CB750 K0/K1 Hybrid

[Shadowjack]

I'm trying to think what would be yellow metal inside one of these engines. Nothing comes to mind.

[Lucien Harpress]

My thoughts are the brass on bearing shells. I'm guessing the crank blew through all the babbit material and got into the brass underneath. Either way, not good.

[Shadowjack]

I don't believe that would result in glitter, but I guess you'll find out.

[robin1731]

One sure sign of a bearing "leaving town" is oil that looks like metallic paint.

[flyin900]

That is really an unfortunate outcome to a lot of hard work and such a great build, along with all those shiny new bits. Those will continue to be new and shiny, so slog on and get the mechanical sorted. Then you will have a wonderful CB750 SOHC bike in your stable.
Just reading through some of your thread, it was a reminder to investigate further when things don't spin right or have tight spots in the internal rotary components.
A machine shop can and does have all those tools needed to measure if you supply them the specs for the internal components. If you only use their measurement expertise and do your own mechanical work, it is a cost effective way for sure vs buying or owning all those measuring tools sets anyway.

[Lucien Harpress]

Truth be told, part of me is glad it's "bad" enough to require a revisit. There's a couple other minor things I noticed I'd like to address. There's a VERY small oil weep along the front crankcase halves- not enough to drip, but enough to feel if you run your finger along it. The big thing, though, is the motor is definitively kind of buzzy. It always has been, but I was hoping a full rebuild would help it a bit. Not so much- the short trip I had it out it vibrated just as bad as it did before.

I'm looking into local machine shops, to see how much it would be to get the crank balanced. I'm not saying it's my problem (I'm not sure if this is ones of these "It's not a bug, it's a feature" situations), but if I've got it apart and the price isn't too bad, it may be worth doing regardless.

[cfairweather]

Cycle-X is the only place I would trust to balance the crank. They are experts and will do it better than the factory. Consider sending it to Ken and let him build the bottom end for you.

[Lucien Harpress]

I would love to say this gets easier. That would be a lie, though.





Thankfully, I didn't scuff up the frame or engine too bad getting it out. The bad news? I've added to my list of things I need replaced unrelated to the engine. My "stripped rear shock mount" was joined by "new coil" because I may have forgotten one plug wire still in the plug well of the engine when I pulled it. The wire came with it, the coil stayed.

That said, I'm definitely leaning toward the crank balance. Cycle-X is very reasonable, and the customer consensus is nothing but positive. It's just as shame- it's ALMOST within driving distance. Shame about the lake in the way.

I think I'll get it apart and start sending out some e-mails.

[cfairweather]

If you let Cycle-X, I would also lighten and balance the alternator. They will take metal off of the main lobes when they do the crank which means you may need different size bearings. Ken usually has a good supply of these and he will install the right size for you if you include the cases. If you call him, he will give you some great advice.

[Lucien Harpress]

Whelp, teardown has begun, and even though I just have the head off, I've got a feeling deeper in is not going to be good.



(THAT definitely wasn't there before...)



(Now this bit of schmutz MIGHT be remains of the old head gasket, but on the other hand it is on one of the oil feed studs, and the others look pretty clean)

I stopped at the bores, because they seem pretty stuck on the block, and I need to find a way to get them off without goobering the paint OR bending the fins. Still, I'm curious what deeper inside is going to look like. Not that I'm going to like it....

[Lucien Harpress]

Cases are re-split, and the verdict is.... not as clear cut as I would prefer. (In the interest of not re-posting the same bearing picture five times I'll just post the album link. All the good stuff's in there.)

https://imgur.com/gallery/omxzH1X

The bad? Lots of crap in the oil pan. I figured I would have some kind of nonsense, but this seems excessive to me.



The inconclusive? While there are quite a few shiny portions of my crank bearings, I'm not sure how much of it is "normal", and this also includes wear from the old engine I took them out of. Still, obviously something is wrong, but it's not so horribly wrong I can immediately pick out what my problem is.

I'll probably pull the transmission shafts, put the crank back in, and torque everything back together. This way I can confirm it's my crank that's binding and not something else.

[Lucien Harpress]

I just got back from a rewarding (albeit a BIT more expensive than I was anticipating) vacation this last week. I took a drive out to Anamosa Iowa to see the National Motorcycle Museum before it closes up shop, then made a few stops in Wisconsin along the way back.





One of those stops, of course, was Cycle Xchange up in Hazelhurst. I dropped off my rod/crank/rotor assembly along with the cases to get everything fitted and balanced up. The rods, crank, and rotor got balanced, along with new bearing shells all around. Everything's getting shipping back tomorrow, and hopefully it won't be too long until I'm able to start getting everything back together again.

[Lucien Harpress]

Time for a check-in. I got all my parts back from CycleX, and after a couple o-rings and things showed up in the mail today, I think I'm ready to button the cases up again.



My experience with Threebond, while probably okay, wasn't the greatest, so for round number 2 I'm trying some Loctite 518 anaerobic sealer. In theory, because it only hardens in the lack of oxygen, any excess on the outside of the block can be wiped off, and any on the inside will get washed out by the oil. Plus I'll have plenty of time to get everything lined up.

I also got a couple of parts for my carburetors that, while not strictly necessary, I've wanted for a long time now.



Of course I had to goober up (rather good) carb sync to get them on, but I should probably re-do that anyway.



Plan is to get the block together in a day or two, then we'll worry about buttoning up the rest.

[Lucien Harpress]

So, it's been a hot minute since the last update, and progress is a bit of a mix between progress (got it together, took it for a test ride or two, had to trouble-shoot some minor issues) and not (carbs came back off to clean up some details, learned that clear-coat on an air cooled engine turns yellow), and we're mostly in hibernation for the winter. That said, I got some goodies in the mean time I wanted to show off.

It's a minor, minor thing, but it's always kinda bugged me I have a bike with 1970 K0 bodywork, but is actually a 1971 K1. Well- I've been shopping.

First- K0 Battery Box



It's not too different than a later box- the only thing I can see is straight cut edges on the top, rather than scalloped like the later ones. There's quite a bit of rust damage, but nothing I can't fix or will be too visible.

Next up- Correct forks



This style (with the hard ridge under the fork seal) was only used on '69 and '70 bikes, and don't show up often. I paid more than I'd like, but less than I expected to.

And finally-





It's going to require clean up, and a small hole patched on the bottom, but in some ways is in better shape than my K1 frame. But now I can say I have a LEGITIMATE k0 bike.

[cfairweather]

Congratulations. Did the frame come with a title? Now you need to find the K0 carbs. They are available, but not cheap.