At 150K I overhauled my 460, rings bearings, valve job etc. It started blowing oil at 245K so I pulled the engine, stripped the block and took it to a machine shop for a boil out, check for cracks, bored 30 over, new cam bearings. I ordered Sealed Power pistons and rings and had the machine shop align the rods and press the new pistons on. I put in the normal items, crank polished, timing chain, cam, oil pump etc. I drove it careful for 3500 miles and decided it was ready to tow. I hooked the fifth wheel up and we headed for Arizona. I drove about 150 miles and noticed the engine was blowing oil again. We turned around and headed home. The pictures show what I found. Five of the eight pistons had the wrist pins shift and migrated into the cylinder walls. I can’t even remove the number 4 & 8 pistons due to the wrist pins moving to far into the cylinder walls. The pistons still look brand new with no scoring or heat marks. I checked the wrist pins and they are well within specifications. The engine never ran over 180 degrees with a 160-degree thermostat and the engine oil ran around 240 degrees. I might have an idea as to what happened, but want to get other opinions. Has anybody ever seen anything like this?

 

the only time i have ever seen something like that happen is with floating pin setup and the retainer clip fails or was installed incorrectly causing the pin to slide out of the piston. should never happen with press pin application, and especially not on all 8.

did the machine shop bore the small end of the rod oversized before installing them. if they were out on the diameter and not within specs, that could cause a loose fit and when the engine heats up, the pin will come loose.

are the pistons designed for a floating pin because sometimes they will come with smaller diameter pins so you don't have to remove as much material from the small end before bushing them for a floating pin. don't know which model # pistons you ordered so can't look them up to see.

my guess would be one of the two. can't see a machine shop installing all 8 pins and pistons incorrectly

that is the only 2 things i can think of that would cause soemthing like that to happen. unless the machine shop really scrwed up and didn't correctly center the rod on the pin but i don' think you can do that with the way the pin lenght and rod width are designed.

i would definetly be going back to the machine shop for some answers.

rgds
Mike

 

This is a press pin applicaion. I can't see why the machine shop would ream them out. The pins were centered on the rods when I installed them. Pins 3,6 & 7 stayed centered all the rest moved. I plan on taking them to a different machine shop first for an evaluation. Thanks for the response, Gary

 

The only reason they would move is they were too loose in the first place and if the shop heated the rod ends to install them they would have never noticed it. As always, you make your own luck in engine building, you have to check and recheck everything. I'd press one out and check the press fit with a good set of mics and dial bore gauge and see just where your at. If it turns out there wasn't enough press in the rod then I'd still call the piston mfgr. Probably won't get anywhere with them, because the builder should have caught that but you should still give them a piece of your mind on the matter.
Sorry to see this. You must be sick over all that money you spent.

 

I am building a 460 for a customer and took everything to a reputable machine shop to get checked/machined. Turns out 2 of the rods were out of spec on the small end and had to be replaced. A good shop will check everything and recommend replacement as needed.

This has got to make you sick, I know it would me.

 

Thanks for all the comments. The amazing thing about this is that I drove this truck for 245,000 miles and never had a pin shift. If it had happened on one piston I could understand it, but 5 out of 8 pistons, after 3500 miles, makes me wonder. Did the machine shop screw up or did the piston manufacturer screw up? I don’t know. I don’t have the equipment to diagnose the problem, so I might take them to a different machine shop and see if they can give me an idea. I wouldn’t expect the truth from the shop that did the work. My next door neighbor is a machinist and he came over with his micrometers and measured the wrist pins and the are well in spec. We did find a blue spot on one wrist pin that might have shown signs of overheating, but that was on only one. I do have a temperature probe in the oil pan and monitor both the oil and water temperatures. The water temperature never went over 180 degrees and the oil temperature rarely went over 240 degrees, so I can’t see that heat was the problem. Now I have to find a block to rebuild and am going to try to find a block with good pistons in it so that I can just rering without boring.