Main bearing wear..

[Jhonno]

Would you call this acceptable bearing wear? It's the only one that seems a bit uneven, the rest are centralised and normal wear..

[Jhonno]

At least 20k..

[Jhonno]

All other bearings are fine.. Just this one is like this. The crank is unmarked.

I will measure it all.

[Jhonno]

Actually I wonder if the other mains are normal wear now..

https://goo.gl/photos/b4YvCufa5QUvf17s9

The next main bearing.

[Jhonno]

Front shell.

[Jhonno]

https://goo.gl/photos/9BHu6y3n1dDbv5RJ9

Thrust bearing.

[Jhonno]

PeterBurgess said:

Is the polishing on the block side of the shell too? I have seen this on five main bearing blocks when a ring gear was coming loose on the flywheel subjecting the crank to extreme vibrations. I have also seen it when someone tried to reinvent an MGB crank by knife edging it and setting up harmonics that vibrated it to death (main bearing cap cracked) and one could see similar polish marks to yours on both occasions. Maybe dual mass flywheel fault if you have one? Flywheel runout horrendous etc etc
Peter

I will have to check the block side.. Can't remember.

I was going to Balance the bottom end anyway, so would find out if it was unbalanced..

[Jhonno]

Oh yeah, I realise the sides are normal due to the reason you mention, it was the rest of the wear.

The shell in the OP was the front most main shell, the only thing rotating on that end is the air con pulley. Well, that and it drives the timing chain.

[Jhonno]

Max_Torque said:

Any sign of any dirt / FO trapped between block and cap face? Looks like cap was tipped sideways!

I will check.. I didn't inspect thoroughly, I just looked at the shells at the time.

[Jhonno]

PeterBurgess said:

The vibration can travel along the crank so doesn't always come from nearest rotating item. I bet a crank whips line one-oh if it could be filmed in slo mo.
Peter

True!

[Jhonno]

99hjhm said:

What engine and use?

Flat plane V8, and "fast road"..

[Jhonno]

Mignon said:

Some interesting answers

First off, please post a pic of the other bearing half in that journal.

Edited by Mignon on Friday 10th February 21:32

I shall get some more pics tomorrow..

[Jhonno]

Interesting.. So is balancing a flat plane crank the same as a normal crank then? Or are there other considerations?

[Jhonno]

Upper shell.. Shows normal wear.

https://goo.gl/photos/LR5VFUoBMdgpBAUDA

No balancer.

[Jhonno]

Crank.

https://goo.gl/photos/QiyobyvsibUXWx1TA

[Jhonno]

Rear bearing..

https://goo.gl/photos/o1JDhA3vsyGCY6LK9

[Jhonno]

Mignon said:

Jhonno said:

Upper shell.. Shows normal wear.

https://goo.gl/photos/LR5VFUoBMdgpBAUDA

No balancer.

Excellent. Thank you for that. The smiley in my post above was meant to gently indicate my opinion of the comments so far in this thread. However my own surmise for the actual reason for the wear pattern in the cap side of the bearing could only be verified by a photo of the shell in the block which I expected to show normal wear. So now let's get into it.

In a normal shell bearing the wear pattern should be concentrated mainly in the centre of the U, extending to about 2/3 of the length of the shell and diminishing or disappearing towards the split line of the shell. The reason for this is simple. Most of the forces on the crank from the pistons act in the up and down plane rather than side to side so near the split line of the cap and shells there should not be much contact. When there is contact near the split line then it is generally because the shell has been pinched in laterally by dirt or burrs under the shell or some distortion in the housing.

However your shell only showed wear on one side. It is absurd to suggest this could be caused by vibrations, crank balancers or anything similar. For that to be the case the crank would have to bend significantly right within the 1 inch width of a single journal which is solid metal. It is preposterous. You could take a 1 inch length of solid steel or iron 2 or more inches in diameter and not be able to bend it one iota with the forces acting inside an engine.

So the problem had to be in that specific cap or the vanishingly unlikely case that the crank journal had been ground bigger on one side than the other.

The answer is therefore simple. The shell was pinched in a bit at the split line just on one side by a burr or dirt right at the edge of the worn side leading to most of the contact being on that side of the shell and also accounting for why the contact extended up to the split line.

Interesting! Thank you for your detailed response! 🙂 I will worry a bit less now. It would seem that might be what has happened with the rear shell also.. In fact you can see a spot in the shell, which I believe would suggest that was where the dirt was.

[Jhonno]

Thanks.. Something to watch out for.

[Jhonno]

Boosted LS1 said:

Valid point but why is there even wear on both pinch surfaces? The shell won't have moved across the cap. I think there is more to this Sherlock ;-) ?

Such as?

Both end mains were showing odd wear on the lower bearing only.

[Jhonno]

PeterBurgess said:

We have had good results, especially on V8s with Rattler pullies.
http://vibrationfree.co.uk/sterling-rattler/shop-2...
Peter

Thank you for that link! Interesting company I shall look into..