Author Topic: CB400F can I check main bearings without splitting cases?  (Read 179 times)

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Offline Alaxy Galaxy

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CB400F can I check main bearings without splitting cases?
« on: January 23, 2021, 08:48:18 am »
As a Winter project, I'm trying out my spare motor in the CB400F (the previous one has started to leak way too much oil for my liking - and my pants). Everything spins freely, the cam-chain horseshoe isn't stuck and compression is good. There is, however, some annoying surface rust in the bottom end. I had to swap out the bearings holding the clutch basket in because they weren't as free as they should be, and the 3 balls in the lifter mechanism were severely corroded (no chrome left at all and they look like they would had they been sandblasted). The rest of the bearings I can see behind the clutch seem good, but the bolt at the end of the primary shaft is also rusty.

I'd like to check the big-ends and the crank journals. Is this possible without splitting the cases?


Offline 754

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Re: CB400F can I check main bearings without splitting cases?
« Reply #1 on: January 23, 2021, 09:02:29 am »
  No
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Offline Alaxy Galaxy

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Offline Deltarider

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Re: CB400F can I check main bearings without splitting cases?
« Reply #3 on: January 23, 2021, 10:17:45 am »
Just try running if first. The bottom end of these CB's is pretty bullit proof.
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Offline PeWe

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Re: CB400F can I check main bearings without splitting cases?
« Reply #4 on: January 23, 2021, 10:28:39 am »
Remove oil pan, look for debris, clean it and all dirt you can see in there.
Run it, change oil and filter after 50km or so.
Change oil again after about 500km. Remove oil pan before new oil and inspect eventual debris. Check filter each time.

Like breaking in a restored engine.

Offline Bodi

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Re: CB400F can I check main bearings without splitting cases?
« Reply #5 on: January 23, 2021, 10:57:19 am »
"The bottom end of these CB's is pretty bullit proof"
Steve McQueen could probably destroy it...

The mains are between the case halves, so only accessible by splitting them.
With the case being cast aluminum rust is less of an issue, the bearings hold oil by capillary action so the crank journals should be OK. The rods and wrist pins are steel but the rod bearings may be OK. If it's rust from a humid atmosphere anything in there could rust but the big and small end bearings also tend to hold oil.
« Last Edit: January 23, 2021, 11:06:24 am by Bodi »

Offline 754

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Re: CB400F can I check main bearings without splitting cases?
« Reply #6 on: January 23, 2021, 09:22:58 pm »
If cylinder is off, you can check rod shake.. that may help ?
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline BenelliSEI

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Re: CB400F can I check main bearings without splitting cases?
« Reply #7 on: January 24, 2021, 04:53:34 pm »
Go with PeWe’s advice. In my experience, 4 out of 5 bottom ends need nothing. Chances are if you split it, you’ll wish you hadn’t..... unless the pump screen is plugged with debris and the sump is full of shavings, leave it alone.