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Author Topic: saving a 1980 KZ750 twin  (Read 60868 times)

Offline 1fasgsxr

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Re: saving a 1980 KZ750 twin
« Reply #380 on: Mar 21, 2018, 07:43:56 »
Its in the detail.  Nice !
http://www.dotheton.com/forum/index.php?topic=41083.0

Life is a journey from the maternity ward to the crematorium....

Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #381 on: Apr 07, 2018, 09:24:18 »
quick question on wiring the nuetral indicator light;
factory wiring has 12V+ to indicator light > then to neutral switch which grounds on the engine.

this wont work in my tach because the indicator light shares a common ground wire. I think I could use a relay to sort this out, but I don't want to use a big standard one. This tiny LED probably needs less than 0.5 amps. will something like this work?

https://www.jameco.com/z/EDR201A12Z-Excel-Cell-Electronics-Relay-Dip-SPST-12VDC-1A-Cont-1K-Ohm-Coil-2_106472.html

Suggestions?

Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #382 on: Apr 27, 2018, 03:47:02 »
I have this spare 20mm GSXR750 axle Id like to use. Its hollow and weighs half of what my solid ones does. The problem is its too long. The end where the threads are is swagged to 18mm. If i cut this portion off and cut 20mm threads on the main shaft I think the wall thickness will be like 1-2mm thick in the minor thread, so I don't think I can realistically do that. I'm thinking about cutting off the hex head, trimming it to length, and soldering  on a new hex. I will pin the hex to the shaft as well for safety's sake. I found this solder which is very low heat (430F/221C) so I believe I should be able to solder the nut on there without removing the temper.
http://www.harrisproductsgroup.com/en/Products/Alloys/Soldering/Lead-Free-Solders/Stay-Brite-Kit.aspx

Is this a bad idea?
« Last Edit: Apr 27, 2018, 03:59:47 by doc_rot »

Offline irk miller

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Re: saving a 1980 KZ750 twin
« Reply #383 on: Apr 27, 2018, 09:55:00 »
I've done similar where I weld on the hex head plus a short length, then machine it back down clean. 

Offline jpmobius

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Re: saving a 1980 KZ750 twin
« Reply #384 on: Apr 27, 2018, 11:23:34 »
I imagine that would work fine, presuming it is silver soldered.  Keep in mind the job the axle needs to do.  While it may seem that it is principally loaded in shear to keep the wheel from falling off, it is also loaded in tension.  The clamping force is much more important than may be intuitively obvious.  Keeping the swing arm (or fork legs), spacers, inner bearing races, and any other components tightly clamped together makes the assembly a rigid structural component that aids substantially in keeping the arm (or forks) from twisting and deforming under load.  So all the mating surfaces need to be nice and square and flat, and at least as large in o.d. as the o.d. of the inner races.  The larger the diameter of these parts, the greater the structural benefit.  As long as your soldered joint withstands the needed clamping pressure you will be fine - so use a high content of silver.  I doubt there is much special about the axle as far as heat treatment, so you should be fine heat wise.  Personally I would not hesitate to simply weld it.

Looks like your little relay would be fine.  Rather a pain to get the neutral light going though!  Any chance you can isolate the indicator so you can power it up inside the tach and use the bikes factory switched ground?
« Last Edit: Apr 27, 2018, 11:26:11 by jpmobius »
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 datadavid

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Re: saving a 1980 KZ750 twin
« Reply #385 on: Apr 27, 2018, 11:50:52 »
I imagine that would work fine, presuming it is silver soldered.  Keep in mind the job the axle needs to do.  While it may seem that it is principally loaded in shear to keep the wheel from falling off, it is also loaded in tension.  The clamping force is much more important than may be intuitively obvious.  Keeping the swing arm (or fork legs), spacers, inner bearing races, and any other components tightly clamped together makes the assembly a rigid structural component that aids substantially in keeping the arm (or forks) from twisting and deforming under load.  So all the mating surfaces need to be nice and square and flat, and at least as large in o.d. as the o.d. of the inner races.  The larger the diameter of these parts, the greater the structural benefit.  As long as your soldered joint withstands the needed clamping pressure you will be fine - so use a high content of silver.  I doubt there is much special about the axle as far as heat treatment, so you should be fine heat wise.  Personally I would not hesitate to simply weld it.

Looks like your little relay would be fine.  Rather a pain to get the neutral light going though!  Any chance you can isolate the indicator so you can power it up inside the tach and use the bikes factory switched ground?
If its hardened its likely to be only an anneal, and not critical in the hex end anyway. Check with a file.

Offline irk miller

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Re: saving a 1980 KZ750 twin
« Reply #386 on: Apr 27, 2018, 12:01:51 »
Most forks are either clamping the axle on both ends, or the fork is threaded at one end and clamped at the other end.  There doesn't have to be any force at all against the hex end.  He could cut the head off completely at right length to meet the outer edge of the fork and would still work fine.  The hex head is there to hold the axle while you thread the bolt at the other end.  It's more a redundant retainer than anything.

Offline canyoncarver

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Re: saving a 1980 KZ750 twin
« Reply #387 on: Apr 27, 2018, 12:04:44 »
I was thinking that was a rear axle, not a front.
--

YZF750/1000R The Fly
KZ 750 Twin
ZRX 1100
KZ400 The Rabbit
65 Norton, My damn Shovelhead chop, and an 86' FXR
more YZF750R's, the KZ's, a Zephyr750...and the unfinished 75' CB550 cafe.
--

Offline jpmobius

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Re: saving a 1980 KZ750 twin
« Reply #388 on: Apr 27, 2018, 13:08:16 »
There doesn't have to be any force at all against the hex end.

With respect, this is simply not so, at least in this context.  I believe this particular bike does indeed have a front axle threaded on both ends (I believe we were talking about the rear, but the parts end up functioning the same regardless of the design).  It is important to understand that the axle assembly is supposed to function just like a fork brace to both stiffen the whole fork assembly in torsion (bars turn, wheel doesn't) and to keep the two forks telescoping together as a single unit.  The larger the diameter of the axle (assembly), the greater the stiffness of the fork.
Indeed, you could leave the axle assembly loose and clamp it into the ends of the fork lowers.  The result would be an assembly that would all stay together, but would loose very substantial strength from two sources.  First, the slack in the loose threaded connections will allow motion in the assembly.  This alone will impact the stiffness of the system, and cause wear in the threads that would never otherwise occur with correct assembly.  But let's say there is no motion here.  If that is the case, the strength of the element connecting the two legs is just the diameter of the axle itself.  The correct procedure is to clamp all the components together with the axle first.  This (in the main) makes the functional diameter become much larger and much stiffer, the same as a large diameter tube is much stronger than a smaller tube of the same weight.  Then, when you clamp the assembly into the fork legs, you gain this very large improvement - the effective axle diameter becomes the same as the smallest o.d.sleeved component (spacer, inner bearing race, speedo drive, etc.).  If the axle nuts are not tight enough, the assembly is much more flexible.  The fork lowers have the clamps because there can't be any axial pressure on the fork legs.  If there is, the forks will bind.  This is not a factor at the swing arm, but the principles are the same otherwise.
« Last Edit: Apr 27, 2018, 15:12:47 by jpmobius »
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 #389 on: Apr 27, 2018, 15:17:49 »
With respect, this is simply not so. I believe this particular bike does indeed have a front axle threaded on both ends (I believe we were talking about the rear, but the parts end up functioning the same regardless of the design).  It is important to understand that the axle assembly is supposed to function just like a fork brace to both stiffen the whole fork assembly in torsion (bars turn, wheel doesn't) and to keep the two forks telescoping together as a single unit.  The larger the diameter of the axle (assembly), the greater the stiffness of the fork.
Indeed, you could leave the axle assembly loose and clamp it into the ends of the fork lowers.  The result would be an assembly that would all stay together, but would loose very substantial strength from two sources.  First, the slack in the loose threaded connections will allow motion in the assembly.  This alone will impact the stiffness of the system, and cause wear in the threads that would never otherwise occur with correct assembly.  But let's say there is no motion here.  If that is the case, the strength of the element connecting the two legs is just the diameter of the axle itself.  The correct procedure is to clamp all the components together with the axle first.  This (in the main) makes the functional diameter become much larger and much stiffer, the same as a large diameter tube is much stronger than a smaller tube of the same weight.  Then, when you clamp the assembly into the fork legs, you gain this very large improvement - the effective axle diameter becomes the same as the smallest o.d.sleeved component (spacer, inner bearing race, speedo drive, etc.).  If the axle nuts are not tight enough, the assembly is much more flexible.  The fork lowers have the clamps because there can't be any axial pressure on the fork legs.  If there is, the forks will bind.  This is not a factor at the swing arm, but the principles are the same otherwise.

You really need to read up on this more.  Here is the picture he posted of the axle.



The parts do not function the same front and back.  By having the bottom of the forks clamp, that is what is stiffening the front end, not having it threaded in or providing force to the underside of the hex cap.  The binding of the forks onto the axle is doing the work.  Notice one end of the axle in the pic does not have a hex bolt.  If it were important to provide force torquing down on that, it would not be designed that way.  Many, many, many axles including my BMW F650 and all modern Suzuki sport bikes are made without a cap at all. 



Here is a VZ800 front end.  The axle is not capped at all.  You thread the axle into the left fork and clamp with the right.  There is zero force squeezing the forks together.  A shoulder on the axle works against the spacers and the bearings keeping the wheel parts tight together, but the fork is separate from that force.