1981 CB750K - Repair/Tune-up

[cdaiscool]

So. Popped open the top hats on the carbs so I could work on the jet kit I got. Instead of just the jetting kit, I also got a nasty surprise!

Good clean carb vs surprise carb. I haven't cleaned either of them.


The bolt on the top rusted pretty bad...


Close up of the 'surprise'.



What is that, rock salt? I can't imagine what would do that! Fuel doesn't get up there, and the bowl isn't particularly nasty looking or anything.

[shinyribs]

cdaiscool wrote

There's no scratches on them... I just accidentally ordered chrome and not
black.

Oh. Well,what's that with the scratches on it?

[cdaiscool]

What scratches?  It be a bit drunk...

On May 11, 2013 2:02 AM, "shinyribs [via Honda CB750'S]" <[hidden email]> wrote:

cdaiscool wrote

There's no scratches on them... I just accidentally ordered chrome and not
black.

Oh. Well,what's that with the scratches on it?

Montvale,Virginia
Experience is something you get just after you need it.

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NAML

[Hoosier Daddy]

cdaiscool wrote

What is that, rock salt? I can't imagine what would do that! Fuel doesn't get up there, and the bowl isn't particularly nasty looking or anything.

That's oxidation. Aluminum doesn't "rust" but it does oxidize. I'd guess the black plastic ring under the "Hat" was missing or failed and let water in for a few decades.
BUMMER!

cdaiscool wrote

What scratches?  It be a bit drunk...
On May 11, 2013 2:02 AM, "shinyribs [via Honda CB750'S]" <
[hidden email]> wrote:

>  cdaiscool wrote
> There's no scratches on them... I just accidentally ordered chrome and not
> black.
>
> Oh. Well,what's that with the scratches on it?

cdaiscool wrote

OUCH! Any ideas how to fix?

In the last pic you posted of a chrome piece close-up looks to us like it's scratched all to hell. Maybe it's just a reflection.

[cdaiscool]

Must be a reflection as it isn't scratched.  And the oxidation? I just rebuilt it last year. Must have happened over the last couple of months while outside. :-(

On May 11, 2013 5:52 AM, "Hoosier Daddy [via Honda CB750'S]" <[hidden email]> wrote:

cdaiscool wrote

What is that, rock salt? I can't imagine what would do that! Fuel doesn't get up there, and the bowl isn't particularly nasty looking or anything.

That's oxidation. Aluminum doesn't "rust" but it does oxidize. I'd guess the black plastic ring under the "Hat" was missing or failed and let water in for a few decades.
BUMMER!

Oh and the last pic you posted of a chrome piece close-up looks to us like it's scratched all to hell. Maybe it's just a reflection.

81 Honda CB750C - Current Project
67 BSA Spitfire MkIII - Next Up (Full Resto)
81 Honda GL1100 - Bob / Cafe´
80 Suzuki GS750L - Bratstyle
72 Honda CB450K5 - Basket Case
73 Honda CB350F Cafe' (Gone but not forgotten)

Don't wait for opportunity to knock... kick the door down and drag the old harlot in!

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[cdaiscool]

OH! THAT! So I was moving the bike, the cable I was using to hold it didn't do a great job, and it tipped over. So yeah, I need to get that fixed. :/

[cdaiscool]

So after seeing the corrosion and rust that's on my carbs, I'm really starting to think I need to redo them again.

So should I get an entirely new carb rebuild kit, or just certain gaskets? Or should I just expect that I can likely reuse everything and just undo everything slowly?

I'm mainly worried that corrosion got into everything (carb sync screws, the top hat of #4 carb, various rust all over) and want to get that all cleaned up. Also, trying to put carb cleaner down the jets it's acting like they're plugged. So I just want to clean them up good and have another go at 'em.

Oh well. With any luck, the exhaust will be on tonight. Going to do a pictorial update of how to do 'em since it confused the crap out of me. Seestheday, I'll have the big ones left over if you want 'em. Just give me your address and they'll be on the way this week, provided my exhaust goes on without issue.

Also need to figure out a good way to put the handles on. I tried just shoving 'em on using hair spray for lube/glue, and they just stick. No good way to slide 'em on. Is soapy dish water okay? Maybe that and hair spray on the handle? Or would the soap/water mix take the crap with it, also ruining the foam grips?

[cdaiscool]

In the spirit of I'm-a-dumbass-and-need-to-be-more-respectful-of-motorcycles I decided I wanted to show the level of work (and money) that I've just learned is going into this thing.

Rear axle is frozen to the hub; it spins, but is quite hard. The brake cover refuses to rotate off the axle. I will need to re-grease the hub and axle.

From there, let's just let some pictures do the talking.



Let's hope I can recover this chain!


So much rust around the carbs, and jets are plugged. Going to need to get another rebuild kit for the screws and springs. Old springs are missing and/or rusty. And not really springy any more.






At least the exhaust is going on. Still unsure how I'll get the foam handlebar grips on though.

Also decided I'm going to do a detailed cleaning to this bike. I've got this Rust Reformer paint-like stuff that chemically changes rust to an inert object. So anywhere I see rust on this thing (battery cage, luggage rack, etc) I'm going to apply this stuff. I'll take pics once I start that part, probably next weekend.

[cdaiscool]

So I went to put the exhaust on last night. Thought I was doing it right, seemed to be doing it right, but after it was tightened down the headers had A LOT of play. Here's what I was doing (I was taking pics to show others how to do it) so where did I go wrong?

Before starting, remove old o-ring from head:




Put collars on the header:


Set half-moons into the collars, flared edges where they'll press against the header flare:


Put the crush gasket into the head:


If everything is done right, it'll end up looking like this:


Obviously, the header isn't pushed out far enough. Any ideas?

[seestheday]

Your half moons are in backwards.

The skinny end goes into the head.

[cdaiscool]

Does the flanged end then go around the flanged end of the header? I'm so confused how that'll work then. 

I guess I'll get to trial-and-error it tonight some. 

On Tue, May 14, 2013 at 2:25 PM, seestheday [via Honda CB750'S] <[hidden email]> wrote:

Your half moons are in backwards.

The skinny end goes into the head.

1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals

My wife's recipe website that I'm trying to help promote: BuffyAndGeorge.com. Yes, I am a lucky man.

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[seestheday]

According to the diagram on bike bandit (http://www.bikebandit.com/houseofmotorcycles/1981-honda-cb750k/o/m2003#sch37732)

The finned thing is called a joint
The half moons are called collars
The copper ring is called a gasket

First take a half moon and make sure that it will fit snugly into the head (not mounted on the header, just pick it up and make sure that the size is right by lightly inserting it into the head - don't force it - the skinny end should go in, or would go in with a little force that gets applied by the header bolts)

Mounting instructions:
- Slide the joint onto the header.
- Put the gasket into the recess in the head (I needed to use a dab of grease to make it stick - got some blue smoke for 1-2 min because of this).
- Put the half moon into the recess in the joint with the bent side down (it should fit snugly into the joint recess)
- Attach the headers to the bike

[cdaiscool]

So doing a dry run of that, there isn't a way for the header to be pressed in. The small collar doesn't hold the header in whatsoever.

More pics!

This has quite a bit of spacing outside of the head, even though it's pressed against the back of the head.


This is how it seems it should go:


Old collar sticking out the joint:


New piece in same place. This is the small collar, not the long one:


Also, anyone know where I can buy springs for the mixture screws? I'm not sure if I lost them when removing them, but when I took them out I only had 2 with springs, and they are pretty worn out.

[Johnnylevi]

I think its supposed to go opposite of how the second picture is. If you flip the piece around so that the collar of that little shim piece is sitting on the inside of the "joint" and the longer piece is sitting on the pipe. That's how mine went. Also some of those shim pieces are different. I got some from a 900c(i think) and they would not fit my 750F "joints". On the 900 they sit deeper in the joint.

[cdaiscool]

I did that before, the 1st time, and even with the joint tightened all the way down the headers were loose. They weren't pressed in whatsoever.

[TOOLS1]

The collars do go like you have them in the picture with the big end against the flange. However they wrap around the exhaust pipe, so they push the flange on the end of the pipe into the gasket.
For your grips, get a can of spray silicone from your local autoparts store, or wally world. Those grips will slide right on.
On the carbs, you should soda blast all the rust, and oxidation off, then get a cadmium plating kit from Eastwoods, and re-plate all the steel parts.
TOOLS  

[cdaiscool]

My goodness, sometimes the obvious answer is the one you never have the ability to consider.

I found this explanation and it finally clicked in my head:
http://forums.sohc4.net/index.php?topic=23967.0
Post 13

Exhaust is on, though not COMPLETELY tightened. But it's definitely on there for good.

Yay!

Now back to finding out what's going on with my carbs and rear tire. And to clean that chain. Yay for projects for the week!

Seriously, thank you to everyone that helped me with my exhaust.

[cdaiscool]

Long time no see in the thread!

Your explanation is spot-on what I was looking for. Thankfully I got them on a while ago.

I'll get some of the spray tomorrow. It won't let the grips slide off after? Should I do hairspray and the silicone spray, or just the silicone and it'll be fine once it sets?

[TOOLS1]

Just the silicone. It will dissipate.
TOOLS

[cdaiscool]

Just found something interesting in my carbs.

I don't know if it was there a year ago when I was redoing them, but it appears as though the as tube between 3 and 4 was plugged with a piece of cotton.  Not sure how it got there. It looks super old, but that's what gas will do to something. I don't remember ever shoving down Q-tips through the tubes, and I remember I was cleaning them and thought there was a piece of metal in between the tubes. Then when I had running issues and tore them down a 2nd time (shortly after rebuilding them) I realized there was gunk in the tubes. So I thought I'd cleaned both of 'em well.

Either way, I think I've sourced one issue of the bike. #4 always had issues, and now I find it was having fueling issues.

Now to go through 'em again, clean them with a guitar string (which I forgot to get before this weekend - grr, maybe some of my guitar friends has an extra e string) and get all the rust off 'em. Then reassembly, see what I'm missing, and order what I'm missing so I can put them together on the bike and get 'er running!

Other news, the axle is definitely sealed to the brake drum cover. I even carefully banged the axle against the ground and still nothing. Going to look more at that tonight or tomorrow (if I have time. Damn holidays busying my schedule up).

At least I'm getting a BBQ out of it!