[Sterly]

I've stripped down a friend's 455 +.030 and found on main bearing number 2, both halves have completely lost their tension (spread?) and just drop into their housings. The mains are -0.010. All bearings were in a mess because the engine had lost cam lobes in the past and a lifter had come apart so I was expecting messed up bearings but not a pair of loose shells. The other main brgs were fine in that respect. No evidence of overheating as far as I can tell. Also no evidence in the cap or block that either bearing had been moving. What might have caused this?
Thanks
Mark

[steve25]

That's strange!

Are you sure neither shell was moving because if it was the number and letter impression from the rear of the bearings would look smeared in the cap and in the block .

On the other hand if there is no impression in just that number 2 cap of upper Bore then something was off even when that motor was put together and even fired and it's lucky that the Bearing did not spin.

I would very carefully check that blocks main webbing for cracks and the Crank also!

[Sterly]

Thanks for the quick reply. All the imprints of the lettering were readable, cap and block, with no smearing - just the same as the others which is why I didn't think it had been moving. Strange indeed.

[Formulajones]

Sounds like possibly a line bore wasn't done properly, or maybe not at all, and that particular saddle just never had enough crush to start with.

[Sterly]

I think the saddle size must be right or close because shells from one of the other positions snap in just fine. I don't have the block at the moment so I can't do any measuring.

[johnta1]

That would be a good thing to know.
I'd check the oil passages around that main, and check the crank around that main area.

[steve25]

Maybe defective Bearings from the get go!

[Shiny]

Any chance the assembler filed or ground the shell to try and adjust clearance?

[Sterly]

Yes, that's what I was wondering

[steve25]

Can you post a picture of that # 2 main bore ( both cap and block side ) and then 1 or 3?

[Sterly]

Unfortunately the block, crank and old bearings are at the machine shop. I don't think the bearings had been filed/ground though.

[Bruce Meyer]

Make sure you mag the crank. I had that happen. The bearings lost their crush. They just fell out of the saddles when I took the motor apart to freshen it up. I took it to the machine shop and showed them. They magged the crank and found it to be cracked. The crank was flexing around and beat up the bearings. Thank God it didn't break all the way.

[Sterly]

Ah, that makes sense. I told them the problem and they said they would mag the crank anyway but they didn't tell me of their suspicions.
Thanks

[Half-Inch Stud]

Dreadful mystery for a loose bearing shell. Can you. determine if 1 or both are shy?

[steve25]

One things for sure if nothing else comes up to say that the block is in some way at fault and the crank mags good I would still replace the crank as could be cracked deep inside and that would mean it would pass a mag test and then fully fail and take
Everything with it!

[49Diesel]

I doubt the bore is at fault , but installation of the caps and measure to compare would verify . Check if the numbers are correct for size on the bearings ( .010 " ) , I've seen a wrong bearing put in the box and if not checked the engine would go together thinking all was correct. Even mic that bearing each 1/2 and see if it is correct .

[Formulas]

I beat the dog pizz out of my old 400 in my 68 GTO spun a rod bearing from detonation / advanced timing the main bearing shells popped out when I pulled the crank out of it

I put it together 4 years earlier with std TRW forged pistons the bearings were fine going in circa 1982

[Sterly]

Thanks for all the replies. The shells definitely had the correct numbering. I will report back when I have some news.