I always thought they were kind of bullet proof... friends comes back with a problem, take the head off, number 5 is melted... called my engine builder, and he says they are known for that, and that is why they are not making 496's anymore and they went back to 502's...

Any truth to : known for melting pistons ????

They are not known for melting pistons and GM has not gone back to a 502 block. They (GM) don't make any big blocks anymore only after market companies do.

Your engine builder sounds misinformed.

If running a **** load of timing or a lean condition a 496 will destroy a piston. They are a hyperutectic piston NOT forged so they are not going to tolerate spark knock.... The are "bullet proof" if running properly (timing and fuel systems in order).....

As far as I know GM quite manufacturing the 8.1L vortec, which was the base for the 496. Mercruiser now makes the 8.2L, which is a 500 ci. Now I believe Mercruiser actually manufactures this block, but I am guessing it is still heavily "based" on the older 496 block......

----Not trying to start anything as I really want to know. Where do the 454s and 502s in GMs performance catalog get made??? I do know that they arent assembled at Tonawanda anymore. Is Mercury building these motors under contract to GM???.......Bill S

Very unusual for a 496 to actually melt a piston. They generally crack or break the piston or piston top ring land from detonation that continues for any period, but to melt a piston if you actually mean "melt" it takes a lot of continous cylinder temperature for an extended period to do that and generally that condition would start detonating before that, set off the "guardian" engine knock sensor control and seriously reduce timing and power to stop this condition. Was this engine a Merc 496 ? Was the knock system working? Why don't you post a picture or so here for us to actually see the "melted" piston.

Best Regards,
Ray @ Raylar

All due respect..GM discontinued this motor a couple years ago..and merc is using the 502(8.2) block again..despite mercs website..call them and you'll find out

if you had a miss of a injector that was not giving the engine the proper amount of fuel it will for sure melt a piston..if the plug looks silver and the ring land is pealed then it wan lein..send the injector for that cylinder out and have it checked..reverse have all of them checked and mark the one with the bad cylinder and tell the guy this one is most important to check..you want full flow readings on it..

they dont want to tell you this but they built a new plant in mexico...