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Crankshaft Bearing Code

Tronco

CB750 New Owner
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Hello guys!

I hope you can help me a little.
I need/want to replace the crankshaft bearings and connecting rods ...

I'm following the manual, but I didn't find all the numbers and letters to know the correct bearings between the crankcase/crankshaft and the crankshaft/connecting rods ...

I don't know where the number is in the case ... and also some in the crankshaft is missing one ...

Can you help me?

Thanks in advance!
Tronco.
 
If you found any the others are in the same place. Case codes are on top case at the very back highest point where engine mount bolt goes if DOHC.

Most people pay WAY too much attention to the bearing colors, they are only valid with very light wear on the engine. Once you have a bigger amount of wear they will not be correct and you must measure the crank and rod journals to get to where you need to be. The difference in each color on the bearings is only about two TEN thousandths of an inch and means you may need to move across them as much as 4 sizes to get where you need. Most people just order yellow as they are the loosest and work in the majority of all cases.

The color thing was to establish a very close tolerance on brand new engines for maximum life, once you are worn you are no longer there unless you re-measure everything to account for specific wear the colors won't touch. They only worked with the brand new parts sizes.
 
Hi,

Thanks for the answer!
My engine have 54K km's... so you think that it is too much wear?

My idea is to measure each one and then sellect the correct bearing in base at this tables:
image6.jpg image7.jpg

Regards!
 
Focus on first pic as it answers the second too.

The 'LM' is a casting mark, it may denote a foundry or a certain forging machine, or even a shift or crew, used by manufacturer only. Look up in the upper left corner for the 'B' code, THAT is a bearing code. You are looking for printed numbers/letters NOT ones cast in, those would be useless and they were there before the crank ever got machined.

The only way you can know about wear is to measure the journals carefully.
 
amc49, my bearing codes on my crank shaft are no longer visible, would it cause any issues in your mind if I just went with all yellow? Or should I have the case and shaft measured?
 
“Gotten away with it” makes me think I should get them measured..... it doesn’t look like my micrometer is calibrated closely enough to measure them accurately (appears off by almost a thousandth of an inch, or my shaft somehow got larger...), so I’ll have to take them to a machine shop. Based on the crankcase lettering (BBBBB), I can narrow it down to nothing larger than a green (D), would I be any safer just ordering all green bearings? Also, any recommendation on somewhere to buy bearings that don’t cost $180 USD for a full set? I’m in the same shape for con rod bearings, no markings left on the shaft, con rods all show “1”.
 
All mikes easily re-calibrate to zero, what the little wrench with them is for.

Nobody on earth makes the bearings except Honda and they have this thing about charging more for parts that sit in inventory over time. The longer they sit the more expensive they get, it being an inventory cost reduction thing. There is no windfall on parts, only getting gouged slightly less at one place than another. I for one haven't bought parts in a good while, knowing Honda did that pushed me to buy any a long long ago. At the last I bought online Western Honda but then they went super high too. Why these are so super expensive to rebuild, more than a bigger Kaw or Suzuki. You'd best own a bank if you have a CBX, same technology.

Never saw a crank, rods, or bearings I couldn't eventually get color codes or digits off of, even ones heavily covered with burnt oil or varnish.

When it comes to plain bearings looser is better than tighter.
 
Damn, that’s what I was afraid of, oh well.

The flattened sections on the crank where the markings should be are completely clean. On one section I can almost make out something that might be a “B”, but otherwise the only markings are from casting. The engine only has 28k on it (at least that’s what to odometer reads...), so I’d expect to be able to read them, but it also looks like it sat untouched for 20+ years based on some of the discoloration. The bearings are definitely worn, so I need to replace them, I’ll give all greens a shot.

Thank you for your help!
 
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