Odd wear on crankshaft bearing.

John M · Aug 9, 2017

Thrust bearing on a 2000 something Mack. Lower has extreme wear on outside edge, top is same way on opposite edge. Wear starts near center and tapers out to the edge The other mains and rods all look perfect. If I can, Ill try to get a pic later.

rustyfarmall · Aug 9, 2017

I will guess that the connecting rod is slightly less than straight and true.

glennster · Aug 9, 2017

pretty weird. if the crankshaft was bent, it would wear all the way around. is it possible the main bearing cap was installed backward? for some reason it sounds like the thrust bearing is sitting crooked in the bore. you may need to get the block align bored.

Janicholson · Aug 9, 2017

Probably a defective original bearing insert. I assume the bearing insert halves were not placed on top of something when installed, cocking them crooked.
was the wear pattern in the cylindrical part of the bearing (radial load) even and similar to the other mains? if so I lean toward a defective original bearing. If it too was uneven and shows tapered wear, I would agree with the line boring of the block. Jim

John M · Aug 9, 2017

Its a main, thrust bearing.

John M · Aug 9, 2017

Thats what they are leaning toward now, but this engine has never been into, so it was done at the factory.

John M · Aug 9, 2017

Jim, its both the upper and lower bearing. Its just on this one spot on each. The other mains and rod bearing look really good for 300000 some odd miles. The 2 in question dont even have ANY wear, where its not wore bad. Im going shortly for a pic, maybe thatll explain better.

John M · Aug 9, 2017

Heres the bearing, hopefully. This is the lower one. Wear in on the back side (Of the engine). The upper one is wore the same way, but on the front side. On both, the part with no wear is perfect, no wear AT ALL. This is the center thrust bearing. The rest of the mains are not this wide, but they look really good.

John M · Aug 9, 2017

Dont know why 2 pics showed up! Couldnt find what he did with the top one, so I couldnt get a pic of that one. When the guys come in Ill ask about it.

Janicholson · Aug 9, 2017

I am not picking an argument but the bearing you have in the picture is a main bearing. Possibly wider, but it has no thrust responsibility. The main cap and block may be milled at that spot for 4 thrust inserts that are not shown, but a thrust bearing is responsible for forces on the axis of the crank. If there is nothing under the insert you have pictured, and its brother in the block, I believe the block needs to be line bored. Jim

John M · Aug 9, 2017

Yea, just used that as a reference I guess. The cap and block are machined for the thrust part, but this is the "thrust" bearing.

Dopp Creek · Aug 9, 2017

If it is the location that has the thrust washers, the bearing may be shaped that way to allow pressure oil to bleed down and lube the thrust faces. The front main bearing of many Lycoming aircraft engine bearings have that feature.

the tractor vet · Aug 9, 2017

You are showing Cap side , how about what the bearing looks like in the block, Is it wore on the opposite side ?? . If so then your block has tweaked and to solve this problem a line bore is needed . Notice i said LINE BORE not line HONE . Bearing ware like that was common on 351 and 400 M Ford engines and on them the block core shift was unreal . Most people would blame a bad oil pump but that was not the case .

John M · Aug 9, 2017

I do believe I mentioned it was.

RodinNS · Aug 9, 2017

I'm no expert on this... but if you got wear on the front of one insert and the rear of the other insert... that says to me that either the shell is not true in the saddle, OR... the saddle is not true... and has been tweaked as suggested. If it was me, I think I would have it line bored for no reason other than piece of mind.

Rod

gab · Aug 9, 2017

I've never seen the inside of a Mack but any thrust brg. I've ever seen looked like this.

docmirror · Aug 9, 2017

It's a machining defect of the main journal. It is not ground perpendicular to the crankshaft centerline.

When the machine, or operator setup to grind that journal, and also to drill and tap the cap holes, there was an angular misalignment with the block. Either the grinding/boring bar was offset, or the block was not set right on the table.

Usually, these holes are done with a long boring bar which does all journals. However, in some cases, a human may have to go back and redo one of them if it isn't right. Also, the alignment of the cap bolts affects the relationship of the bearing saddle to the shaft.

That journal is just kinked a bit in relation to the other journals and the crank. I'm betting that engine was TIGHT from the factory, but not quite bad enough to spin the bearing. it just ground away at the bearing material until it had enough clearance to run.

docmirror · Aug 9, 2017

The other possibility is that the journal on that crank was ground on an angle.

John M · Aug 9, 2017

Its a 3 piece bearing. If you look at the pic, you see a slot on the sides. This pic is what the other pieces look like. The one with the tab goes in the cap end. These are the exact one, but the best pic I could find on the net. The dealer came and got the truck earlier, and took all the parts with them.
here.

John M · Aug 9, 2017

A rep from the dealer came just before lunch, since the engine has never been into. He confirmed the factory parts. They are going
to try and find out what happened and theres a possibility, even with the miles on it, they will replace the engine. It left for
the dealer about an hour ago.

Mike M · Aug 9, 2017

Why was it pulled apart in the first place ?

I see the dealer has it and hopefully if it was made wrong they will make it right. I'm surprised they even came to look at it.

John M · Aug 9, 2017

Lots of little metal filing on the drain plug. Boss said to check it out.

T.R.K. · Aug 9, 2017

My opinion:

Your block still had some stress in it when it was machined and now that journal in the block is twisted. That is why they used to 'age' castings for several months after they were made, so they would relieve their inner stress and the final machined surfaces wouldn't 'move' or twist.

You don't say how many hours or years or whatever miles is on it.

I am thinking the proper repair would be to line-bore or line-hone the crank bores to get them all back in line with each other.

On the other hand, it has 'machined'(worn) its own clearance and if you put it back together with the old bearings, and it doesn't move any more, it will probably run a long time. If you put new bearings back in it, it will probably freeze the crank when you torque the caps. Or spin the bearing soon after you crank it.

High Octane · Aug 10, 2017

Dirt under the inserts ?

docmirror · Aug 10, 2017

(quoted from post at 12:51:22 08/10/17) Dirt under the inserts ?

Under both bearing shells? hmmmm

As above that though, could be the casting has moved after machining, and caused the cradle of that machined journal to bend a bit after some heat/cold cycles in the field.

Not surprised there was some light swarf in the oil pan. Check if it's magnetic. If so, it's not bearing shell material.

Odd wear on crankshaft bearing.

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