Not fully understanding Big End Bearings & colour codes.

[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)]

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.

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)]

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

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?

[Bryanj]

If you are absolutely certain the pins are all the same size use the shells from the marked rod that you know the colour of in the unmarked rods with plastigauge and see what the clearance alters too

[McCabe-Thiele (Ted)]

If you are absolutely certain the pins are all the same size use the shells from the marked rod that you know the colour of in the unmarked rods with plastigauge and see what the clearance alters too

Hi Bryan,
I am slightly confused by your comments about the pin sizes  as conrod 1 is marked 3 and conrod 4 is marked two I assume these are the pin size as its an etched marking like the weight codes? Different pin sizes but the same Green shells are fitted in two of my conrods. In the absence of the two missing pin conrod numbers as I see it this is my only option to work out what the bearing codes are.
If the clearance changes it might give me a clue as to where to go next. Plan B is to keep the original shells throughout as the engine didn't rattle when I ran it last year.

[waffey]

Oddjob,

where would the markings be on the crank as I cant see any on mine so I 'm guessing they are faint but  i do not have a clue what area they are in

[Bryanj]

Ted,
Take conrod 1 and get a plastigauge reading with its shells on its pin, then put those shells in an unmarked rod and check again on the same pin if clearance goes up rod has bigger hole if down smaller hole if same its same size

[McCabe-Thiele (Ted)]

Ted,
Take conrod 1 and get a plastigauge reading with its shells on its pin, then put those shells in an unmarked rod and check again on the same pin if clearance goes up rod has bigger hole if down smaller hole if same its same size

Thanks Bryan,  Yes in my elongated  way of explaining that is my plan - just waiting for the Plasigauge  to arrive - the last batch of Green were the wrong size range completely. Ash put me on the right path via a PM.

[waffey]

Oddjob,

thanks, I cant see any markings on mine. Damn

I have numbers on the conrods though. that's a start

Macabethiele

are you using grey plasiguauge?

[waffey]

git these pictures

[McCabe-Thiele (Ted)]

2nd pic is wrong part of the crank.

3rd pic looks right, try wetting it with petrol and checking then, I can almost see the markings but can’t make them out enough to read them.

Third picture looks like the weight code C for the conrod - all mine are C's like that.

[McCabe-Thiele (Ted)]

Oddjob,

where would the markings be on the crank as I cant see any on mine so I 'm guessing they are faint but  i do not have a clue what area they are in

I have after much looking using a LED torch beam plus some petrol as a cleaner found the markings in off white on the bottom edges of the crank webs they are as follows.

No: 1 journal is marked 1A
No: 2 journal is marked 1B
No: 3 journal is marked 1A
No: 4 jounnal is marked 1B

Tried on conrods 2 & 3 but nothing has shown up. Still awaiting my new Plastigauge delivery - Friday probably.

Oddjob you can just about read the markings in the photo below.

.crank web markings by Macabe Thiele, on Flickr

[McCabe-Thiele (Ted)]

Yes I can see them Ted.

I was spot on saying number 1 would be A and number 4 would be B.

I'm 99% sure the colour for 2 and 3 is green as well Ted, I'm thinking that number 2 rod is 2 and number 3 is a 3. Bryan is perfectly correct in saying that the shell markings are meaningless except yours are all the same, that means when the guy in the factory went to fit the shells he's almost certainly gone to the same box for them all, hence why the batch number is the same.

There is another way to look at it, if you fit a green in number 3 that's the thickest shell listed for a conrod marked A and number 2 is marked B and the green shell sits right in the middle of the selection choice. They used to say you could go up or down a shell size but better to go up than down.

You can check of course but I'd be happy to say fit a set of Greens if your fitting new.

 I have a full set of NOS Greens on the way so I'm minded to fit them anyway - it's amazing that having advice on here  plus looking at an old post from 2016 by Laverda Dave has edged me slowly in the right direction - a lot to be said for taking ones time on rebuilds.

I must have looked at my crank at least 5 or 6 times since it's been out and failed to spot any markings as I was mainly looking at the web sides & not looking hard enough or cleaning enough. Much like the Sterogram 3D pictures on the ceiling at our dentists eventually you find the  dolphin in a sea of dots.lol