My Nighthawk: 750SC

[pb641]

Awesome work and amazing progress.

This is my first post having just joined today, but now that I am fully inspired, I am taking my lazy butt out to the shop and get busy again on my 81' cb750.  Thanks for the motivation!!

[mk3brent]

Thank-you. :)

I did just get the rear tire in.

I dunno how much this tire will expand once inflated, but the 3.50-16 looks skinny as hell.

Little worried I might have the wrong size that I need.

I'll get them mounted up then get some pics, in cases others might be wondering about tire sizes too.

[mk3brent]

Put the swing-arm back in.
Accidentally scratched it, not careful enough.

The old swingarm bolt was an extra 1.5" longer to mount the rear passenger pegs.

I swapped a smaller bolt, then resumed.

Just a couple pics.


Going to get the tires mounted Saturday, then maybe get the rear wheel painted.

[mk3brent]

Today was a bit of an emotional roller-coaster.

I finally got everything setup to do my compression tests.

The battery I had was essentially dead, so I hooked it up to charge overnight.

After getting everything ready to go again, I noticed still that cranking was sluggish and some squeaking could be heard.

I realized the starter to flywheel sprocket and gear were not sitting on the pin correctly.

After I resolved that, I was able to crank the engine smoother.

Performed my test dry and cold, and got 150psi in each cylinder... except #3.

#3 had 30psi.

Fearing the worst, I decided to pour a little oil in the cylinder to see if the rings weren't sealing.

Nothing. Still 30psi.

Next, I hooked up my leak tester and found the problem.

The valve clearance somehow got tight after I adjusted it. (Strange because I checked and re-checked all the shims the week before.)

But, yeah... the valves weren't closing all the way.

Re-shimmed the valves, and we're in business.

Looks like this engine will run based on the compression tests.

Spec should be 170 +/- 14psi. (Considering my test was cold and dry, I'm fairly certain the compression will bump up some when warm.)

Here are my videos of the progression:

Low compression:

Leak-Down test, the rushing air sound is louder in video than in person (thus the oil and bubbles)

Leak-Down, re-test:

[shinyribs]

I think it's be safe to assume that 150 psi is better than most bikes of this age on the road to today.

I'm digging the seat on this bike. Where'd you find it?

[mk3brent]

I think so too.
I'll get ready to put the engine in the CB750 frame this week.

Will probably need some help for that, who wants to come over and break their back with me? :-)


Seat is just something I found on flea-bay. ABS plastic.

[mk3brent]

Also.

Can someone take a picture of the front wheel of a dual disc brake setup? (I am missing some spacers i think, and want to see what they look like.)

Thanks.

[mk3brent]

Worked on my gas tank bracket before leaving work today.

Made a small sketch of something I wanted.




Then, with the materials I could find I made these:





Chocked up some 3/4" stock into the lathe, and put a 1/2-13 UNC tapped hole.




Tig welded them together:




Next, mill flat and drill clearance hole.




Now, welded the bung to the bracket.





Sand blast, then chase the threads.



Done.



When attaching the tank to the frame, it will be a 1/2-13 button head similar to this:



And where it will go on the frame:

[shinyribs]

 Mill envy alert!!! Nice work on that bracket man. That looks sharp!


As far as the dual disc goes,have you downloaded the Factory Service Manual (FSM) from the homepage yet? It may have what you're looking for in there.

[mk3brent]

Hey,

Yeah. I have a bunch of manuals and I've seen the part in an exploded view. But it's a drawing, and there are no exploded lines pointing in the direction the part is supposed to go.



#18 is the bearing
#16 is a dust seal
#5 COLLAR, FR. WHEEL DISTANCE 44620-ME1-670

But it shows #5 on the inside of the wheel, not outside. (So I'm guessing that's a spacer the bearings slide on and allow the front axle to ride through. I don't even know if I have that part either.

#4 is COLLAR, FR. WHEEL SIDE 44311-460-840, and I think that's the piece that fits into the fork.


I'll keep looking for pictures online.

Otherwise, I could just get everything mounted then make my own I guess.

[mk3brent]

It's this time now!

All is well with the engine, so I'm going to slap her back into the frame.

This engine cart I made is really handy, though I wish I could just roll it into the bike frame and bolt it in.

Maybe the next design will do that. Gotta give that more thought.

I'm thinking maybe get it on some 2x4's to kind of wiggle it under the frame, then lift with the jack to get the bolts through.

I'd hate to put this frame on its side and do it that way... don't want to end up breaking a fin.


Any tips?

[mk3brent]

Maybe i'll put the engine on my workbench, then lift the frame up and over the engine.

That might work.

Like how I got the engine out in my earlier posts.

Sorry about the bandwidth thing, got too many people looking at the pictures and they should be back up and visible at the end of the month.

[mk3brent]

Well, here's what I did.

Didn't feel like breaking my back.

[Hoosier Daddy]

Lovin the detail and quality of the posts on this thread!
Nice use of the pipe clamps for the tank mount too!

[mk3brent]

Thanks!

I follow your thread closely, and think the same of yours.

[mk3brent]

Just a quickie.

Got all the  brackets bolted up and engine is in!  

Started painting the rear wheel, hope to get it all assembled by the weekend.

[mk3brent]

Test fitting some parts.

Starting to look like a bike again. :)

[jensaai]

Nice work man! I will follow this! :)

[mk3brent]

Put the new sprockets on.

Gotta lose a few links on the chain, so I'll probably work on that tomorrow or something.

[shinyribs]

Nice Are you tired of those rims yet? I'll gladly take them off your hands.