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Author Topic: Cracking Rear Mount  (Read 832 times)

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Offline BrickWoll

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Cracking Rear Mount
« on: April 11, 2021, 10:01:19 PM »
Hello all,

I have spent the winter rebuilding the top end of my '77 CB550.  This weekend I was looking at areas that might need cleaning before I put the cylinders and head back in the frame and noticed what looks like a small crack at the rear of the case.  It's where the case mounts to the frame.  Is this a known point of failure on the 550s?  Possibly over-tightened bolt by the PO? 

Thanks for checking it out.
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'77 CB550 K3

Offline caluser2000

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Re: Cracking Rear Mount
« Reply #1 on: April 11, 2021, 11:12:45 PM »
My '76 cb550f has done 164,000 plus kms without cracking there.

Bike may have been crashed in its past life possibly..
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Offline bryanj

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Re: Cracking Rear Mount
« Reply #2 on: April 12, 2021, 01:15:14 AM »
Are you sure its a crack and not a casting/paint flaw is the first question.
I have never seen one crack there in use, could have been dropped but those casings are very robust.
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Offline dave500

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Re: Cracking Rear Mount
« Reply #3 on: April 12, 2021, 01:45:16 AM »
im with bryanj,a few have posted over the years with these cracks here n there that aint cracks.
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Offline BenelliSEI

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Re: Cracking Rear Mount
« Reply #4 on: April 12, 2021, 06:27:53 AM »
Quote from: dave500 on April 12, 2021, 01:45:16 AM
im with bryanj,a few have posted over the years with these cracks here n there that aint cracks.

+1. Move ahead.
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Offline 754

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Re: Cracking Rear Mount
« Reply #5 on: April 12, 2021, 09:40:21 AM »
Likely cracks in the casting die. It it is   itl will be raised..
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Offline BrickWoll

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Re: Cracking Rear Mount
« Reply #6 on: April 12, 2021, 09:44:28 AM »
Quote from: bryanj on April 12, 2021, 01:15:14 AM
Are you sure its a crack and not a casting/paint flaw is the first question.
I have never seen one crack there in use, could have been dropped but those casings are very robust.

bryanj - I'm not sure at all.  It could be paint, but it's raised to the touch, which would be odd if it was just a thin paint coat cracking.  Maybe I'll take it down a bit with a brass brush to confirm.  Thanks. 
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'77 CB550 K3

Offline BrickWoll

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Re: Cracking Rear Mount
« Reply #7 on: April 12, 2021, 09:46:55 AM »
Quote from: 754 on April 12, 2021, 09:40:21 AM
Likely cracks in the casting die. It it is   itl will be raised..

754 - This seems correct as there is definitely texture to the cracks.  Thanks.
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'77 CB550 K3

Offline BrickWoll

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Re: Cracking Rear Mount
« Reply #8 on: April 12, 2021, 09:49:00 AM »
Thanks for the feedback everyone.  I'm going to press on with the install.  Riding weather is rapidly approaching here in the PNW.
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'77 CB550 K3
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