stuck seatpost
- Thread starter cudfather
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'have patience grasshopper' , but seriously I had this problem when I bought my P7 it had a 27.2 post with an alloy shim to take it up to the 29.8 seat tube size .
The first thing to try is to apply some fast heat( boiling water? ) to the frame the rapid expansion may work , next try gripping the post in a vice and carefully twist the frame see if that will break the bond.
Last thing , which is what I had to do was cut the seatpost (I actually didn't have to do this as I sheared the post while twisting in the vice) about 2.5" above the frame then cut from the inside at 12 , 3 , 6 and 9 o'clock positions VERY CAREFULLY as you get almost through try to peel the seatpost away from the seat tube ,at this point it can be a bit easier to apply a bit of wd40/gt85 type lube.
Brown sauce is also a really good penetrative releasing agent!!
I now run a thermoplastic shim to avoid corrosion problems.
The first thing to try is to apply some fast heat( boiling water? ) to the frame the rapid expansion may work , next try gripping the post in a vice and carefully twist the frame see if that will break the bond.
Last thing , which is what I had to do was cut the seatpost (I actually didn't have to do this as I sheared the post while twisting in the vice) about 2.5" above the frame then cut from the inside at 12 , 3 , 6 and 9 o'clock positions VERY CAREFULLY as you get almost through try to peel the seatpost away from the seat tube ,at this point it can be a bit easier to apply a bit of wd40/gt85 type lube.
Brown sauce is also a really good penetrative releasing agent!!
I now run a thermoplastic shim to avoid corrosion problems.
Thanks for that Carlos,
I think i'm going to try the cutting method as I don't have access to a vice. For some reason I'd left the seat quite low in the seat tube and as a result I don't think I'll be able to get enough 'purchase' on it with a vice anyway.
Why did I start laughing at brown sauce and penatrative being used in the same sentance?....
I think i'm going to try the cutting method as I don't have access to a vice. For some reason I'd left the seat quite low in the seat tube and as a result I don't think I'll be able to get enough 'purchase' on it with a vice anyway.
Why did I start laughing at brown sauce and penatrative being used in the same sentance?....
sastusbulbas
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Hi,
I just had this problem myself.
First of GT-85 and WD-40 are pretty much useless for badly oxodised alloy posts within steel frames as these are pratically bonded to the steel. The alloy oxidises and therefor expands and bonds to the metal as this process ensues, therefore you need something to dissolve the oxidisation.
I did read Coca Cola can release such, but I think thats a load of rubbish.
Ammonia is apparently usefull for removing oxidised alloy, but if it is really bad it may be difficult to get the ammonia to penetrate between frame and post.
another method I have read about is to wrap boiling towels around the top of the seat tube, and use a Co2 tyre inflater to freeze the alloy post. due to the metal expanding with heat and alloy contracting with cold this is apparently a method which can break the bond.
Personally when alloy bonds chemicaly to steel it can be very difficult to break that bond within a tube.
The only two methods I have ever found to solve this is the cutting method or Caustic Soda, the cutting method is by far the easiest, though you run a risk of marking the inside of the frame.
Important thing is patience, this process takes time and is best handled by giving yourself a few nights where you spend a little time working at this. I use either a standard hacksaw blade or carbide, I also put a couple of wraps of tape around the end so as it does not cut into the frame. Use a pulling cut as this helps andtry to get a start at the bottom of the post and create a straight line, I do another 5mm or 6mm to the side of this cut, then another two at each third way round. I also sometimes work the edge of a D file into this grove to aid in rolling/folding of the post within itself. The 6mm gap allows you to create a bigger gap by removing the material between cuts, which will aid in folding, or may be all that is required for a vice to break the bond.
Use a large pair of grips to hold the pin as you try and turn it, aim to bend the edge in as you turn, make sure the frame is secure.
Never force it within a vice, you can either damage or missalighn the frame, or end up with a stuck post with a messed up chewed end which is difficult to work with.
Patience is the key.
Caustic Soda requires even more care and patience, it has to be dilluted to a certain strength, and you should keep it away from the outside of the frame. I don't recommend this method unless desperate, and then I suggest a bit of research and time trials with mixes and bits of alloy before applying the method.
Of course you can always cut 4 slots 2/3rds into teh frame, and use caustic soda to cut the rest of the way through the four groves?
Steve
I just had this problem myself.
First of GT-85 and WD-40 are pretty much useless for badly oxodised alloy posts within steel frames as these are pratically bonded to the steel. The alloy oxidises and therefor expands and bonds to the metal as this process ensues, therefore you need something to dissolve the oxidisation.
I did read Coca Cola can release such, but I think thats a load of rubbish.
Ammonia is apparently usefull for removing oxidised alloy, but if it is really bad it may be difficult to get the ammonia to penetrate between frame and post.
another method I have read about is to wrap boiling towels around the top of the seat tube, and use a Co2 tyre inflater to freeze the alloy post. due to the metal expanding with heat and alloy contracting with cold this is apparently a method which can break the bond.
Personally when alloy bonds chemicaly to steel it can be very difficult to break that bond within a tube.
The only two methods I have ever found to solve this is the cutting method or Caustic Soda, the cutting method is by far the easiest, though you run a risk of marking the inside of the frame.
Important thing is patience, this process takes time and is best handled by giving yourself a few nights where you spend a little time working at this. I use either a standard hacksaw blade or carbide, I also put a couple of wraps of tape around the end so as it does not cut into the frame. Use a pulling cut as this helps andtry to get a start at the bottom of the post and create a straight line, I do another 5mm or 6mm to the side of this cut, then another two at each third way round. I also sometimes work the edge of a D file into this grove to aid in rolling/folding of the post within itself. The 6mm gap allows you to create a bigger gap by removing the material between cuts, which will aid in folding, or may be all that is required for a vice to break the bond.
Use a large pair of grips to hold the pin as you try and turn it, aim to bend the edge in as you turn, make sure the frame is secure.
Never force it within a vice, you can either damage or missalighn the frame, or end up with a stuck post with a messed up chewed end which is difficult to work with.
Patience is the key.
Caustic Soda requires even more care and patience, it has to be dilluted to a certain strength, and you should keep it away from the outside of the frame. I don't recommend this method unless desperate, and then I suggest a bit of research and time trials with mixes and bits of alloy before applying the method.
Of course you can always cut 4 slots 2/3rds into teh frame, and use caustic soda to cut the rest of the way through the four groves?
Steve
sastusbulbas
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Yes, which is why I recommend this only as a last resort, electrical tape, plastic wrapping and such can be of help though.
Patient gentle cutting of many grooves around the inside alloy post, and buy one of those handles which allows you to use the blade properly.
Patient gentle cutting of many grooves around the inside alloy post, and buy one of those handles which allows you to use the blade properly.
Try tons of Plus Gas first - it's a two week project of anointing it every morning and evening. Best is with the bottom bracket removed and through the bottom of the seat tube.
Surely you have something like a workmate to hold the bike to? I would recommend the vice and brute force method first before drastic cutting attempts.
Surely you have something like a workmate to hold the bike to? I would recommend the vice and brute force method first before drastic cutting attempts.
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