1974 Kawi G4 Expansion Chamber Build

Element

Element

New Member
Hey guys. First post on the forum. I've looked everywhere on the net and I can't find the answer to this problem.

I'm attempting to build an expansion chamber for the bike I'm working on. It's a 1974 Kawasaki G4TR-E. I've done the required reading by Gordon Jennings and A. G. B, mapped the head, designed the pipe, created the 12 cone layouts for the pipe, and now I am trying to figure out how to roll the 12 pieces. I see a lot of guys using a slip roll to do the work, problem is that the pieces are anywhere from 100mm in diameter, down to 24mm, and the smallest any shop in town will do is 2".

I've seen people do 'micro breaks' where they make 20-30 bends in the metal to achieve the circular shape, but I like the appearance of the smooth-rolled material.

Any suggestions?

Thanks
 

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I think one of the only other options is hydroforming but that gets pretty involved as a DIY sort of thing.

PICT0069.JPG
 
All good ideas I'll have to look into. Does anyone know how small of a cylinder the H.F. slip roller will make? I suppose it must be limited to the diameter of the rollers. Thanks.
 
HF rolls are 25mm dia. Here is a pic of pipes I built using the HF type rolls. Good luck!
 

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650hardtail said:
they really that shitty ?
Click to expand...

It depends what you are going to use them for. I made my pipes using 22ga mild steel sheet and the HF rolls worked fine. Now, if I was going to be making a set of exhausts every week I'd probably consider a better set.
 
It also depends on how long of cones your gonna roll johnu pipes are art but the cone lenghts are short the last set of pipes i built had no belly section the cones met on the big end and they were long as crap my sliproll is 24inch long it came from summit. my buddy has the three in one sliproll break shear from hf it doesent do any one of the three things well and its three hundred pounds for some reason. ive hever had luck with hf customer service eather summit sent my two roller becouse of a broken knob and the didnt want the broken one back
 
the smaller sizes you mentioned in the first post you will need cut your shape roll as small as your roller will allow and form the rest by hand and finish with a cone anvil and body hammer
 
the smaller sizes you mentioned in the first post you will need cut your shape roll as small as your roller will allow and form the rest by hand and finish with a cone anvil and body hammer
Click to expand...

Thanks for the info. I was wondering what the last step was on the smaller pieces. For some reason, no one talks about this!
 
Due to racing 2 stroke guys have always keep spec and pratices close to there heart and 40 years out it ant much better. the difference between a 1000 dollar pipe and a 100 dollAr pipe are sizes and methods of construction but there both the same in function. in the modern days of downloadable tuner programs and the world wide web its not as important but the old guard has old habits so ask alot of question and sooner or later some one will point ya in a direction. youtube if used correctly will show you how to hydroform a pipe with a electric pressure washer
 
Brad is right about the fact that you can only make cones up 12" long on the hf rolls, however if you have a cone that is say 18" long you can always make it in two pieces of 9". This is often a good thing as you can make the join at a place where the pipe needs to change direction therefore you can angle the ends of the two cones to go where you need it. I got lots of advice from people on the web but I am originally a fabricator by trade (many years ago) so I have a good background for this sort of thing. I am far from an expert but I will answer any questions that you may have as will others on here. My biggest tip though would be to use 22gauge material, it is plenty stong enough and easy to form and the pipes weigh virtually nothing when completed.
 
22 gauge? That seems really thin. An article I read recommended 20 gauge and so that's what I started with... Seems like a thinner gauge would be much easier to form, but how does it stand up to a rock strike at 60 mph? Or are they both going to get a ding no matter what?
 
Element said:
22 gauge? That seems really thin. An article I read recommended 20 gauge and so that's what I started with... Seems like a thinner gauge would be much easier to form, but how does it stand up to a rock strike at 60 mph? Or are they both going to get a ding no matter what?
Click to expand...

20ga will work it's just harder to work with and the pipe weighs more. Depends how big of a rock we're talking about, I can't see it getting dented very easily though with normal use.
 
The thinner you go, the better your welding technique needs to be!

Looking forward to seeing where you go with this.

Crazy
 
That's true, I sometimes forget that it is an issue for some people ;) I gas welded my pipes, if you have tig available it would be far better.
 
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