Topic: Pin2Hot's 73 CB750

[Pin2Hot]

I've been messing around with the swingarm spacing using my now-useless swingarm.  Let's just say the DOHC swingarm modification is NOT as simple as "just cut all off from one side" if you're looking to be symmetrical on all fronts.  That is, center the wheel to the swingarm and the swingarm to the frame.  Because I'm converting to a monoshock suspension, I need everything to be centered relative to the backbone of the frame.

After millions of measurements I think I got it sorted.  It'll end up requiring custom wheel spacers but the wheel is in the "visual center" of the swingarm, the swingarm pivot is along the centerline of the frame and the sprockets line up.  I ended up cutting off 0.385" off of the chain side of the swingarm pivot and that placed things where I needed them to be.  I haven't performed surgery on my new donor swingarm because I'm waiting for my monoshock hoop to come back from my guy.

Speaking of which, the hoop is also asymmetrical due the shape of the swingarm.  Long story short, pretty sure my fab guy hates me now...  I'll post pics when I get it all mocked up. 

Here's the useless arm fitted in place, note the gap on the right side:


I also go the rear sets were mounted this weekend.  They're not fully shaped and/or pretty but the rear set mounts are tapped and things appear to fit.  Of course, now that these are fitted, it's opened up a whole new world of problems but I'll deal with them.

Rough shape with CBR900RR sets in place:


Both sets mounted:


Full shot of the bike with rear sets mounted.  Note the custom cardboard seat.  Sitting on the bike has made me think the upward angle of the seat is a bit much.  It pitches me a bit farther forward that is comfortable so I'll revisit the angle once I get the rear suspension on and the bike sits normally instead of on jack stands:


Finally, the shift side of things.  Here's where it gets interesting.  I could make up some crazy linkage system to get it working or simply flip the shift lever around from its stock position and get it under my toe.  This obviously shifts the pattern to GP style, 1st is all the way up, 5th all the way down.  I'm willing to entertain this idea simply because it's an easy fix and it's my only bike.  If I had multiple bikes this may cause some confusion and not be good.  The old peg / engine mount bolt will be shortened so ignore that.

[LokisTyro]

I really like the upward angle on the seat. Maybe some extra foam up front would help, but that may become uncomfortable having your bits mashed into the seat. Careful shaping might work unless you're going for a flat seat. Just a thought. Nice build so far.

[Pin2Hot]

I really like the upward angle on the seat. Maybe some extra foam up front would help, but that may become uncomfortable having your bits mashed into the seat. Careful shaping might work unless you're going for a flat seat. Just a thought. Nice build so far.

Thanks dude.  The seat will be pretty flat, essentially embedded within the seat frame itself.  It won't be the most comfortable seat in the world but I'm used to riding a supermoto so it'll be a step up.  Plus, this ain't gonna be a long haul machine so an around-the-town trip will be about the limit for the seat.

Got the rearsets figured out last night.  All it's gonna take is a simple modification to the shifter arm on the transmission itself.  I need to add 3/4" to the bottom of it so that it reaches further inward to get the linkage arm away from the shift lever, see below:


Overall:


I've always kept the parts that come off of bikes and from parts I've replaced from being an idiot.  I kept the broken shift lever from my first big crash on my old Wee-Strom so I'm going to cut part of that off and use it to lengthen the shifter arm.  Hopefully no one gets too upset that there's a tiny bit of Suzuki on this bike...

[Pin2Hot]

My guy delivered the bend to me last night and I got busy mocking things up.  This allows me to finish a lot of outstanding problems I've been facing such as exhaust final position / mounting, seat angle and monoshock placement.  Lots of things moving quickly now, getting exciting!

Monoshock mounting:


HOOOOP DREAAAAAMS 


I'm not certain where the bottom of the monoshock will get officially mounted.  Obviously I want it directly on the end of the hoop directly in line with the shock but there may not be enough room.  Once I cut down the hoop to size, I'll be able to formally fit it up but I mayyyyy end up having to put the mount 90 degrees out of line on top of the hoop.  We'll see.


Preparing the new donor swingarm for final fitment


I also got the shifter arm mofidied.  I'm almost embarassed to put this on the internet . . . look, aluminum is hard, OK?  I'll shape it up all nice and neat soon but it works!


Lots more to do but it may be rolling very shortly.

[Rnobx67]

Nice job on your bike, you have done great work on it

[SOHC4 Cafe Racer Fan]

I'm sure everyone would like to make "weldporn" dimes but sometimes you get posted on @thefabpolice. I'm no one to talk.  I don't know how to weld, yet.

[Pin2Hot]

I'm sure everyone would like to make "weldporn" dimes but sometimes you get posted on @thefabpolice. I'm no one to talk.  I don't know how to weld, yet.

Frantically googles @thefabpolice . . . . ok good, I'm not there. 

[SOHC4 Cafe Racer Fan]

I'm sure everyone would like to make "weldporn" dimes but sometimes you get posted on @thefabpolice. I'm no one to talk.  I don't know how to weld, yet.

Frantically googles @thefabpolice . . . . ok good, I'm not there. 

You are nowhere close! But it is an entertaining IG.

[Pin2Hot]

It rolls.  For the first time in 9 years, this bike rolled on its own two wheels.  Ok it actually fell off the jack stands as I was putting the rear wheel on TO roll it but I caught it in time.  I was then stranded in my garage holding it up until my wife heard me yelling to come help.  I should probably figure out the kick-stand . . .

I spent all weekend working the rear hoop to get it into place.  I needed a way to find the center 10mm of the hoop tubing so I printed a little jig to help me measure it.  I placed it over the tube and marked the center channel to remove so that the hoop will slip over the vertical swingarm . . . arms.

Jig on tube:


That allowed me to cut out the proper channel using my trusty 4" cutting wheel.  It was a lot of take a bit here, measure, take some more, measure again.  But eventually I got it.


On the bike with shock in place:


From the rear:


Wheels:


I also spent a lot of time fixing some out of whack tacks I had.  Basically, the entire bike is straight and aligned.  I was able to sit on it and feel the suspension work which didn't compress nearly as much as I thought it would so that's good news.  Gives me more range of motion than I expected.  I'll be gusseting the rear hoop with three, maybe four support strut things so don't worry, I'm not leaving it hanging out there like that.

I'll get the exhaust hanger figured out next and make all of my final welds as a lot of tacks are holding things in place at the moment.  It feels like I've turned a corner on this project and I'm already thinking about disassembly for paint.  Exciting stuff.

[SOHC4 Cafe Racer Fan]

Pin,

For those slow folks like me, can you explain what considerations and "math" you have done to figure out the angle of the rear shock mount.  Since it's movement is not in a direct line to the compression of the shock, how does that impact those calculations? Also, are you using an off the shelf shock or having one custom built for your application?

[Pin2Hot]

Pin,

For those slow folks like me, can you explain what considerations and "math" you have done to figure out the angle of the rear shock mount.  Since it's movement is not in a direct line to the compression of the shock, how does that impact those calculations? Also, are you using an off the shelf shock or having one custom built for your application?

I honestly don't have much math to back up my design here.  But since the angle of the shock is slightly off the straight line by about 10 degrees, most of the force is going in the horizontal direction.  ForceHoriz = totF * cos(10).  ForceVert = totF * sin(10).  So let's say totF = 2500 Netwons, ForceHoriz = 2462 N.  ForceVert = 434 N.  So while there's definitely some "up/down" force there, a majority is along the length of the shock.  Is this the right way to do it?  I have no clue.

The angle itself is a result of the length of the shock I used and the length of the hoop.  I'm using a rear shock from a 2007 CBR600RR.  I was hoping for a more in-line angle but I would have had to go with a custom solution which project budgets (my wife) won't allow at the moment.  I believe you can swap on the spring on this particular model if I need a larger/smaller spring rate.  I don't claim for any of this to be the "proper" way to do a monoshock conversion but I do believe there will be enough strength in this design to keep me alive.  Famous last words?

I was very happy with the amount of sag I experienced sitting on the bike.  I'm not really sure how that will translate to real-life road riding experience but it seems I have a lot of travel in the bank for big holes.  A downside to my design is that I'm locked in to this shock.  I've seen some other designs that allow for some adjust-ability but I ain't got none of that.  I just wanted a wide open space back there and I think I got it.

[Pin2Hot]

What you might find is your design can work but would require a shock that allows both low and high speed compression adjustments. Given the range of motion, one or both of those adjustments could bring the rear to heel with your modification.

Cal, this shock does offer some high and low speed compression adjustment.  I mean it'll be as adjustable as a stock shock can be but at least it'll give me some tuning room.

[SOHC4 Cafe Racer Fan]

I didn't mean to rain on your parade, Pin2Hot.  I have seen many monoshock builds where people install a shock that spans the space of the mounts but most of those do not provide later feedback about ride quality and performance.  I am not suggesting yours would end up this way, mind you.  I hope yours works out (preferably out of the gate) without much trial and error.  I just don't know enough about spring dynamics to know how much "room" you have to work with any given shock and spring.

As you probably know, there is more to just having the wheel be able to travel up and down from the ground, so it will not only absorb bumps, but also hook up the rear under a variety of conditions.

Out of most of the current build threads, BLAC is one of the few that worked with suspension engineers to make sure that his monoshock designed worked effectively as built then had a custom rear shock designed/built for the specific bike based on the bike, rider specs and type of riding.  What appeared to be cautious planning, however, turned out well.  I suppose if you discover issues, you can get similar input from suspension professionals like Bryan aka BLAC.

I know that Tony Foale has suspension software programs that helps with modeling and engineering suspension.  Some of the hardcore number crunching, however, goes over the heads of those new to it (like myself).

[Pin2Hot]

Yup I've been following BLAC's build, pretty impressive stuff.  Certainly, sending it to the pros is the right way of doing things.  Perhaps I'll do it on the next bike.

No offense taken at all in your response!  It's thoughtful responses like yours that help keep an extra set of eyes on things I may have missed.  I'll be sure to mention ALL the shortcomings and positive aspects of this build once it's done. 

[SOHC4 Cafe Racer Fan]

Yup I've been following BLAC's build, pretty impressive stuff.  Certainly, sending it to the pros is the right way of doing things.  Perhaps I'll do it on the next bike.

No offense taken at all in your response!  It's thoughtful responses like yours that help keep an extra set of eyes on things I may have missed.  I'll be sure to mention ALL the shortcomings and positive aspects of this build once it's done.

I hope it's all positive or close enough to let you just enjoy riding it.

[Pin2Hot]

Been a busy month at work.  Finally got to spend some time in the garage and hammered out (sometimes literally) the copper oil lines.  I'm not totally happy with the supply line, kinda kinked in a few places and may make another one but overall, I'm super happy with how it worked out.  It made relocating the petcock worth it.  But, as always, no matter how much you plan ahead, you overlook a few things.  I realized that syncing the carbs is gonna be pretty tough now that my tank HAS to be on the bike if I want oil running to the engine.  Maybe it's just an excuse to make a new tool that reaches in to adjust the carb stems . . . who knows.

Routing the lines:


More routing:


Pretty much done (aside from the hard line mounts), still gotta do the rubber hose from the tank to the return line but I'm waiting on two more twistlok fittings before I can finish it up:


A couple things I've learned: Russell TwiskLok hose is too damn tough to work with.  It doesn't give as much as I'd like and holy hell is it hard to put ends on.  I still have to attach hose clamps but by how hard it was to get them on, it doesn't seem like I need them.  Sonofa#$%* is it hard.  Also, bending copper tubing can be annoying.  I know I'm going to have to clearcoat the lines to make them stay shiny as well.  They dull up pretty quickly.

Next up is going to be tank work.  I'm pretty sure I'm going to have to do the body work BEFORE I can seal it in the event I end up needing to braze a few holes closed or beat on the tank some more.  After that, I think I'll be able to finally start it up to check for leaks.  Before tearing the whole thing apart for paint and other various frame mods.  It never ends.

Hopefully some of you were able to see the eclipse, it was absolutely stunning here in Missouri.  Here are just two photos that don't do it justice:

[Pin2Hot]

Oil lines are basically done.  I was able to bend up a new supply line because the other one looked so terrible.  The flexible ends for both lines were also completed and actually fit!  The return line is slightly pinched between the frame support under the tank but I over sized these lines to account for possible pinch points.  The next step is to actually cycle oil through the system.  I'm got some high zinc oil that I'm going to use to flush the system and make sure I can build oil pressure.  I'll change the oil filter and then put in the actual break-in oil to fire it up.  I made the mistake of searching for oil recommendations . . . hopefully we don't re-open that can of worms here.  People sure do have some hardcore opinions on oil...

I also got my spark plug wires made up.  I'm using resistor core wire for use with my Powerarc system.  I measured the total resistance of each cable and since cylinder 2 and 3 are shorter, they obviously have a lower resistance.  Cyl 1 and 4 are approximately 10k Ohms, 2 and 3 are about 8.1k Ohms.  Is there an upper or lower limit to what the resistance SHOULD be?

Routed oil lines:


Return line going between tank and frame:


Underside of tank:


Old (bottom) and new (top) supply line:

Spark plug wires:


Since I've been having to put the carbs on and off a lot lately, I got super tired and beat down trying to utilize my old "refurbished" insulators.  Soooo I did something I told myself I'd never do and got new ones.  I hated spending that much but I think it'll save me tons of time in the future chasing down leaks.


Oh I also got the front caliper refurbished after pressing out my old rusted one.  I made a video of me pushing it out using brake fluid.  Check it out here:

[Pin2Hot]

So I've either got the oil lines mixed up or I'm air locked somewhere.  I tried to prime the oil system tonight by pumping oil using the starter motor.  I was checking for oil pressure and noticed I wasn't losing level in my oil tank.  Million dollar question (embarrassed to actually ask): which fitting on the engine is the supply and which is return?

Anyone else had problems with an air locked oil system?

[Pin2Hot]

jk jk jk I totally knew which line was correct ...   

Turns out I had the lines correct.  I just wasn't patient enough to build oil pressure. 

And for the first time in 10 years, oil once again flows:

[markreimer]

Oh man I missed this one, such an awesome bike!! That concealed oil tank is amazing. So if you need to pull the tank off, how do you disconnect the oil lines without dumping all your oil? Are those fittings designed to block the lines off when they're disconnected or something? VERY cool bike!

[Pin2Hot]

Oh man I missed this one, such an awesome bike!! That concealed oil tank is amazing. So if you need to pull the tank off, how do you disconnect the oil lines without dumping all your oil? Are those fittings designed to block the lines off when they're disconnected or something? VERY cool bike!

Frantically googling "8AN check valve" . . . . ok they exist!!  Looks like you just solved a problem I hadn't really considered.  I had planned on draining the oil tank each time I needed to remove the entire thing but knowing that check valves exist, I can put one on the supply side and not really worry about that.  Thanks for the kind words and great idea!

[Pin2Hot]

I was able to start some of the wiring on the bike this week by extending the alternator wires out of the side cover.  I'm using paracord to dress up all the wires on the bike and found the process really satisfying.  Each and every wire on this bike will get dressed up as most will be exposed.  I extended the wires further out because the reg/rectifier will be mounted beneath the seat, along with the mUnit.



Once those wires were extended and prior to buttoning up the engine covers, I was able to time the engine.  Since I'm using the PowerArc optical ignition, I used some welding rod as a pointer and a piston stop to find TDC.  It was a pretty interesting process.  I simply used a 12mm bolt as my piston stop and carefully rotated the engine forward and backward finding each end point.  By counting the slots on the wheel, I was able to find exact TDC.  Once I found TDC, you rotate the slotted wheel until the the TDC light illuminates on the module.  I tightened down the wheel and double checked the timing.  It was off by one degree so I rotated the entire board until the TDC illuminated once again.  Boom, timed.



SO, this means it's time to fire it up.  Hopefully the next post is a video of it running and not a photo of piston rods / shattered aluminum all over my garage floor.

[Pin2Hot]

Holy, crap.  It runs.

Cylinder 2 wasn't firing during this short video but a stuck float bowl was to blame.  Firing on all cylinders and I couldn't be happier.  Thanks for all of the help everyone, I couldn't have gotten here without this community.

[markreimer]

Woooo!!!!! Congratulations!!


Sent from my iPhone using Tapatalk

[Pin2Hot]

Here's a longer, better video of the bike running.  Doesn't run all that well but I've only bench synced the carbs and haven't put on the air box.  Although I did put the muffler on and it sounds really great.  It's just loud enough.