Topic: Dents in 4 into 1 headers

[CB750F2]

G/Day All. No. 1 pipe on my spare set of chrome 4 into 1 headers has a number of dents that I would like to remove. I do not wish to use heat because the chrome is in good condition. Any ideas? Thanks, Pat from Nth Qld

[Harry]

Put a cork in the ends and BLOW  He, he, no, I heard of putting a piece of broom handle or round piece of timber which fits the diameter of the pipes in the pipes and banging the dents out, but that depends on where the dents are.

[TwoTired]

I've seen a device, though I can't remember where just now, that consisted of a very small ram attached to a hydraulic hose.  The ram and hose were fed into the pipe and positioned where the inward dent located.  The ram, whose ends were contoured to that of the pipe's wall radius, would then be expanded with a hand pump to push the dent out from the inside.  There were bend radius limits as to where the ram could pass,  And, dents occuring where there was a bend in the pipe were much more difficult expand correctly due to distoriion of the opposite wall.  The operator needed some skill for proper positioning of the ram.  Of course, this technique wouldn't be useful in double wall pipe applications.

I believe the device was an adaption to a bodywork tool.   I just can't remember where I saw tool used.  I can still picture the shape of the ram in my head, though.  Rounded bump on one side of the ram and a contour shoe on the other.

FWIW...

[Geeto67]

it depends on the kinds of dents. Creases you are SOL, but nice evern concave dents can be removed. Try taking it to a body shop that can do paintless dent repair. There are paintless dent kits sold in most autoparts stores but they tend to be crap, the industrial grade is what you need. Another way is to get what is known in the trade as a "spoon" which you can use to work the dent out from inside. Eastwood sells one but I think it may be too short for your application. An autobody supply house should be able to fix you up with what you need if you wanna DIY.

I am sure someone here will chime in with the ice trick, where you fill it with water, cork the ends and freeze it. The expansion will pop the dents, supposedly. It may also pop the seams and distort the pipe till it is unuseable. I have tried this trick twoce on gas tanks, once it worked ok (the paint still lifted) and another time it expanded the tank over 5 inches and split one seam. It is an amature trick with unpredictable results.

If it is a stock pipe, they are removable, why not just replace that one pipe with another one in good condition?

[SteveD CB500F]

If they are stock headers, are they not dual-skinned?

If they are, any attempt to push out dents from the inside is doomed...

[CB750F2]

Thanks for your replys. The dents are not too bad but look ugly. The pipe is part of the standard Honda setup which means the pipes are double walled - correct me if I am wrong. Also, it is No.2 pipe that has the dents not No.1 - sorry for giving you incorrect information. However, I think that I may be able to remove it by carefully grinding the weld that attaches the pipe to the header. I have been trying unsuccessfully to find another secondhand header which has a good No.2 pipe.

[Geeto67]

the paintless dent repair at an autobody shop attacks dents from the outside of the pipe, sorry I was unclear about it before. Basically either suction or epoxy is placed on the center of the dent and a slide hammer or screw is used to pull the dent from the outside. The consumer grade epoxy isn't strong enough but the commercial grade stuff works enough that the dent may just pop right out, provided there are no creases.

[CB750F2]

     Thanks for your replys. The dents are not too bad but look ugly. The pipe is part of the standard Honda setup for a 78 F2 which means the pipes are double walled - correct me if I am wrong. Also, it is No.2 pipe that has the dents not No.1 - sorry for giving you incorrect information. However, I think that I may be able to remove it by carefully grinding the weld that attaches the pipe to the header. I have been trying unsuccessfully to find another secondhand header which has a good No.2 pipe.
     What do you think of the following? Blank off both ends, fit a removeable plug and grease nipple in one end, fill the pipe with oil, and then pressurise the pipe by pumping grease into the pipe. Precautions to prevent injury and oil splashing would have to be taken.
     Is the above worth a try? Pat, from Nth Qld.

[Geeto67]

if it is doublewalled you need to attack it from the outside so grinding the weld off wont do you any good.

[TwoTired]

I am not certain about your header pipe being double walled.  Should be able to determine that by measuring the thickness while it is removed.  Applying pressure to a tube inside another tube, and predicting the distortion effects on the outer tube, seems a difficult task, indeed.

One of the physical properties of steel is that it "work hardens" when it is bent.  To avoid work hardening, the metal is heated before or during the bending process. The dent in your pipe is now bent metal, and likely stretched a bit as well.

To restore this area without heat, you will need to apply point pressure in the opposite direction of the bend.  If you use the entire pipe as a pressure vessel and increase the internal pressure to the point where the metal will distort, the distortion will likley first occur everywhere inside the pipe but where the metal has been hardened, i.e. your dent, and any other bends that occured since the metal was in a heated, plastic, state during the manufacture of the pipe.

If it were possible to remove the dent, and I suspect that it might be, how much is it worth to you?  Lots of very difficult and complex tasks can be performed, given adequate resorces.  Do you have a monetary value of the work you wish performed?  Are you willing to risk the loss of your current pipe in experimental attempts?  Is it worth making special tooling to remove the dent?

Might be cheaper to just fill in the dents and have it rechromed, though not nearly as adventurous.
Cheers,

[CB750F2]

Thanks TooTired and others. I will hold off in the hope of finding a good No.2 pipe or a another complete set. Thanks for all your comments and suggestions. Pat from Nth qld

[MRieck]

I think I have a #2 pipe for that header.I have several loose pipes that I know came off the F2.  I would a pic (or something) to know which pipe you need.