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My 71 has stopped running a couple of days ago, and tonight, I removed the head to see how the pistons were, and found out that #5 piston was melted(?) at its edge. How did this happen??? Lack of lubrication?? The oil level was pretty low. There was a lot of carbon build up, but I don't think that could cause melting. Could I have damaged the cylinder wall as well?? I have a N42 block with dished pistons, and just had a p90 high comped to work with it. I am pretty sure that the piston is trashed, and need to be replaced. Should I just replace the whole motor, or have the pistons replaced?? Are there any advantages to using F54?? How difficult is it to replace pistons?? Any special tools?? I really need help on this one, and don't have much time, so, ANY input will be greatly appreciated.
Thanks in advance.

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What indicates that it's melted? I don't know how that could happen--you have to go above 2000F to melt steel. Lack of lube would cause problems, but more like scoring of the cylinder walls from the metal-to-metal contact. If it really is melted, I would have expected it to take bits of the cylinder walls off, so they would probably be suspect.

The F54 block is not much different from the N42, except that there was more webbing (whatever that means) between the cylinders, which is supposed to "provide more rigidity and promote better cooling" (http://www.geocities.com/MotorCity/2824/engine.html). Also, in non-turbo models, it came with flattop pistons, and its dished turbo pistons were a different design.

I don't think pistons are hard to replace, the only tool you should need beyond some sockets and a torque wrench is a piston ring compressor to get it into the block. (I haven't looked at the manual on this, so caveat lector.)
 

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Were were you timmed at? I have done this a couple of times with small block Chevys. If you run the timming to far advanced you will melt a piston every time. Its a fine line between more power and keeping the motor from destructing. Your block should be fine. Just pull the piston and hone the cylinder. Since your that far you should pull and check all the pistons.

JOE
 

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F54 webbing

The webbing is also called siamesed cylinders, what it is: metal webbing in the water jackets between some of the cylinders (not all) this provides more rigidity under high rpms allowing less deformation of the cylinder walls and therefore less piston ring blowby. This makes it an ideal block to use with a 3mm or even a 4mm overbore.

Nick
 

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If are turboed and running lean on a cylinder it will happen real quick under load, if N/A it will just take a little longer. I would agree with JOE. Check your total timing. Not just what it's at at idle. You could have a broken spring on one of the weights causing too much mech adv.. I would not rule out fuel though. If you could hear a light pinging under patial/full load(even N/A) you have too much timing.
 
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