K2 / Proflex Riders Group
General => Tech Forum => Topic started by: shovelon on February 06, 2008, 08:07:18 am
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Both my shiny bikes, 957 and 956LE have cracked below the seat clamp and above the upper water bottle block. To my determination, there is a lot of flexing at the slot because of the flexy carbon seatpost I use on both of them.
The crack is just to the left and right of the slot. I repaired the 957 about 65 months ago and rid the mast of the blocks(genious weight weenie move whist correcting the problem ::)). Now 2nd time.
I blame the combination of the blocks in combination of flexy carbon post.
I hope to secure pics of the situation soon.
Terry
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I used to have a child seat mounted on my seatpost on my xp-8 with a 30lb child on it, yet it never cracked - I'm guessing because I always used an aluminium seatpost? Strange. Least you're in a position to fix these things! If I did it then the bike would have to be binned as I don't know anybody locally who could do it!
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I've heard that cracked seatmasts can be caused if you don't have the post all of the way into the mast (i.e. sticking out a bit at the bottom) by causing uneven forces. I assume that this wasn't the case?
Col.
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Seat post is all the way into the mast, but the pinch slot has that block welded over it causing the crack above the block. With the carbon post being so flexy I think it is creating a stress riser there. No matter, as I will chuck the blocks.
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So, you don't recommend using a carbon seatpost? I have one to put on the bike and, by some coincidence, I was going to put it on today.
I don't know how flexy it is, since it's brand new and I never tried it...
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So, you don't recommend using a carbon seatpost? I have one to put on the bike and, by some coincidence, I was going to put it on today.
I don't know how flexy it is, since it's brand new and I never tried it...
Do you have the 2 water bottle blocks just under the seat clamp? If so, there may be a problem. I will be posting pics of the situation.
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Terry,
I wonder if you're getting cracks for all the reasons you said, plus the radical terrain you're riding...
We just hired a new guy at work from your 'hood and his bikes are THRASHED from barreling down California fire roads and barren hillsides. This guy has a Heckler that looks like it was thrown off a cliff into a gravel pit 3 times a day!
Are you that harsh on your poor XC Proflexies?
Will
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Do you have the 2 water bottle blocks just under the seat clamp? If so, there may be a problem. I will be posting pics of the situation.
Yes, I have. My frame is a X57 style frame.
The seatpost I have has no setback, which I believe will help not to crack the frame so easily, as the pressure on the seatpost doens't cause so much torque on the seatmast.
The original proflex aluminum seatpost also has some flex, and it has a quite long setback.
I will give it a try, as it seems to have a thick wall of carbon and was a gift. It's a Look carbon seatpost.
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Do you have the 2 water bottle blocks just under the seat clamp? If so, there may be a problem. I will be posting pics of the situation.
Yes, I have. My frame is a X57 style frame.
The seatpost I have has no setback, which I believe will help not to crack the frame so easily, as the pressure on the seatpost doens't cause so much torque on the seatmast.
The original proflex aluminum seatpost also has some flex, and it has a quite long setback.
I will give it a try, as it seems to have a thick wall of carbon and was a gift. It's a Look carbon seatpost.
I must admit that my easton ct2 posts are probably the problem, as they are pretty flexy, of which I love the feel. They have two flats on the front and reat of the post for some reason, and need a great amount of clalmp pressure. Those blocks are giving the mast a good workout, breaking in time.
I will try to document my repair so you can see the sitution.
Terry
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Terry,
I wonder if you're getting cracks for all the reasons you said, plus the radical terrain you're riding...
We just hired a new guy at work from your 'hood and his bikes are THRASHED from barreling down California fire roads and barren hillsides. This guy has a Heckler that looks like it was thrown off a cliff into a gravel pit 3 times a day!
Are you that harsh on your poor XC Proflexies?
Will
Oh, yeah, that's it! ::)
Nah, it's probably my big butt wreekin' havoc. ;D
But this weekend is lookin sweet! Sunny and 70 to 80 degrees F. I'm gonna thrash something fer sher.
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Well, my seatpost is on and took the first beating today (although not as much as me...).
This is the original proflex seatpost (cut to fit the previous way big frame):
(http://img442.imageshack.us/img442/872/08020819211ol6.jpg)
This is the new one:
(http://img338.imageshack.us/img338/7753/08020819221jo3.jpg)
Old vs New (i needed a bigger seatpost - the new one is already cut to 320mm):
(http://img144.imageshack.us/img144/6742/080208192211tn8.jpg)
I flexes a bit but not much. I tightened it with a low torque and it didn't move, even going down on top of the seat.
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This is the crack. You can see from flexing over the block that the cracks develope. This time it cracked on both sides before I caught it.
(http://img.villagephotos.com/p/2005-6/1036595/956LEseatmastcrack.jpg)
Repair without blocks that propagate cracks.
(http://img.villagephotos.com/p/2005-6/1036595/957seatmastcrackrepairedwithoutblocks.JPG)
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do your seatposts go right through the mast and out the other side???ie right down to the stop.
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do your seatposts go right through the mast and out the other side???ie right down to the stop.
My seatposts are cut to bottom out on the stop bump on the inside. My carbon seatposts tend to slip a bit after a while, so I use those stops to my advantage.
Terry
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Whisperdancer,
I like that Look post you have. I do like the feel of carbon.
Terry
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Is this a particular problem with proflex's
Im about to buy a seat post mounted luggage rack, but talk of stress cracks make me worry!
Is the added weight of luggage (full load with added tent and sleeping bag for longer touring) going to cause problems with the frame?
Andy.
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as I say - never caused me a problem with child seat and child on the back of mine. Maybe I was lucky...
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Whisperdancer,
I like that Look post you have. I do like the feel of carbon.
Terry
Thank you Terry.
When I looked at it for the first time, I only thought of change it for another one, as I always thought about one with a setback that, after all, wasn't necessary.
But now I like it very much and it looks really good on the bike, with that mate finish it has.
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Is this a particular problem with proflex's
Im about to buy a seat post mounted luggage rack, but talk of stress cracks make me worry!
Is the added weight of luggage (full load with added tent and sleeping bag for longer touring) going to cause problems with the frame?
Andy.
I think it has something to do with those blocks in combination with a REALLY flexy seatpost. I used to pull a hitchhiker and my daughter mounted to my 97 beast with no problems. But the beast had no blocks, and I used a Thompson elite seatpost.
Terry
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Is this a particular problem with proflex's
Im about to buy a seat post mounted luggage rack, but talk of stress cracks make me worry!
Is the added weight of luggage (full load with added tent and sleeping bag for longer touring) going to cause problems with the frame?
Andy.
I use a Delta Post Porter on my XP-X (with bottle mount blocks and original Aly post) and it's been fine for 10 Years, see my gallery piccies.
(http://idriders.com/proflex/coppermine/albums/userpics/10284/XP-X_20-05-04.jpg)
(http://www.discountbicycles.co.uk/accessories/carriers/postsilver.jpg)
http://www.discountbicycles.co.uk/biz/product.php?xProd=4645 (http://www.discountbicycles.co.uk/biz/product.php?xProd=4645)
I used it everyday to work on tarmac and several times a year on week long off road expeditions with two small (actually front) panniers and a top box bag. Probably up to 30lb in there all told. No sign of any probs...........
Col.
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Had time to get this done last night. No need to strip bike. Total time about one hour.
(http://img.villagephotos.com/p/2005-6/1036595/000_0356.JPG)
Cut off the blocks from on side and break off.
(http://img.villagephotos.com/p/2005-6/1036595/000_0357.JPG)
Groove out crack. See how block covered slot.
(http://img.villagephotos.com/p/2005-6/1036595/000_0359.JPG)
Lock mandrel and apply ground clamp on bare frame, not anywhere where current would have to go through bearings or gease.
(http://img.villagephotos.com/p/2005-6/1036595/000_0361.JPG)
Weld crack with full penetration to mandrel.
(http://img.villagephotos.com/p/2005-6/1036595/000_0374.JPG)
Remove mandrel. Brown heat mark shows weld penetration held flush to inside.
(http://img.villagephotos.com/p/2005-6/1036595/000_0364.JPG)
Check inside for full penetration. Incomplete penetration must be redone.
(http://img.villagephotos.com/p/2005-6/1036595/000_0365.JPG)
Smooth of weld with sander.
(http://img.villagephotos.com/p/2005-6/1036595/000_0366.JPG)
Sand off old block welds. Use schotchbrite pad to shield shock and buff.
(http://img.villagephotos.com/p/2005-6/1036595/000_0370.JPG)
Polish with knorristal, and reassemble. Let sit for 1 week to allow grain structure to reset via natural ageing.
:)
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Dang... You make that look so easy. Which I know it isn't. I can't weld anything.
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jeez terry, im well impressed. i cant weld to save my life!!
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Beautiful fix Terry.
I'm still amazed that K2 welded a fixed block on either side of a flex joint. Just by tightening the seatpost clamp the stress on the tube would be transferred away from the intended split.
Now why aren't you a full time frame builder?
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i see the problem and i think it is partly due to the blocks interfering with the degree of flex in the seat tube when you clamp the seat post. The longer the split the more flexible the metal and the less likely you will exceed the elastic limit of the metal in that area. On my xp8 frame the problem you have is less likely as my frame is a way large and the bottle mount blocks are a lot lower and are no where near the split in the set tube. removing the blocks as you have done is the correct way to go and i think the quality of your work is excellent!!! ;D ;D
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Now why aren't you a full time frame builder?
Uhhhh, did back in the early 90's. Company called Natural Dynamics contracted with us to assemble hardtail frames that had an arcing seat stay and bottom bracket. The idea was that while climbing, you could rotate the seat forward, and descending arc backwards. Actually it worked as promised, but the designer would not budge on rear suspension. So it ended up being just an overweight hardtail, that really never went anywhere.
Natural Dynamics closed their doors a couple of years later, but their work with ceramic-metal matrix aluminum was really fun. Stronger that steel, lighter than conventional alum, kind of like scandium alloy of today, it welded well, but was kind of messy. All the welds had to be ground down like all of the Cannondales of the day. PITA!!!!
Bob Girvin and his cohorts just amazed me. I can't hold a torch(pun) to what they did in the 90s. That and being an "American", I am not allowed to buy 7005 like China can. If I could, I would be building frames like a demon. The mindset is that I design, and sub the frames out to China. Bull-pucky on that.
The only way Easton will let me have 7005 is to buy from Nova Cycle supply. Conspiracy???? Have you not noticed that all the boutique bulders are using 6061 and 4130 steels?
I would rather tinker and ride right now than have no time to ride. ;D
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wwhat are the neatly welded frmaes in the bckground....?Please dont tell me they are Terry,s modular shelves he knocked up with offcuts!
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wwhat are the neatly welded frmaes in the bckground....?Please dont tell me they are Terry,s modular shelves he knocked up with offcuts!
Ha! :-X
Chuck Norris knocks up shelves! :o ;D ;D