and closes in 1/50th of a second..... Kinda hard to comprehend... It gives the terms "ramp speed" "lift" and "duration" a whole different meaning....

Oh, BTW, the tried and true GM stamped steel rocker arms are the 8th wonder of the world. Looking at them up close, there's no way they'll work....BUT they DO......
Ray
 
#26 · (Edited)
I have gone threw 2 496 horeman 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?
Considering that Merc had nothing to do with the assembly of the engine as new, it makes you wonder who they are contracting the "remanufacturing" to, and what specs and QC they are holding them to.

Do "remanufactured" long blocks get new springs, or just checked? If new springs, whos the supplier? If new pistons, from who?
Would be interesting to know how many reman long blocks are failing.



 
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