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Not fully understanding Big End Bearings & colour codes.

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McCabe-Thiele (Ted):
After some anxiety I think have got my head around main bearing shell colour codes  as the crankcase codes are easy to spot, if the colour code on your old main shell is illegible you can mic the crank and from the tables work out the shell colour code you need.

Although my big end shells are in pretty good condition it got me wondering about how the big end shell colour codes are arrived at. I can understand the journal measurements running along the top of the table but this time instead of numbers running horizontally  there are letters with number running vertically instead of letters. Looking at old posts here it talks about markings on the crank web & con rods - in the absence of any visible markings how do you work out the shell size? At present the only markings I can see on my con rods are the letter "C" that I believe are to do with weight.
My crankshaft seems devoid of any markings although I have not cleaned it with petrol for a possible new reveal. Does this mean that the con rods have coded numbers for the rod internal diameter that in the absence of any numbers I need to measure the con rod diameter to establish if it's a 1,2 or 3 then from the crank jiurnal establish the appropriate letter range? Is it likely that all the conrods will have the same bearing shell size for a given weight code.

Sorry if I sound dense but it is as though they have deliberately switched the rules between the con rod tables & the mains!

Bryanj:
No conrods with same weight code are not necessarily same bore size.
Honda used air gauges to determine bore and pin sizes, if you imagine a faily tight fitting but slideable cylinder that has  an air feed to centre and radial holes the bigger the gap to the bore being measured the lower the maintainable pressure will be, these are accurate enough to give 100th of a thou variations.
As to markings, they are there but frequently appear to have been added with an etch pen

McCabe-Thiele (Ted):

--- Quote from: Oddjob on April 24, 2021, 10:55:14 PM ---If you can see the C I can't work out why you can't work see the number, it's on the opposite side and is etched exactly the same and at the same time as the weight code, if ones there they should both be there. If you finally see the number there are usually only 2 possible colours that fit. Sometimes 3 if it's a 400 but not 100% sure of that without looking. Unless the shell spins the size of the conrod opening never changes.

--- End quote ---

All four of my conrods have the C weight markings on the front.  After much intense examination I have established that No:1 is marked 3 it's a Green marked shell. No: 2 & 3 have no visible markings or shell colours - No:4 is marked 2 it's also marked as a Green shell. All  8 shells are marked with batch  STD D61A. Crank jounals are all 32.00 minus 0.01 or -0.02)

My big end shells are all in pretty good condition with just one showing some wear ideally I would replace that one jounal - it's conrod No:2 that is the worst so I have no color code or number to go from although they all have the same shell batch makings.

Any comments / advice welcome.

Bryanj:
Shell markings mean absolutely nothing, the last thing done to them is measure them and allocate a colour code after machining

McCabe-Thiele (Ted):

--- Quote from: Bryanj on May 02, 2021, 05:35:45 PM ---Shell markings mean absolutely nothing, the last thing done to them is measure them and allocate a colour code after machining

--- End quote ---

Without a number code on two of the conrods my thoughts are that if I get a Plasigauge reading on all four big end bearings with the existing shells in the original position then measure the clearances.

If I then rotate the Green shells fitted in 1&4 with 2 & 3 then take another Plasigauge reading across all four journals.

If the  Plasigauge clearances are still close this would confirm that 2 & 3 are also Green. Green are the most common colours in the tables appearing in all 3 columns, followed by Brown & Yellow. Red & Black appearing least.

Is this idea flawed in some way?

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