Topic: Alan's CB750K3 RestoMod version 2.0

[Alan F.]

Hey there, I've been working on this one for a while on paper, picked up a few parts here and there and finally I've got some progress to show for my efforts.
The bike is a 750K3, stock wheels were a little too far gone and for the money I'd spend.... anyway I figured I could update my forks and front brake in the process, as well as drop to an 18 or even a 17" front wheel, and a 17 out back while retaining my drum brake.

We've all read about grinding the weld off and pressing out the steering stem....yada yada.... I'm not interested in wrecking any stock parts to get this one done. 
I'm going through this one with a minnimum of part modifications, I'm adapting, and not reinventing.  Sound interesting?
Here's a pic of this weekend's progress.

[coyotecowboy]

So did you just make a spacer for the lower bearing on the trees?  And did you figure out anything on the trail?  I'm really tossing this idea around.

[Alan F.]

Yeah, it's a little bulky, and I'll probably mill off the excess when I've decided I'm finished tinkering with the design.  The spacer will also serve as my steering stop. I've got to decide how close I want the forks to get to the tank and mark the location on the spacer then get the spacer out and drill holes and drive in my steering stop pins.  Here's a few photos of the spacer, notice the blue circles I've added to the second pic.  To help adapt the longer steering stem I also had to make a spacer to relocate the lower bearing race, too bad I couldn't find that huge washer from the all-balls kit...now that I know where it goes.  I'll probably make one in steel sometime, just for peace of mind.

I haven't figured out the trail yet, I really think Honda lied about having 95mm of trail, I calculate 110mm with the stock setup (like most modern sportbikes have) and about 104mm with this setup.  I'm going to use a 130/70-17 rear tire, which is .81" lower on the radius than a stock 110/90-18, and that should change the neck angle enough to add up to some acceptable trail, every tenth of a degree of added rake calculates out to 1.01mm of increased trail, so I'm not too worried anymore.  I'll post here when I do measure it though.

[Retro Rocket]

I'm not interested in wrecking any stock parts to get this one done

Hi Alan, i don't know what you mean about "wrecking any stock parts", i have reused my old clamps with no problems at all. The clamps are alloy and the stem is mild steel....what welds  do you refer too?.

Mick

[Alan F.]

The lower triple tree on 69-76, 77-78 CB750K's as well as the lower triple tree you see in my previous post which is from a 91-03 CB750 Nighthawk, are made I believe of cast iron, the steering stem is steel and is press fit into the lower clamp and is welded in at the underside.  Your alloy lower clamp may have a bolt to hold the stem tightly in position instead?  I suppose they'd weld it too if aluminum and steel could be welded together.... 

By "wrecking any stock parts", I need to mention that every part I'm using on my K3 for this swap will directly bolt on to my Wife's 92 750 Nighthawk, I'd hate to modify any parts beyond use on either bike.  I like the idea of being able to use "off the shelf" parts with as few custom parts as possible to complete the adaptation.  Besides, I've got detailed drawings of each part I fabricate, this may seem like a one-off, but with the hard part already done...anyone can bolt one together.

[Retro Rocket]

Hi Alan, yes i can see where you are  coming from, i don't want to physically modify things too much thats why i shopped around to find things that bolt straight in. You have me curious now as i can see nothing but the interference fit that is holding the steering stem in place on my Suzuki clamp, steel stem and alloy clamp.....

Mick

[andy750]

Looking good Alan and Ill be watching with interest to see what you create. Of course look forward to seeing it in Spring even more!! Get a move on!

good luck
Andy

[Alan F.]

i can see nothing but the interference fit that is holding the steering stem in place on my Suzuki clamp, steel stem and alloy clamp.....

Just a press fit?  I would think the stem has a flange at the bottom, so that when you tighten the stem in place the bolt won't simply pull through and out of the lower clamp.  Is the lower clamp rather thick?  I would think it'd have to be pretty strong.

Looking good Alan and Ill be watching with interest to see what you create. Of course look forward to seeing it in Spring even more!! Get a move on!
good luck
Andy

Thanks Andy!  I'll be doing my very best, thanks to Phil the Groundhog I've got another six weeks to get it done.

[Retro Rocket]

Is the lower clamp rather thick?

Yes the Suzuki clamps are definitely more substantial than the Honda ones.

Mick

[HavocTurbo]

Most aluminum clamps and steel stems are press fit....

Stem looks like this....

Top
  |  |
  |  |
  |  |
  |  |
------
Bottom


Then they are frozen and dropped in.

That's how we do it when we change stems on newer bikes.

[Retro Rocket]

Thanks Havoc, i can sleep easier now.....

Mick

[HavocTurbo]

Thanks Havoc, i can sleep easier now.....

Mick

lol is that sarcasm??? 

[Retro Rocket]

No that was relief.....   I was thinking i would be flying round some corner hit a bump and loose the whole lot....

Mick

[HavocTurbo]

No that was relief.....   I was thinking i would be flying round some corner hit a bump and loose the whole lot....

Mick

Just to add a wrench into the mix... Some companies made aluminum stems and welded them to the lower clamps. Those can BREAK!!!!

With the alloy steel mix, there was less chance of the stem breaking.

You need help in removing I can walk you through it.

[Retro Rocket]

Thanks for the info Havoc. I had the mods done by an engineer that fabricates one off frames for drag racing and a lot of other other custom bike stuff, Thanks for the offer.

Mick

[Alan F.]

I finally got a bit of free time to spend on the project, tonight it's the steering stops.  I drilled the lower triple spacer and pressed in two stainless pins.  Have a look at that last pic, fork tube to tank clearance is about 1/8 inch.

[HavocTurbo]

Wow....

Guess I never realized how BIG that spacer actually is.

[Alan F.]

Yeah, it's .950" thick, and those pins are 1.5" long.  The whole rig is about 4" across and weighs about a pound.  With the stock 736 and Kerker pipe I should have no problem keeping the front tire on the pavement...

[FunJimmy]

Alan

That fork swap is looking great. If you need a little more fork/tank clearance just slip some clear vinyl tubing over the stop pins.


Cheers
FJ

[Alan F.]

it's like you're reading my mind....  I must be on the right path.

Thanks FJ!

[Alan F.]

Today I picked up some aircraft stripper and some graphite colored wheel paint, and some red loc-tite for those cylinder studs....   I've gotta get that white paint off the front wheel and find out what I'm working with, pics will be posted when it's stripped and ready to repaint.  Maybe I'll shoot the forks in that same color, and the airbox, headlight bucket and fork ears too! 

That'd be a good look I think.  Any comments?

Here's a pic I found in the Gallery, it's Einyodeler's CB500 K1, he's painted the fork lowers and headlight bucket the same color gray as the rest of the bike, sweet.
I'll have a stock seat, shiny engine covers and no emblems on my 750 though, and no more spokes!

[Alan F.]

After reading the label on the Aircraft Stripper, I decided it'd be best to remove the crappy tire that's on there before I strip the white off of my front wheel.  I think I'll go with some new bearings and seals too while I'm at it.   

I did however try to fit my K3's idiot light panel onto the Nighthawk upper triple's rubber mounted handlebar clamps. It fits great, spacing is the same after all these years.

I'll be milling the ignition switch bracket and clutch cable loop off of the top triple, and drilling two holes to mount my K3's clocks, they'll sit a bit lower due to the rubber mounted handlebar clamps being an inch or so higher, it might look pretty cool...... or I'll have to thread on some standoffs to make it look better.

So much for not modifying any stock parts... at least I gave the nicer top triple (of the two I had) a fresh coat of paint before it went onto the Nighthawk last summer... I won't mind so much hacking up a beat up part like this one....especially where it's gonna make the difference between a half-a$$ed gauge mount, and a clean looking trick one.

[fastbroshi]

  Now what the heck do you remove those fork caps with?  A big ratchet extension??

[Alan F.]

I remove them with a bolt clamped in a pair of vise-grips, works like a charm.  I should make up a tool for that I think, thanks for the idea.  Seriously I'll probably either swap them for some CBR units that allow preload adjustment, or I'll drill and tap them for air lines and a cross over line, I haven't quite decided but I'm thinking the air assist would be more useful.

Tonight I made up some seat pins, the old one (only one) that I had will be retired.


This is the paint I picked up for wheels, fork lowers, etc... Anyone got any experience with it?


This is my idiot light panel mounted to the 90's NH top triple, should do the trick.


And I paid $10 to a local independent shop to pop the junk tire from my front wheel, in conversation with the guy there I realized that this wheel is 3.5" wide, now I have to run a 120/70-17 or a 110/70-17 instead of the 110/80-17 I had planned, it just won't fit the wheel.  Oh well a few more millimeters of trail lost...

[cdoggy81]

Keep up the good work!