Topic: Pin2Hot's 73 CB750

[Pin2Hot]

I've been lurking for longer than I'd like to admit but cannot thank each and every member for their input as it's helped me make decisions regarding my project, a 1973 CB750.  I actually bought this bike back in January of 2008 and have been steadily working on it since then.  When I bought it, I barely had a place to work on it so during this long span of time, I've slowly built a workshop at the same time.  Unfortunately, my main reason for starting this thread is that I now have a massive reason to finish this project: I'm moving!  So, instead of moving parts, I'd like to haul a completed bike.  I have 5-ish months to get this bad boy fired up and I think it's attainable, but only with YOUR help!

Goals and inspiration for the bike:

Engine: Total rebuild
     Inspiration: Manliness factor and the experience
Frame / Chassis: No major changes but would like to lower the front for a more aggressive look, possibly an after market swing arm to accommodate a wider rear tire.
     Inspiration: My GSXR and all modern sportbikes
Controls: Modern clip-ons, rearsets.
     Inspiration: More aggressive riding position, mix modern with vintage.
Tank: Custom fiberglass / CF tank
     Inspiration: My brothers and I race Kevlar / CF canoes and have composite experience and have been making smaller molds so why not try a tank.  This thread gave me a TON of inspiration on doing just that.  While I'm not a huge Ducati guy, I don't think many people can complain about the tail section of the current GP10 GP bike.  I'm shooting for something similiar to this for the rear section.  We'll see just how realistic that is.
Wheels / Tires: Modern rubber, wider than stock in the rear if possible, same sized rims front and back.
Exhaust: Custom stainless 4 into 2 similar to the RC212V (we'll see how realistic that is as well!)

The bike as it sat 1/08:




Sweet custom high-beam switch!


Next post will be the entire engine tear-down and progress thus far.

Thanks for looking!

*edit 11/21/16 - edited the first post with a healthy dose of reality...

[Pin2Hot]

After lugging the engine down into my basement, (thanks brother Dave!) I set it up in the best place to work on anything: the floor.  Got myself an impact hammer (best tool ever) and let loose.

Btw, a MAJOR MAJOR help and inspiration/encouragement was because of the classic Rebuild for Dummies thread.

Also, I take a $HITload of photos of everything I build so prepare yourselves.

Results:

"Virgin" engine:


I should probably be using a different hammer BUT these things are el-cheapo!


Sneaky last two


Lots of cobwebs elsewhere but the valve train looks decent


Speaking of which:


Headless!  (if you don't have a slop sink, GET ONE!)


I think Cyl 4 had some issues, the others looked just like 3.


Offending piston:


Unfortunately I don't have many photos of the bottom end tear down but the only real issue I had was with the cotter pin holding in the kick start assembly.  I probably need a new one. 

Disemboweled:


Taking out the studs to be replaced with heavy duty hotness.  I used the nut on a nut method to get them out.  The astute reader will notice a brand spankin new work bench I'm building on, I'll post some build pics of that too!:


More teardown pics in the next post!

[Pin2Hot]

I had the frame sandblasted and primed and realized that I really should have waited to do so because I know I'm going to be grinding off more tabs and unnecessary items.  I absolutely love the empty space look under the seat where the oil tank usually resides so I'm getting rid of everything that goes there.  That means that I'll have to figure out an oil tank solution but I think I'm going to make one up and fit it in the tail section like this bike.  I'm also aiming at recreating that exact tank in fiberglass (progress pics in a later post).  Those Danes sure know how to build a bike.

Blasted frame:


The void:


A hint of the tank to come:


More to come!

[Pin2Hot]

Enough of the tearing down, how bout some progress already?!

I took the engine to a local machine shop where they bored the cyls twice over, flattened the head mating surface because "boy, I ain't seen nothin that out of whack in a long time".  I'm not entirely sure how much was taken off, but what effect will that have on compression? A fellow member of SOHC found me a set of .5 pistons and rings so I'm good to go!


I also had new valve guides (CycleX) pressed in because mine were pretty loose.



CycleX high flow valves were also lapped with love:



Question, will this pitting completely screw me?  Or do I need a valve job?


Engine powder coat and other schtuff next!

[Pin2Hot]

After digging through the pros and cons of powder coating an engine vs painting it, I bit the bullet and powder coated it.  Will I regret it?  Time will tell.

The look I'm shooting for is very similar to some European spec CB1000s, which, btw, we're FINALLY GETTING in the US.  Black cases / cyls / head with a brushed nickel look for the covers.  I'm trying to find a picture of what I'm talking about but cannot.  Has anyone ever attempted to make aluminum look like brushed nickel?  The finish I'm after is exactly what some door knobs and other fixtures look like.

The same machine shop ran the cases, jugs and head through their crazy powerful washing machine to prepare it for media blasting and powder coat.  This is what the surfaces looked like afterwards prior to blasting:



As every bachelor should have: an entire motor (minus innards) on my dining room table.  You can see the tank mold and fiberglass as well for the tank project. I was getting everything together to give to my powder coat guy (who also painted my GSXR):



I wear it with pride:


Glossy black:

















Will update with the progress on the covers in a little bit.

[Pin2Hot]

The covers are an ongoing issue at the moment as my hand gets crazy tired while sanding out some of these scratches (read: gouges).  I've been using 150 grit sand paper to get some of the huge scratches out and have been working all the way up to 400 to make it smooth.  I like how the 400 leaves some nice "brushed" looks to the aluminum.  I'll clear coat all of these pieces but need to figure out how to add a patina to the metal to give me that brushed nickel look I'm after.  Any tips would be great!

Box o' parts waiting to be sanded:


I guess the previous owner liked left turns:


After some 150 grit:


After a LOT more 150 grit.  I'll probably leave a few of the deeper gashes in there on purpose, just to give it some character (also my hands hurt):


Gear shift cover comparison to effed up stator cover:


This is the overall look I'm going for minus the patina, this is the breather cover:


Getting at the valve cover with a dremel tool and a polishing wheel (side note, don't use a dremel tool with the stainless steel brush wheel indoors and then walk around barefoot unless you're prepared to have ENDLESS tiny metal splinters.  I can be pretty dumb sometimes):


That's pretty much where I am today, I still have a LOT of sanding, a LOT Of parts to order and a LOT more molding to do on my tank (I'll post photos later).  I'll keep this updated!

[Haywood]

Bump, let's see this thing!

[greenjeans]

check with your powder coater - there are so many powders these days.   Might be as easy as a tint of something in the clear powder.

Everything looks great so far.   I'm watching this one.

[Pin2Hot]

After a move back to Missouri, 5 years, 8 months and 6 days later, I've FINALLY started to assemble things.  A few things I've learned in the past 6ish years: riding motorcycles in Chicago is not fun (in the city at least) and having a garage to work on a project motorcycle is a must.  I was also pretty naive to believe all of the big plans I had for this bike would all work out . . . there are simply too many design ideas for one simple bike.  So here we are, almost 6 years later, my CB750 project is finally going again with a more simplified aim.

Now that I finally have a (dirty) workbench, I started with the forks.  I assembled them using Race Tech cartridge emulators and their springs.  I also polished up the lowers using the various grades of scotchbrite pads which I found to be the easiest way to achieve the "brushed" aluminum effect I was looking for.  I wish I'd found this solution years ago when polishing up the covers for the engine.  I'll take a quick pass on them with the various grades again so that they'll match the forks.  I'm also using Cycle X 2" shorter fork tubes here as well.



Before and after:


Drilled out oil passages and new dampening rod seals:


Close up of the new now useless holes:


Ready to go back together:


Fully assembled before realizing that I'd forgotten one of the dampening fork seals:


Up next, engine assembly.

 

[Pin2Hot]

Two steps forward, one back, then two more back...

After plastigauging the crank bearings I found that I needed green shells for all 5.  I also gauged the rod bearings and those were well within their tolerance so I left them alone.  None of them appeared to have any real wear issues so I think I'll be alright there.  I cleaned up the case halves, replaced all of the clutch plates (fiber and metal) and assembled the shift drum and forks.

Case halves and new bearings:


Put in a new final drive seal and crank seal and torqued down the cases:


Put in new heavy duty APE studs and torqued them down as well:


Only to come back the next morning and find this:


I split the cases again and found that I probably wasn't as careful with the assembly lube as I had thought I was.  The entire seal surface was slippery as well as the surface of the case.  I'm guessing that the pressure from the case halves just spit out the seal.  I spent the next hour scraping liquid gasket off of the surfaces and cleaning each mating surface.  Things went back together well, this time with no assembly lube where it shouldn't be.

Thinking I'm ready to take the next step, I started to assemble the shifting mechanism.  Only to have this happen:


Off to the store to get a better drill bit so that my crappy easy-out might have some purchase in there...any suggestions here would be great.  Very frustrating.

[Pin2Hot]

I won.


Let's just say I'll be more careful with my torque wrench next time.  The replacement bolt is on its way now.  I'll probably be honing the cylinders over the weekend and then the rest of the top end will go together.

[Pin2Hot]

Something a little different today.  I've been working on the electrical schematic for the bike for the past week.

I got an m-Unit by Motogadget which is a super slick little unit.  It acts like a little PLC for a motorcycle which simplifies the wiring quite a bit.  I think I have everything m-Unit related sorted out in this schematic but the field coil and some of the other generator related wiring isn't shown.  I'll add that when I get there.  Terminal numbers for the relays I'll be using will be updated as well when I actually figure out which ones I'll be using.  I had to pull some tricks using the relays to power the turn signals and some accent lighting I'm planning to use which I'll post later this week when the LEDs come in.  If there are any other m-Unit users out there who see some mistakes let me know!

[Pin2Hot]

I got in some LED strips last night to test them out for their use on the front of the bike.  If these work out, they'll be used as the signals and an accent halo for the front of the bike but it already looks like the amber is too red (can't really tell in the photo but it is) and the LED density is a bit too low.  More are showing up today (there's a massive LED distributor in my city which makes testing things nice and quick) so I'll try those out when they get in.



I also assembled the shifting mechanism last night after the replacement bolt showed up.



I noticed that while downshifting, the gears don't mesh up as nicely as one would think.  I'm assuming that's because there's no load on the final drive and the engine isn't turning quick enough / under load to allow the gears to mesh up.  Does that sound right or should I be able to rip through the gears sitting still?

[Pin2Hot]

See if this thread helps... there's a diagram at the end

http://forums.sohc4.net/index.php/topic,159934.0.html

Hey thanks!  Looks like you've had some experience with the mUnit.  Any other quirks than what you mentioned in that other thread?  I'll be testing the wiring setup on the bench for now until it's time to really start wiring the bike.

[Pin2Hot]

Brief update, not much work this week other than figuring out the pin-outs of the controls from an 07 CBR600RR.  I picked these up years ago and plan to use them with the mUnit by chopping off the OEM connector and wiring them up as I showed in the schematic.  All it takes is a multimeter and some patience and you can determine which wires are which for each button / switch.  I'll post that up when I get it all sorted.

[Pin2Hot]

I updated the schematic.  I moved the turn signal relays and ignition module down to the AUX output so that I didn't inadvertently leave anything on while the ignition is off causing the battery to drain.  I also updated the generator and field coil wiring.

[Pin2Hot]

Why are you using relays on the turn signals?

I'm making a number plate headlight for the bike that will have a white LED halo lining the outside.  Within that halo will also be two strips of LEDs for left/right turn signals.  I want to be able to turn off half of the halo when the appropriate signal is turned on (like a newer Audi).  Since the inputs on the mUnit are triggered by grounding the input (except for the lock input), a normally open relay contact will connect the input to ground, triggering the signal and the normally closed relay contact will cut power to the appropriate halo section turning it off (lines 52 and 53 on the schematic).  The turn signal switches just take power from the aux and activate a relay, actuating the NO/NC contacts.  I'm sure there are other ways of doing it but this seemed the easiest to me.

[Pin2Hot]

The halo will be separated into two independent white LED strips, left and right, so that half of the halo turns off as the turn signals come on.  Yeah the signal LED strips are amber / orange.  I got some better, more dense LED strips in the other day.  I'm going to diffuse them with some semi-transparent plastic so that there's even color around the entire halo/signal.

I don't think I totally follow you, would the "running lights" be powered from the left/right signal outputs of the mUnit or elsewhere?  What would trigger the relay for the signals in this case?

Here's the white:


And amber/orange:

[Pin2Hot]

Yeah I think I get it.  I'm going to build the circuit this weekend and test it out what I've drawn in the schematic and maybe shoot a video of it in action. 

[Pin2Hot]

I wired up the m-Unit according to the schematic with one minor change and it worked!  The only change is instead of powering the external relay from the Aux input, I powered it directly from the battery.  It will work either way.  Check out the video:

[Pin2Hot]

Good questions.  I haven't thought about the halo's functionality when the high beam is activated, disabling it through another relay would probably be the best idea like you mentioned.  I'd run the high beam switch similarly to how I wired the signal switch and then run both halves of the halo through the N.C. side of the high beam relay to deactivate both sides when the high beam is active.

These LED strips don't pull much current.  The spec says 7W for the entire strip, of which, I'll be using less than a full strip for both halves of the halo.  The strips come with cut marks so you can chop it up as you see fit.  Hopefully it doesn't put too much strain on the stock charging system.  There are other options if it is.

I'm not entirely sure what the state says about this set up, I'll cross that bridge when I get there.

[Pin2Hot]

Some non-electrical updates: I rebuilt the wheels with new bearings, spokes and powder coated rims.  They've been sitting around collecting dust for quite some time but I should have this thing rolling soon.

[Pin2Hot]

I took the heads to get a valve job on them after learning I should have gotten that done after pressing in new valve guides.  I got them back today and they look great!

After having these parts in bags / bins for literally the past 6 years, it's a very satisfying feeling to put them back into service and throw away the old bags.  I put in some CycleX high flow valves / valve guides and APE heavy duty springs.  I re-used the stock keepers and retainers.  One of the valve seals that I got from the Vesrah gasket kit was missing the top spring that pulls the seal around the valve so I've got new ones on the way.  One thing I didn't realize about that Vesrah kit is that is doesn't have the 6 nickel pucks that seal under the cam towers.  Very frustrating so those are on the way as well. 

The next step will be pistons.  I had the cylinders bored to the 2nd oversize because of rust in cyl 4 that had accumulated in the bike when I originally got it.  I have new oversized pistons but the oil control rings that came with them are the older slotted style one piece ring.  I'm having trouble finding +0.5mm 3-piece oil control rings for these pistons so if anyone out there has some for sale, I'm looking for some.  If I can't find any, I'll just use the one piece rings unless there's a compelling reason not to.

Head:


Close up of a valve/spring:


New seal:

[koendd]

must indeed be nice to unpack everything that's looks as good as your engine!

good luck with the rebuild!

[Pin2Hot]

I found a compelling reason to go to a 3-piece oil ring: by snapping a one piece ring.


I had just finished gapping the rings and seeing that they were all within spec when I stretched this one just a little too much getting it onto the piston.  I bought these pistons/rings from another SOHC4 member years and years ago so I don't even know who makes these pistons.  They're an aftermarket 0.5 oversized set of pistons and rings with no manufacturer name so I have no idea where to look for another set.  Or at least that matches these pistons.  I actually had another set of rings (13031-300-014) but the gap was out of spec for my bores by quite a bit so they won't work.

If anyone has a set of 0.5mm over standard bore piston rings, I'm more than willing to take them off your hands.

*edit: After thinking about this, I believe I've made the wrong assumption about the pistons/rings that I'm using.  I gave them to my machinist and had him bore the cylinders to fit them thinking they were 0.5mm larger than stock.  However, after seeing that the stock Honda 0.5mm piston rings had a gap that was too large, that tells me that the bore is larger.  I'll measure the pistons when I get home to see just how large they truly are.  THEN I'll get a new ring to replace the one I snapped.