Hey all. I have a big problem to deal with regarding my engine in my truck. It’s a 1997 F-150 Supercab 4x4 with a Windsor style 4.6L V8. The engine is a rebuild through Ford with only 50,122km on it (warranty is only until 40,000km). Since the rebuilt engine has been installed, the dealer (under warranty work) has installed 2 new heads, a piston in cylinder 3, and a coil. I didn’t own the truck at those times but now I do and have a broken piston in cylinders 2 and 4. I have had numerous people looking at the breaks ranging from heavy-duty mechanics to automotive mechanics and none of them is able to give me an exact solution as to why this happened, nor have any of them seen a break like this before. They are almost identical in size, shape, and location as you can see from the picture. I used to sue Wal-Mart brand synthetic oil (5W-20) with a Fram synthetic oil filter. I recently put a duel exhaust on the truck (and pulled both the cats and resonators) and didn’t install the 02 sensor simulators and have gotten a couple engine codes, catalysis system inefficiency, and engine system running lean. I cleared the lean code with my code reader and about 3 weeks later, my truck started to shake violently one day coming home from work and it also had no power. I happened to have my code reader with me and read a cylinder 4 misfire. Upon inspecting the plug, it was deformed somewhat and flattened out, so I pulled the heads off and found 2 broken pistons. I also noticed that the timing chain looked as if it was off one link but I’m not entirely sure. The truck also used to have a clicking noise or high pitch ticking noise coming from the top rear of the engine under load at about 3000-3500 RPM and was getting significantly louder before the failure. The valves, heads, and cylinders all look real good. There is just some spatter on the two valves in cylinders 2 and 4 (I am thinking the piece of piston just disintegrated into tiny pieces, being cast aluminum) but the valves are fine scotch bright will take it right off. Please give me some insight as to what happened and how I can fix the problem. I am putting in 8 new pistons to eliminate bad casting problems with the pistons, the 02 simulators for the exhaust, and Amsoil synthetic oil, oil filter, and air filter. Please help!!!

View photos here:

https://www.f150online.com/galleries....cfm?gnum=9705

5 pics in each album

 

Detonation? You just don't clear a running lean code. You have to chase down the cause and fix it.

JMC

 

umm, ouch

 

Looks like casting flaws. Btw, you HAVE to have the front O2 sensors installed in your exhaust.

 

You mean I need to install the O2 sensors that were near my cats right?

 

Your stock engine has 4 O2 sensors. The FRONT 2 ( one on each bank before the cats) are used for A/F ratio determinations... The REAR 2 ( one on each bank and AFTER the cat's) are used to monitor catalytic converter efficiency. The REAR 2 provide NO useful info to the engine. The FRONT 2 are essential for proper engine function.

 

I'd tend to agree with this. It looks like detonation broke out the ring land. I bet the wrist pins are tight (another sure sign of extreme detonation).

 

I didn't get headers so really there should be no change to the O2 sensors at the front right? Doesn't each sensor go into the pipe off the manifold before it Y-pipes into one (stock). I thought that you would have to change the ones that went into the cats since I pulled them and now they are just going straight into each pipe. I figured the two up front would be running at the same temperatures since nothing change there. I am new to this stuff so please help me out a little haha.

 

I have a 5.4 and I figured they would be the same, but since we're not on the same page, I may be mistaken.

 

I usually agree with JMC but not this time- I don't see pock marks and aluminum ***** that usually accompany severe-destructive detonation

I have seen this before on race engines

The engine builder speciallized in building alcohol fueled engines for sprint cars. Alcohol engines run very cool compared to gasoline engines

When he built a gas engine for a modified stocker he used the same ring gaps as he used for the alky engines.gas engines need a wider gap than alky engines due to increased expansion from the higher operating temps. when the engine warmed up during the race the lack of sufficient gap would cause the top ring to sieze in the bore and break the top of the piston off. just like in your pictures. only the top ring was seizing since the top ring runs hotter than the second ring.

It took the engine builder about 4 or 5 blown engines before he figured out WTF was going on.

so I would remove the two pistions and carefully remove the top rings and insert into their respective bores and measure the ring gap.


If I am right just score another victory to the laws of chemistry and physics and also let me know if wrong ring gap is the problem.

 

My obvious lack of experience with the internal mechanics of this particular engine may come to light in my following comments, but...

Is it possible that the block was decked too low, or the wrong head used, or you have a damaged bearing resulting in the piston hitting the head? Notice that it is at the bottom of the cylinder.... Foreign objects would tend to fall in that direction..... I know it might be a long shot but....

 

I would go with the lean condition causing the problem. I had much the same problem on a carborated car that I modified. All the rings were busted, not the piston, but the cause is the same.. lean mixture is NOT good for the engine. You said it yourself.. lean codes tell you there is something wrong. And you ignored it.

 

Looks like pock marks to me on the left side of the piston. Some of the other pics show them also. Those little chunks out of the carbon were caused by the sharp and powerful explosions of pre-ignition. Basically, the fuel exploding while the piston is still going up. Very hard on the piston.






Also, the original poster said: The truck also used to have a clicking noise or high pitch ticking noise coming from the top rear of the engine under load at about 3000-3500 RPM and was getting significantly louder before the failure.

Ticking under load is a very strong indicator there was detonation.

 

You're very observant.

 

I have the pistons out now and the break isn't consistent with a lean condition. If I was running lean enough to take out a piston there would be melted marks around the break or the edges of the break would be well rounded, instead they are just slightly rounded and the area where the piston broke is carbed up like the rest of the piston, suggesting to me that the pistons were like that for a while. Also, a piece that size would HAVE to leave some kind of mark either on the piston, cylinder wall, valves....somewhere. The cylinder walls are spotless. One merchanic suggested that the piston may have been dropped and broken, and someone installed the piston anyway to cover up their !@#$up. Wouldn't the engine be running hot if running lean enough to do that to a piston? My temp needle was barley at a quarter.