Topic: CB750K5...Strictly For My Entertainment

[WCJonesJr]

As the title suggests, this project is strictly for my entertainment.  A great source of entertainment for me is designing and building components and systems.  The end result will be a cafe racer style CB750.

The bike as received was showing about 12,000 miles??  It was equipped with a Vetter fairing, king & queen seat, sissy bar and I believe higher than stock handle bars.  It had 3 mufflers with 1 MIA, the passenger peg brackets had been cut, heated, bent and rewelded to get the pegs above the mufflers and a 17 inch wheel 5/16 of an inch wider at the axle than the stock wheel had been shoehorned into the stock swingarm.  It came out with a resounding bang and fortunately no apparent lasting effects on the swingarm.

The basic project plan calls for a Gordon style frame kit and cafe style seat.  Bumping the engine displacement to 836cc along with cam, headwork, electronic fuel injection, a custom stainless 4 into 1 header and some other internal engine improvements.  Most likely Honda Comstar wheels and dual front disc brakes.

Let the entertainment begin!

[Jerilee]

Watching especially for the fuel injection, I don't think I'll be doing it on my current project, but when I get to frame 2's build, it's pretty much a given!

Good luck, have fun!

[seanbarney41]

sounds like someone put a k7-k8 wheel (those are k7-k8 pipes too) on there, probably with the wrong combination of spcers...I would be checking your engine numbers right about now

[WCJonesJr]

Watching especially for the fuel injection, I don't think I'll be doing it on my current project, but when I get to frame 2's build, it's pretty much a given!

Good luck, have fun!

If you haven't already, check out forum member 750essess thread  http://forums.sohc4.net/index.php?topic=30624.0  There's a great deal of info on EFI conversion for the 750.  A lot of hard earned knowledge in that thread.

sounds like someone put a k7-k8 wheel (those are k7-k8 pipes too) on there, probably with the wrong combination of spcers...I would be checking your engine numbers right about now

Thanks for the info on the wheel and pipes, it all makes sense now, to a degree.  I had wondered about the engine also and it is in the correct range for a K5.

[WCJonesJr]

The Gordon Style Frame Kit

I liked the idea of having the removable frame section over the engine for service access.  With this modification being within my capabilities, I decided to roll my own.  A study of the forum posts concerning the Gordon kit gave me enough info for a good start and not have to reinvent the wheel.  Thanks to Gordon and other forum members for sharing their experiences.  I elected to use metric fasteners to keep them consistent with the rest of the fasteners on the bike and stayed close to the original design in size and location.  I made some detail changes to the parts and to lend them to a TIG welded installation.

Material Specs:
Tube connectors are made from 1018 cold rolled steel bar
Connectors for the sheet metal triangle are made from 6061 aluminum
Threaded rod is ASTM A193 Grade B7 M14x2, AISI 4140, 124,000 psi minimum tensile
Jam nut is DIN 934, M14x2, Class 10

[Jerilee]

If you haven't already, check out forum member 750essess thread  http://forums.sohc4.net/index.php?topic=30624.0  There's a great deal of info on EFI conversion for the 750.  A lot of hard earned knowledge in that thread.

I've actually got that thread bookmarked!  A lot of very good info on there.

The Gordon Style Frame Kit

I liked the idea of having the removable frame section over the engine for service access.  With this modification being within my capabilities, I decided to roll my own.  A study of the forum posts concerning the Gordon kit gave me enough info for a good start and not have to reinvent the wheel.  Thanks to Gordon and other forum members for sharing their experiences.  I elected to use metric fasteners to keep them consistent with the rest of the fasteners on the bike and stayed close to the original design in size and location.  I made some detail changes to the parts and to lend them to a TIG welded installation.

Material Specs:
Tube connectors are made from 1018 cold rolled steel bar
Connectors for the sheet metal triangle are made from 6061 aluminum
Threaded rod is ASTM A193 Grade B7 M14x2, AISI 4140, 124,000 psi minimum tensile
Jam nut is DIN 934, M14x2, Class 10

Your frame kit looks amazing! As good as any kit I've ever seen on here.

[WCJonesJr]

Jerilee

Thank you for the kind words.

[Bankerdanny]

If there's one thing that gets universal admiration on this forum it's the ability to engineer and fabricate your own stuff. What I would give for some drafting and machinist skills.

[WCJonesJr]

Alternator Upgrade, The Rotor

When first planning the EFI conversion, I wondered if the stock CB750 alternator would be up to the task.  Thanks to forum member 750essess, I quickly found out that it wasn't.  With that, I elected to use parts from a CBR1000RR to get the necessary higher current output.  The CBR1000RR rotor doesn't have enough meat in it for attaching the starter clutch, my take on it, so I took the CB750 and CBR1000RR rotors and cut away the necessary material from each to allow them to mate up.  This change also netted a rotating weight reduction of almost a pound and a half.

[WCJonesJr]

Alternator Upgrade, The Stator

The CBR1000RR stator required an adaptor to mount it into the CB750 alternator cover.  The adapter is made from 6061 aluminum.  The stator change further reduced the bike weight by a little over 3 pounds.  Total weight reduction for the alternator is a little over 4-1/2 pounds.

[SOHC4 Cafe Racer Fan]

Given the significant lightening of the rotor, it sounds like your motor will rev fast quickly.  Will the reduction in mass also reduce the flywheel effect so that it loses low end torque?

[Jerilee]

Another amazing and professional looking mod, kudos!

[WCJonesJr]

If there's one thing that gets universal admiration on this forum it's the ability to engineer and fabricate your own stuff. What I would give for some drafting and machinist skills.

I've found that when you're blessed with skills, whatever they may be, it can be a curse because when you know how to, you feel obligated to execise those skills on things that aren't necessarily as much fun as working on bikes. 

Given the significant lightening of the rotor, it sounds like your motor will rev fast quickly.  Will the reduction in mass also reduce the flywheel effect so that it loses low end torque?

Absolutely, the reduction of flywheel mass will affect the available torque when starting from a stop.  An adjustment in riding style may be necessary due the reduced rotor and crankshaft (lightened by APE)  mass.  No free lunch, just one of the compromises we make for a little more acceleration.

Another amazing and professional looking mod, kudos!

Jeri, again, thank you for the kind words.  I truly enjoy the creative part of this hobby.