Topic: Main bearing replacement.

[CB750R]

I’m inspecting the 77f engine I purchased recently and I found repaired damage on the valve cover right where the cam chain and sprocket are. It has an intact top end including cam chain and sprocket now, but it looks like this engine snapped a cam chain once. So I wanted to check the bottom end to see if there was any signs of left over debris or additional damage. I found scores in the main bearings I could catch my finger nail on and one worn to the point where it looks brassy in one spot. Visually the crank looks fine and rotated smoothly in the engine. The rods all feel smooth with no play but I assume I should inspect them too for any evidence of wear while I’m here.

No metal bits found in the bottom end. Im guessing the cam chain was repaired and bike was running before it ended up being parked.

I have bearing shells with D7C STD stamped on the bottom side. I see green on at least 1 shell but can’t see it on all. My crank has 77.3.22 marked on it.

Will it be safe to assume all the bearings be "green" ?
My other engine (damaged cases)  has shells that have D5G STD and at least 1 is marked red (is this brown ) it’s crank is marked very faintly my best guess is 5072 if that helps, if it’s worth salvaging some parts from.

What’s best practice for next steps? 
Measure main bearing journals? Platigauge existing setup?
Inspect the big end bearings of con rods and measure con rod journals?

I have a basic set of micrometers and t expanding bore gauge set, would this be sufficient for measurements?

Thanks for advice and feedback.

[Don R]

 Sorry the video is on youtube made by Hackaweek the cb750 series.

[CB750R]

Hey Don that video just goes black screen when i tried to play it. Shoot me the link?

[Geoff Hastings]

On my K5 the main bearings were down to the brass backing in several places. The crank however was still perfect with virtually no wear so just fitting new bearings did the job. You will need a micrometer and some plastiguage and there is a set of very feint numbers on the crank web you will need to note before ordering the shells.

[bryanj]

Numbers/letters on the shells mean nothing about size and are purely production lot numbers, you will need to cross refer casing stamps to crank marks and then check with plasitgauge, expensive if you get it wrong

[Little_Phil]

Numbers/letters on the shells mean nothing about size and are purely production lot numbers.

But presumably all D7C STD are all identical and in this case green or is that not the case?

[Geoff Hastings]

It’s the colour that is the reference point. The down side of this Honda precision fit is, you order the bearings, fit them and then check with the plastigauge and might find it out of spec so you then order another set which ain’t cheap. When I did mine I just replicated the colours on the shells and luckily for me when I checked the clearances they were spot on.

[CB750R]

Numbers/letters on the shells mean nothing about size and are purely production lot numbers, you will need to cross refer casing stamps to crank marks and then check with plasitgauge, expensive if you get it wrong

Crank marks being the 77.3.22 I posted an image of? Or the other mark I posted? I haven’t found any markings in either set of casings I’m obviously not looking in the right spot. Where should I be looking?

[CB750R]

Finally found the answer of where to look in a thread about lightened cranks.

Surprised not to find in a FAQ page or one of the first 10 searches!

[CB750R]

From what I can barely read on the crank it looks like I have AAAAA main bearing journals and BBBBB stamped on the case. The correlates to the Green bearing shells that are installed.

Going to do my best to mic the mains to see if there’s any change in diameter before I order new shells.

[PeWe]

I heard for many years ago that green is a general good size