I'm Stumped, please explain these markings!

[GI-John]

Tearing down the engine I picked up, I noticed these punch marks on every piston. I've never seen this before. Someone PLEASE explain the logic to this.

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[babywag]

Someone trying/tried to free up a locked engine?

Someone trying to remove the pistons the hard way?

[GI-John]

I should mention that I have no clue as to the history of the engine. The guy I bought it from claimed it was out of a 72 J truck. The amount of crud on it made me think that it had not been opened up.
The heads have an 83 code on them. (I'm guessing that's the year)
The cam and lifters had some wear on them, but nothing that looked out of the ordinary for a 30-40 year old motor.
The crank and rods, as well as the bearings were okay, I think I might be able to get away with just polishing the crank. I've never built an AMC motor before, but I'm working with my mechanic buddy who is the Maintenance Manager for my shop.

[CheapJeepBrad]

That is either the highly-sophisticated science of piston balancing or somebody dumped a sack of bbs in the carb.

[mokurt]

That is either the highly-sophisticated science of piston balancing or somebody dumped a sack of bbs in the carb.

BB's came to my mind also.


What do the heads look like?

[fsj454]

piston nerl

They do that to expand piston in bore .That is a redneck piston nurl .Works good

[mattmopar440]

has to be "man made" no way something internally caused that on every piston

[Carnuck]

I haven't seen that done since the '70s!

[pineymike]

Punched?

Are there matching marks on the heads,I agree they look to be made on purpose? for some reason? who knows?

[mokurt]

Yep someone could have swaged the tops to try to reduce the clearance.

[serehill]

So

If that was going on to expand the piston & it would only expand the top & bottom then the expansion would be egg shaped? Why did they not do the sides. They are gapped. Wouldn't the mark be concentric & not so close to the edge. Just curious I've never seen this done. I would think ball bearings or BB's also. Weakening the edge of the piston can't be good. It would be a great reason to sell the motor.
The fact there are matching marks on the head dispels the piston expansion theory to me. The fact there are marks on the head make me believe they were bearings not BB's. It would have to be something awfully hard to mark the head.

If he still has the vehicle it would be interesting to see what's in the muffler.

I certainly would not trust the rods. This could be similar to Hydro locking.

[Adam_Tinkerer]

It's braille, for blind engine builders!

[GI-John]

There are no other marks on the heads; they look pretty good. My father in law also thought that it was a redneck way to fit the pistons in the bores.

I think there was another sign that the motor was rebuilt but didn't think about it until now; the rods were already marked. This wasn't something that the factory did, was it?

I'll find out more later this week when I hear back from the machine shop.

[Carnuck]

Most of the ones I took apart were already marked in post '70 vehicles.

[Ristow]

lol. doing that would do nothing to make the piston fit tighter in the bore.

those pistons would go in the scrap bin.