First of all, 5.8L, '93 F-150, 4X4, E4OD

Had a very bad engine knock so I figured it was rod(s) and took the truck to get the engine rebuilt. The builder just told me it wasn't a rod knock at all (spun bearing) but that some pistons were actually broken! He didn't have the time on the phone to go into how/why, but what would do this?

AFAIK, the engine had been rebuilt -/+50K ago (high-comp pistons, quality parts, MSD ignition, K&N filter...). I was running it on premium because of the compression. I'm not challenging the builder nor anyone else, I just don't know what could have happened to BREAK 5 of the 8 pistons (and the damn truck still ran enough to drive it up onto the tow flatbed).

Any ideas? If the problem is external to the engine I absolutely don't want to go through this again.

 

Maybe the pistons were damaged, but not broken. I really don't see a truck getting itself up a flatbed with 5 out of 8 pistons physically broken.

 

A spun rod bearing can allow the piston to make contact with the head if the bearing and or crank journal wear enough from the damaged bearing. If all 5 had severely spun bearings then all could break from this condition. If this happens then that particular piston can break from the impact. If the engine still runs those small broken pieces can migrate through the intake valve port (past the valve) into the intake manifold. From there they will bounce around and eventually get sucked into one or more of the other cylinders. Those pieces can then affect the clearence between the pistons and cyl head and cause the those pistons to break as well. A hydrolock can bend a rod causing it to distort/twist putting side loading on the piston and cause the piston to break as well. Detonation is another cause of piston failure and there are other phenomena that takes place as well. I don't think anything external would be responsible unless you're only driving it 1/4 mile at a time... The pistons can break into two or three large pieces and still be intact on the wrist pin/rod and still function. If the piston top ring lands are broken only then it's more than likely from detonation.

 

Cast or forged pistons ? Sounds like they just threw the pistons in there and didn't check all the clearance area's. With that many broke pistons there's a comon factor somewhere ??

Was timing retarded with the high compression pistons and a longer duration cam match to the pistons ??

 

Don't know about cast vs. forged, but the engine did (supposedly) run for a couple years with this build.

So unless there was something that entered into the combustion/fuel chamber, the problem is almost absolutely mechanical...? How about if the cam chain slipped - with hi-comp pistons, wouldn't there be a likelihood of valve contact? Don't know about a high-lift cam or not.

Thanks so far.

 

The key here is the spun bearings. Once they have spun or seized, there is little or no oil go to the pistons. The cylinder MIGHT pick up some spray from a neighboring cylinder but eventually the piston is going to over heat and crack or break. You need to expect to have a complete engine exchange. The crank is not going to carry any major load anymore as it is damaged. The block most likely is going to be scored from the lack of lubrication. But I would want to be there when the engine comes apart and be looking for reasons for failed lubrication. If you have any of the oil left from it, I'd suggest having an oil analysis at Blackstone or any of the other labs across the nation. They might be able to tell you what the failure was from the report. A ferrography will tell you but I doubt you want to spend the bucks for the test.

 

LOL Ya this engine is definetly a boat anchor at this point Labnerd. I would think that since the mains feed the rod bearings then the only piston affected by oil loss should be the one with the spun bearing assuming the others are not spun and unless the piston debris is now starting to block the oil sump pickup screen. I would be curious to see if the other broken pistons are still connected to the rods via the wrist pin. In some cases when you lose lubrication to the pistons they tend to start micro welding from the bore to piston friction. When this happens the resistance is to much and the wrist pin will pull free from the piston dome. On the next up stroke of the crank the rod will be out of control and will make contact with the now dead piston and launch it up into the cyl head and valves breaking the piston in most cases. Another scenario is if you have floating wrist pins and a C clip migrates out of place in its groove this allows the wrist pin to move in the direction of the dislocated C clip and this puts to much wrist pin pressure on one side of the piston causing piston failure. In regards to oil analysis I have only been on the side of collecting samples and reading the results when returned from the lab. So Labnerd with crankshaft material, bearing material, block /bore material, and combustion chamber contaminates such as raw gas present in the oil are you confident that the root cause could be determined through and oil sample? I'm not trying to be funny here as I respect your opinion and knowledge on this just curious as to what you would look for in an oil sample as a primary indicator of a catastophic failure. Thanks.

 

My 89 F150 with a 302 started to burn oil so I pulled it apart and found the oem cast pistons were cracking around the oil rings. Replaced the pistons with aftermarket ones and now have 250 K miles on that motor with no problems. I heard Ford had some issues with pistons back then ??

I had a 302 with forged 12-1 TRW pistons and one of those pistons ate a bolt and washer when an internal bolt on my 2 piece tunnel ram came loose. Piston beat the hell out of it and still looked really good. Just had to replace a valve and was good to good, never did find the bolt or washer.

I got another 302 with a 275 shot of nitrous and still running strong for 10 years now and it has forged pistons too.

So I bet somebody use some cheap pistons or hyper ones. If you going to rebuild it go with some high quality forge pistons.

Forged pistons can make a bad tune look good but if they are cast then

If the valve's hit the pistons you should be able to see round marks on the piston's, and may have bent valves too if that happen. If so I bet the engine would be making alot of noise too.

Now if the engine has detonation issues due to high compression, timing or fuel then that will do alot of damage if not corrected quicky to pistons and bearings.

 

Dynotech, I'm sure ya'll probably destroyed more 302's on purpose than most people have seen. I'm betting that there are more than one bearing, toast. We've seen these bearings with failed lubrication completely launch and fall into the pan. After that, there is no lube of any kind in the engine as the pump is just pushing oil out the now empty bearing port. In regards to the oil report. We all assume incorrectly that the oil used is on grade. ILSAC has expressed concerns to the API that in their findings, 20% of the oils you are buying are failing to meet standards. Some disastrously so. Then you have oils like the M1 5w-30 that blatantly has failed the IVA testing now for over a year. Filmy may have rights under law that should the oil fail testing requirements, he could sue the maker. The spun bearing is a direct result of a lubrication issue. Finding what caused it and having documentation is critical if he intends to hold liable the oil company. Doesn't necessarily mean it was the oil as it could have been a sludge issue at the screen and other things but for the $20.00 he'd spend on the report, I think it's just a great investment. The ferrography would tell him what parts were suspended in the oil and MIGHT give him a clue as to where the failure started. But the oil report should be the first step...if he wants to find out what happened and eliminate or pin point the oil as the culprit.

 

Good info. Thanks.