Topic: CB750K4 what did I get myself into?

[BrockCB750]

@denward17 in the process of reading your entire build thread. Lots of great information there.

As far as mileage the gauges have it at 15,535. It also last ran sometime in the 80s as far as I can tell. The original pictures in this thread do a great job of showing the condition it was found in.

[PeWe]

A good bike when ran last time in the 80's can, if stored incorrectly, have an engine full of rust. Run it and it will cause wear.

Guides and valves must be ok after only +15000 miles.

[BrockCB750]

I spent VERY little time looking at the head and engine once I got it pulled this morning but if you look back at the pictures posted lots of carbon it seems but I haven't seen rust anywhere internal to the head or cylinders. Oil came out dark but didn't seem to ever have water introduced.

But this is just 2 min of looking things over.

[PeWe]

Open side covers.
Clutch cover to have a quick look inside.
If clutch outer steel basket does not have deep rust, a good sign.
Open oil pan to see if any debris is gathered there.

[Mark1976]

Not sure what your overall goal is, but I would check for valve seat leakage with some type of fluid in the ports.

If leaking take valves out and repair, check valve guides and seals.

Take cylinder off and inspect pistons/rings/cylinder walls, clearances and such.

Before you start tearing the motor down further, what is the original mileage? Often, you create issues when none exist in an attempt to verify conditions that would otherwise not be an issue on a low mileage motor.

For instance, you can rotate the crank and do a visual inspection on the cylinders without disrupting the seating. Drizzle a bit of oil in them and see if the rings wipe the oil. It's not as exact as a bore mic, but it is pretty reliable.

This is good advice, there's such a thing as, 'a learning experience.' And then there's A LEARNING EXPERIENCE, a money pit with no for seeable bottom, just because you don't know any better. Ask questions, post pics just like your doing, one step at a time.

[BrockCB750]

Thanks for the great advice. I have some work to do with the impact driver to get the cover off but thats next on the list before I do anything else.

[BrockCB750]

Walked to the garage and snapped a couple pictures. Cylinder walls are smooth as far as I can tell. Some slight discoloration:

[calj737]

Smooth is better than gouged, but you do want a cross hatching still visible for the oil draining/ wiping. But do add some oil to the cylinders and rotate the crank. Watch the oil trickle. If it comes down in sheets, you might need a simple hone on the cylinders (removal of pistons required).

The carbon on the underside of cylinder 3 (head) can easily be cleaned off. Careful removal and tracking of the valves, springs and retainers will provide better access. If you can, you might even find a machine shop locally that would be willing to plop your head in their hot tank parts washer to get the ports and chambers cleaned up nicely. That’s all needed if you do want to pursue checking tolerances and performing any corrective surgery.

[BrockCB750]

calj737 thanks for the advice. I will look up a picture of what the cross hatching should look like. Maybe try to get a picture that shows the condition of mine.

I couldn't help myself and broke out the impact driver and got this far into the clutch. I have had the special tool already on the way for a week now but it looks like it shipped from China and might be a few more days. I have a lot to do and could probably use a break from the engine. Probably time to continue stripping the frame down.

[MauiK3]

First, great project, I’m a “mostly stock” kind of guy, I think you’ve got a good one there.
I sent my K3 head and cylinders to Hondaman for refurbishing, excellent job. Shipping was a little tough from here on Maui but well worth a wonderful job.
As for your tank, it’s totally salvageable. Here are some photos of a before and after tank on a bike I am (stalled) working on. If no one you know will touch it I do, it’s just that he is on Oahu. Great guy, perfect work.
Same tank, he pulled all the damage. He recently worked on my Acty too, another great job.

[BenelliSEI]

The Acty looks great!

[PeWe]

The Acty look sweet and useful without taking much space!

[MauiK3]

The bed is flat with no wheel well humps, very useful. I make a diaper with a tarp to fill it with green waste. Our 12 month growing season makes a lot! We do our own gardening.
Sorry for hijacking the thread.
But seriously, if anyone has a unique fuel tank they want to save William Hannibal of Cycledelic Creations is the guy. He’s a very nice guy, one man operation. We really didn’t give him much detail on what we wanted for the Acty, he stripped it and went to town.
The Z1 tank is a miracle.

[BrockCB750]

Spent a couple very hot hours in the garage...

Got the frame apart!

[MauiK3]

Be careful with that VIN plate! Guard it any way you can.
Looking good.

[BrockCB750]

Not sure what you mean about the VIN plate?

I actually did grab a picture of it yesterday because as I am building my parts list I noticed some parts changed within year and are pased on serial number.

But yeah, the VIN plate has seen better days...

[BrockCB750]

Okay got the kickstands off.

Looked the frame over the rust is just surface rust, nothing looking like it compromised the frame. So huge win there.

However there is a small dent:



Wire brushed some of the paint and rust away:





Frame looks nice and straight as far as I can tell. Should I be concerned about allignment of the frame?

[HondaMan]

If the dent happened with the engine in-frame, it should still be straight.
It's not such a nice story if the engine wasn't installed at the time, though: been there!

[calj737]

A dent in the tubing there will have zero effect on the straightness of the frame.

As you go along stripping the frame, inspect for other dents or cracked paint which are evidence of stresses. Also, surface rust is not to be ignored.  Take an ice pick or something similar, and peck at the frame in areas. It should be super solid. If you encounter any area that seems “punky” then you likely have internal rust degrading the wall thickness of the tubing. That needs to be looked after.

[BrockCB750]

Genuinely appreciate the reassurances. It didn't seem like a big deal but googling around I thought I should ask the question. I will tap-check (for a lack of a better phrase) along the frame as I go to make sure its not rotting through.

[MauiK3]

Areas around the kick stand sometimes have issues. Yours is looking fairly good so far. If that dent bugs you I’m not sure what I’d suggest as a repair. Others here might have good suggestions.

[BenelliSEI]

I once filled a small ding by leading it over and filing it back round. Last time I saw the bike the patch was still invisible. If you’re unfamiliar with lead as an alternate to body filler, watch a few videos. As you can flip the frame and literally “pond” it in that spot, might be the best solution? Curious what others think?

[calj737]

I once filled a small ding by leading it over and filing it back round. Last time I saw the bike the patch was still invisible. If you’re unfamiliar with lead as an alternate to body filler, watch a few videos. As you can flip the frame and literally “pond” it in that spot, might be the best solution? Curious what others think?

A classic and all but obsolete approach to body work. Mostly due to toxicity. The fumes are rather harmful and our EPA has nearly made it criminal as a technique. Works well and millions of American cars were jointed that way up until the early 60s.

[Mark1976]

I once filled a small ding by leading it over and filing it back round. Last time I saw the bike the patch was still invisible. If you’re unfamiliar with lead as an alternate to body filler, watch a few videos. As you can flip the frame and literally “pond” it in that spot, might be the best solution? Curious what others think?

A classic and all but obsolete approach to body work. Mostly due to toxicity. The fumes are rather harmful and our EPA has nearly made it criminal as a technique. Works well and millions of American cars were jointed that way up until the early 60s.

   A rather unfortunate sign of the times, I still use this method when working on motorcycle gas tanks once the repair itself has been made. It really is a great way to cover seams or small indents/repairs, it's not ever coming off and it won't age, shrink or crack like most body fillers do as they age. I'll agree, it's definitely not a health friendly medium, it's lead. When I learned this process literally 50 years ago, it was considered an obsolete process of repair then, the only time it was being applied was on restorations or custom work. But it still has it's own useful applications.

[BenelliSEI]

All good points. When I started as an apprentice plumber, one of the first things I learned was to “wipe” a lead connection…… work outside and place a fan blowing the fumes away from your face.