Galvanic Destruction of Bearing Material

[bc.gold 3,403]

I once purchased an Onan engine that had been completely rebuilt before it was put into storage, I needed to swap out the stubby generator crankshaft with the one from my CCKB to use in my tractor.

 

The engine was as the seller had claimed with all new parts inside, much to my surprise the connecting rod bearings were pitted, the tin in the babbit had migrated leaving the shells badly pitted.

 

The bearing shell below is from a Lister I have recently dismantled, hopefully you'll be able to see the pitting along with discoloration.

 

This is what can happen to barn finds that have sat in storage for years.

 

NASA Tin Whisker (and Other Metal Whisker) Homepage https://nepp.nasa.gov/whisker/

 

In the galvanic scale below any metal above those below it will react with those below and none above it.

 

Edited October 7, 2018 by bcgold

[bc.gold 3,403]

Those pits do not look particularly bad but they're a good place for grim and grit to hang up which could lead to early bearing or even crankshaft failure.

[bc.gold 3,403]

Here's one I missed, electrostatic electricity caused by loose drive belts can prematurely wear out your engine bearings.

https://www.machinerylubrication.com/Read/638/failure-analysis-bearings

Edited October 7, 2018 by bcgold

[ebinmaine 70,751]

I remember that chart from many years ago.

Interesting stuff.

Thanks for sharing.

 

[oliver2-44 10,370]

I've been around engineers discussing galvanic corrosion discussions at work for years, but am far far from any expert.   What I find interesting is mild steel (crank shafts) and lead and tin (bearing material)  or even aluminum (rod material) are not very far apart on the "Galvanic scale" so that should mean there is less galvanic potential (battery effect)  between them, which translates into less probability of galvanic corrosion.  They always said if the materials are more that 3 apart on the galvanic scale, then theirs a reasonable galvanic potential that could cause damage.  We used sacrificial zinc anodes on steel floodgates to protect the steel. The zinc anodes had to be replaced about every 5 years and zinc and mild steel are 3 apart on the scale.

 

so while I'm not doubting your findings, there something more to this than I comprehend at the moment!

[bc.gold 3,403]

One of the uses for silver nitrate was on steam powered ocean ships a sample of boiler water was removed then a few drops of silver nitrate were added if a cloudy white precipitate ( silver chloride ) formed then the engineer knew seawater had entered the boiler jacket.

 

I'm no expert either and started my study late in life.

 

 

 

Edited October 7, 2018 by bcgold

[bc.gold 3,403]

I think that aluminum connecting rods are made from an alloy family with a high copper content same for outboard engines and other aluminum marine related gear.