CB750 rod bearing replacement

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CB750 rod bearing replacement

Doode
This post was updated on .
New member!

I have a friends cb750 which was a fresh top/bottom build, had the oil lines crossed and seized before ever seeing any miles.
Upon disassembly, everything looks okay except a single rod bearing is toast. The plan is to clean up the crankshaft surface and install a new rod bearing.

I've checked the FSM and am lost in the spec chart, and am hoping someone can help decipher. I've done a few searches which reference different colored bearings... All I pulled out are silver. I'm totally missing something.

Attached is the seized bearing.

I'll post the rod code later today. I didn't record it before buttoning it back up. All work is done in my dusty backyard, so best chances of keeping things clean are to reassemble the cases and side covers, and valve cover of needed, each time I work on it. Fun, right?

Thanks for the help!

Edit: the shell of the bearing has code D5J-A STD

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Re: CB750 rod bearing replacement

TOOLS1
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What you want to do is take the crank to a machine shop and have the journal polished. Then find an oversized rod bearing that corresponds to the amount of material removed from the journal. Your bearing is marked "STD" so this should not be hard to determine what size you will need.
Also, your rods should be stamped with a "weight code" on the side where the rod bolt goes through, and the crank should have numbers stamped on the side of the crankshaft weight that faces the cam chain sprocket. These numbers should also tell you what size bearing you have.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."

1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: CB750 rod bearing replacement

Doode
Thanks for the reply! Good timing as I had just started to look around.
The rods are

D1 - D2 - D1 - D2

I wasn't able to locate any markings on the crankshaft, other that what looks to be a date and a squiggly B
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Re: CB750 rod bearing replacement

TOOLS1
Administrator
This post was updated on .
There should be a series of markings on the weight in the middle facing the cam chain (I'm sorry, it will be on the primary drive sprocket side) sprocket. You will want the first set of numbers.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."

1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: CB750 rod bearing replacement

Doode
Sorry for wasting your time. I found them. Should've read the manual better... Found the marks but will need different lighting before I can read them. It's too bright out at the moment.
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Re: CB750 rod bearing replacement

Doode
Wow. Those are some hard to read markings!
I wrote down my best guess, AAAAA and 44-??
Will update once there's more action to report.
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Re: CB750 rod bearing replacement

Doode
Oh man, I cannot seem to get the cam chain off the sprocket. I don't want to break it, but can't imagine there is any other way.
Is there a trick, or is the flat link chain a break only?
Slotted sprocket and fancy cam.
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Re: CB750 rod bearing replacement

TOOLS1
Administrator
You need to loosen the cam chain adjuster, I just remove them. Then work the sprocket off to the side so that it drops off its seat on the cam, then you will have plenty of slack. Also since it is a slotted sprocket, you will have to degree the cam in, or go back to a stock sprocket.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."

1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)