View Full Version : Cat D2 D3400 Main Bearing Babbitt Separation - What Causes This?

10-14-2019, 08:58 PM
I've been working on a D3400 out of an old 5J, this engine had previously sat with straight water in the cooling system and froze hard, destroying the block and head. After we got it home we drained 3+ gallons of water out of the crankcase before any oil came out (have no idea how long it had water in the crankcase but assuming a couple of years anyway). Surprisingly the internals of this engine were still in very good condition both wear-wise as well as very minor corrosion, it looks like the oil pump and pickup tube/screens bore the brunt of the damage. But upon teardown I noticed that two of the lower main bearing inserts had the Babbitt layer flaking off of the backing - see attached pic. All others appeared fine and running clearances were still at the tight end of the spec with crank journals still perfect. I've since found a complete NOS main bearing set to replace these with so I'm not worried there, just wondering what causes this type of deterioration - poor adhesion of the Babbitt during manufacture, water contamination, improper oil?

10-14-2019, 10:17 PM
Hi Toby,
my guess from the pic attached and Cat literature with similar pictures of spalled bearing surfaces is Cat say from :- exceeding the expected life of the bearing.

By the wear pattern low on the bearing shell I could suspect excessive clearance from undersize journal or as said above just plain fatigue of the bearing material over many hours of operation.
Lugging by operating in too high a gear when towing etc. may play a part too.

Maybe do some clearance checks and see what you find. Also suggest check the crank for truth, ie. bend, twist, etc.

Google could come up with many pix and other scenarios too.

Interested to see what you can come up with.

Eddie B.

wimmera farmer
10-15-2019, 01:37 AM
I know I must be dreaming but it looks like a hammer blow near your thumb. Metal has been displaced to the side.

10-15-2019, 03:57 AM
In the IH world the big v8ís can wipe out cam bearings if sitting for a long time. The recommendation there is to prime the oil system before turning the engine so you donít wipe out the babbit layer. Were there any chips of babbit in your oil pan?

10-15-2019, 03:06 PM
That looks to me like typical erosion caused by water in the oil.

10-15-2019, 07:59 PM
Thanks for the replies everybody, I appreciate the help. I'm mainly curious about what caused the damage so as to avoid it happening again, if possible. Some specs from teardown -

Crankshaft endplay .008" (spec .009"-.015", max allowable .020")
Rod bearing clearance, aluminum .007" (spec .0055"-.008", max allowable .013")
Main bearing clearance, Babbitt .006" (spec .003"-.0055", max allowable .012")
Crankshaft main journals measure 2.748"-2.749" or .001" out of round with no taper (new spec 2.749"-2.750" with max. out of round .006", max. wear .007")
Crankshaft rod journals measure 2.623"-2.625" or .002" out of round with no taper (new spec 2.624"-2.625" with max. out of round .006", max. wear .007")

I have not had the crank checked by a machine shop yet for bends, twists, etc. but I do like what I see with the above measurements. Again, I have no idea exactly how long this engine sat with water in the sump but I would guess at least a couple of years from the story the previous owner told me. Even the pistons, pins, and rings show no real signs of wear anywhere and all clearances were still well within new spec. so we decided to find good replacement block and head castings and see if we could take all of the good "insides" combined with new liners, rings, and other minor parts as needed to make a running engine again - we'll see.:crazy:

A few better pics of the old bearings in question, first pic is a better view of the original bearing I inquired about, I like Andrew's description of "erosion" because it appears that something "washed away" some of the babbitt, and the darker discoloration around the missing and cracking material seems to indicate that something was breaking down the Babbitt. The spots that appeared to be hammer blows are sections of Babbitt that have cracked and are shifting away from the backing. Second pic is the other lower shell that began losing material, again both of the bad bearings were lower shells and their upper counterparts still looked pristine. Third and fourth pics are the two bearing sets contrasting the lower damaged shells next to their better upper shells, notice in the third pic the upper shell has visible lines going across it, those are high spots that were in heavier contact with the main journal, you can feel them when you run your finger across the surface - kind of strange to have a textured surface like that on a main bearing.

10-16-2019, 06:38 AM
It looks like electrolysis removed some component or impurity of the babbett. Maybe there was some slag that got into the pour.

Rome K/G
10-16-2019, 08:32 AM
Welding on the machine. Not properly grounding close to your weld area will arc bearings.

10-23-2019, 04:12 PM
I had the same thing in my D4-2T:
There were rust pits through the bottom of the water jacket where anti-freeze was seeping into the oil but it wasn't enough to notice. There was enough sediment in the bottom of the water jacket to keep the holes plugged somewhat, but after cleaning it out, this is what was left:
After finding this, I assumed that the bearings were dissolved by anti-freeze.

Old Magnet
10-23-2019, 05:15 PM
Yes, seen it before. Worst case I've seen was Jack up in Hood River Oregon (if I recall right) when he was going through the building of his D311 bio-diesel generating plant. Looked like worms had eaten the bearings. Product of water in the lube oil and acid formation that eats the bearing material.

10-24-2019, 02:29 PM
The area where the grooved steel backing is visible looks like fatigue failure.

But wait! Are these babbitt, or aluminum bearings? I have heard Cat uses aluminum. If so, aluminum pits badly in water...OH ions dissolve it. So I will vote for electrochemical pitting from the water. Also, if plain water w/o corrosion inhibitor was used, maybe it corroded around the liner seals, and there was water in crankcase while machine was operating, which decreased hydrodynamic support and increased load on bearings and caused fatigue, also.

Send the pics to a bearing mfr . like Federal-Mogul, if you can get hold of one of their engineers.

10-24-2019, 05:19 PM
Hi Team,
hear what you say about corrosion/galvanic action, BUT, I would expect the surfaces so reduced/etched to have a dull matt grey sand blasted look non shiny finish of uneven shape as these shells do not seem to show.

The polished fairly square edged ruts we see appear to have been polished by the loosened fatigued pieces moving about--telling factor would be if the loosened pieces from such a fatigue failure would still have been in situ, on the sump pan floor, in the suction screen or smaller particles in the filter, or even cleaned out of the pan and ignored by others.

Bond separation would show similar signs to what we see also--if these are Babbitt coated bearings--but usually covers a singular larger area than the ruts we see.

These are My thoughts and experience, you are all entitled to yours.

Eddie B.

10-25-2019, 08:28 PM
Thank you for the replies everyone, much appreciated.

10-26-2019, 06:59 PM
Hello, Guys,
The old D2 engine on my generator is still ticking away, crank bearings and all. This fall I pulled off the lube oil rail and put new gaskets on it and the filter base. The gasket sealer I had used didn't work very well and I was leaking about a quart /week. At around $16/quart, I was getting a bit concerned. I used old #3 Permatex this time. so far, so good. This is the only service work this engine has needed outside lube oil, has probably 2500 hours since build.

On to my experience with bearings: I found it impossible to find undersized bearings for rods or mains, so started hunting around. I found a couple shops that said they could rebabbitt old shells. When I told them that the shells were aluminum, they backed off. Nobody would commit to a claim that they could stick babbitt to aluminum, and I believe that, unless possibly it could be done with silver. My main supplier found me a very good shaft with set of bearings, so the hunt for inserts ended and I am back to standard size.

The bearings in the pictures look like my thick aluminum 5U inserts. I have never been into the bottom end of my 5J engine, but I believe it had the same bearing scheme as the 5U engine.

It doesn't take much to corrode aluminum, especially when it is next to steel, and especially when there is water present.

I heard more recently of a repair done by machining steel inserts that could be babbitted, cannot remember who it was but I think it was on this BB.