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olderbeemer
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Central Missouri
Joined: 02/09/2011
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Hi All ...... Long time lurker here with a question. In the process of rebuilding a set of wheels, I found hairline cracks in one of them at several of the rivets as shown in the attached photos. Has anyone seen this before?

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schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6327
I took the opportunity to

I took the opportunity to contact Duane Ausherman and ask about his experience on this. He had a number of questions and a solid guess as to the problem.

- does this bike/wheels have any sidecar history?
- is it every rivet in the hub?
- front or rear hubs?

Duane's thoughts were that this is almost certainly due to the heat build up when breaking, and especially more heat when a sidecar is attached. Also, while the front brake does most of the work, the rear brake doesn't get as much cooling. The steel part of the hub, to which the brakes are attached, will transfer heat to the aluminum. Aluminum expands quicker than steel and thus the aluminum will grow in size and create the forces that will stretch the hub and open up such a crack.

Sometimes when installing rivets, a small nick is put into the metal. It's possible that's why the cracks started where they did and grew to the free edge, breaking the ligament.

Duane feels that this is of no consequence. He's have one of his former mechanics check a couple of his hubs to see if the problem exists elsewhere. Now that the crack has become visible, it has stress-relieved itself. If you were concerned, you could recheck these locations to see if a crack has opened up on the other side of the rivet. Unlikely, though.

This might also be a good question for a sidecar forum. In any event, Duane will really be interested in your response as he probably will consider writing an article for his website. He has indicated that the only reason he put his website together was, for the most part, to answer owner's questions about their bikes!

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

olderbeemer
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Central Missouri
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Thanks so much for the reply!

Thanks so much for the reply! Also a big thanks to Duane for his insight. I actually consulted his website before posting this to see if historically there had been any instance of this happening in the past.

To answer Duane's questions:

-I know of no evidence that the bike ever had a sidecar attached. I have had hacks in the past, so I do understand the added stress on the wheels.
-The cracks are limited to (4) rivets.
-The wheel was on the rear of the bike. The front wheel hub had no cracks.

If you look closely at the photos, it appears that when the rivets were "set", the aluminum was deformed slightly inward at the crack locations, so your comment of a "nick" could be spot-on. There is no indication of the cracks radiating outward from the rivets, or any other location that I could find.

I wanted to see if anyone had experienced with this before re-lacing the wheels. I'm happy to hear that Duane feels like this is not an issue.

Again, I certainly appreciate the help and advice!!

Roger Linneman

Twocams
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Joined: 03/16/2014
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Wonder if you can "drill

Wonder if you can "drill stop" those cracks. Not sure what they call it today. Drill a little hole at the end of the crack so it wont spread. Not drilling clear threw,just shallow?

twocams

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Twocams
69 R69S 03 K1200GT
92 R100RT

schrader7032
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San Antonio, TX
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The crack probably starts

The crack probably starts under the head of the rivet. The crack has gone completely through the ligament between the edge of the rivet hole and the free edge...there's really nothing to stop-drill. Now if the crack starts on the other side and begins to grow, that's a different story.

But Duane said there's no reason to not go ahead and just use the hub as is...in his estimation, it won't be a problem.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

olderbeemer
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Central Missouri
Joined: 02/09/2011
Posts: 10
Thanks for the reply Twocams

Thanks for the reply Twocams ....... I understand what you are proposing, but I'm of the same opinion as Kurt, the rivet hole itself prevents it from spreading any further.
Thanks again!
Roger

olderbeemer
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Central Missouri
Joined: 02/09/2011
Posts: 10
Kurt, thanks again for your,

Kurt, thanks again for your, and Duane's, help on this! I will watch them after I put it back in service and post any changes I see in them.

Roger

scottiesharpe
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Joined: 04/18/2011
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Cracked hub - use or not

The iron drum insert is pressed into the aluminum hub with a significant interference fit. It's tight! The rivets secure this fit. I doubt you have anything to worry about.

The next time the iron drum insert is changed out, the machinist will tig weld the hub and remachine it (and redrill the rivet holes) to repair it.

Until then, just run it but keep it under 100mph!

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Scottie Sharpe, Proprietor
Scottie's Workshop, Santa Clara CA
Full Service repairs, maintenance and restoration workshop for vintage and classic BMW Motorcycles http://blog.scottiesharpe.com

olderbeemer
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Central Missouri
Joined: 02/09/2011
Posts: 10
Thanks for the information

Thanks for the information Scottie! I follow you on FB, and you do some great work. I'll do my best on keeping it under 100 mph! lol
Thanks again!
Roger

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