Do I need to rebuild/check the engine?

[Ccheese4]

I recently got a hold of my Dads old 1981 CB750K. He stopped riding it many years ago, and the bike has not run in 25+ years (haha, since before I was born). I'm working on getting it back running. I just finished a complete reassembly of the carbs and got it a new-used gas tank. It needs new brakes (the originals are mysteriously missing), battery, ignition control modules, tires, headlight assy, and there's rust everywhere (I'm sure there's more that I'm missing as well).

My question right now relates to the engine. It only has 5200 miles on it, so do I really need to take it apart? Are there seals that would have gone bad or something? Would the oil have clogged up vital components? This is my first real experience with anything like this, so I'm very much still learning.

As a side note, is there anything else you guys can think of that I should check or replace? My current goal is just to get the engine running. After that, I'll focus on getting it roadworthy, then work on the aesthetics last.



This is the bike as it was before I touched anything (well, I moved all the junk off of it. You wouldn't even be able to see it if I had left it).

[Butcherblock]

She looks pretty good to me! The origional 4 into 4 exaust looks like it is in great shape. She should be a great bike to learn on.

 My advice would be to get it running, and work will magicaly start popping up. Download the factory service manual at the top of this page, and start going through the bike, doing basic maintenence and getting into the finer tuning as your abilities advance. You will be surprised at how much maintenence stuff these bikes require, but once its done, you will have a great understanding of these machines.

Look for other build threads for the DOHC bikes (79-82) and peruse them, you will gain a lot of knowledge about yopur own bike.

Work hard, but most of all have fun!

[TOOLS1]

Only "5,200" miles. That engine is not even broken in yet. Just change the oil, and start it up. If anything starts leaking, then replace the gasket/seal.
TOOLS

[shinyribs]

^^^Exactly!!!  New oil in the crankcase,flush and refill the forks,NEW TIRES...and ride. With so few miles the chain and sprockets will not have enough wear to need replacing. You should still check the chain for rust. Surface rust won't really hurt anything,but if it has any kinks or tight spots it should be replaced.

That's a heck of a start you got there! Welcome to the forum and good luck with your project. Keep us posted

[Ccheese4]

Butcherblock

Yeah, it's in fairly decent condition. That picture doesn't really show the rust though. I read somewhere that the stock exhausts rusted out fairly easily. If that's the case, then the mufflers may be no good. The bike spent some of its down  time outside down here on the gulf coast. Salt + humidity = rust. It definitely spent at least the past ~21 years in our garage though (based on pictures and my childhood memories). I'll put some close up pictures of the rust at the end of this post so you can see what I'm talking about. I hope to be able to use them though. I absolutely love the look!

Tools and Shinyribs

I was actually quite surprised at how low the mileage was when I looked. However, I still thought I would check with you guys. Didn't know if the 25 years of sitting would cause an issue. Better safe than sorry!


All

Thanks for the welcome! Maybe I'll start a build thread up here one day


Rust pictures

[cdaiscool]

... that's all the rust there is? Am I missing something?

~ 5 minutes with steel wool and that surface rust will be a memory, memorialized in these pictures.

I myself have a 1981 CB750k and have done a fair amount of work. Let me know if you need any help or anything. And agreed with TOOLS - the motor isn't even worn in yet. Clean the oil, run some seafoam, re-do another oil change, and have fun with the salty air in the helmet!

[FastCletus]

Wow, looks like a hose soap and water and that bike will shine.  5200 miles.  Damn you scored.  I would probably flush the brake lines too.  Agree with previous post, get it running and sit back and wait, if a problem arises you will see it!

Good luck

[Ccheese4]

yep! well, the rust on the no. 2 pipe is similar to what's on the mufflers. The rims and spokes are also quite rusty, but you guys have made me feel better about it! You can see on that corner of the crash bar where I did some polishing on the rust, just to see how difficult it would be to get out. All the surface rust came off no problem, but there was a bit of pitting.

I am incredibly excited to get it back on the road again though! Hopefully, that will happen this summer as long as school doesn't get in the way.

[Lucky 1]

A very sad story.  
I always wonder why anyone would let a bike sit for 25 years
without at least spraying some WD40 on it or kicking it over from time to time.

Of course it will need new tires and a new battery.

[Cabreco]

Fiona was in basically the same shape when I got her (but with 22K miles)
After you get here going, the cosmetics will be simple but tedious work.
Use steel wook for the big surface rust. After that get yourself a tube of Flitz.
Then polish the chrome work. BTW if you use Flitz with a dremel or drill with buffer attachments
you can easily shine the side engine covers to chrome like finish.

Before



After