CB750 Nighthawk build:

MK3Brent · May 18, 2013

It's weird.. Even clean, and reassembled they'll move freely for a while, then when left alone for a few hours they get sticky again. Now that I know how they're assembled, I will clean them each myself again and possibly replace the springs with my other CB750 carb springs. They just may be very weak. They are 31 years old after all.

Here are a couple pictures of some more goodies I'm going to use to build this thing.

Thinking about using them for the coil trigger wire harness and CDI boxes.

Haven't given it much more thought than that yet.

Here are some photos:

MK3Brent · May 19, 2013

More bad news.

Since I finally got a crankshaft bolt on the rotor side, I found out the engine on my clear title bike is locked up.

I'm going to try and un-stick it, but I do have a spare CB750 engine I could use.

Guess I'll try the diesel fuel and marvel mystery oil flush, and see if that breaks her loose.

MK3Brent · May 22, 2013

looks like someone didn't have the correct spanner to get the clutch input shaft nut off and boogered it up with a screw driver. it's this a right or left handed nut? also, notice the sprockets alignment here... it's that normal?

MK3Brent · May 28, 2013

Well, decided to just yank her out.

I'll open her up after I swap over my other CB750.

Couple snaps:

MK3Brent · May 29, 2013

Pulled #2 tonight... It was a serious #2.

1st one was a breeze, this one fought me all the way.

woodlandsrider · May 31, 2013

Hey there! Awesome thread! I have the same issue with my cb750, these things apparently are notorious for locking up? Sucks! I cant even get my cam chain off to take off the head. Let me know if you figure out what happened!

-Sam

MK3Brent · Jun 5, 2013

Thanks.

I haven't opened up the 750cc.

But I was pleasantly surprised when I looked closer at the 2nd engine I just pulled.

I thought it was strange that it had an oil cooler on it. Turns out it's a 900cc.

So I'm working at getting it cleaned up.

I added some swivel wheels to my engine stand I built, so I'll roll it around the side of the house today and soda-blast it clean, and then paint.

MK3Brent · Jun 7, 2013

Soda blasted the engine, and am using chemical stripper to get the last bits of paint off.
Then I'll re-paint or something.

Also got a nice mint gas cap lock/strap.

Couple pics:

MK3Brent · Jun 12, 2013

Cleaned some parts.
Ready for paint.

I ordered some brass brushes for the dremel to get into the fins of the engine.
I soda blasted the whole thing, but I want to get in there a little better to clean it out, then paint.

Here are a couple pics.

MK3Brent · Jun 13, 2013

Working on engine a little, getting her cleaned up.

MK3Brent · Jun 28, 2013

I don't know if anyone is reading this thread, but I'll update it anyway. :lol:

Began cleaning the other brake caliper

Stripped the frame down to the steel, then etched it with primer:

Clean caliper, vs. original caliper:

Painted engine pieces:

The process of cleaning the calipers:

Going through the top end, adjusting the valves:

Serious need of adjustment:

Pistons/sliders after cleaning:

Bucket tool, to get the shims out:

Need to modify the frame, this won't do!

Break out my favorite tool, the porti-band:

Say goodbye, rear-end.
The tail section will be looped, but not traditionally.
It will be looped to match the curvature of the seat:

The CB750 SC has a center section that cannot exist with the 900F tank:

Let's trim up the tape, and see what kind of lines we can make:

Much better.

Photo of the swing arm, painted:

Cleaned up the 4-into-1 exhaust:

MK3Brent · Jun 29, 2013

Rear suspension:

Exhaust clamps:

FedEx dropped off the front tire this morning:

Waiting for the rear.

woodlandsrider · Jun 29, 2013

I am still following! Keep up the great work! By the way, would you have time to tell me how exactly the valve chart works? and what to do. Thanks again!

Mydlyfkryzis · Jun 29, 2013

Are you sure that's a 750?
Says 903 CC on the cylinder....

MK3Brent · Jun 29, 2013

Yes, it's a 900.

The 750 was locked up, so I swapped a 900.

MK3Brent · Jun 29, 2013

woodlandsrider said:
I am still following! Keep up the great work! By the way, would you have time to tell me how exactly the valve chart works? and what to do. Thanks again!

It's very simple.
There needs to be clearance between the lobes of the cam, and the buckets. (tappets)
Over time, things wear and these clearance measurements change.

You measure with a feeler gauge (calibrated shims of steel of varying thicknesses), then measure the thickness of the shim in the bucket.
Once you know these two measurements, you install the correct thickness shim to get the clearance back in spec.

The table helps for people calculate the correct shim.

For example, I insert my feeler gauge between a cam lobe and the shim with the cam lobe pointing straight up relative to the head and get a reading of .14mm, then I know this is .01mm out of spec. (We need to install a shim to get that .14mm down to .06mm through .13mm.)

In our case here of the .14mm measurement, we now measure the shim.

The shim measures for example 2.50mm.

If you look at the top of the chart, you will see "Present shim size."

Move along the top to find 2.50mm, then look down that column till you see .14mm on the "Valve clearance" values.

.14mm clearance, with a 2.50mm shim = 2.55mm shim replacement.

So our example shim is .05mm larger than our measured shim, thus reducing the clearance from .14mm to .09mm. (remember our target tolerance is .06mm to .13mm.

I hope this helps.
I can explain further if you have more questions.

MK3Brent · Jun 30, 2013

Popped all 16 shims out to measure their thickness.

Here are the calculations:

I will see what I can do to mix and match what I have, then order the correct missing shims.
Before going much further, I will also perform a preliminary leak-down test. I want to make sure I have a relatively similar % leak between cold cylinders.

Next, I will attach the electric starter and get it to crank once the correct shims are installed. (I'm curious what the condition of this engine is.)

MK3Brent · Jun 30, 2013

Couple more pictures:

Time to clean up, getting messy.

MK3Brent · Jun 30, 2013

I needed shims, so I decided to cannibalize the locked up 750 I had to pull out of the bike in the beginning.

After getting the cams out, and the shims, I thought I might just take the head off to see what's wrong in there.

I guess the previous owner put rust in there.
Did a really good job too, cause this thing is sstttuuuck.