[DwNwRdSyNtHSiS]

I have a 99 Schwinn 4 Banger All Mointain that has developed a very slight headtube hairline crack and looks like there might be one in the BB as well.

My question is, since this is like the most awesome bike ever, would it be possible to have these hairline cracks welded or fixed in some way? I would really like to keep this bike for XC and some light freeriding. My new 04 SGS DH Pro is for the tuff stuff!

~Colby

 

[Kornphlake]

Aluminum gets very soft when it's welded because of the heat put into the material, you'd have to heat treat the frame after it's welded, depending on the alloy schwin used this could be very expensive. Unless you're really in love with the frame, your best bet is to toss it, a frame that old will probabally develop cracks in differant places in the future anyway, you'll endlessly be welding and heat treating the frame.

 

[binary visions]

...it's too bad, too, because Schwinn really nailed it with those 4 banger and Straight 6 frames - my buddy had a Straight 6 and it was just a huge amount of fun to ride.

But that carbon swingarm won't last forever either, and neither do those linkage plates for the dropouts since they seem to be made of cheese. You may love it, but the frame isn't going to be worth the hassle in the long run. Time for a new one!

 

[gschuette]

I bet the crack is on top of the BB and in front of the seat tube. Is it? If so you are experiencing the problem that at least half the guys, that came into the shop I worked in, had. Do a search on the net for frame werlders. There is one guy that I know of who specializes in welding cracked frames. 4 Bangers are notorious for cracking. It does suck because they are a nice bike.

 

[caputo1989]

All i can say is find a good welder. It is too easy to burn holes in "Al".
I know from making my tall bike, ( there are manny hoes in it). but i still ride it.

 

[tazzmenn]

Yes it can be fixed. The person that does the repair has to be very knowledgeable in aluminum alloy compositions. Different alloy blends require different considerations. There are alot of good welders out there that can do a good repair for you. Look for welders that work in aviation repair, they tend to be the best at determining penetration rates as they do a lot of work with Titanium. Aerospace welders are the best at fixing aluminum and titanium.

 

[DirtEveryDay]

Aluminum gets very soft when it's welded because of the heat put into the material, you'd have to heat treat the frame after it's welded, depending on the alloy schwin used this could be very expensive. Unless you're really in love with the frame, your best bet is to toss it, a frame that old will probabally develop cracks in differant places in the future anyway, you'll endlessly be welding and heat treating the frame.

There may, of course, be other procedures, but I worked with aluminum for 8 years and the "heat treating process" is in an oven at 350 degrees for 3 to 8 hours, depending on what was required. Not that complicated. I used to take the raw chunks of scrap home, form it into what I wanted and then throw it in the oven.
The racks we used to heat treat the aluminum were also aluminum and they only lasted a few months before they were scrapped after having been rewelded 50 times. Aluminum gets brittle.
My opinion is to consider it scrap, or do like my is with his busted-ass STP, LAKE JUMPER!

 

[Kornphlake]

There may, of course, be other procedures, but I worked with aluminum for 8 years and the "heat treating process" is in an oven at 350 degrees for 3 to 8 hours, depending on what was required. Not that complicated. I used to take the raw chunks of scrap home, form it into what I wanted and then throw it in the oven.
The racks we used to heat treat the aluminum were also aluminum and they only lasted a few months before they were scrapped after having been rewelded 50 times. Aluminum gets brittle.
My opinion is to consider it scrap, or do like my is with his busted-ass STP, LAKE JUMPER!

it really depends on the alloy, but you're right the heat treat temperature is pretty low, the problem mainly lies in keeping the frame aligned during welding and heat treating as I understand it. Some alloys require a solution heat treat, where it's submerged in some heated liquid. You're probabally more the expert than I am though and even you don't recommend welding a cracked frame so I guess that's the only advice that really matters.

 

[DirtEveryDay]

Definately no expert! I also run a 4x4 shop and fix and re-fix broken junk and I know what happens to metals!
So, again I say...LAKE JUMPER!!!

Can you tell I'm excited for summer to get here?

 

[El Santo]

Although they have been defunct for a while now, you might still give Schwinn a try. I cracked my '00 4B in 2002, right after Schwinn was bought out by Pacific. They had an extra 19" 4B homegrown front triangle laying around and still warrantied the bike, even though my bike was beyond the 1 year warranty period.

About a year ago I got new pivots from Schwinn as well, so they likely still have parts. Although not the newest bike on the block, I love my 4 banger as a trail bike.

1-800-SCHWINN