Topic: Potential 1970 CB750 K0/K1 Hybrid

[Lucien Harpress]

I've done enough work that I figure I should probably start a proper build thread.

First off, a bit of background.  I've owned a CB750 for a couple of years now, mostly because I lucked into a basket case that turned out to need a lot more work than I was anticipating.  Because of this, my 750 has never really had a proper "year", but is really more a rotating collection of parts.  The first time I restored it I settled on a vaguely 1972-ish outfit, which was fantastic.



This was fine, UNTIL I managed to snap a chain and hole the engine case.  Thankfully, I had a spare set of cases in the back yard.  UNfortuntely, this meant I would need to do a ground-up rebuild, again.  But while teaching myself how to do a CB750 engine rebuild, I got a crazy idea- if this bike has always just been random parts, why not rebuild it into the bike I REALLY wanted?

Thing is, I've always loved the look of the K0 models.  Not for the cultural significance necessarily, but the looks.  The louvered sideovers, the colored airbox- it really is the best looking model of 750.  But I'm never going to be able to afford a proper K0.  So, I did the next best thing- took the spare '71 frame I had, sprung for a Yamiya body kit, and plan on doing my best to get a (mostly) visually correct K0, but with some quality of life upgrades from later models (two cable carbs, metal chain guard).  For the record, I DID try to grab a proper K0 frame to start with, but those were prohibitively expensive.  Especially since I had a spare '71 frame for free.













And here's where things currently stand today.  I want to do some polishing and cleanup before I get the rear wheel and brake parts back on.  I've got K2 gauges, but I'm fairly certain I can take then guts out of them and adapt them to K0 gauge plates and housings, so the parts to do that are on the way.  The ultimate goal is to get it done for the Gilmore Car Museum show in Kalamazoo on June 11, but it's going to be tight.

[Don R]

That's a sweet build.
  My cheapo buy K0 had been heavily parts swapped with a K3. I built it as a rider but it's gradually returning to its K0 roots.

[WideAWAKE]

I like where this is headed.

I much prefer the K0 carbs to the push/pull style.

I had later carbs on my K0 then swapped em out to proper ones and they are much more responsive.

If you do decide to get some K0 carbs keep an eye on eBay. I got mine for about $125 from Germany as they were listed as later 78 carbs. 

[Lucien Harpress]

I'll keep it in mind about the carbs.  I think I prefer the later style myself- much less to futz around with.  But it's nice to keep the option open.

Work continues.  I was hoping this weekend to get the back wheel on, but I ended up doing pretty much everything but.



Electrical is done, minus the handlebar and headlight bucket area.  The seat is just on temporarily because I was curious how it looked.  It's a Vietnam re-pop, but looks close enough for my tastes.  It's a bit flatter than stock, but apart from the cute little ducktail, I actually like my bike seats a bit flatter anyway.  The pan is a rough finish vs a stock gloss black, which is a bummer.  But because it has the actual teeth holding the cover on (vs the later style with the chrome edge that's bonded to the cover and almost impossible to replicate) it's much MUCH easier to re-cover later if I want something closer to stock.



Pretty much all of the rear brake hardware is installed.  The parts that needed it were cleaned up and re-plated.  I thought I got lucky with the rear brake spring and didn't have to struggle with it, but then I found out the lever needed to go in FRONT of the swingarm, and surprise surprise it was a struggle after all.  But still, it's on, and a proper K0 brake lever (which is different from later models, I just found out) is on the way.

Good progress.  As a last little fun bit of trivia, remember how I said this was always a pile of parts bike?  The very first photo I posted has a 1975 frame.  So this thing has never been close to ANYTHING.   

[BenelliSEI]

Nice project! Turning out Well! Yamiya makes a red foam kit for the “duck tail” seat, but I need one too and they have been out of stock for months.....

[Don R]

 Red foam has been out of stock for more than a few months, I missed (cheaped) out on getting one before JT Marks passed away, Now I wish I had gotten two.

[BenelliSEI]

Red foam has been out of stock for more than a few months, I missed (cheaped) out on getting one before JT Marks passed away, Now I wish I had gotten two.

Frustrating. I have a seat pan and cover all prepped and ready......

[Lucien Harpress]

Yeah, I'm keeping an eye on the foam.  I don't really trust sitting on the bike TOO much with no back wheel, but from a couple quick tests- this seat is quite firm.  More than I was expecting.  But of course, at this point speculation is kind of pointless.

In any case, progress continues.  I got shafted on my new rear sprocket (it would fit on the 750, but the photo did not match the product I got, so it's not even CLOSE to stock looking), so instead I did what I could to get the front end together.  I had to swap my K2 controls for a K1 (possibly K0 as well?) replica.  It's not 100% identical, but close enough for me.



I also got all the stuff run up front (minus the tach and speedo cables), so I pulled another piece out of the Yamiya box and got it mounted.



I still need to connect all the electrical in the bucket, but I figure I'll wait on that until after I get the gauges done (parts for THOSE on track to show up next week).

[Lucien Harpress]

The plan was simple- replace the rear sprocket, get the back wheel on, get the bike from the barn to the garage, then finish up where I had a bit more space.  Well, getting that rear sprocket took SO LONG I pretty much ran out of other stuff to put on in the meantime.

(For the record, the first sprocket would've fit, but didn't match the picture, and didn't look period-correct.  Then the second one got lost in the postal system for half a week so it showed up late.  But all is finally well.





I'm fairly certain everything I need has been purchased.  The gauge parts are a couple days off, so with any luck I'll get those done this week and lock down all the electrical.  I'm doing a bit of song and dance with my carbs before I put them on (I want to make sure the jetting I have works with the exhaust I have), but I'm happily running out of things to do.  Goal is still to get it done by June 11.

Just for fun I threw the tank on, to get the whole picture.  I like it.

[RAFster122s]

Looks good, be tough not to like that. Glad you are enjoying it and the rear sprocket setback got worked out...

[newday777]

That looks great Lucien 👍

[Stev-o]

Great project....

[BenelliSEI]

Lovely!

[Lucien Harpress]

After doing a couple last-minute checks with the carburetors, I deemed them worthy of being re-installed.  I was planning on getting the rubber dust caps, but at $80 a set I kind of ran out of money.  They're still on the list, but if I want to make Gilmore they can wait.



(A new set of intake clamps might be on the list at some point too.)

In other news, the mail finally got it's act together and a bunch of cool stuff all arrived at the same time.  In no particular order:



- Front MC line dust boot, which means I can FINALLY bleed my front brake.

-New (aftermarket) header clamps.  Mine were kind of rusty, but REALLY killed the look of the front of the bike.  Still waiting on bolts, but those should be here sooner than later.

-90% of what I need to convert my K2 gauges to proper K0 units, including the chrome plates for the backsides.

The good news is that I popped open my gauges, and the internals are quite clean.  The bad news is that I still need to figure out the tubes for the idiot lights.  If I can't find the correct size tubing at a hobby store I may have to get some thin sheet and roll some by hand.  The stock parts are nothing special, so it can't be that hard.

The only other annoying bit is that the K2 lights use a much smaller rubber socket than those on the K0, and I don't feel like spending $150 on a replacement wire loom.  I'll find a way to get the lights I have to stay.

[RAFster122s]

You could roll some surgical tubing over your K2 rubber socket. Just use some silicone grease on the outside of surgical tubing when putting them into the back of the gauges.  That would increase the diameter of the rubber idiot light sockets and still be pliable. Or, check out plastic tubing...to bush the light tubes.

[rickmoore24]

Awesome! I love the unicorn triples, I regret selling the ones I had. Bike looks great!

[HondaMan]

Red foam has been out of stock for more than a few months, I missed (cheaped) out on getting one before JT Marks passed away, Now I wish I had gotten two.

Don: have you tried contacting his newer JTMarks77 seller? I think it is his daughter (wife?), as I got a girl's name with thanks on my last order from there.

[newday777]

Red foam has been out of stock for more than a few months, I missed (cheaped) out on getting one before JT Marks passed away, Now I wish I had gotten two.

Don: have you tried contacting his newer JTMarks77 seller? I think it is his daughter (wife?), as I got a girl's name with thanks on my last order from there.

It is JT's daughter. Has her own family now.

[Lucien Harpress]

Long day in the garage today.  I've still got a couple of minor issues (stripped bolt hole here, a mis-aligned light tube there), but for the most part my gauges have been converted over.



There's probably never been a set of 750 gauges with more pop rivets in them...     That said, while it was a bit annoying to have to drill and rivet all the light deflectors, using the rivets worked out better than I hoped. 



Tips might be a bit too orange.  Oh well.  I like it.



While I was told the gauge holders do a good job of keeping the faces and backs together, I discovered that was not the case with mine.  Still, it was a simple as a couple screws through the sides and everything is now solid.  I need to chop off a locating tab on the inside of the rubber trim, but for right now things look awesome.

I'm still fishing around for solutions for the bulbs themselves.  Does anyone have a handful of spare sockets lying around by chance?   

In an odd little quirk, I did notice that my odometer is slightly wider than those on a real K0.  I had to bend the light tube for the blinker indicator a bit, which means there is a small dark corner when that indicator lights up.  Annoying, but still beats paying full price for a "proper" gauge.  And I get to keep my mileage!

[Lucien Harpress]

Success!

I finally got it to a point where I could splash some gas in it.  The goal was to a least get it to fart or pop, and go from there.  Turns out, it runs pretty well without doing anything.  The rocker arm cover was off just so I could make sure the top end was getting oil, and between that and the bubbles in the oil tank, I've got a pretty good idea that I've got good circulation.

This motor has always been a cherry (despite everything else I've done to it), so I'm glad that hasn't changed.  The only issues right now are minor- I'm keeping an eye on what looks like a slow oil seep from the front engine case seam, even though I can't do much about it if it is a legitimate leak. 

I also didn't have a working oil light initially, but after a bit of a ride around the yard (to make sure the drive chain worked) that fixed itself.  However, in the meantime my neutral light STOPPED working.  So that's fun.  I'll keep an eye on it.

Next up- test rides!

[Lucien Harpress]

Good news!  The bike runs and rides, quite well, actually.





The bad news?  After about 20-30 minutes, it started to run worse.  It would slow down at idle, until I was struggling to keep it running at stop lights.  I got it home, let it cool down, and checked the oil.

Bad news?  A bunch of non-magnetic grey crap in the bottom of the oil tank.

Worse news?  Gold flecks in the drained oil.

Yeah, looks like I goobered up a bearing or two.  I had a nagging suspicion I did that part wrong.  I DID plastigauge the crank before it went in, but I'd bet it's out of round, and I only ran one strip per main bearing.  While spinning it by hand I did have one spot that was stiffer than the rest, but having never rebuilt an engine before, I had no frame of reference of what constituted "too tight".  Oh well, live and learn.

After giving things a few days to marinate, I figured it was time to dive back into this mess.  I went back and forth between fixing what I had and getting a new bottom end, and eventually I settled on finding proper bearing shells.  I'm not looking forward to pulling this engine again (especially with the rest of the bike together AND with a paint job I don't want to ruin), but it's gotta be done.

[grcamna2]

I love that color 

[jakec]

Red foam is back in stock now on Yamiya. It is $350 now plus $200 shipping to the US.

There are no other sources out there as far as I know.

[HondaMan]

Such a beautiful bike!

I always wrap cardboard around the frame (with Ty-wraps holding it in place) when R&R-ing the engines. This prevents the scratching on the new frame paint.

[WideAWAKE]

Red foam is back in stock now on Yamiya. It is $350 now plus $200 shipping to the US.

There are no other sources out there as far as I know.

Just dye the white foam red???

Can’t be too difficult.

It’s been on my list of things to figure out over the next few months.