Topic: 1977 CB750k - Reviving a forever project

[rugger81]

This is going to start with a sob story. You can skip the next paragraph, but it's mostly to set context for this project. The TL/DR; is I inherited this project from an idiot (my younger self). It's a project bike that hasn't ran since 2008, and I'm trying to set things straight.

It really pains me to say, but my CB750 has been a point of great shame in my life for the past decade. I bought it right out of college, rode it for a couple of years, and then decided to rebuild it. What started as a top end rebuild, turned into a full rebuild, and then everything ended up sitting on a garage shelf for 10+ years. For all that time it really ate at me, and I frankly had developed a fear of restarting the project. This is my last go at it, to try to get things going. I promise you I will shed a tear at the end of this because its finally running, or I've failed and forced myself to sell it off to someone who will finish what I couldn't.

So anyways, with that out of the way. The current state is the engine is out, stripped down to the bare cases. Cases have been painted, and everything is ready to assemble. Problem is how long everything sat unattended. As it sat for so long, every single part will need to be reviewed to determine if it should be replaced. I already have all the normal parts to replace on hand when you do this type of build. Plus the following parts:

MRieck stage 3 head (The pièce de résistance of the build)
wiseco 836 kit
BCR 4-2 peashooter exhaust
Webcam 63a
new coils w/dyna ignition
Terry in Australia custom oil cooler

I also have the M3 tensioner / guide but honestly I think I might just replace it with a new stock part. I hear now some people have had issues and I'd really just want to not have to open these cases again.

As for non-engine items, time will tell. I will be keeping a stock look though with the standard handlebars, seat, body panels, and airbox. I'll refresh the brakes, suspension, and maybe a few other things.

I don't have any good picture of my bike in any real glory, but I just got the workspace finished up for this project. Ran new electric, installed a light, and put in a new shelf above the workbench solely in preparation for this project.



So far the only work I've done is cleaning and oiling the cases, body, and head. They're all in decent shape, save for the bottom case. Loads of pitting on it, but nothing too serious. Should be good to go. Next step is inspecting the crankshaft and determining replacement bearing shells. I plan on replacing all the shells, as the case is open and I may as well. Hopefully the crank is in good enough shape.

[TjTalan]

What’s that old saying, better late? Honestly sounds like you’ve got things under control. Push past the mental block, things will fly together!


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[rugger81]

What’s that old saying, better late? Honestly sounds like you’ve got things under control. Push past the mental block, things will fly together!


Sent from my iPhone using Tapatalk

Thanks, Tj. Just looking to make some consistent progress at this point.

[BigJimG]

The TL/DR; is I inherited this project from an idiot (my younger self).

I have a few of these projects laying around myself, at least it feels that way sometimes. 

[evoskuil]

Sounds a lot like my project. Though mine sat for 25 years after barely failing to complete the rebuild of my college cb750k5. Big bore, dyna, full case paint, etc. I know that shameful feeling, but we kept the bikes, and are back at it.

[SOHC4 Cafe Racer Fan]

Don't beat up on yourself. Now that you have motivation and focus, go with it.

[Stev-o]

Don't beat up on yourself. Now that you have motivation and focus, go with it.

+1.  And now that you've start a build thread, we can help keep you motivated. 

A tip that has helped me in the past:

Try to do something EVERY day, even if it is minimal. Keep it moving...

[evoskuil]

Given you have the case apart, have you stripped the clearcoat and anodizing from the exteriors? It doesn’t look like it, but not sure. If you haven’t I highly recommend you do so now. The factory coatings can’t be cleaned up.

Something even little every day is great advice. Even just reading or parts shopping.

[calj737]

Given you have the case apart, have you stripped the clearcoat and anodizing from the exteriors? It doesn’t look like it, but not sure. If you haven’t I highly recommend you do so now. The factory coatings can’t be cleaned up.

Something even little every day is great advice. Even just reading or parts shopping.

There are no factory anodized coatings on the cases. It’s painted or chrome. He’s already painted them years back. And factory coatings can be cleaned up, but hard to make them look new again. Strip and paint works well. Or vapor blast and protect.

[evoskuil]

Are you saying they clear coated directly over cast aluminum? As far as I could tell the clearcoat sits atop an anodization of the aluminum (not an electroplating). 28 years ago I chemically stripped off the clear coat (don’t think you can get those chemicals anymore, but a hell of a lot easier than paint stripping, the coat just slid right off under a hose), blasted away the anodization, base etched, acid neutralized, and painted with flat black rust-oleum hi temp bbq paint, mirror polishing the bare side covers. The paint still looks as good as the day I finished it. Good tip on the paint from Curt Jordan who did my big bore.

Maintaining the factory clearcoat doesn’t work, it needs to be stripped or the aluminum corrodes under it and cannot be polished. Painting over the underlying surface certainly is, though it’s usually corroded wherever the clearcoat was nicked. Polishing the corroded and surrounding areas did not result in the same surface, which implied to me that it had been anodized, which certainly would have been wise in terms of both corrosion control and paint adherence.

[evoskuil]

Also, yeah - I missed the part where he said he had already painted :/.

[evoskuil]

This hack-a-week episode is informative.

I also used drano for base etch. He doesn’t strip the paint for the valve cover initially (though does for the breather cover?), so nothing is happening. Then he strips it and retries. The different coloring between the outer and inner surfaces is pretty obvious at that point.

The NaOH then uniformly produces a black coloring over the exterior but not the interior. The casting is an alloy, which would be chemically distinct from an anodized surface, which is also why they would polish differently. The etch will eventually remove anodizing as well, but takes longer than one might desire to have the whole part immersed. Eventually he resorts to mechanical means to remove the blackened outer (only) surface.

After stripping and blasting I etched with drano. The parts went in and came out the same color on both sides (bright silvery matte-finish aluminum). I left them submerged in the trash barrel-sized solution long enough to full a full sized trash bag over the barrel with hydrogen gas. I ignited the bag to confirm the expected chemical reaction (also for fun).

It doesn’t seem possible to me that the aluminum surfaces are not anodized. If they are bare cast (or even polished) surfaces, the chemical reaction would be uniform on all sides, as it was for me. Having said that, it’s not clear to me why only the exterior would be anodized, but from a corrosion and adherence standpoint, that’s all that is required.

But if I’m mistaken, happy to learn something new. I tried for some time to find a description of the surface process from Honda, to no avail.

[calj737]

You answered your own question: if the parts were anodized, the entire part would be. Inside and out. They were not anodized (the cases, covers). They are cast parts of some alloy concoction. Then painted. Paint will stick to aluminum and the aluminum below will then stop oxidizing because it is no longer subject to the atmosphere.

[evoskuil]

I do understand the stickiness, and oxygen depriving characteristics, of paint. Yet the covers are internally coated in oil, and therefore do not oxidize either. How then is there such a dramatic difference between the inner and outer surfaces, especially when subject to NaOH, and why is this difference removed if the outer surface is blasted clean? It is not impossible to produce parts that are anodized on one side. Anodizing has clear benefits in terms of corrosion resistance (presumably Honda knew that paint scratches, as the coating only held up for about 3 years), paint adherence (the surfaces are painted), and coloring (AL anodization can achieve many tints, including a high silver polish). If the surfaces were not anodized they would have had to been highly polished, presumably manually, to achieve the under-paint finish. That’s a good chunk of work on the head especially.

Do you have a Honda reference for their coating process, or are your basing this on your observation of the surfaces?

[calj737]

  Aluminum oxidizes immediately. Despite being internal and subjected to oil, the case still oxidizes. But much more slowly and only to the point where the oxidation is resisting the atmosphere.

Face it, they’re not anodized. Get over it and get on with it. FFS.

[evoskuil]

I don’t understand why you sound hostile. This is a learning process. I’ve wondered about this for a long time. Have had this particular bike since 1984. It seems you are basing your conclusion on observation and not anything documented. That’s fine, but I don’t necessarily come to the same conclusion. I’d like to find something more definitive. Maybe I’ll just buy and unmolested case and spend some time on it.

[calj737]

My observation is that you are beating a dead horse in someone else’s thread. When you were corrected, you cling to the cliff to be right. Go research it all you want. Stop mucking up someone else thread with your diatribe.

Anyone who has been around these motors (and nearly every UJM of the time) knows they’re not anodized. Cast alloy of the day was not reliable for anodizing. Certain alloys don’t anodize reliably and the time it would have taken to do so in a production environment is cost and time prohibitive. I’m not hostile, I’m just right and you don’t accept that you’re mistaken.

[rugger81]

Thanks for the motivation guys. Honestly I'm not being too hard on myself. Just needed to get it off my chest, and it's easier when it's to those who likely understand where I'm coming from.

For the cases, I know of anodizing and if I had the right stuff I'm sure I could do it. Sourcing the right liquids, and the time it would take I'd probably just take it somewhere. Just going to stick with painting though as it's the normal way to go about it. The cases are painted, and I'll probably give it another few coats before it goes in the bike. I bought some more cans of Duplicolor DE1615. A little too cold to be painting this week though. The insides of the cases definitely have some sort of paint or something, but I'm not going to mess with that. Anything I'd do would I'd just mess it up probably. Whatever is on the inside though is definitely stripped from the bottom set, hence all the oxidation on just that one. I took the cases somewhere, and had them hot tanked. Whatever the shop did, they did it a little different between the two.

Since my update I've done the following:

*Cleaned and inspected the crank. It's got a few marks that are just a bit much to ignore. It could probably make due is a stock bike, but not with the added HP I'll be throwing at it. I need to source a new crank. I looked at a local one, that should do the trick. I need to decide though if I want to go nuts and get a cycle-x crank or stick with a swap. Not quite in the budget, but for everything else I'm doing I need to be 100% confident in the crank. I also am going to be getting all new bearing shells. All the case shells are too oxidized from storage, they are all getting replaced. 6-8 of the rod shells look decent, but if I have to replace 12, I may as well replace all 18. Plus with the new crank I will likely need to replace all of them anyways. Hondaparts-direct seems to be the cheapest, but it's going to be very expensive.

*Inspected the rods. 3-4 look good, but 1 is a no go. Deep scratches on the small end. Will need to get a new set of rods as it appears you cannot mix and match sets of rods.



*Started looking at the oil pump, but I realized I hadn't fully disassembled it. I have some new JIS screwdrivers coming in I am going to wait for. Also, I ordered new o-rings I'll need to wait for.

*Ordered all new bearings for the transmission, clutch, and primary drive. I got all of them either my local dealer or honda parts direct. Only one I had to order from ebay, 91004-300-000, the one on the end of the primary chain. I got it quick from ebay, but it was completely stuck from whatever it was stored it. I soaked it in MEK for a good bit, and oiled it. Not 100% sure on if it will be good. I want to compare it to the others I get in eventually.


So in short, I did a bunch and really nothing all at the same time.

[rugger81]

Bump to show this is still alive.

This has definitely been a hurry up and wait sort of thing. I've gone in the garage and done at least something every day, but currently two things are holding me up.
#1, sourcing parts. Especially with what's going on in the world right now, getting parts is basically order it and wait. I have a hodge podge of parts I've ordered in the past, but I'm likely going to go overboard and replace every single rubber part on this bike.
#2, I haven't 100% figured out by crank and rod situation.

About the crank. My choices are currently between a balanced stock weight crank from cycle x. $270 to my door, great condition with some slight improvements. Or 2, buy a local crank for $60 and maybe get a shop to polish the journals.

About my rods. I ordered an extra oem set from ebay that look decent. I plan on taking my 7 rods to a local machine shop and getting them reconditioned. Basically check for roundness on the ends, balance (weight) them, and take the best 4. This shop could also do the polishing if I go with a spare crank.

Lastly. I am currently figuring out my bearing situation. Most are no longer available from Honda. I've been scouring the forums, and found good info on other sources. Still not 100% sure though as those posts are all about earlier models of the 750. I also don't know if all the bearings have a 100% 1=1 off the shelf replacement with standard bearings. I'll sort it out though.

[scottly]

About my rods. I ordered an extra oem set from ebay that look decent. I plan on taking my 7 rods to a local machine shop and getting them reconditioned. Basically check for roundness on the ends, balance (weight) them, and take the best 4.

Just a note about terminology: "reconditioning" connecting rods is a process where a small about of material is ground of the mating surfaces of the big end of the rod and cap, making the bore slightly oval. It is then honed back to round to the desired size. I've never heard of this being done to sohc rods, but I suppose it might be possible? What you are describing is more of inspecting and selecting the best parts.

[rugger81]

About my rods. I ordered an extra oem set from ebay that look decent. I plan on taking my 7 rods to a local machine shop and getting them reconditioned. Basically check for roundness on the ends, balance (weight) them, and take the best 4.

Just a note about terminology: "reconditioning" connecting rods is a process where a small about of material is ground of the mating surfaces of the big end of the rod and cap, making the bore slightly oval. It is then honed back to round to the desired size. I've never heard of this being done to sohc rods, but I suppose it might be possible? What you are describing is more of inspecting and selecting the best parts.

Yea, i may not be using the right terminology, but thanks for the heads up. Basically I know 1 of my stock rods is no good, so I bought another set. The new set might be fine, but I was going to have a machine shop check and balance a new set for me. Also, check roundness if possible, but tolerances are so tight it might be hard to be 100% on that sort of thing.

I did have a conversation with Ken at cyclex though, and he told me roundness was something to watch for on stock rods. He says the only time he tried to work with stock rods, he had a big stack of them to work with and they were pretty much all out of round. Had trouble making a good set of 4 he felt confident in. Figured I'd have my machinist check for it as there is a spec for roundness in the manual

[ozpacman]

Regarding that small end issue.

Years ago I had a bit of a hot rod XL350 (420cc, ported & polished, carb & cam etc) The small end wore just like yours and I took it to a local engineering shop where I knew the owner. He machined it and made up a bronze bushing which he fitted and then reamed to size to make a nice sliding fit for the gudgeon pin. I flogged that thing for years after that and the small end remained perfect.

If you can get something like that done it would save you the effort of sourcing replacement rods. 

[rugger81]

Regarding that small end issue.

Years ago I had a bit of a hot rod XL350 (420cc, ported & polished, carb & cam etc) The small end wore just like yours and I took it to a local engineering shop where I knew the owner. He machined it and made up a bronze bushing which he fitted and then reamed to size to make a nice sliding fit for the gudgeon pin. I flogged that thing for years after that and the small end remained perfect.

If you can get something like that done it would save you the effort of sourcing replacement rods.

Interesting to know that I don't have to completely count that rod out, thanks for the heads up.

[Jehovanf]

I also have a k7. Also about to get into the engine. I think I'll only go into the top end though. I'll be following this thread as reference for my own work. Anyway good luck, we gotta keep these beautiful machines on the road!

[70CB750]

Following.