Repairing/upgrading a Used GT ZuM

[conspiracyx]

I've just obtained what I consider a very nice GT ZuM at a police auction for $200. The bike is in pretty good shape and seems to need only a few repairs and a tune up. Here is all I know about the bike parts-wise:

GT 6061 frame
Shimano Acera rear derailleur
Shimano Alivio CS-HG30-8I cassette
Truvativ Isoflow crankset with a single 38 tooth chainring
Shimano Alivio shifter (SL-M410?)
Alexrims Ace17 rims with some Kenda road tires

And here are the known problems/qualms:
1. The derailleur is either loose or bent because when I am on the innermost gear it starts hitting the spokes. See attached photo.

2. Some allen-head bolts on the frame are rather heavily rusted, and at least one to the point of being stripped.

3. I think I like having only one shifter and 8 gears, but the 38T chainring is a little too "easy" for me so I was wondering if I have to go up/down a size to make the whole set be geared a little higher. I live in Chicago (pretty flat here), so the first 3 gears in this configuration are useless to me.

4. It caught my attention that as I gain speed and go into higher gear the derailleur is actually dropping the tension in the wire and I have to "crank it" back to get down. Therefore as I gain speed I hear the chain being dropped loudly and something about this makes me think it is more likely to jam vs having it being "cranked/dialed in." Can the derailleur shifter action be reversed?

5. Chain seems excessively greasy to me, bike could probably use an overall tuneup.

6. Since I will be riding in the city, it would be nice to replace all the quick releases (tires and seat) with something a bit more theft proof.

This is my first somewhat serious bike and I would like to make it fit to my liking and make it last, but all the same I don't want to drop too much money on it. I am also rather new to bike repair and maintenance, but I am no stranger to picking a wrench or screwdriver, only to all the new bike tech. So what I am asking here is if I want to at least get points #1, 2 and 5 fixed quickly and efficiently should I just bring it to a shop, or can I do it myself with a basic set of tools one day on the weekend? I think points #3 and #6 are more of something I can do myself with guidance and #4 is really a general concern. Thoughts?

[DaveM]

1. Can't be sure from the photo. But I think either your derailleur or the derailleur hanger (piece where the derail screws into the frame) or both are bent. If it's the hanger, you're frame probably has a replaceable part for this. If it's the derail, probably best to get a new one rather than try to straighten it unless the bend is very slight.

2. Any bike shop or hardware store with metric bolts should have these.

3. If the chainring is held onto the crank with bolts (and not welded) you should be able to replace the chainring easily. You'll just need to get one with the same bolt diameter (BCD).

4. I don't quite understand what you're describing (or why you would want to "reverse" the shifter). But it may all be a part of the bent derailleur. I'd worry about fixing #1 first and then check your shifting adjustment to see if that cures this problem.

5. ...

6. Changing the wheels to bolt on meaning swapping out the axles. Not major, but not minor. There's a variety of "locking" QR levers you can get and other options for locking QR wheels. But if you're locking this up outside in the city, you really need to lock both wheels and the frame with either U-lock or hardened chain (no cable locks). Remember that bolt on wheels (and many of the locking QR systems) can be removed from the bike in about 2 seconds with a pair of pliers. So they really don't mean much in the way of security. There's a lot of ways to secure the seat to the frame better. Seats are usually only a theft target if you leave them completely unsecured so it's not as big a deal as wheels.

This all sounds like stuff you should be able to handle yourself if you have a little time and the inclination to learn. Congrats on the new bike!

[conspiracyx]

Thanks for the reply Dave! I needed some the reassurance on that derailleur issue. I looked at some videos on this site and got a better understanding of it. Now that I think about it, I will probably just buy all the basics I need (oil, some of the basic tools I am missing, etc..) and the parts I want to replace and just take matters into my own hands over a few weekends.

The only thing I would like to know: if I want pedaling to be "harder" (or geared higher, I don't know the lingo to explain #3), do I need to buy a smaller (with less teeth) chainring or a bigger one?

[Joe_W]

(04-11-2010, 01:07 PM)conspiracyx Wrote:  [...]
And here are the known problems/qualms:
1. The derailleur is either loose or bent because when I am on the innermost gear it starts hitting the spokes. See attached photo.

Go through the tutorial on dérailleur adjustment. If it doesn't help: go to the bke shop to have them look at the dérailleur or hanger, might be bent.

Quote:2. Some allen-head bolts on the frame are rather heavily rusted, and at least one to the point of being stripped.

Replace that bolt soon, nothing like having to drill out a bolt that has been stripped and is rusted in place. Look at the rust removal tips in the forum

Quote:3. I think I like having only one shifter and 8 gears, but the 38T chainring is a little too "easy" for me so I was wondering if I have to go up/down a size to make the whole set be geared a little higher. I live in Chicago (pretty flat here), so the first 3 gears in this configuration are useless to me.

Get you cadence up! http://sheldonbrown.com/gears/ tells me that with a 11 tooth small sprocket your speed at 90 rpms should be about 39 km/h (~25 mph). That is not that slow. Get a road style cassette for closer gear spacing, e.g. 11-25 teeth. Replace chain when replacing the cassette. You could also replace the chain ring, you'll (most likely) also have to replace chain and cassette then.

Quote:4. It caught my attention that as I gain speed and go into higher gear the derailleur is actually dropping the tension in the wire and I have to "crank it" back to get down. Therefore as I gain speed I hear the chain being dropped loudly and something about this makes me think it is more likely to jam vs having it being "cranked/dialed in." Can the derailleur shifter action be reversed?

Don't really understand the problem. The direction of the dérailleurs is (in 99%) tighten -> larger sprockets, loosen -> smaller sprockets. I think Shimano tried something different some years ago, was a failure (maybe somebody else remembers better than I do?).

Quote:5. Chain seems excessively greasy to me, bike could probably use an overall tuneup.

Check chain wear, maybe replace. If chain wear is excessive, replace cassette too.

Quote:6. Since I will be riding in the city, it would be nice to replace all the quick releases (tires and seat) with something a bit more theft proof.

Pit lock is a good tip for that. You can also use hose clams to clamp the QR levers in place, is "safe enough". Look at http://www.youtube.com/watch?v=Den2TJcbPf4 on bike locking. Also invest in a good lock (Kryptonite or ABUS, the expensive and higher rated ones).
You can do the checking and dialling in yourself, the tutorials on this site are very good. In order to replace chain and cassette you need special tools. You also need a special tool to check if you have a bent dérailleur hanger.
I'd also check the brake pads and brake and shifter cables and housing, also the bearings and the tyres / tubes and maybe replace those.

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(04-12-2010, 03:38 AM)conspiracyx Wrote:  Thanks for the reply Dave! I needed some the reassurance on that derailleur issue. I looked at some videos on this site and got a better understanding of it. Now that I think about it, I will probably just buy all the basics I need (oil, some of the basic tools I am missing, etc..) and the parts I want to replace and just take matters into my own hands over a few weekends.

The only thing I would like to know: if I want pedaling to be "harder" (or geared higher, I don't know the lingo to explain #3), do I need to buy a smaller (with less teeth) chainring or a bigger one?

Bigger. Do the math!