Topic: CB750K2 Bionic Mongrel Build

[SOHC4 Cafe Racer Fan]

Since I'm making some progress on my K7 build, I figure I would start a new build thread to document my next project.  I picked up a weathered CB750K2 about 6 or 7 years ago for a couple hundred dollars off ebay.  She cost more to ship from the Mid-West (Wisconsin, as I recall) than the purchase price.  Since that time, I completely disassembled the bike down to the bare frame and sourced a host of parts for the electrical system, engine, front suspension, etc.  The goal of this project is to strip off unnecessary weight and add significant performance (handling, brakes and power).  It will feature a modern front end, an aluminum gas tank and seat, and a stronger power plant similar to Doctor D's CB750F (featuring a Stage "4" Mike Rieck head and Wiseco 836 kit, Cycle X back-cut transmission, lightened and balanced crank and rotor, Cycle X Super Rods, and Cycle X improved tensioners for the primary chains and camchain).

Here are some pictures of the K2 when I purchase her (sorry the sissy bar and king/queen seat are long gone!):

[SOHC4 Cafe Racer Fan]

The more popular transplant is a GSXR front.  I found a smoking deal I couldn't pass over on a 2008 CBR600RR Front End (triple trees, forks, clipons, master cylinder, clutch/brake levers, throttle, switchgear brake calipers and axle) -- allowing me to keep it Honda -- but still be a mutt:



Here's what it looks like on the CBR600RR:

[goldarrow]

Should be very interesting with all the mods mentioned above.  Will definitely follow. 

I hope you still have the stock pipes, if do I'm interested. 

[SOHC4 Cafe Racer Fan]

Should be very interesting with all the mods mentioned above.  Will definitely follow. 

I hope you still have the stock pipes, if do I'm interested.

I should let the scavengers know out of the gate that the tank, pipes, rims, seat, side covers, handlebars and fender are long gone. I had a buddy who was working on a restoration and let him have the parts I no longer needed.

BTW, a couple of the pipes were rusted through.

[tweakin]

Count me in on this one.

[SOHC4 Cafe Racer Fan]

Preparing to mock up the new front end (note, I kept part of the passenger peg mounts to mount Tarozzi rear sets -- I'll detab the frame more thoroughly later):



Pressing out the CBR600RR stem and transplanting in the CB750 stem:




Presto:

[SOHC4 Cafe Racer Fan]

I enlisted Ed Millich (writer, engineer, racer, and shop owner -- www.guzzipower.com and www.ducpower.com) since he has proficient machining skills to fabricate me some adapter plates to mount Brembo snowflake rotors (they match the CB750 hub pattern) and spacers to the stock front hub so that the radial calipers match up.  This is where a Cognito Moto HONDA kit would come in handy!!





Aluminum stock for the adapters:



Cut to the appropriate width:



Cutting out the center hole for the axle:



Ring finished:



Bolt holes:



Ed's notes and mock up without the spacers:



They fit (mounted with the spacers, Brembo rotors and CBR600RR bearings)!

[SOHC4 Cafe Racer Fan]

Since the CBR600RR front uses 310 mm brake discs, and the Brembo Snowflake discs are 320 mm, spacers were required so the radial brake calipers will match up with the "new to me" discs.

Again, Ed Millich did a precision job this time machining some spacers.





Now with the new front mocked up:





No, this is not a chopper (the front looks longer because it was propped up:

[lwahples]

Nice start! Well on your way to yet another cool bike.

[snowman]

Looking good, wants me to change the front end to a set of USD forks. I guess I'll start scanning eBay.

Subscribed

[Cragdog]

Looking really great, can't wait to see the end result!

[Jay Ace]

That's going to look so mean!

[SOHC4 Cafe Racer Fan]

Thanks, guys.

My inspiration for this bike is a collection of Bill Tweakin's bikes, Doctor D (David Hiller)'s Super Sport (especially since our engines happen to share most of the specs) and Cameron Rusty Olive's builds among others.  I was also inspired by Vincent's CR750 for the street build with a gorgeous aluminum tank.

Originally, I was going to order a CR750 style gas tank from either Mead Speed or Holt, since I knew I wanted an aluminum tank, but then I decided I wanted something to set this bike apart.  I really like the lines of the 70's Bimota gas tank (Air Tech has fiberglass reproductions) and Carpy's Black Mamba build, especially how they narrows to the seat.





The trick has been finding an aluminum tank fabricator (and one who does not want a kidney) to fabricate a bespoke tank.  I finally engaged Denis Curtis of CMR in Canada to make the tank.  Unfortunately, the tank's production was delayed due to a hand injury Denis sustained while vintage racing. 

In the interim, I have sourced the following engine parts:
Cycle X HD primary chains and tensioner
Cycle X race transmission
Slightly Lightened and Balanced crankshaft
Balance rotor
Cycle X Super Rods
Wiseco 836cc big bore kit
Cycle X Super Gasket set
Mike Rieck Stage IV port job, Kibblewhite 5mm valve conversion kit (34mm intake/28mm exhaust valves, guides, seals, springs, Ti retainers,
spring bases and lash caps), Serdi valve job, head milling
HD Cam Chain
APE adjustable cam sproket
APE HD studs
Cycle X CX-7 cam
Cycle X racing cam tensioner
Cycle X Cam Tower Stabilized Valve Cover
Cycle X Spin-Off Oil Filter Mount
Setrab Oil Cooler
Finned Breather Cover
Complete Joker Machine engine dress up kit (dyno, clutch, alternator, starter and tappet covers, and tach and oiler plugs)

Given the fact that this engine is nearly a twin of Doctor D's torque monster, I am having a pro wrench tear my donor motor apart, PC the crankcase and assemble the mill together for me right the first time.


Oh year, and a Gordon Frame Kit to accompany some detabbing and gusseting work on the frame.

[SOHC4 Cafe Racer Fan]

One of the reasons for this build was to build a bike to keep up with my riding buddies, who ride modern sport bikes.  When we ride together, I usually ride my '05 RC51.  I thought it would be great to have a vintage bike that could keep up respectably with newer bikes.  I also thought it would be bada$$.

So, the order for the build is better, lighter, faster, stronger -- kind of like Steve Austin (the Bionic Man for all of you too young to get the reference).

"Adding power makes you fast on the straightaways.  Subtracting weight makes you faster everywhere."  Colin Chapman
Of course, "If you aren't fast with 50hp, you won't be fast with 150hp."  My goal is not to go tear-a$$, but to have a faster, more nimble bike for the street/canyons/mountain roads.

[tweakin]

Great goal for the build, I love shocking guys on modern bikes when I am out riding my 915.  When we stop all they can say is Sh*%...

One of the reasons for this build was to build a bike to keep up with my riding buddies, who ride modern sport bikes.  When we ride together, I usually ride my '05 RC51.  I thought it would be great to have a vintage bike that could keep up respectably with newer bikes.  I also thought it would be bada$$.

So, the order for the build is better, lighter, faster, stronger -- kind of like Steve Austin (the Bionic Man for all of you too young to get the reference).

"Adding power makes you fast on the straightaways.  Subtracting weight makes you faster everywhere."  Colin Chapman
Of course, "If you aren't fast with 50hp, you won't be fast with 150hp."  My goal is not to go tear-a$$, but to have a faster, more nimble bike for the street/canyons/mountain roads.

[SOHC4 Cafe Racer Fan]

The cylinders are off to be bored to match the Wiseco 836 pistons.

I am trying to decide which color to powdercoat the crankcases.  I'm leaning to a gray or gunmetal.  The cylinders will be black along with the Joker Machine finned parts.

I'm also debating whether to stick with spoked wheels for this build.  I'm checking out my options for Morris-style wheels with RSD.

[BPellerine]

you make things look fast and easy Don!bill

[SOHC4 Cafe Racer Fan]

you make things look fast and easy Don!bill

"The only easy day was yesterday."  The cool machining work above was capably done by Ed Millich, an engineer/vintage racer who has some real skills.

I can turn a wrench but I have no fabrication or machining skills to speak of. I am far better at designing and sourcing what I want, selecting finishes, prepping and then handing off the more complicated tasks to a pro wrench, machinist or welder/fabricator. For this build, I disassembled the bike down to the frame about four plus years ago and I've taken my time picking up parts along the way. Now that my K7 is nearing completion, I'm finally ready for the building portion to start.

[BPellerine]

nice bike all the same now I don't feel so slow having been collecting for about a year to have a good start.merry Christmas Don.bill

[SOHC4 Cafe Racer Fan]

nice bike all the same now I don't feel so slow having been collecting for about a year to have a good start.merry Christmas Don.bill

Thanks, Bill.  Yeah, I've slowly been collecting parts for this bike for the last two plus years.  I used to have a genuine Dresda boxed swingarm, but someone pilfered it.  I had to replace it with a Carpy knock off, but I have been interested in the swingarm Devin at Cognito is developing.

[BPellerine]

at least you seem to have a clear idea of what you want in the end that is the part I have trouble with.bill

[SOHC4 Cafe Racer Fan]

at least you seem to have a clear idea of what you want in the end that is the part I have trouble with.bill

Well, Bill, in all honesty it has evolved over the years.  When I first purchased the K2 in close proximity to the K7, the K7 was going to be a cafe rat bike, and the K2 was going to be sort of a show pony.  Then one thing led to another and the K7 had so much work done, I wasn't sure what to do with the K2.  First it was going to be a new/old hybrid with a Ducati Monster single-sided swingarm, then a CR750 replica for the street (which Vincent S. is doing a much better job than I could imagine).  Then, it just sat FOREVER in limbo.  About a year and a half ago, I started gathering parts for it, and that's when the idea of faster and lighter with a modern front stuck.

[BPellerine]

lighter is good as these bikes are heavy.but lighter and faster is REAL good cant wait to see what you dream up.do you think the cx7 will be good on the street?bill

[SOHC4 Cafe Racer Fan]

This thread has a time lapse factor built into it since it is recapping some progress over the last few years.  Fast forward to this summer, when Denis Curtis of CMR Racing Products in Ontario Canada (http://curtisracingframes.com/contact-cmr.html) began work on my one-off aluminum tank. 

Thankfully, Denis had a CB750 frame on hand, as well as an R6 front end for mock-up purposes (combined with the specs I gave him for my CBR600RR front), so he was able to fabricate the tank without me or the bike there.  Denis is a vintage racer and builder originally from Lincolnshire (home of Guy Martin), and an incredibly gentile person.  He is an incredible craftsman who takes pride in his work.  If you are in the market for an aluminum tank, he should be on your short list; his production time is much shorter than the Tank Shop of Mead Speed.

Due to the reduced (from stock) offset for the modern front, the design of the front of the tank needed to be modified so that the forks and triples could clear the front of the tank.  It is slightly less squared off at the front end (to provide clearance for the forks and trees), and slightly shorter in length -- since I did not want as much of a long reach over the tank and less seat room.

[SOHC4 Cafe Racer Fan]

lighter is good as these bikes are heavy.but lighter and faster is REAL good cant wait to see what you dream up.do you think the cx7 will be good on the street?bill

Mike Rieck selected the CX-7 based on the engine build specs and the goal of a hot street motor (not a track bike).  The bigger debate is whether to run Mikuni RS34s or CR29s.  Mike and Dave H. (Doctor D) both recommend the Mikunis.