What caused all the small pits in my grease covered NOS wrist pins?

[asstor]

Hi Gang.

I have an interresting case for you. An observation on some NOS pistons and wrist pins I purchased for my M37's T245 engine. The outer boxes stated that they were packaged in 1951. The outer boxes were all in perfect shape with no physical damage or water stains.

Inside the outer box the piston was wrapped in a cotton cloth which was submerged in wax, creating an air and moisture tight wax layer. Inside this was a covering of grease paper, and inside this was the piston - coated in a layer of soft brown grease. The grease was almost like petroleum jelly - no idea if it was cosmoline or something else. The wrist pin was inside the piston, again covered in a grease soaked cotton wrap, and then a grease paper and a thick layer of grease. All this layering surely created a moisture tight package.

After unpacking and cleaning I noticed that the surface of the NOS wrist pins were dull (but smooth) and seemed to be stained, while the aluminum pistons looked as new as the day they were cast - no stains at all. So, I pulled out my handy pc microscope camera.

I took pictures of the wrist pin that clearly shows pitting in the surface. These pits are about 1/1000th inch across and seem to follow the contours of the surface staining.

At first I considered that the pits were inclusions (voids) in the metal. Maybe to hold oil or maybe due to inferior steel used back in '51. That is my question. Are the pits from corrosion or due to the structure of the steel itself?

Here are some pictures of the pitting. (these pits are about 1/1000th inch across). Notice the darker rings or stains that surround many of the pits. The pits themselves are very well defined and appear to be pretty deep and have sharp edges.

Here is a picture that show an area that does not have any pitting.

Any ideas on what the cause may be, but more importantly - are these wrist pins usable? Dimensionally they are spot on, and as I mentioned previously the pits are small - about 1/1000th inch across.

Thanks guys.

 

[zak]

Bad metal from the start or from the hardening process? But if they were like that and passed the inspection process, are they usable today. Where is a good engine rebuilder when you need them

 

[SCSG-G4]

I agree with zak, it was there from the start. Could be improperly mixed carbon steel or a humid day when packed (improper surface prep trapped tiny amounts of water on the surface). BTW, the 'grease' looks like cosmoline, or at least the same stuff I remember cleaning off firearms parts that said they were dipped in cosmoline. Try to look at it this way, the tiny holes will trap some oil and thus give you a slight edge on the lubrication in the wrist pins.

 

[M-37Bruce]

Bad batch?, 1951, maybe they were in a rush to meet production quota's?
Did these parts come from Europe, via epay?

 

[RANDYDIRT]

Dam metal mites.

Dirt

 

[asstor]

LOL, those **** metal mites....

Thanks for the replies guys. I purchased them from a source here in the US, but have no idea where he sourced them.

Louis.
1951 M37

 

[crasheej]

I would use them.

 

[m376x6]

Here's a kicker, they weren't originally made for the M37. They were made for the WWII Dodges which the 3/4 and 1 1/2 Tons used the 230 engine. These were made for depot rebuilds on these trucks which were being sent to Korea and lendlease countries that wanted the old trucks. Given the low compression design of the engines, super fine tolerances and manufacturing techniques required today weren't needed back then, 60 years ago. They'll work just fine in a T245 (M37 230 flat head) but understand, you probably won't get a 100, 000 miles out of them.

 

[WillWagner]

I dunno, the wrist pin is a high stress area. If it were me, I'd mic the old ones and reuse them rather than use the NOS ones. You have no idea if those are surface blems or if the flaws go throughout the pin. Not only that, each time the cylinder fires, it puts downward force on the pin. Those holes could put impressions in the pin bore on the piston and the upper end of the rod and over time cause a piston pin bore crack or seize the pin in the rod, then the piston comes apart or the rod breaks. Don't know which failure is worse, the wrist pin breaking, the piston breaking or the rod failing. I have seen all these failures and they have the same result, a junk block.

 

[M-37Bruce]

Feeshing weights?

 

[kc5mzd]

Aluminum and steel don't mix. When the two are together they can create very small electric currents that will cause corrosion. I would have a local machine shop magnaflux both parts. If the machine shop says they are good after testing them I wouldn’t give it a second thought.

For more info Google "galvanic scale"