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Old 12-23-06, 12:42 PM   #1
timmreck
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faux-horizontal dropouts?

I have recently acquired an older (late 80's early 90's?) schwinn impact mtb from a guy on craigslist. I bought it with the intention of building it into a solid single speed commuter... but upon closer inspection (when i initially saw it and inspected it, we were in a dimly lit parking garage) what appeared to be horizontal dropouts are actually.... well... i don't know what you'd call them. They have the shape of horizonal dropouts, but most of the horizontal plane is filled in with metal. Essentially, there is only enough room for the axle to fit snuggly. In other words, i guess they're 'technically' horizontal dropouts that are effectively equivalent to vertical dropouts.

My question then, is can i safely file away at this excess metal inside the dropout? I can't really see any reason why i shouldn't, but i thought i should ask just in case this is considered dangerous. Also, if i do decide it's safe, how should i go about doing it?

I really appreciate any feedback... thanks a bunch.

samuel
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Old 12-23-06, 12:50 PM   #2
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Post a photo so we can see what the dropouts look like.
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Old 12-23-06, 02:03 PM   #3
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I would assume mtbs from that era would have semi-horizontal dropouts?
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Old 12-23-06, 02:12 PM   #4
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So how much did you pay for the frame and what are you going to use it for if you don't single-speed it?

If it was my bike I'd probably take a chance on modifying the dropouts. If, for any reason that doesn't work, I'd chalk the loss up to experience. Some people pay tens of thousands of dollars to go to engineering school to learn about stuff like that and some people just try it out and see what happens. Either way the money is never wasted.
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Old 12-23-06, 02:51 PM   #5
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I would post a picture, but i don't have a camera.

I bought the complete bike for $60. It was a pretty good deal (at least as far as i can tell):
4130 tubing, a really cool reddish-brownish-crome-like finish, brand new tires, and everything else that makes a bike a bike. The suntour components are in great shape, as well the diacompe cantilevers. If i don't make it a single speed, i'll still probably ride it... i just don't want to deal with deraileurs and what-not in the snow and slush and grime of minnesota roads.

I guess it's a tough call because i don't want to ruin this bike... it was a good deal and i want a rigid mtb for winter. Really though, i don't see how doing this would be harmful... but i also know nothing about frames, or metal, or structural engeneering, or whatever.

If i do decide to do it, i need to ask again... what's the best way to go about it?
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Old 12-23-06, 03:37 PM   #6
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Some people pay tens of thousands of dollars to go to engineering school to learn about stuff like that and some people just try it out and see what happens.
for 60 bucks and a bit of effort even if you did spend tens of thousands of dollars going to engineering school the easiest solution is to try it out and see what happens!
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Old 12-23-06, 03:43 PM   #7
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There are a few schwinns of that era that came with the pseudo-horizontal dropouts. Who knows why. However, if you're going to convert it to a single speed, there's no reason you can't just use a chain tensioner. The surly singleator is supposed to be pretty good, but since single speed mountain bikes are pretty popular, I would guess that there are a ton of chain tensioners available in just about every price range.
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Old 12-23-06, 07:36 PM   #8
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It (the axle) either has room to move in the dropouts, or it doesn't. It's pretty simple actually. The latter is vertical, everything else is not.
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Old 12-24-06, 09:32 AM   #9
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Originally Posted by sivat
There are a few schwinns of that era that came with the pseudo-horizontal dropouts. Who knows why. However, if you're going to convert it to a single speed, there's no reason you can't just use a chain tensioner. The surly singleator is supposed to be pretty good, but since single speed mountain bikes are pretty popular, I would guess that there are a ton of chain tensioners available in just about every price range.
Here is a chain tensioner you can knock together pretty easy.

This is being used on a bicycle that has been converted to electric drive so that’s the reason the big sprocket is on the wheel and the unseen electric motor sprocket is obviously much smaller. An old skateboard wheel with a groove cut in the middle keeps the chain tight. An easy alternative is simply use a sprocket from an old derailleur.
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Old 12-24-06, 11:57 AM   #10
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You could also get an eccentric rear hub that allows you to adjust the chain tension by rotating the hub relative to the axle. White Industries makes one. Its high quality and not that expensive (of course it would cost more than your bike, but you will likely need a new rear hub to build up a singlespeed).

http://www.whiteind.com/ENO_Products/eric.html
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Old 12-24-06, 12:19 PM   #11
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Thanks for the input everybody.

However, I didn't ask for alternatives to making fixed/singlespeed machines... i know i have those options. I asked about filing away at my dropout and whether or not that's safe.

I would still appreciate advice...
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Old 12-24-06, 12:52 PM   #12
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We can make a better guess if you can post a pic, but a guess is the best we can probably do. If there's enough material left after filing, I'd say go for it, but without a picture, we have no idea.

How exactly are you planning to file it? I sure wouldn't want to do it by hand. You might need a way to keep the filing straight, also.
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Old 12-24-06, 01:04 PM   #13
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Quote:
Originally Posted by timmreck
Thanks for the input everybody.

However, I didn't ask for alternatives to making fixed/singlespeed machines... i know i have those options. I asked about filing away at my dropout and whether or not that's safe.

I would still appreciate advice...
Looking at the 1989 Impact specs and the catalog photo, I can see what you're talking about.

The specs say the dropouts are forged, and it looks like the steel fillet you're talking about probably does provide some reinforcement, but if it were my bike and I wanted to convert it to fixed gear, I personally would take a dremel tool to the fillet without being concerned that I was compromising the structural integrity of the dropout for normal street riding; the fact that the dropouts are forged should provide plenty of strength without the fillet. If I were going to do a lot of jumping with the frame, I'd probably leave the fillet because it obviously does provide some reinforcement.

Just out of curiousity, what is the thickness of the fillet material compared to the thickness of the dropout?



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Old 12-25-06, 12:06 PM   #14
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I've modified plenty of these dropouts with a cut-off wheel and a file, time consuming but not a big deal.
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Old 12-25-06, 08:19 PM   #15
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I've done it before, no problems. It's just metal, not rocket science...
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