Topic: Pin2Hot's 73 CB750

[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.

[Pin2Hot]

Hey!  It's been a while but things are still moving along.  I've found a few issues with my oil system since starting the bike but they're all manageable.  The biggest concern was a leak at the supply fitting and main oil drain.  A rubber gasket solved the oil drain issue and I'm still working on a solution for the supply fitting but I don't think it'll be a long term concern.

I had 3 problems preventing me from actually riding this thing.  Rear hoop support, swingarm pivot bolt and rear wheel spacers.  I picked up a tubing roller from HF and it did the trick.  There's a lot of slop in the device but I wasn't expecting too much accuracy.  The tubing ends up getting a bit skewed as it rolls through the bender but it ended up working out to my advantage as I needed mirrored tubes to support the rear hoop:



I wanted to avoid the chain so I used two pieces of bent tubing to form the main hoop support:



Ended up working out quite well:



It looks great on the bike too:



However, now that I see how nice these curves look, I mayyyyyy end up swapping out the straight sub-frame supports for two new curved pieces. 

[Pin2Hot]

Big milestone this weekend.  I got the rear end pretty much finished.  I've got to fully weld out the rear monoshock support but otherwise it's done.  I was able to get three things done: ream out the swingarm pivot, make spacers for the rear wheel and finally get the swingarm bushing and bearings sorted out.  Everything lines up beautifully. 

Reaming out the pivot holes wasn't something I had planned to do but getting a shim made to fit the old 73 pivot bolt didn't seem like the best solution.  I got this tool from McMaster and spent a LOT of time slowly expanding it to get the fit I needed.  My arms are tired.



I ended up going with the offset rear sprocket from Cognito Moto because it put the wheel exactly in line with the center of the bike.  Of course, any stock spacer that came with either the 73 or 80 swingarm was now useless.  I ended up making a 6.5mm spacer on the brake side and an 11.2mm spacer on the sprocket side.  This put everything all nice and centered.  Of course, anyone else doing this swap will want to measure and cut your own spacers.

Brake side spacer:


Drive side spacer and chain w/offset sprocket:


Years ago when I replaced the chain on my V-Strom I got this DID chain tool.  It's certainly paid off by now, makes putting on and taking off links a breeze:


I'm hoping to ride it this week to see where any weaknesses may be and then it's time for everything to come a part for final welding and paint.

[markreimer]

Man this is looking really good!


Sent from my iPhone using Tapatalk

[Pin2Hot]

Happy new year everyone.  I've spent most of the time since my last post figuring out a few things.  First, tuning the bike with my integrated oil tank is straight up impossible.  Accessing the carbs is a royal pain so I picked up a spare oil tank off of eBay to help get things tuned without wanting to set the whole bike on fire.  Definitely a downside to the design BUT I think this is a manageable solution.

I was having some serious trouble getting the bike to idle properly or to come off of idle without dying.  The only way the bike would rev from idle at all was with the choke on.  This fouled the plugs pretty quickly:



After reading literally every carb thread here, I did what I should have done from the very beginning: listen to the Honda engineers.  For whatever reason, I had my 657A carb needles set at the middle notch AND was using a needle from a carb rebuild kit instead of the stock Keihin units.  Setting the needles to the 4th notch from the top, ensuring my float levels were at 26mm, confirming my idle jet was 40 (main jet is 120 for the open exhaust), I finally had success:



Granted, this is only from idling for about 10 minutes but it revs great off idle, sounds so much more smooth and doesn't smell like I spilled gasoline all over the place.  I set up my homemade manometer to make an attempt and balancing but it looks like I need a reducer to prevent the fluid from getting sucked into the engine. 



I may just wait to balance things once final assembly occurs.  The main exercise here was to get a good gut feeling that my engine is healthy and I can move on to fit and finish items before the tear down begins.  I still need to make the battery box and get my rear brake figured out.  Oh, and a seat too, I guess...  Anyway, here's another video of it running last night.  Don't mind the smoke at the end, SOMEONE forgot to put a gasket under the valve cover and oil sometimes leaks out onto the pipes.  Hey, at least there's oil at the top end!

[Rnobx67]

  Raally good job Seems you can go further

[Pin2Hot]

Making some progress.  Mostly I've been addressing some issues with my embedded oil tank.  The original location of the return line hose connection was making life extremely difficult in terms of assembly and usability.  My solution, I'm sure, will cause some heartburn with some people but I think it's a reasonable trade off.  The return hose beneath the tank was being squished between the frame support triangle thing which shifts the tank to one side.  I wanted to go through the triangle but the flexibility of the hoses and the ability to get the tank on the bike made that solution impossible.  SO, I chopped out a section and welded in a hoop.



Solution?


Reality:




Turns out, threading my new return line through the new frame support hoop AND actually seating the tank don't work.  I had to cut the hoop in half to make it all work.  This isn't ideal but I don't think the bike is going to bend in half as a result of it.

I learned a few lessons with those braided line hose fittings by over tightening one of them and snapping it off.  I don't believe I'm using the right fitting as they never seem to want to seat against the ferrule without exerting some extreme force on the fitting itself.  I'm gonna order some new ones and make a new line anyway so we'll see.

I also worked on the headlight a bit.  Kinda interesting to see how many custom bikes I've seen lately have been using wood as well.  I thought I was being unique when I first planned this a year ago but looks like it's catching on.  Still a bit of work to do on it such as cutting the dado to inlay the LED strips for the turn signals taht run around the perimeter of the plate but essentially this is what it'll look like when it's finished.  I'm pretty happy with it but don't really have any idea how it's going to be mounted to the front of the bike.  I'll cross that bridge when I get there.

[calj737]

Your welded solution works just fine 

[Pin2Hot]

I started working on getting the tank to look somewhat respectable this weekend by converting some rust and starting on the body filler.  I used Eastwood's Fast Etch to prepare the surface of the tank to make sure I had zero rust.  PS, definitely wear a respirator...

Soaking:


After:


ALL of the rust disappeared and I ended up with a uniform tank ready to apply filler.  I'm using a commercial brand body filler (Fastline - Fast Light) that a friend at a paint store set me up with.  Doesn't have much work time but I was able to fill the big dings and dents.  I've got a LOT of work still to do but it's nice doing the first real cosmetic work to the bike.



I also got busy working on the battery box which was one of the last big items to tackle.  I'm going to weld a mounting bracket to the frame and the battery box will bolt to it.  I went this route because in the event I need to use a different battery due to a Li-ION meltdown, I can build a new box and bolt it right up.



It'll weld the bracket to the frame above the chain, on the left side of the bike:

[Rnobx67]

I think you gonna be check those powerfull LED lights, some of them could be very hot ! need a big aluminum plate for heat dissipation. And sometimes also a fan, but maybe I'm wrong.

You are a perfect welder again otherwise

[Pin2Hot]

Thanks for the kind words. 

The lights I'm using have massive heat sinks on the backs of them.  You can them sticking out from the back.


The fins will be exposed to the air so hopefully I won't need a fan.  I'll definitely keep an eye on the temps as they're running though.

[Pin2Hot]

It's time to dismantle.  I got all the oil fittings sorted and routed so I no longer need the engine in the frame.  I'm to the point where I can take everything apart and get it ready for paint.

I cleaned the workbench up to make room for the engine and to give me some space to weld on the frame.  A lot of the sub frame is just tacked into place so now's the time to weld it all out.



Taking the engine out:


Everything disassembled:


I still had the center stand mounts to take care of:


I evened up the holes left by chopping down the frame, getting ready to weld those holes closed:


Holes closed up, will grind things down to make them pretty:


I ended up shoving my thumb into a portaband making those damn plugs so I'm typing with a big fat bandage on my thumb.  I deserved it though, wasn't being safe and it could have been a lot worse.  But now I can barely take a piss without my thumb throbbing.

Next steps: final welding on the frame, media blasting all parts that need it along with priming.  Then it's time to paint!  Hopefully things will start to look final soon enough.