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Author Topic: 72 cb500 fork bridge fracture  (Read 2261 times)

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72500john

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72 cb500 fork bridge fracture
« on: September 21, 2011, 02:24:09 PM »
hello new to the forum and have a question. just picked up a 72 500 four. after riding it a while i found the r/h side of the fork top bridge fractured  at about 12 o'clock from the pinch bolt.. first i put it off to age and could not find anything obvious.  but when i went to order a new one i noted that there where spacers not installed on mine at the fork pinch bolt gaps.
fall is coming so i am going to take advantagethe down time/crappy weather and check a few more things with the front end such as the triple tree bearing,wheel bearings, forks etc. i am thinking this was the culprit. anyone else have any good input or advice. all is welcome!
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KingCustomCycles.com

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Re: 72 cb500 fork bridge fracture
« Reply #1 on: September 21, 2011, 04:16:41 PM »
Cracked trees are result of leaving out the spacer washer.  It is not repairable, and do not ride the bike in that condition.
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72500john

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Re: 72 cb500 fork bridge fracture
« Reply #2 on: September 21, 2011, 04:29:57 PM »
i do not plan on doing either and the replacement parts are on the way. thanks for the reply
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Offline MattInVA

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Re: 72 cb500 fork bridge fracture
« Reply #3 on: September 21, 2011, 04:34:47 PM »
Apparently the washers are hard to find. I think some folks on the board sell them. Try the search function.
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Offline nancy

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Re: 72 cb500 fork bridge fracture
« Reply #4 on: September 21, 2011, 04:59:29 PM »
While it is plainly better to replace,...I don't agree that it is not possible to repair the bridge. It is not a desirable or even "recommended" thing to do. Mine (750) had a similar break and has been professionaly welded back together by an auto machine shop - been fine for a year and 8,000 kms. I will admit to looking at it often just to satisfy myself it is holding up. I think the lower fork bridge takes more stress and I wouldn't go near a repair there. Upper bridge repair cost me $70NZ..or about $50US at that time. I couldn't get a new part for love nor money at the time....apart from 1 on e-bay at US$160...plus shipping of about $60US...so I said  F%^k that.
Regards
Mark
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pat english

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Re: 72 cb500 fork bridge fracture
« Reply #5 on: September 21, 2011, 05:13:50 PM »
i got a set of 72 cb 500 trees if you need them pm me.
                                                                                     pat
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pat english

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Re: 72 cb500 fork bridge fracture
« Reply #6 on: September 21, 2011, 05:14:54 PM »
whoops..i missed the post saying you already got some on the way...
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Offline tlbranth

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Re: 72 cb500 fork bridge fracture
« Reply #7 on: September 21, 2011, 05:16:13 PM »
The washers on mine (and I bought the bike new in 1970) were obviously standard washers with a flat ground on them. Both sides of top triple tree broke in the same place. I was lucky enough to find one (a unicorn) for $90 or so on ebay. I made my own spacers this time by combining washers 'til the top clamp was 'just snug'. No breaks yet after 2 years of 2-up riding.
With the price of unicorn top triple trees now at $400, it seems like we should be able to gang up to have some CNC machined from a billet or maybe forged. There's gotta be a pretty good call for them.
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pat english

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Re: 72 cb500 fork bridge fracture
« Reply #8 on: September 23, 2011, 03:22:42 AM »
i just sent dude a pm offering the top tree for 20 bucks..they are not worth 400.
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Offline dave500

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Re: 72 cb500 fork bridge fracture
« Reply #9 on: September 23, 2011, 03:54:51 AM »
funny how ive never seen such a spacer on even dirt bikes,ive never wrenched these up too tight also,ive had a few 500/550s and this spacer is always missing,,ive never seen a snapped one,,some people treat every nut like an automobile wheel nut?
« Last Edit: September 23, 2011, 04:00:07 AM by dave500 »
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Offline xsmooth69x

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Re: 72 cb500 fork bridge fracture
« Reply #10 on: September 23, 2011, 04:09:43 AM »
Quote from: tlbranth on September 21, 2011, 05:16:13 PM
The washers on mine (and I bought the bike new in 1970) were obviously standard washers with a flat ground on them. Both sides of top triple tree broke in the same place. I was lucky enough to find one (a unicorn) for $90 or so on ebay. I made my own spacers this time by combining washers 'til the top clamp was 'just snug'. No breaks yet after 2 years of 2-up riding.
With the price of unicorn top triple trees now at $400, it seems like we should be able to gang up to have some CNC machined from a billet or maybe forged. There's gotta be a pretty good call for them.

i sell my cb750 unicorn top triple trees for $150 +shipping....
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Offline bryanj

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Re: 72 cb500 fork bridge fracture
« Reply #11 on: September 23, 2011, 10:34:33 AM »
The spacer IS a washer with a flat ground on it!
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Offline phil71

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Re: 72 cb500 fork bridge fracture
« Reply #12 on: September 23, 2011, 11:13:13 AM »
OOH! SPACER THREAD!
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Offline lone*X

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Re: 72 cb500 fork bridge fracture
« Reply #13 on: September 23, 2011, 01:10:00 PM »
Yes, a washer with a flat spot, but not a generic thickness.  The correct thickness has been posted before so it is possible to make a replacement if you can find the post.

OK, just found it: http://forums.sohc4.net/index.php?topic=65425.0
« Last Edit: September 23, 2011, 01:13:39 PM by lone*X »
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Lone*X  ( Don )

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Offline tlbranth

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Re: 72 cb500 fork bridge fracture
« Reply #14 on: September 23, 2011, 05:56:38 PM »
Quote from: pat english on September 23, 2011, 03:22:42 AM
i just sent dude a pm offering the top tree for 20 bucks..they are not worth 400.
If you have any more at that price (unicorn), I'm in.
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Don't own a Vanagon
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1970 CB750 K0
1975 GL1000
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pat english

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Re: 72 cb500 fork bridge fracture
« Reply #15 on: September 23, 2011, 08:49:35 PM »
mines not the unicorn style..its off a 72 cb 500 though..
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Offline Steve_K

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Re: 72 cb500 fork bridge fracture
« Reply #16 on: September 24, 2011, 06:09:43 AM »
I am making some this weekend for my  73 750s.  3 of 4  washers are missing so I have a washer to copy.  I will either make them from stainless steel or aluminium bar stock.  My 550s(76K & 77K) are missing them, too.  I think 550 washers are different.  Fishe file or manuals show some 550 do and don't have washers.  More searching before making 550 washers.
On the plus side, nothing broken. 
Steve
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Steve_K

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Offline tlbranth

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Re: 72 cb500 fork bridge fracture
« Reply #17 on: September 24, 2011, 09:23:03 AM »
FWIW I don't think the originals were thick enough. I stuffed different sized washers in there 'tl it was snug and no more. The original tree broke with oem spacers.
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Don't own a Vanagon
Don't work at Boeing
Life is good

1970 CB750 K0
1975 GL1000
1999 GL1500
2002 VT750-CDA ACE - Momma's bike
Terry

72500john

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Re: 72 cb500 fork bridge fracture
« Reply #18 on: September 25, 2011, 09:46:24 AM »
thanks for all the good input and replys. got two top bridges on the way (spares are great!!) and thanks to the links you all supplied..i now know what thickness to make the spacers. :) going to replace the steering head and front wheel bearins while i am at it, best guess is they are original.
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Offline ataylor136

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Re: 72 cb500 fork bridge fracture
« Reply #19 on: September 25, 2011, 04:51:23 PM »
I was working on my 71 CB500 today and noticed my top triple clamp is broken, if anybody knows where i can find one I would greatly appreciate it, I'm getting close to finishing but keep hittting setbacks.
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72500john

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Re: 72 cb500 fork bridge fracture
« Reply #20 on: September 25, 2011, 06:03:18 PM »
found one on ebay and one on this forum. anyone out there got one for this guy?
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