CB750 K0/K1 Hybrid

[Lucien Harpress]

For sure, for sure. I've got no reason to take the rods off, so far as I'm concerned that whole assembly can stay together.

I'm still making baby steps. I don't want to go a lot farther before my donor cases are cleaned, scrubbed, and possibly painted. But the momentary downtime got me waxing a bit philosophical. See, this bike has always had a bit of an identity crisis. Part of being a bike cobbled from parts, I suppose. Thing is, I only called it a K2 because that's the paint job it had when I got it. But the only parts I saved from that original K2 is the engine, and now I don't even have that.

My new lower cases are now stamped as a 1971 engine, and I'm still running my 1976 frame. My back end is early CB750, my front end is late CB750, and... you know what? Part of me wants to (eventually) rectify that. With parts all over the place, "period correct" means absolutely nothing. So why not correct it to the period I choose?

Yeah, I'm thinking of back-dating it to a K0 status.

Now, this comes with a VERY heavy "eventually". Luckily, the K0 having the cult status it does means all the needed parts are generally available (as replicas, usually), if not necessarily cheap. And I'm NOT going to even think about starting until my Dream (and possibly my KZ1300) is 100% done. I'll probably try to pick up parts here and there until I have everything I need, then pull the trigger on a paint job and put it all together then.

It may annoy some Sandcast purists, but like I said- "stock" means absolutely nothing to this bike. So why not?

[Shadowjack]

In my state, the year is whatever the frame is, and you need a title that matches that. Unless it came from a state where they titled on the engine number at the time, like Wisconsin. When I bought one of those bikes and went to title it here, that got me a couple of nonplussd looks from the inspectors.

[Lucien Harpress]

Yeah, mine's titled as a '76 (matching the frame), but that's because it was the cheapest solid titled frame I could find. I have the original (which is a '72, but THAT one's titled as a '73), but the bottom is rotted out. Hence the frame swap.

Now, I COULD restore it as a '76, but I have almost zero '76 parts on hand. And the looks of the later bikes don't really do anything for me.

And turning the most frankenbike of frankenbikes into one of the most desirable models of 750 when it really, REALLY isn't is funny to me. (Plus those slotted sidecovers look GREAT.).

I haven't ruled out keeping an eye out for a '70 frame, but I would have to be paying next to nothing for it, and I don't see that happening.

[Lucien Harpress]

Alright, enough navel gazing. Back to more practical issues. Mainly, cleaning the donor cases.



After round 1 of powerwashing, things are... promising. It still needs some help in the really cruddy areas (probably some scraping and hand-scrubbing in my future), but very VERY nice considering it sat outside in the dirt for a couple years.

[Shadowjack]

I really wish places that do vaporblasting were more common in this country. I see the results in Brit bike mags and they're beautiful.

[robin1731]

I really wish places that do vaporblasting were more common in this country. I see the results in Brit bike mags and they're beautiful.

Those cases I would bead blast first then vapor blast. I can bead blast cases but my vapor blast cabinet is too small. In that case I just paint the cases after bead blasting.

[Rednaxs60]

Vapour blasting is great, but can't paint afterwards unless you rough up the surface, defeats the purpose. Should use a protectant on the surface after vapour blasting. I had my '85 1200 Limited Edition engine and parts vapour blasted last year, not inexpensive but a great job. Looked for a good protectant because the engine, was told about some that are a liquid film, but these attract and keep crud/dirt and such. Finally settled on CERAKOTE MC5100 air dry product for all aluminum finishes, including vapour blasting. One coat application, brush or spray, works a treat and nothing sticks to it. Wipes clean with a damp cloth. Painted the bike as well and used this on the non-plastic parts such as swing arm, centre stand switch covers, wheel rims, and more. Still good after almost a year. No affiliation, just like the product.

[robin1731]

I had some of my parts that were vapor blasted coated with clear ceramic. Same place that does my powder coating. Works very well.

[Lucien Harpress]

Blasting it would probably be the proper way to do things, but I'm definitely balancing costs at the same time. For what I'll be using it for, a scrub-down and paint will (probably) be more than enough.

While my bottom end soaks, I turned my attention to the top end. I've got heavy-duty cylinder studs ordered, and started pulling the old ones in the meantime.



The good news? Of the 16 that had to come out, a vast majority didn't give me any issues.

The bad news? It's always the last one...



I've got some industrial strength penetrating oil on it right now, and will probably let it soak overnight. Heat didn't seem to do a whole lot, at least today, but I'll try again tomorrow. I'm not overly worried (because there's still quite a bit to grab on to), but don't want this whole project to come to a screeching halt because I did something stupid either.

Never a dull moment.

[Lucien Harpress]

Luckily, this story has a happy ending.

[Lucien Harpress]

Because I was getting antsy about crank bearing shells, and it was high time to do it anyway, I decided to go ahead and split the crankcase.



Honestly? Nothing I wasn't really expecting. It's a good thing I didn't just try to patch the block, because there is a lot of crap floating around inside from the chain detonation.





As for the crank bearing themselves, well. I checked out the comparison tables in the manual (the block and crank are stamped, and you cross-reference between the two to see what size you need), and while the bearings in the block I just split aren't technically right for the block they're going in, I may try to use them. Between crank wear and the differences in sizes (I'm just one off), I'm hoping they'll still work. I'll still plasti-gauge things regardless.

Now I could pick-and-choose between bearing shells on my donor case, but my dumb butt decided he didn't need to keep any of them straight when taking things apart. Normally this wouldn't be the end of the world, as the bearings are color-coded and some of the paint is still there on some of them. BUT I also decided to mix up the crank and con-rod bearings as well, so I can't be sure about any of them.

Regardless, I still may be able to make it work with what I have. I'm still debating about painting the cases before or after loading them up, but either way I should be able to start swapping stuff over fairly quickly.

[Rednaxs60]

Like following your progress. I would paint the cases first. As for the bearing shells, may need to set them out on the bench. Take some measurements, determine what fits, make your best technical assessment and use. I know it's good to have everything just right, but I do believe we tend to overthink the issue a lot.

Cheers

[Lucien Harpress]

After taking a bit of time for a quick vacation, I'm back to work on the ol' CB. I finally got everything around to check crank bearing clearances, and lucky enough everything specs out right to where it should. This is a huge relief, as this could have turned into a bigger (and more expensive) adventure than I really wanted to have. Thankfully, I don't have to worry about it.

Next up is finishing clean up of both cases, then temporarily bolting them together for paint. I'll probably go all the way with primer and clear, just because I will be manipulating them so much after the fact (loading them, bolting things together, etc.), but I'm eager to start putting things back together, rather than just tearing things apart.

Until then!

[Lucien Harpress]

Somehow between freezing weather and the bit of oil I sprayed into the block halves to help preserve them, I was able to start laying some paint down.

[cfairweather]

Looks nice.