SOHC.co.uk Forums > CB750

New Main and Big End Bearing Shells

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adriangsmith:
what is the consensus regarding ordering new bearing shells?
Do we go by the original markings or do we need to measure the diameters to allow for any wear?
I understand the procedure for matching the originals via the stamped markings but concerned about wear on the journals etc.
Also i cannot read the size markings on my conrods. I can see the letter K on all of them but no further markings.

At £180 all in i don't want to get it wrong!

AshimotoK0:
Really one for Oddjob, Bryan or Trigger .. I would run your fingernail across the journals and see if there is any scoring or or obvious visible wear. The crank stampings, relating to the journal sizes,  are only valid when the crank was new. Also send us some close up shots so that we give you an opinion. I had mine 'mic'ed up' by someone who had the right micrometer, experience and feel. At the factory they would have used air gauging to measure them.
 
Take digital photos of where the con rod marks should be and play around with the contrast on the image and they will probably show up. One letter is for the weight and the other mark  for the big end shell size OD (obviously this dia.  doesn't wear unless the shell has rotated in the con rod which is highly unlikely IMHO).

The attached service bulletins are useful.

Trigger:
Need to see the letters, numbers, crank, con rods and old shells.

adriangsmith:
Hi All,
Here is what i have so far:
crankcase BBBBB
Crankshaft AAAAA 4444

All crank journals measure at 35.96 - 35.97 (will take it into work tomorrow and measure to 3DP)
Main scoring is on the centre main journal.
All main shells show a pitted finish but not through to the copper.
All big end shells are through to the copper in places and some are scored, no scoring seen on the corresponding crank journals.
Pictures below.

adriangsmith:
Hopefully this shows the state of the big end shells

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