Got two f700's with 429 engines. Both trucks/engines have been completely overhauled with new parts and completely cleaned on two separate occasions. Both times, when the engines were broke down, we found 3 - 4 pistons (two on each side) with large holes in them about the size of a half dollar.

This blowup provides absolutely no warning. The last occurrence happened when the truck was running about 30mph. After overhaul, the longest an engine has lasted was about 50,000 miles with the least about 5,000 miles.

It seems odd that the same thing happens to different trucks/engines and multiple times. We have been advised to and completed the following: vacuum leak, new distributor, and exhaust. The only thing we haven't done as recommended is replace the computer(s), or sensors.

Does anyone have any idea what could be causing these engines to blow so frequently? A friend suggested that it may be "leaning out", where the motor isn't getting enough fuel and this causes detination.

Your help is appreciated!

 

More info please, carbed? injected? Which cylinders on each bank (ie. inner 2, outer 2?) Some one here will know or be able to point you in the right direction. also sounds like you have been given a good start as to where to start looking and chacking. Let us know and good luck. OBCB

 

The engines are injected. If I had to guess (it's been a year or so since we last tore into one), it was the inner 2. I have two blown up now that I haven't started on. Don't want to overhaul them until I can figure out why they are blowing.

 

Ouch! Were the blown cylinders the inner 2 on both banks? You said 3 to 4 cyls were failing on each engine, correct? How many different units/ times have had failuers? I'm not familliar with this exact inj. system. Throttle body on a manifold or individual injectors in intake runners? Sorry for the barage of questions, but this has gotten my attention/challenged me. I believe your original assesment of a lean condition is the direction to persue, but wether a vacume leak or fuel starvation is the next ? A hole in a piston crown is usualy detonation, but what brought it on is truly the problem. Hope I'm stimulating the thinking process and not wasting your time.OBCB