Dent removal on 2 stroke pipes

[Dono113]

Anyone tried the freezer method or Air and Heat ??
Cheers
BretD

[Cabmkr]

Bret,
   I used the air pressure heat method on my YZ250H pipe I took out a few reasonable sized dents on the main part of the expansion chamber. For the small end I ued a plug from a boat, the other end a rubber plumbing plug and a regulator from a leak down tester. Also I used a MAP (yellow can) torch for more heat then propane

Cheers, Chris

[Slakewell]

When useing the heat method make really sure there is no fuel residue in the pipe otherwise you are making a bomb.
Compressed air + fuel + heat = unhappy 

[Dono113]

The pipe is forked and I've told old mate to buy a new( rebuilding his 99 kx125 for him as he's not real mechanically minded at all) and I've got nothing on the boil, just thought I'd have a crack at pulling some dents out of it for practice.

[Cabmkr]

When useing the heat method make really sure there is no fuel residue in the pipe otherwise you are making a bomb.
Compressed air + fuel + heat = unhappy 

Yes for sure, when I did mine it was already beadblaseted and I blew out and torched the inside also before i pressurized it

[FAT-TOY]

  Bret  I use air pressure to repair the odd pipe, it can be a time consuming excercise.  I use expanding bungs for both ends of the pipe which I secure with wire because they can blow out if the pressure increases to much which it can when you apply heat.  I have a tyre valve fitted to one of the bungs this allows me to pump the pipe to about 35 pound of pressure then heat the section you need to pop out using a small hammer tap around the outside of the dent, sometimes they come out quick most times they dont, it's all trial and error.  The dents on straight sections seem to come out a lot easier then dents on the bends in fact if you have to much pressure they will move to much and also it can split the seams, I always keep a check on the pressure with a guage to stay safe.
       Zane

 

[Dono113]

The dents and creases were pretty harsh so I slip the pipe at the centre joint and hammer and dolly them out

[Scootern29]

I use your method Zane, the only thing I don't do is safety wire the plug. It's a lot more fun when it is over pressurized and launches like a mortar. The grand kids love it. 

[Davey Crocket]

I can relate to a "blow up"....about 10 years ago was restoring a 34 Chev coupe of a mates (he's owned it from 1968 and bought it off the original owner....still has it btw), anyway the fuel tank was pretty dented underneath so I thought that I could "blow" the dents out a-la motorbike pipe style...we washed the tank out half a dozen times times over a few week period, made up some adapters to block the holes off, put a tyre valve in one (had already run the oxy  in it to get rid of any fumes), pressurised it to about 40 psi and started heating....well it lasted about 5 minutes until the "bomb" went off....everybody shit themselves, we where rolling around the floor with tears in our eyes we where laughing that hard...after about another 5 minutes we looked at the tank...it was now pregnant....it tapped into shape quite good. 

[Suzuki Brother]

A friend of mine swears by the Freezer method.  He's done it on his modern KTM300 and said it worked great.  He told me he plugged one end (didn't need to be a high pressure plug, just water tight) and filled the whole chamber with water and plugged the other end in a similar fashion.  Put it in the freezer for a few hours and let physics do the rest.  As the water freezes it expands a bit and slowly pushes outward on the pipe wall (as seen when you put a bottle/can of your favorite beverage in the freezer to cool it down quickly and then forget about it).  He told me that he froze it once and it got the majority of the dents out most of the way.  He repeated the process 2 more times trying to get it looking perfect and on the third run the pipe split on a seam.  His advise to me was to use this method once only, and maybe twice if you're game, to get the dents out as far as they will come "practically".  Apparently when he split on a seam (3rd time in the freezer) it didn't explode violently and get wildly out of shape & he repaired the split quite easily and neatly.  I think that once a split pipe it de-frosted and drained you just need to close up the split (maybe using a large hose clamp) and then weld it up like a crack.

I haven't used this method myself yet but I can vouch for my friend, he knows what he's talking about and he has done it before.  It made sense to me, sounds easier and safer than air pressure and heat,  "Safer" only if you're wife isn't going to kill you when she finds an exhaust pipe in the freezer.
Good Luck

[popeye]

I've got one FMF pipe I'm going to try a stud gun that they use for dent removals, then rub it back and get it re nicholled....

[piney]

be careful popeye, tried one of those once on a cb750 tank. after cleanjng and blowing out tank, it imploted 

[Montynut]

A friend of mine swears by the Freezer method.  He's done it on his modern KTM300 and said it worked great.  He told me he plugged one end (didn't need to be a high pressure plug, just water tight) and filled the whole chamber with water and plugged the other end in a similar fashion.  Put it in the freezer for a few hours and let physics do the rest.  As the water freezes it expands a bit and slowly pushes outward on the pipe wall (as seen when you put a bottle/can of your favorite beverage in the freezer to cool it down quickly and then forget about it).  He told me that he froze it once and it got the majority of the dents out most of the way.  He repeated the process 2 more times trying to get it looking perfect and on the third run the pipe split on a seam.  His advise to me was to use this method once only, and maybe twice if you're game, to get the dents out as far as they will come "practically".  Apparently when he split on a seam (3rd time in the freezer) it didn't explode violently and get wildly out of shape & he repaired the split quite easily and neatly.  I think that once a split pipe it de-frosted and drained you just need to close up the split (maybe using a large hose clamp) and then weld it up like a crack.

I haven't used this method myself yet but I can vouch for my friend, he knows what he's talking about and he has done it before.  It made sense to me, sounds easier and safer than air pressure and heat,  "Safer" only if you're wife isn't going to kill you when she finds an exhaust pipe in the freezer.
Good Luck

The problem with this method is good old pyhsics works against you . The water freezes in the smaller areas first expands equally in all directions so it tries to expand the pipe in every direction and this tends to straightens the pipe. That is why it split. This method does even greater damage to fuel tanks etc. The plug, pressure and local heat is by far the best method.

[GMC]

The ice method always bothers me, how does the ice know where the dents are??

I have used the pressure / heat method for 20 years on what would probably be a couple of hundred pipes by now with out any real drama, (well I have lost a couple of plugs over the years)
Localised heat gives you control over what comes out and what stays.

http://www.geoffmorrisconcepts.com/16/exhaust-repairs/
Should probably take some photo's of some vintage pipe repairs.