Bicycle Mechanics - Gouge on my seatpost.
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03-12-11, 10:15 PM
So I have a huge scratch on my seatpost and was wondering if anyone had any ideas what might have cause it. It looks like this:
I felt inside the seattube and it didn't feel abnormally rough. Is this something I can fix (or at least prevent from happening again/getting worse)? Also, will the current scratch cause some problems down the road?
03-12-11, 10:57 PM
I would hit the frame with a cylinder hone or a file down the back of the frame to eliminate the bur of the slit. If this is an aluminum post it will be fine. If it is carbon then I would say that you are over tightening the post with the QR. Most carbon posts on the newer carbon frames are only tightened 5 newton meters or about 60 in lbs.
03-13-11, 08:09 AM
yeah, it's just an aluminum post, so I thought at first the scrape was due to it sliding down since I'd under tightened it. Even though I have it tightened as far as I can by hand, It dropped about an inch yesterday when I rode it for an hour. Should I be using a wrench on the nut? As it is I have a hard time closing the QR. The seatpost is fairly new (and I've always had this sliding problem even though it's supposedly the same size as what came out of there. I guess I should get the calipers out and check, though I don't have the old one to compare to. How much bigger should the tube be than the seatpost when not compressed by the bolt?
03-13-11, 04:03 PM
I have it tightened as far as I can by hand, It dropped about an inch yesterday when I rode it for an hour. Should I be using a wrench on the nut? As it is I have a hard time closing the QR.
How much bigger should the tube be than the seatpost when not compressed by the bolt?
The seatpost should not slide when riding the bike. Looks like you have two possible causes:
1. QR skewer. Exposed cam skewers like the one on your bike require more hand force to achieve the same amount of clamping force. An enclosed cam skewer will help, or just get an allen bolt. Not as convenient, but possibly less chance of getting your seatpost stolen.
2. The seatpost shouldn't be any smaller than the inside diameter of the seat tube. Of course it has to be slightly smaller to fit, but there should be a little friction when sliding it down. If there's not any friction it can still be ok, but there should definitely not be a big amount of wobble without the QR tightened. You should not be able to see or feel a gap between the post and tube. If you can, you bought a seatpost that's too small.
03-13-11, 04:24 PM
At first it's a bit of a challenge getting the post in, but then it slides with just a little friction. Don't have visible open space. I put some grease in there (Park Polylube), because the lubricant I'd had in there wasn't visible. Hope that might help with tightness too. I think I'll stop by the lbs about getting an allen bolt for the that location as I am partial to my new (to me) saddle and would hate to lose it while my bike's parked outside while I'm at work.
03-13-11, 04:28 PM
Sounds like the post is the correct size. If there's an excessive amount of grease in there at the clamping area it may be more difficult to lock it down. I suspect changing to an allen bolt will solve your problem.
You might want to double check for a burr at the top inside corner, but since it slipped while clamped, I'm not surprised at the scratch. You want to clamp it harder, but sometimes it's hard to get a good grip on carbon posts which are slipperier than alloy posts.
Carbon posts need grease or anti-seize in alloy frames to avoid galvanic corrosion, but the grease lessens gripping so you're in sort of a catch 22. Here's a way to get both anti seize protection and grip at the same time.
Don't grease the post, apply a smear of grease to the frame below the clamping area, and rotate the post as you insert it to get even coverage. Don't go below the desire height, then straighten the post and clamp the dry area. If you want still better hold, do the same but first apply a band of coarse lapping compound or carbon assembly paste to the part of the post that will be at the clamping area.
Suggest you get the verniers out and check both the seatpost and the inside diameter of the tube. Thats not a bare tube - its been anodized black and for steel to gouge aluminum oxide like that - something has to be seriously out of round.
So check for maximum and minimum dimensions. You`ll still have to get rid of that metal thats causing the gouge, but quantifying your starting point is a good idea. You can ream it if you want to but if your good with your hands a dowel and wet sandpaper may be all you need and will remove less material.
On another note, accepting that FB may have missed your post about this being an alloy post - whats all this talk about galvanic corrosion? I`ll buy lunch for the first person that can get a continuity reading off a carbon seatpost that hasn`t been so badly damaged that the carbon fibers have been exposed. At which point it might be a good idea to look for another seat post anyway!
03-14-11, 09:10 AM
Given where the gouge is and the fact that I'm a clyde (probably 230-240#) and that there's maybe 6-8" of post exposed with the saddle as far back as it'll go on the rails (and that I squirm a lot on the saddle going up hills - and am not in the greatest shape in general so there's more weight on the saddle than there should be) I wonder if I'm just pushing the post back as it slides down and it's scraping on top where the frame raises up almost to a point right before the gap. I don't know if all frames sweep up to such a point as it looks like mine does in the picture or not. I'll definitely try feeling around in there again for any burrs, but I just didn't feel anything the last time, though I'll be the first to admit my fingers aren't super soft and sensitive.
03-14-11, 09:17 AM
I'm not sure I did come out and say it, but this is an alloy seatpost (el cheapo something or other 26.0 by 400 mm job from jenson) and a steel frame. I didn't pull the calipers out when I was greasing the seatpost on Sunday, but I'll recheck that it isn't supposed to be a 26.2 or something.
Is this gouge going to affect the long term integrity of the post as long as I can stop it from getting worse? Should I buy a new post even if I can fix it?
Doesn`t matter how much you weigh, some things aren`t supposed to move if secured properly. That includes the handlebars, gooseneck or steering stem, wheels and seatpost. Those are all safety related. I`ve heard of riders bending seatposts so that should give you some idea.
The damage is cosmetic and you don`t need to replace the post (unless its actually the wrong size), but you really need too resolve that slipping situation. I suspect a size issue because thats the only thing I can think of that would distort the pinch bolt clamp area enough to cause gouging and still let it slip.
Which is why I suggested the vernier. If the seat tube clamp area has been distorted you`ll need to measure in several directions to get an idea of the real situation.
Since thats a cheepo post - it may be as simple as a QC issue too. The actual dimension may not match whats stamped on the post.
03-14-11, 04:13 PM
Do you need to remove the seat post? this a theft of saddle worry?
lower wear and tear if you set it and use a regular bolt, instead of the QR.
03-14-11, 10:37 PM
Oh once I get it set and dialed in, I have no desire to remove it. Well it is a leather saddle (selle san marco regal) and I hope to do more commuting with it so I probably don't want to leave it outside at work if it's raining, but really there's no reason for the QR once I get the height set where I want it. Just trying clipless pedals for the first time this weekend so there might be a period where I go through some height adjustments yet. Yeah, it's a cheapo seatpost (less than $20, so there might be a QC issue), so replacing it isn't a huge investment (might go with one that's not quite so long next time).
03-15-11, 01:26 AM
Use a cover or plastic bag when leaving it out in the rain, and you'll have little reason to want to remove the post once you've got a regular bolt in there.
03-15-11, 11:03 AM
Well it is a leather saddle (selle san marco regal)
FWIW, Rather deluded on that, look underneath, it's a Nylon base,
there's some dense padding sandwiched between it and the leather cover,
there is leather but its thin, and the rivets are for style not structure
Unlike Brooks, Ideale and some of the leather newcomers .. :rolleyes:
03-15-11, 11:12 AM
Yeah I know it's plastic at the base, but I just thought that the leather cover could be damaged by rain. If that's not a worry, I'll just throw a plastic bag over it to keep my butt from getting wet the way I did my last vinyl-ish saddle.
03-15-11, 03:41 PM
Looking at seatposts online, I'm not seeing much in 26.0. Is that not a common size?
03-15-11, 04:01 PM
Yea, A plastic bag will do .. personal fave: the Plastic Bladder out of a 5L box of wine.
I have ridden days with a couple layers of plastic bags over even my Brooks saddle .
Kalloy is one source of seatposts in all diameters..
03-15-11, 04:11 PM
Kalloy is one source of seatposts in all diameters..
That's the one I have. If it turns out that the post is narrower than desired due to poor QC, I'd be looking for an alternative to them, though I suppose a shim might do the trick.
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