Crank plain bearings

[daverclasper]

Hi. I've had the bottom end of 4 stroke Jap motor bikes apart before, though never a car engine.

On the bikes, the bores for the bearing shells seemed to be machined out, though I always replaced the shells in the original order to retain the bedding in/wear foot print.

I was surprised to read in my factory Vitesse/Gt6 manual that crank bearing shells need to be replaced in original order "as the shells are fitted onto the block, then lined bored out".

If this is the case, then how can new shells be fitted and the bores still line up?.

Have I missed something basic here?.

Cheers, Dave      

Edited March 13, 2021 by daverclasper

[johny]

I think it means the bearing caps are bolted into place and then line bored which is why the caps are marked so they are always used on the correct bearing... 

[DanMi]

The shells are definitely not bored out, but as Johnny said It is line bored with caps in place.

[daverclasper]

Ah thanks. Maybe I missread it.

All clear now, I was thinking how do they then put the different metal layers onto the shells.

[Nigel Clark]

The old JAP bike motor probably had white metal bearings, not 'modern' shell bearings like our Triumph cars.

As said above, the big end and main bearing caps on our cars are line bored and must go back in their original positions. Most Triumph engines seem to have their bearing caps stamped with numbers from the factory, clearly indicating where they fit. Make sure with the new bearing shells' locating tabs fit correctly and the oil holes align with the drillings in the block (main bearings) and conrods (big ends).

Nigel