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Author Topic: saving a 1980 KZ750 twin  (Read 67938 times)

Offline jpmobius

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Re: saving a 1980 KZ750 twin
« Reply #150 on: Jun 29, 2016, 12:36:27 »
Sounds interesting getting the spring out of the pipe after bending..

Right!  I've tried that long ago with much smaller tubing - both inside and outside but no heat.  Total failure.  I'd expect an internal spring to lose all its support strength heating the tubing sufficiently, and be impossible to remove, but it is just a guess.  I would expect the bending to seriously clamp the spring, and then contracting when cool to make it a permanent assembly!  Sand,compacting, caps, and heat definitely works though, but you need a seriously big torch!
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #151 on: Jun 29, 2016, 17:21:11 »
Ill bring my good camera with me the next time I try and and get a video.

Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #152 on: Jul 03, 2016, 06:51:38 »
I'm wondering if need to face reality and just give up with the sand bending. Ive gotten better, but the small radius still crushes. It is thinning down to 1.37" diameter from 1.5". I doubt this would have much of an impact on the exhaust performance, but I just don't like the way a crushed tube looks.

Thing I have learned;
>Thinner tube does not crush easier than heavier tube
>set the torch to a  high reducing flame (more fuel than O2) to get a nice even heat on the tube.(use A LOT of gas)
>use as little as heat as possible, heat till red NOT orange.
>use dry sand (duh)
>taping the tube on the ground  and welding on sheets to cap the ends is just as good as welding a nut and rods on to the ends to "pack" the tube
>heat the area you want to bend and extra 4" on either side.

This is something I could chase for a long time and spend a lot of money on materials. I think it may be time to cut my losses and buy some mandrel bends. At the very least buy the small radius curve and sand bend the rest. This is the best result i had. I also found that because of the frame clearance i had to use studs and acorn nuts to secure the flanges.
Thoughts?

Offline irk miller

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Re: saving a 1980 KZ750 twin
« Reply #153 on: Jul 03, 2016, 08:30:37 »
Thing is Doc, a mandrel can be cinched as well.  You have to make sure you get full diameter bends. 



Kits like what TC Bros sells are not full diameter.

Offline jpmobius

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Re: saving a 1980 KZ750 twin
« Reply #154 on: Jul 03, 2016, 10:48:36 »
I think your pipe looks great in the pics, though I can see noticing any lack of uniformity being a lot more obvious in person.  You may have the right idea combining manufactured bends and torch bent sections.  Personally I like the more organic look of the hand bent pipes but if you can't make the tight radius portions acceptably than grafting in a pre bent piece for that portion would seem to be a way to get the best of both worlds.  Deviant, your pic is not a drawn over mandrel tube.  In the main, a mandrel is an internal die like a round ball on the end of a long pole that is kept located inside the tube where the forming operation is happening, but the term mandrel is often used for all sorts of fixtures including outside parts so there is some ambiguity.  Proper mandrel bent tubes have perfectly round sections and are indistinguishable to the eye from the straight tube.  Here is a 2 1/4" dia stainless steel tube with a very tight bend.
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline irk miller

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Re: saving a 1980 KZ750 twin
« Reply #155 on: Jul 03, 2016, 10:54:28 »
I think your pipe looks great in the pics, though I can see noticing any lack of uniformity being a lot more obvious in person.  You may have the right idea combining manufactured bends and torch bent sections.  Personally I like the more organic look of the hand bent pipes but if you can't make the tight radius portions acceptably than grafting in a pre bent piece for that portion would seem to be a way to get the best of both worlds.  Deviant, your pic is not a drawn over mandrel tube.  In the main, a mandrel is an internal die like a round ball on the end of a long pole that is kept located inside the tube where the forming operation is happening, but the term mandrel is often used for all sorts of fixtures including outside parts so there is some ambiguity.  Proper mandrel bent tubes have perfectly round sections and are indistinguishable to the eye from the straight tube.  Here is a 2 1/4" dia stainless steel tube with a very tight bend.
THat's why I said he needs to get full diameter bends.  Here's a drawing of the process.  My point in bringing it up, is the process is usually a custom process and off-the-shelf  full diameter kits are typically not offered.  The majority of local shops don't offer it either. We always run full diameter pipes on our drag cars. 


Offline jpmobius

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Re: saving a 1980 KZ750 twin
« Reply #156 on: Jul 03, 2016, 11:05:08 »
Cool drawing!  Pics worth a thousand words!
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #157 on: Jul 03, 2016, 17:59:24 »
I was gonna buy the bends from Burns stainless, which is where that pic is from i believe. I'm gonna order the slip for the muffler as well. I did the math and double the internal volume of a 1.5" tube is a hair over 2" tube, so I'll go with 2.125" tube for the collector.

Offline jpmobius

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Re: saving a 1980 KZ750 twin
« Reply #158 on: Jul 03, 2016, 20:31:13 »
how about that!  I found that pic at random from a quick search - had no idea where it came from!
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline teazer

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Re: saving a 1980 KZ750 twin
« Reply #159 on: Jul 03, 2016, 21:10:10 »
Check with Megs/Cone engineering.  According to a table I downloaded a while ago, 2 into 1 collectors require an outlet of 150 to 175% area of the primary pipes.  That works out to 1.875 to 2" and use the smaller size for a more torquey motor.