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Old 10-25-11, 09:29 AM   #1
scozim 
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Yikes!!!

Working on my dad's Spectrum this morning and was swapping some pedals out. I noticed an irregularity on the left side crank arm at the bolt hole and started investigating a little further. His slow speed crash last week due to inattention may have been a good thing - this looks like it could be seriously catastrophic. Cracks on both sides all the way through. Who knows how long they've been there.

Too bad - these are really cool Sampson lightweight cranks from the mid to late 90's. Guess I'll be on the look out for a lightweight 130bcd square taper crankset




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Old 10-25-11, 09:30 AM   #2
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probably a design flaw if they are on both sides. i'd return them
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Old 10-25-11, 09:36 AM   #3
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Ouch...

I wouldn't toss them out though, before having a competent welder check them out. That's too bad, they are real nice looking parts.

If you're looking for aftermarket cranks, these Topline units are not too hard to find(ebay,CL). I am happy with the quality, and they are nice looking pieces.



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Old 10-25-11, 09:47 AM   #4
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I would at least look at trying to fix the Sampson cranks first!

Those Toplines sure do look good!
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Old 10-25-11, 09:53 AM   #5
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I've emailed Sampson - doubt they have any hanging around in their warehouse - but you never know. A couple of years ago they still had cleats for their old Stratics pedals.

Can aluminum be repaired safely? If I do replace I'll definitely keep them for the display case as they are pretty cool.

Roger - any idea on the weight of the Toplines? Not that it matters much for me but my dad built this bike as a weight weenie.
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Old 10-25-11, 09:59 AM   #6
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I don't have a small scale, so I can't weigh them here. I did some searching on the internet, and found more than one source that claim 369grams for 172.5 road cranks(w/o BB)

For comparison, these 6500 series Shimano cranks are claimed to be 527grams


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Old 10-25-11, 09:59 AM   #7
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I have had billet aluminum repaired on my motorcycle before, the piece came out great, but it didn't take the stress of a crank.
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Old 10-25-11, 11:53 AM   #8
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Received a response from Sampson in less than 30 minutes today. Would be awesome if they had an old set laying around.

"We are aware of the issue, and it is why all the Sampson cranks were sold with precise mounting instructions ---and all cranks sold after 1995 also had a full warranty registration that required the installer to sign the form and fill in the torque setting-- While it is standard now for cranks to have a torque setting-in the 1990's most people ignored it, and the result would be a fracture as you describe, which was the result of simply pushing the cranks too hard onto the taper of the bb-

Can you provide me any information as to when you purchased the cranks, and who installed these and on what type of bb? And DO NOT RIDE these cranks, they are subject to fail at anytime per your description. "

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Old 10-25-11, 12:14 PM   #9
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Well, it is your dad's bike... lol!

Did you ask if they had replacement cranks?

Good luck!
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Old 10-25-11, 12:32 PM   #10
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I doubt if that crankset can be welded back correctly as how will you do a full penetration weld on it. You'll most likely end up with a weld near the surface and still a crack inside the arm which is not 100% good. You almost have to gouge out material close to the full depth of the crack and then fill it with weld, then grind/polish it back to spec, then you still have to grind out, clean out and re-tap the extractor threads for both. Lots of (expensive/labor intensive) work and who knows if you might end up overheating the part and end up with something weaker.
I think the crankset's toast, time to look for another one....
BTW, did you check if by any chance the cranks were torqued down on the spindle too far/much which might have contributed to the cracking??

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Old 10-25-11, 12:37 PM   #11
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Ah, the joys of CNC cranks...

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Old 10-25-11, 12:41 PM   #12
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Definitely not worth welding. If you managed to get enough penetration, you'd have to remachine the mounting hole. Way too much work!
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Old 10-25-11, 12:53 PM   #13
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Ah, the joys of CNC cranks...

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Is that a hint that CNC = more chances of stress risers?
I imagine if the CNC machining from billet (in contrast to casting/forging) might produce more sharp angles on a crank design, you might have a good point there.

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Old 10-25-11, 12:56 PM   #14
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I love how the email admits to the design defect and then blames the installer. Typical American Corporate response.
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Old 10-25-11, 01:13 PM   #15
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Quote:
Originally Posted by Chombi View Post
BTW, did you check if by any chance the cranks were torqued down on the spindle too far/much which might have contributed to the cracking??

Chombi
Got a follow up email from Eric Sampson - definitely appears to be a torque issue which is too bad. He looked at the photos and confirmed that. I'd love to find another set in 170mm or 172.5 but am doubtful that will happen. I'll also keep an eye out for a Topline. Talked to my dad earlier and he'll definitely want to go with a lighter weight crankset.

On a side note - I had to tighten the bolt on the left arm the other day as it was creaking but don't think I tightened too far. I could have - it's hard to say. I didn't touch the right side arm so I know I didn't cause that problem.
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Old 10-25-11, 01:18 PM   #16
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Yes, folks, parts do sometimes fail. I seem to be having a bad year in that regard. Luckily only the parts broke.
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Old 10-25-11, 01:40 PM   #17
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There are a wide varietry of aluminum alloys, not all of them can safely be repaired back to full strength by welding.
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Old 10-25-11, 03:28 PM   #18
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Definitely not worth welding. If you managed to get enough penetration, you'd have to remachine the mounting hole. Way too much work!
Ditto this. Looks like the Campy bolts held up well, though
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Old 10-25-11, 04:10 PM   #19
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Broken stem, discovered whilst tearing down a new bike today.
- And this is not even the "death stem" !

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Old 10-25-11, 04:40 PM   #20
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Broken stem, discovered whilst tearing down a new bike today.
- And this is not even the "death stem" !

I have the same stem. Mine was cracked up from the base where the wedge would go.
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Old 10-25-11, 06:07 PM   #21
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Cast aluminum in a high stress application is not very amenable to repairing, weld or otherwise. Forged/billet, possibly, but without a full post-heat treating process, the original strength will not be regained, albiet that the resultant strength may be adequate for a reasonably long second life.
I would attribute the Sampson crank failures to a flawed marketing & delivery strategy. I.e., given the sensitivity of the design to installation torque, they erred when selling in a manner that permitted installation by lay end customers. They probably should have required installation by authorized dealers only. Probably hard to control this, especially after initial installation, so really they were out in left field putting out a product with such a narrow design margin.
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Old 10-25-11, 06:11 PM   #22
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I've got a couple of those Philippe stems; I drilled a small hole at the end of the relief cut to keep any cracks from starting. I really, really hope nothing does start.
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Old 10-25-11, 07:37 PM   #23
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I love how the email admits to the design defect and then blames the installer. Typical American Corporate response.
+1. what a joke. this isn't a carbon crank. we shouldn't need a torque wrench.
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Old 10-25-11, 10:21 PM   #24
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Have to say C&V on Bike Forums is absolutely the best. I was contacted by another member today who has a 170mm Sampson crankset like the one on the bike. My dad is definitely interested so the deal will be done. I also have the torque specifications from Sampson. My dad was really impressed that I could get some resolution this quickly (gotta admit so was I). Just another reason I spend 95% of my time here at C&V.
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Old 10-26-11, 02:09 PM   #25
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Originally Posted by scozim View Post
Working on my dad's Spectrum this morning and was swapping some pedals out. I noticed an irregularity on the left side crank arm at the bolt hole and started investigating a little further. His slow speed crash last week due to inattention may have been a good thing - this looks like it could be seriously catastrophic. Cracks on both sides all the way through. Who knows how long they've been there.

Too bad - these are really cool Sampson lightweight cranks from the mid to late 90's. Guess I'll be on the look out for a lightweight 130bcd square taper crankset




About 102% of those (completely) CNC'ed cranks from the USA from that time period broke. Bad, bad way to make cranks. The only ones that aren't broken by now are NOS in a box. Run very far away from any of those types cranks, imo.
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