4.6 stroker issue

[jeepers creepers]

Hi everyone guys,
this is my very first post here, i've been looking on the net to find suitable info but i didn't find that much so i hope to get the attention of someone that went through a similar problem.
A buddy just built a 4.6 stroker using an '88 XJ block, cast# AMC8933002665, '92 YJ HO head, piston part #IC944KTM-030, '88 XJ connecting rod and a '3727 crankshaft, there are a lot of more performance parts like Comp Cam camshaft, floowkooler high flow water pump etc, 62mm throttle body, JBA headers, '00TJ intake, 24 lb fuel injectors etc etc ,so... engine was running find during the very first test drive,coolant temp was just over the 210 F but steady, driving in the freeway temp was fine as well and even less than that then, he told me that pushing a little bit more on the gas pedal and hit the 4000 RPM coolant temp increased a little bit more but everything seemed just fine until he heard the engine knocking pretty bad, idle was pretty rough so he turned it off.
So, he took the engine apart and found four seized pistons, crankshaft and bearing were just fine, so we think is not an oil pump related problem, double checked the clearance pistons/cylinder that is correct to the manufacturer recommendations, rings have the right gap, water pump impeller is ok, same thing for the oil pump, so looks like that everything was fine ,there's nothing but the seized pistons.
My concern is about air trapped in the coolant system that made the temp sender to act funny, coolant temp was way higher than the one the gauge was telling and the engine just overheated so bad.
The interesting thing is that all pistons were seized on the driver side.
Another concern was the water pump, if i'm not wrong XJ's water pump has a different rotation compared to the TJ so i thought the impeller might turn in the wrong side but my friend told me they checked that too and pump is ok.
Do you guys have any suggestion, feeling, advice, tip or idea about that? Any help would be greatly appreciated, i'll try to attach some pic of the piston that might help you out.

[Cheromaniac]

Both the TJ & XJ water pumps turn counterclockwise so that isn't the issue.
However you mentioned that you used IC944 pistons on 4.0L rods. I suspect that the squared off balance pads on the rod small ends weren't rounded off to gain the necessary clearance from the undersides of the pistons to allow them to swivel fully when the engine's hot. If the swivel is restricted, the pistons will eventually get stuck in the bores as they expand from the heat.
The newer generation of IC944 pistons have extra clearance built into them thus avoiding the need to grind the rod small ends anymore.

[jeepers creepers]

that's interesting!we will check that out and let you know , thank you!

[jeepers creepers]

hi, here some pic of the seized pistons and cylinder wall, hope this help :

upload

invia immagini


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caricare immagini

[Cheromaniac]

Seems my diagnosis was spot on. The piston and bore are only scuffed on the thrust side.

[SilverXJ]

As chero said, check the rod on the under side of the pistons. If the clearance wasn't there there will be witness marks. Also, you can't tell proper clearance from a damaged piston.

A few additional questions. What was the clearance used? What was your air fuel ratio?