Minor Frame Repair

A

AverageJoe

New Member
I've been a long time lurker and finally took the plunge and purchased a '74 cb360 project. The bike's in rough condition to say the least and when I removed the gas tank I noticed what looks like tool marks and a small dent in the left top tube. The dent is small (about the size of my thumbnail) and I was just wondering if this is something that needs to be addressed or am I worrying about nothing? I just don't want to run into any issues when I take it to be safetied/I don't want to be riding a structurally compromised bike. Assuming that it needs to be repaired what's the best/easiest way to go about fixing this? Would an experienced welder be able to "fill" it in or would it be better to cut a piece of tube with a matching radius and weld it over top?
I really appreciate any advice offered. I tried to search the site to find similar threads but didn't come up with much.
Thanks,
Joe

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It should be welded up but I wouldn't lose sleep over it after that
 
Fill the dent with bondo, smooth it, paint it and forget it. 8) There is no structural damage there at all. It's all just cosmetic...............................
 
Not arguing or looking to start a fight, but be careful when suggesting that there is no structural damage. A tube provides strength from it's cylindrical shape, the moment the cylinder shape is altered the strength of that component is drastically reduced.

Example: Suspend a weight in the middle of a length of pipe across two supports so the weight hangs freely. Add more mass to the hanging weight until the pipe sags in the middle with about an inch of deflection from straight. Now remove the weight and length of pipe, and take a punch and hammer a dent into the length of pipe similar to the photo close to the middle of the length of pipe. Resuspend the weight on the pipe as it was before and slowly let the pipe take the load. Let it hang there if the pipe will support it and leave it over night, my bet is the pipe will collapse not right away but soon afterwards.

Now I am not saying that the damage as seen in the photo is going to cause a failure, because there are many aspects to take into consideration. But with the right forces applied that tube will fail before an undamaged piece would. I would have a welder fill the void and then grind it smooth, I wouldn't use Bondo except for minor imperfections in surface finishes. :)
 
I think he was probably joking. Should be made more clear though. If someone was actually dumb enough that could get them into road pizza pretty quick. lol.
 
rider, I wasn't joking. I am a welder and metal fabricator and I can safely say that the area is well supported all the way around the damaged area. The welded tube that is damaged is welded to the center support less than a 1/2 inch away. If ya'll are worried that the tube might collapse or fail, that is not going to happen. If stresses were ever exerted on the frame at that damaged point enough to make it fail and it did, that would be the least of your worries. :o cqyqte, No argument or fighting intended here either but I still suggest to just bondo it. Thats my opnion and I'm stickin to it............ :)
 

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I appreciate all the feedback. I think I'll play it safe and have a welder fill it in and then grind it smooth. I plan on powdercoating the frame eventually and bondo won't conduct a charge to attract the powder. I did manage to find some fillers designed for powdercoating applications but they're prohibitively expensive.
 
Filling it with a weld isnt really they best idea

The goal in any repair should be to restore the area to the original strength.
Make it stronger and you run into issues just like if you leave it weaker

Now in theory it may not need to be repaired, and in other theories it will.

Could you leave it as is and run for years with no issues? Maybe
Will filling it with weld fix it? Maybe
If left alone could the damage spread and crack the frame? Maybe
 
Holy Crap, Its just a small ding in a piece of metal that is already massively over engineered ::) The part that is damaged is not even a complete circular tube. That section of the frame tube is cut at a sharp angle and is welded to the center post only 1/2 inch away from the damaged area. The loss of integerty of that area is negligible, minute or just not worth talking about. :-X
 
Surffly, Theories don't come into play here. This is a matter of physic's. It is physically impossible for that small damaged area to affect the integerty of the frame as a whole. Sounds like your playing the "if " card.
If left alone could the damage spread and crack the frame? Maybe
Click to expand...
Do you know what my ol' grandpappy used to say about if? "If my aunt had balls, she'd be my uncle"......................... ;D
 
Is the frame cracked there or is that gap from the factory? If the only damage is the ding then don't worry about it.


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The metal wasn't welded there from the factory, it's probably safer to leave it than to weld everything closed.
If your worried about structural integrity, use a box section between the frame tubes to brace one side against the other (pics in my 360 build/blog)
BTW, it isnt cut and welded to center pressing, its a loop like on the 400f, taker a look at neevo's build to see shape
 
crazypj said:
BTW, it isnt cut and welded to center pressing, its a loop like on the 400f, taker a look at neevo's build to see shape
Click to expand...
I see said the blind man 8) to the deaf man :-[ ......................I see now that the center pressing as well as the ridge back for the frame section thats under the tank are all welded to the tubular frame loop.
 
Yep, it's just a dent, body filler will work fine, heat it up and beat the edges back to shape first
 
I just had something like this come up. I've learned A LOT more since last post.

Do yourself a favor and use "Lab Metal" filler for any future dents in metal. It's powder coatable so you can do parts up right. Also I weld all seams on frames now to strengthen them up.
 
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