Topic: It's a chopper, baby. My CB750K0 rebuild (warning LOTS of pics)

[mystic_1]

Absolutely.  There's a teaser up there in post 27, here's the bike as of about Aug 2014:















Since then I've added a pad to the sissy bar and done a few other minor things, but what you see here is about how she sits today.

mystic_1

[Desert-SOHC]

Love it!

[budman]

That *is* a throwback.  Super cool.  I see you drilled your rotor so it fans in the opposite direction of what you usually see.  I did mine the same way.  Don't know that it makes a difference.

[mystic_1]

Thanks gents.

The rotors came to be already drilled, I have a pair that are mirrored because I was thinking of attempting a dual disc conversion, but ended up not doing it for the time being due to the complexity on the K0-K2 forks.

I don't know the swirl direction makes a difference either.

mystic_1

[mystic_1]

So the first step was to get the frame down to bare metal and survey the damage I knew to be there already.  It's minor.

Disassembled.  You can see some tape lines where I was thinking of making cuts.  I didn't end up cutting into the backbone.


Paint Stripped:


This damage was just rear of the seat hinge and forward of the shock mount, on the right side.  It had been filled with fiberglass, I'm assuming this is a sign of a previous crash at some point in the distant past, but, the frame around this area is completely fine with zero signs of damage.  What you're seeing is a depressed area with cracks at the bottom.








The kick stand tab had been cut off at some point in and re-welded by a tribe of orcs.  I sourced a replacement section from another frame and will try to weld it back to the stock angle.


The front seat hinge had been cut off and replaced with what appears to be metal pipe hanger strap.  I'm assuming they fabbed up a hinge replacement that subsequently snapped off.


The right side centerstand mount had been cut off in order to clear the 4-1 you see in the early photos.  I'll replace this so I can run a centerstand, and go back to 4-4 exhaust.


Starting the process of checking to see if the frame is straight.  Leveled the frame on the stand using a bunch of levels on magnets.


Also rigged up a crude angle gauge using an old carpenters square with a built in spirit bubble.


Measured 27 degrees at the steering head, which is stock (actually 27 degrees 10 minutes).


Finally, managed to source a replacement centerstand mount from a donor frame.


More to come...

mystic_1

[mystic_1]

Since I was going to be basing my final measurements off the bike itself I decided it would be prudent to get the suspension sorted out well before I dove into frame changes.

I hadn't torn into the forks so I was able to reinstall it as a unit.  (note that I later swapped out this aftermarket lower tree for a chromed stock one)...


...after installing new tapered bearings.  Plenty of good threads here on the forum about this so I'll skip the details.


I sourced a chromed swingarm...
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...and decided to take this...


... and pull it out...


... so that I could do this...


... which made it look like this...


... enabling me to do this ...


... to make it look like this ...


... so that I could take one of these ...


... and put it here:


These are standard Zerk fittings which actually fits my grease gun properly, don't remember if they're 6mm or 1/4 inch.  Made a big difference in my ability to get grease into the pivots.  Made sure to purge the inside of the bolt afterwards by pushing through grease until all metal chips were removed.

The wheels actually had pretty recent bearings in them already so they were good to go at this stage.




These are the 13.5" shock that I'd been running.  I wanted to lower the bike as much as possible so I also have a set of 12.5" shocks to try out, but I don't want to loose too much cornering clearance.  Hoping to come up with a geometry that would let me run the shorter ones but also be able to switch back to stock length if I wanted to.



Ho hum, nothing too interesting here.  These will get a polish later on.




More to come...

mystic_1

[mystic_1]

I wanted to go ahead and mock up the front fender at the same time, so I drilled out the rivets on my factory fender and liberated the fender mount/brace.




Note the asymmetry on the early fender brace, to go with the K0 forks.  This make dual-disk harder to do so I shelved that idea for the future.


I drilled out the rivets from the Harley front fender from earlier....



... and cleaned up the fender a bit, this was a NOS swap meet fender which had never been mounted but had rusted in storage.  Got it for almost nothing.



The fender then dropped right onto the stock bracket.




Slid the fender back and forth until I found the location I liked, then drilled new holes for stainless hardware.  I had to use a lot of imagination here because I knew that I'd be changing the angle of the forks, so I had to picture the final location of everything and anticipate to get the fender to land where I wanted in the end.




More to come.

mystic_1

[mystic_1]

So here's what the rear end looks like with stock-length shocks.


and here's what it looks like with the lower shocks.


I really like the way this looks, with the swingarm horizontal and parallel to the upper frame rails, but again final decisions will be based on ground clearance.


In order to mount the new shocks I first had to drive out the center bushing from their upper mounts.


I used an allen bolt whose head was the same diameter as the inner bushing,


... and a CB750 rear wheel axle spacer ...


... like this ...





and stuck the whole thing into my vise to create a rudimentary press.













No problemo.  Lubed up the shock and it slid right into place after a little wiggling.



The inner bushings were, btw, exactly the same size as the boss on the shock mounts.


mystic_1

[MCRider]

Nice job!

If its going to be a chop, gotta use the shorter shocks if they work, ground clearance, bottoming out etc.

I'm sure you've covered it, but what's the story on the tank? Looks good.

[Desert-SOHC]

Nice, cant wait to see the frame mods!

[mystic_1]

The next thing I wanted to figure out was how to wedge the Harley rear fender into place.


This clearly wasn't going to fit like this.




So I cut off this:


Ahh, there we go.


Slid the rear fender around trying to decide how I liked it.


Established where I wanted the bolt holes to be, and then made up a little jig in order to index them off of existing holes in the fender, to ensure symmetry.



Meanwhile started closing up holes I wasn't going to use.  You can also see where I'd marked out places to weld reinforcing washers inside the fender bolt holes.








I discovered that by cutting off the rear of the factory stock inner fender, I was able to slide it into the front of my new fender, and it fit almost perfectly!



Inside you can see where the edges even lined up with the wire channel clips in the Harley fender. 





I trimmed up the front of the Harley fender to meet the lip on the inner fender nicely.  Later I'll come back and finish off all of this more nicely, and secure the fenders together with small bolts etc.



Welded in the reinforcement washers...




... and then it looked like this:



To mount it to the frame, I wanted as tight of a bolted connection as possible, so I re-purposed some dowel spacers, having discovered that they fit the frame mounting holes perfectly.  I reamed out the holes in the fender mount to match, and put a plastic washer between the frame and the fender to protect the paint.



Bolted it all up...




... and then it looked like this!




The "ears" on the plastic inner fender are snapped back into their usual mounting tabs on the frame, the two fenders lock together, and so it's supported front and rear.  My plan at this point was that the fender would not support much weight, so I was OK with using the plastic fender section for some support.  I ended up changing tack on this later on in the project, I'll detail that bit later.


mystic_1

[mystic_1]

I'm sure you've covered it, but what's the story on the tank? Looks good.

You'll see my Fibre-Mold brand tank in many of these photos, the bike came to me with it, but it's an old-school fiberglass tank and while I love the looks I ultimately decided for safety reasons to run a metal tank.  Fiberglass tanks can shatter from impacts that would just dent a metal tank.

Also, ethanol.

The tank you see in the finished pics above are a swap meet tank that I cleaned up, re-shaped a but with hideous amounts of Tiger Hair reinforced fiberglass body filler, and then painted   It's a later K tank with the left side single-spigot petcock.   It's OK, but I really love the Fibre-Mold's shape much more, in spite of it being only a little over two gallons.

I also went this way for simplicity, so that I could dedicate more time to chassis work than fabbing up a new tank.  Always time for that later.

mystic_1

[MCRider]

I'm sure you've covered it, but what's the story on the tank? Looks good.

You'll see my Fibre-Mold brand tank in many of these photos, the bike came to me with it, but it's an old-school fiberglass tank and while I love the looks I ultimately decided for safety reasons to run a metal tank.  Fiberglass tanks can shatter from impacts that would just dent a metal tank.

Also, ethanol.

The tank you see in the finished pics above are a swap meet tank that I cleaned up, re-shaped a but with hideous amounts of Tiger Hair reinforced fiberglass body filler, and then painted   It's a later K tank with the left side single-spigot petcock.   It's OK, but I really love the Fibre-Mold's shape much more, in spite of it being only a little over two gallons.

I also went this way for simplicity, so that I could dedicate more time to chassis work than fabbing up a new tank.  Always time for that later.

mystic_1

Yeah, I wouldn't run a glass tank either, but it does look good. And only 2 gallons would get old real quick.

[SOHC4 Cafe Racer Fan]

Are you welding in a replacement cross-member?

[mystic_1]

Are you welding in a replacement cross-member?

Heh, I was wondering how long it would take someone to call me out on that one

The answer is no, sort of.  I couldn't bring myself to spoil the nice clean look I had going on out back by putting a hoop back over the rear fender.  I was, however, totally aware that I would be giving up some rigidity back there as a result.  Not as badly as some chopper builders do, but enough to make me think about it a lot.

What I did end up doing was to weld a big honkin brace inside the fender. 


This was made with material nearly 1/8" thick, and it ties into the reinforcing washers I added above.  Since it doesn't follow the shape of the fender perfectly, there's an ever-so-slight airgap in places, so as a result we have two differentl 3-D shapes interlocked into a sort of truss-designed-by-insane-cavemen.



Total fender thickness at the weld seams approaches 1/4".  It's very rigid.  In my mechanical fantasies, this combined with the close fitting and large surface area of the bolted connection above, helps offset the loss of the rear frame hoop at least a bit.


While I was at it, I also layed out and built some sheet metal extensions to finish off the front ends of the metal fender section. 




I didn't end up doing the additional frame gussets you see here, I decided they wouldn't really add anything, are hidden under the seat, and would mean I'd have to be much more precise with gaps.


In doing so, I also noticed that I could add some little tabs to the front and bolt through those into the frame tabs that the plastic fender snaps into. 




This gives me four points of support on the metal section of the fender, which is now much stronger and more rigid than before.

Also welded in some bar stock at the front edge to stiffen up and reinforce it. 



BTW,you're seeing all of this buried under a bit of filler and sealer, these pics are actually from later in the project when I was about to paint.  I don't have good pics from earlier in the process, sadly.


In this last pic you can also see the little holes that I'll use later to bolt the metal and plastic sections of the fender together using M6 hardware.




All in all I was pleased with how it all came together, since I started out with no plan whatsoever.  You may not be able to tell from the pics but I also had to dish the sides of the fender slightly in order to give me nice gaps where the fender passes the frame rails.



In the time I've been driving it since the work was completed, I've not noticed any loose feeling out back, or signs of things flexing where they shouldn't, but it's not like I push this thing in the corners like some of y'all do

mystic_1

[mystic_1]

So, here's the ugly truth about the frame, and the worst of the damage I discovered.

I wanted to check the frame overall for straightness.  For starters, I hung a level with a line laser function from the ceiling so I could shoot lines onto the floor and objects below.


A piece of 1/2" condiut fits right down the center of the steering stem.




Aligned the laser to the conduit and also down the center of the backbone. 


The laser is hard to see here but it's there.


More visible here.


Laser passes through the space where the battery box would be, and hits the swingarm in the center, you can see it's also aligned with one of the bolt holes in the engine case.


At the cross-gusset just forward of the shock mounts, the laser hit the frame just to the left of my center mark, by a tiny amount.  This would suggest that the frame is shifted slightly RIGHT at this point, by well less than 1/16", BUT...
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.. when I centered a ruler across the rear of the frame at the top I discovered about a 1/16" deflection to the LEFT.


Measured the inside of the swingarm and marked the center.  Discovered a little more leftwards deflection here, I want to say I measured this at just about 1/8".


Hung a bunch of plumb lines from the frame and checked for alignment to the axle using a square.  Everything is parallel, the front of the frame is straight, and the axle is level.  The center rear plumb bob in this pic also shows the axle misalignment, compared to a piece of rod stock laid down the center of the swingarm.



I also took a bunch of cross measurements for example from the center of the swingarm pivot to the center of the shock mounts on each side, from the tips of the upper rear rails to the center of the steering head, and so forth.  The leftwards deflection you see above is literally the only misalignment I was able to detect withing the limits of my ability to measure.  Possibly the frame is bent "trapezoidally" but if so I couldn't find it for sure.

It's also possible of course that the swingarm was tweaked, but I did check it with the chrome swingarm from above and got similar results.  The chrome swingarm was deflected less but still obviously off to the left slightly.

Now, given the quality of the factory weld especially on early 750s (its my understanding they were cranking them out as fast as possible) I gotta wonder how straight the frame was from the factory.  The damage I mentioned earlier made me suspect the bike had been hit at some point but all other measurements were dead on so I'm at a bit of a loss to explain the deflection at the axle, with the axle still being at right angles to the rest of the frame.  Both swingarms being bent would explain it, but really they were very close to each other.

In the end I decided this wasn't worth persuing, it seems like a very small misalignment and I'd already been riding the bike around like this for 20+ years with no issue.  At any rate, I had a known starting point now and a goal of keeping any misalignments from future mods to less than this amount of tolerance.

mystic_1

[mystic_1]

My next move was to straighten out the seat hinges.  The remaining hinge on the bike was bent, so I cut it off and measured it up.


Sorry this is so blurry but should still be readable.


I made bases by making two cuts into a piece of pipe just larger than the frame rail, so that the pipe's ID was the same as the OD of the frame rail.  I then cut the pieces free and had four identical pieces (only needed two).




Another smaller piece of pipe was found which the seat hinge pins fit into nicely.  Sliced out four pieces of this.




I made up a spacer that fit into the old hinge and used it to set the distance between the pivot tubes.  Between the base plate and the pivot tubes is a bit of flat stock that raises the pivot tube to the correct height and gave me a nicer weld angle.  You can see here that I welded the flat stock to the smaller tube, then cut them to length.



Welded them up...




... and ground them smooth.







More to come.

mystic_1

[mystic_1]

I wanted the replacement hinges to go into the stock locations even though I wasn't planning on using a stock seat.  I figured having standard hinges would keep my options open in that regard.

So, what better way to align the hinges than to use a factory seat?







All of the frame bumpers were in place and the original hinges and latch plate were present.


Another swap meet find, again got it cheap.

The cover was trashed, and when I peeled it off the foam was staring to go too.  But, the base pan was sound if a bit rusty, and that's what I was after anyhow.  Surface rust only in a few places, you'll see later that it cleaned up real nice.






Shot it with a laser and marked the centerline of the pan for reference.


Set the pan onto the frame and secured it using zip ties, down through the vent holes, around the frame rails, and then back up through the hole and secured over a long screw.  This mounted the seat firmly into the correct position.






I bolted the new hinges to the seat pan's hinges using a long straight threaded rod with nuts so that I could index things back and forth.  You can sort of make out also that I'd trimmed the bases down into more of an oval shape for aesthetic reasons.  Once I had them where I wanted them, I used screw clamps to hold them in place.








Tack them into place and then burned them in.




That last picture also explains the strange damage I'd found in this area earlier, it was from removal and moving the rear seat hinge.  I'd always thought that the rear hinge on the frame was in the correct location but you can see here compared to earlier pics that the hinge had been moved forward in order to mount the huge king-queen seat you see in the first pictures.

By this time I had something different in mind, so putting the hinges back to stock was definitely the right move.

I was pretty happy with the results.
















mystic_1

[mystic_1]

Oh forgot to mention, in order to close up that damaged area I cut a small patch, fitted it to the damaged area, and welded it into place, then ground it down.  This was all done prior to the pics above.

mystic_1

[Desert-SOHC]

Nice work.

[MCRider]

Oh forgot to mention, in order to close up that damaged area I cut a small patch, fitted it to the damaged area, and welded it into place, then ground it down.  This was all done prior to the pics above.

mystic_1

Welding. Something I never learned to do. I'm at their mercy.

[mystic_1]

Ron,

It's an open question as to whether I have learned to do it either lol 

I know you can't ride any more but there's no reason you couldn't learn to weld so long as you have the manual dexterity left.  You're a really detail-oriented guy so I'm sure you'd pick it up easily.

Maybe you won't be going about cutting up frames and such, but there's a lot of things you can accomplish simply with a welder that would be challenging otherwise.

I know your bike is more-or-less complete now but if you're anything like me then it's never really "done"

cheers
mystic_1

[mystic_1]

So while all of this was going on (and the engine build was progressing in the background, see above) I was also acquiring additional parts to complete the rebuild.  You'll see some of these knocking around in the mock up pics to come.

Found a seat that I really liked. 



One of my goals was to reduce the height of the passenger seat, for a couple of reasons.  First, my wife found it uncomfortable.  Second, lowering the passenger also lowers the overall center-of-gravity of the loaded bike, and every bit helps handling, especially on a chopper.  In addition to all this, I never really liked how the old seat followed the line of the rear fender (it didn't).

This is a Corbin Gentry seat. 





Unfortunately it's a 350 seat, and someone cut a huge hole into the pan at some point.





"#$%* it," he said.  "I have a welder, I'll make it work."   


For headlights, I'd been collecting up these old lights I kept seeing at swap meets, usually buried in piles of junk parts.  No idea of the brand.  There's a few variations of these out there, some have indicator lights, some have slightly different bezels, etc.  Possibly different production years of the same brand of light.  I eventually managed over the years to come up with five of these, and mixed and matched the best parts to make up a decent pair.



I really dig these both for their overall look and the fact that they have real glass lenses with this cool bevel in them.



Unfortunately they are also 6V twin filament bulbs with a reflector design that's completely inadequate.  Never really seen bulbs like this before.  I'll dream something up to fix this later in the build. 





In the meantime also scored a dual headlight bracket.  I believe this is a Harley piece but lots of Honda chopper guys run these on the lower triple tree pinch bolts.  Not perfect condition but pretty clean overall.





You've already seen the chrome trees in earlier pics.  The original unicorn tree that came with the bike has badly failed chrome and I swapped it out for a later set years ago.  I still have the original instruments although they're in terrible shape.





So, I decided to run mini speedometer and tach.  Speedo has built-in LED indicator lights, for a clean dash.



I bought side covers from LPM Plastics.  These are decent reproductions and a good match to the originals, which had many damaged areas.  I like them.



















My only complaint about these is that they lack the retaining tabs for the grills that are supposed to go behind the vents.  I still haven't done anything about that yet but have plans to epoxy something in place to retain the grills, and probably go for something like stainless expanded metal mesh.





And I had been picking up up a couple other things as well during this time (not all swap meet junk, either! lol  ).



More to come.
mystic_1

[mystic_1]

Coming soon:

CARNAGE!


(sensitive viewers may wish to look away)

[mystic_1]

Right, so here's the main event! 

With a temporary crankcase bolted into the frame to keep the engine cradle secure, I once again used my trusty laser level to strike a line across the two main frame down tubes.  (these pics are from my test run with the donor frame, but same idea when done for reals).





You'll note that I left enough length below the cuts so that I could get my slugs into the frame tube to a decent distance before interference from the motor mounts or the bends at the top.  Also marked the locations where I'd be cutting out the auxiliary backbone tubes...



... and then cut them out. 


You can see in this picture how the cut ends have a tendency to shift after the cut due to internal stresses in the frame.












Put a bunch of level on various points so I could keep track of things and make sure everything remained straight.



Set up a little platform to support my bottle jack, with a plate of 1/4" steel supporting the backbone...



... and then made my cuts across the down tubes.  Once again some deflection after the cuts are made.











Pressed the Play button on "Thus Spake Zarathustra" and started pumping the jack handle.












Jacked the opening to just below the calculated four inches from my plans, and then lowered the bike until the wheels were almost touching the ground, then used the jack to fine-tune the distance.  I decided to start with a little less than my calculated 4" of gap, because I swapped the shocks back and forth between the longer and shorter ones from earlier, and chose a geometry that would leave the frame/engine level with the longer shocks and slightly at an up-angle with the lower shocks.  This would allow me to run either set safely.  If I'd gone with more gap, and then decided to go with the longer shocks in back, the frame would then in fact be tilted down in front.



Turns out that a piece of 4x4 was basically ideal for holding the gap open, so I could remove the jack.






"Hot damn, Martha!  That boy done ruined his frame!"



mystic_1