My name is Lance Hogan and I am currently rebuilding my father's 1996 Ford Explorer engine. When tearing the engine down, I found a piston with major dings in the top of it (the head has apposing dents). These marking are only on one piston and corresponding cylinder head location which makes me think that this cylinder experienced major detonation.

I would like to replace the piston and the only number I can find is located within the piston body with the numbers 3476 b. Does anyone know who made this piston and if can get a replacement? I checked Oreillys website and they have a sealed power piston H816CP listed, but I dont believe this is a correct replacement part because the H816CP piston comes with skirt coating and the pistons I removed from the engine did not have skirts that were coated. Any information would be much appreciated.

Respectfully,

Lance

 

Dents that are both on piston top and corresponding cylinder head surface are almost certainly caused by a piece of foreign matter (screw etc.) that got into the engine. If the damage is confined to the top of the piston, it is probably okay to reuse. A picture would be helpful.

The 3476 B number you found on the piston is part of the Ford part number for a piston. The original pistons in that engine are made by Ford.

 

Your engine has hypereutectic pistons, detonation usually results in a shattered piston, not dents in the top. As was posted above, your pistons are manufactured by Ford. When ytou have the new piston mounted on the rod, make certain the rod is oriented the same way it came off before. It only works one way in that cylinder.

 

Piston is basic part number 6108.

 

Thanks for all the feedback. As requested, I have included two pictures. One picture is of the piston and the other is of the cylinder head.

 

Looks like a chunk of piston shattered off, and its pieces bounced around the cylinder, causing the dings. Did you find other pieces of aluminum in the cylinder? Or, maybe they'll look like sputtering of melted aluminum deposited on other surfaces.

Detonation like this in just one cylinder suggests severe lean-out, like maybe the injector was not opening properly. I would check that out before running the engine again.

 

That's detonation damage, although hyper's usually shatter when this happens. Ford may have changed the make-up of the pistons to prevent this from happening.

 

Thanks for all the feedback. The block is currently at the machine shop. I am going to wait until I hear from them before I order a replacement pistion just in case they have to overbore the block.

I have a question about the cylinder head. Do you guys think that I should have the head shaved to remove the indentations?

 

Yes do have the heads milled. A .010 cut should clean up the surface and not cause any problems with the sealing of the intake manifold.

The 1996 Explorer V8s got GT40 heads. Does the letters GT appear on the heads? Or are there 3 "bars" on the end of the heads? If so you have good heads for that 302. Have the machine shop port the exhaust a bit. Removing the "hump" in the exhaust port wakes these heads up for very little effort.

 

Yes, this engine has the 3 bar gt40 heads. They cc'd at 65.

 

Shouldn't be any Thermactor bump in the GT40 ports. Mine didn't have them, and they're off a Lightning motor.

 

Mine are off a 1993 Cobra Mustang and they did have the "hump".

 

I checked out the exhaust ports and there is a recessesd dimple in each port the size of my pinky finger. Based on this recessed area, I don't believe these heads have the thermactor bumps. Please let me know if I am off base.

 

Searching "3476 b" and Ford and piston on the Internet produces results that give pretty good evidence that this is a stock Ford piston, even though I agree with Number Dummy's observation that the basic Ford piston part number is 6108.

I respectfully disagree that the engine damage, particularly the sharp dent on the cast iron of the quench area of the cylinder head, is caused by detonation. I would suggest that whatever made that dent must be harder than aluminum, so most likely something made of steel that got into the intake tract.

 

Good point; it's not likely that molten aluminum will cause the dings in the cast iron head. My next guess would be bits of the ceramic insulator breaking off the spark plug and bouncing around, from detonation. Unless that cylinder somehow sucked in a rock.