capnjonny 

At the Bike Exchange a few weeks ago I took a bike home to work on. It was a mess as donated with its chainrings hung on a zip tie and looking very abandoned. It had a light frame and 3 bottle cages and it intrigued me.

I did some research and decided it was an 83/84 Specialized Expedition which is apparently a sought after bike.

It had a dent in the down tube about 4 inch behind the steer tube and had the fork replaced with one that didn't fit and the folks at the Exchange said it was a throw away.

The fact that the fork was replaced leads me to reason that the frame got the dent because something caused the fork , which was at the time perpendicular to the frame, to be bent into the frame with the fork crown hitting the frame tube.

As far as I can see there is no other damage. There is no visible bend in the top tube or down tube behind the steer tube or other damage to the frame.

I didn't want to give up on it and found a youtube video that showed how to work out dents with "frame blocks" which in the video were made from a billet of aluminum with a hole drilled through then sawed in half and then clamped on the frame tube with a vice.

I would like to try this as a way to salvage the frame.

If I can get most of the dent out this way will the frame be sufficiently strong?

As far as I can figure the down tube is mainly in tension rather than compression. Is this correct?

Is there anything else I can do to strengthen the frame?

CliffordK

Post a photo of the dent and dented frame.

Exactly where is the dent (top, bottom, side)?

Is the downtube straight, or bent? Direction of bend?

fietsbob

What shop facilities do you have access to, in order to "strengthen the frame" ..

unterhausen

it sounds like this is the result of a head-on with a curb. If so, it's not really a framebuilder issue, or at least most framebuilders will not touch the repair. If you really want to repair it, you can probably find someone with one of the old Park frame jacks. I never had a lot of luck with those, but I probably only used them on heavier bikes. A lightweight bike probably will straighten out a lot better.

capnjonny 

As I said in my original post, there does not appear to be any frame damage other than the dent. If you look at the attached photo it is on the underside of the down tube just in front of the shifters.

The Bike exchange has a fairly well equipped shop but there are no "frame tube straightening" tools and none are needed except to work out the dent.

Again I ask "is the down tube in compression or tension?" If it is in tension I would think a dent would be of little significance.

So, does anyone have the expertise to answer my original question?

If I can get most of the dent out this way will the frame be sufficiently strong?

CliffordK

For the most part it is in tension, except during hard frontal impacts.

See the Slingshot bikes.



Your headtube and seat tube look close to parallel.

You can try to roll out the dent if you wish, but I think I'd just leave it alone & build a good "rider" bike. Original paint. Good-enough parts.

Andrew R Stewart 

Looks like a parking rack damage to me. It always makes me cringe to see bikes lifted up and over the "picket fence" style of rack and the DT is placed on the top pipe of the rack.


I hope the OP gets rid of that unicrown fork... Andy

Andrew R Stewart 

I should have actually offered some help with the OP's questions. This dent will be a hard one to tube block out. It's located in the thick section of the butted tube, is real close to the shift bosses and fairly large. Were this frame mine I would confirm alignment and wait for a repaint before doing anything about the dent. Andy

unterhausen

I wouldn't do anything about that. I also wouldn't bother to repaint, just ride it.

capnjonny 

Thanks for the replys,

Sounds like there may be some life in this old frame. I am still going to try to roll out the dent if I can. The experience will be educational . I am going to make frame blocks out of some maple I have in the shop. I may have a little piece of hard rock maple . If I do that would be the wood of choice. I used it to support the gimbaled stove on my sailboat and it worked great . Super dense and hard.

If I can get the frame fixed it will make a great foundation for a project bike.

Andrew R Stewart 

Expect a lot of paint scraping/damage. While wood blocks won't chance a surface gauging like burred metal would they also will compress and give more easily then the tubing. Not a bad thing but not what one wants for best dent removal. Good luck and post back with results. Andy

Sangetsu

Don't bother to roll out the dent, or try to work the metal. The easiest thing do to would be to fill the dent, just as a dent in a car body would be filled. The paint is already scratched, you just need to sand the dent clean, and use a little two-part epoxy to fill the dent. Buy some of the quick drying clear epoxy from your local hardware store, mix a peanut-size (a single peanut) amount, smooth it into the dent, and wait 30 minutes for it to dry. Then apply more and more until the dent is filled. Then sand the expoxied area smooth.

fietsbob

Looks like they damaged the fork on what was a Specialized "Expedition", then replacement was that chrome Unicrown.

Willing to get it repainted? For added Strength Brazing a part of a steel Tube Over the dent will cover the dent and double the amount of steel in that portion of the frame..