Author Topic: '77 CB750F Resurrection  (Read 4738 times)

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Offline IDontKnow

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'77 CB750F Resurrection
« on: July 04, 2012, 09:43:09 AM »
Well I picked up this '77 CB750F last Thursday.  The gentlman from whom it was purchased claimed that he rode it a few times after purchasing it a year ago and it sat in his shed since then.  He aparently purchased it as part of a lot of three CB750's, and from the looks of things this was the parts bike.

I didn't look it over particularly well when I checked it out before purchasing it; I knew the motor wasn't locked up and that it seemed to have decent compression based on my kickstart test.  That was enough for me. 

Once I got it home and started looking over it more carefully I found all sorts of little problems.  So my dream of bringing it home, putting a fresh battery in it, and cranking it right up were dashed.  All the better I suppose because now it gets a teardown and refresh.

Here is the picture from the craigslist listing that caught my eye to begin with:


And what it looked like after getting it home, taking the seat off, and unbolting the rear fender:

 

And am hour of so later:



And then it sat for a couple days till I had time off work again.  I suppose I might have gotten a bit carried away:




A few things that make me wonder about the previous owners care for this bike:
-The triple trees weren't actually clamped down on the forks... the bolts literally looked like they had been turned in a few turns by hand and then left there.
-Rear brake linkage was more of a decoration (a poor one at that) than a functional part.
-Rear of the frame was hacked off with no effort made to control moisture entering the frame.

-Carbs stick open when opened fully.  Hodgepodge of different screws used in reassembly after apparent cleaning:

-Weld bead bump stops.  Apparently needed because the tank was raised by tacking a threaded rod onto the top of the frame.

-Case broken on top rear mount.  No apparent effort to weld or adhere broken part; just reassembled like nothing was wrong.

-Engine case and valve cover rattle-can-painted Red and Yellow.... REALLY?


Anyway, enough of the horror story.  Believe me, I was just getting started. 

The plan is:
- Get inside the motor and strike gold.  I.E. open it up and find it only needs a re-ring, valve lap, valve seals. cam chain, tentioner, head studs, and gaskets.  Wish me luck on that.

- Remove everything non-essential on the frame, strip it, bake it, weld a u-bend onto the back where it was hacked off, and powder-coat it red.

- Port head.... by myself. 

- Rebuild carbs.

- Fresh wheel bearings, tires, stearing head bearings, swingarm bushings, fork springs, emulators, fork seals.

- Pick up Dyna 2000 ignition and build a fresh harness for the rest of the bike from scratch.

- Delete oil tank, replace with large front-mount oil cooler of substantial volume.

- Fabricate SS 4-2-1 exhaust that joins cyl 1-2 and 3-4 almost immediately and then joins secondaries just before muffler.

- Fabricate seat.

- Reassemble, ride.

Things I am daydreaming about, as I have a tendency to do, but need to research more-
-Microsquirt engine managment (so obviously intake manifold, TB's ect...)
-Alternator swap.
-Custom battery... yes I mean fabricate a smaller, lighter, disguised battery.
-Custom triple trees and modern USD forks.
-Single disc front brake, single disc rear; both plumbed to the brake lever; proportioning valve.
-Custom front and rear sets.

Updates forthcoming.

Offline harisuluv

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Re: '77 CB750F Resurrection
« Reply #1 on: July 04, 2012, 02:53:33 PM »
Ooof.  Some real amateur work done on that bike.  Looking forward to it coming back to life.  Properly!

Offline SOHC4 Cafe Racer Fan

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Re: '77 CB750F Resurrection
« Reply #2 on: July 04, 2012, 07:03:53 PM »
Ambitious "to do" list.  Good luck.  We will be following.
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline BeSeeingYou

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Re: '77 CB750F Resurrection
« Reply #3 on: July 04, 2012, 10:23:07 PM »
Looks like the tank is from a Yamaha XS650.

Offline IDontKnow

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Re: '77 CB750F Resurrection
« Reply #4 on: July 05, 2012, 12:08:39 AM »
That explains its' being a somewhat odd fit.  Could have sworn I saw a picture of a CB750 with the same gas cap though. 

Offline IDontKnow

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Re: '77 CB750F Resurrection
« Reply #5 on: July 05, 2012, 04:36:50 PM »
Well I pulled the engine partially apart this afternoon.  A few more previous-owners-were-cycle-sadist gremlins came out to play. 

Things looked relatively clean under the valve cover;


But this was pretty disturbing; bolt in the end of the cam was on it's way to falling off:


Got the rocker assemblies out and carefully set them aside:


Then unbolted the head, removing the nuts in proper order:


Wasn't happy to see this:


Apparently, running straight carbs with no filter pods isn't really the best idea.  I didn't take a picture of it but there is similar damage to the chamber face for cyl #4.  After I got the cylinder case off I inspected it pretty thoroughly.  The bores don't appear to have been affected apart from the very top where the rings never reach, and even then it's very minor. 

I think I might as well go ahead and bore to 65mm and throw fresh pistons in.  Noticed a cheap Chinese cast piston set on eBay for a too-good-to-be-true price.  Wonder if anyone has experience with it.  Otherwise I've only seen forged kits in the $500 price range.




I had some trouble trying to get the head studs out.  The threads on the OE flange nuts were too soft to double-nut; they just strip.  Was too late to make a trip to Fastenal for some higher class M8x1.25's.  Did pick up some nuts without flanges from the auto parts store and when double nutting them I was able to line them up well enough to get a deep well impact socket over both but still had the same stripping problem. 



« Last Edit: July 05, 2012, 04:41:17 PM by IDontKnow »

Offline harisuluv

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Re: '77 CB750F Resurrection
« Reply #6 on: July 06, 2012, 01:25:29 AM »
Checking out your progress, nice job.  About the pistons, Hondaman just started a thread recently about his lackluster WISECO pistons.  He was saying that he got some that were off and there were some quality control issues he wasn't happy about. 

I believe he or someone else in the thread went on to say that those cheapo too good to be true pistons on ebay were actually pretty good and were machined well and backed it up with some hands on measurements.  I would go check out that thread, I believe it is in the general SOHC bikes section.  Hope that helps.

Offline IDontKnow

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Re: '77 CB750F Resurrection
« Reply #7 on: July 06, 2012, 06:46:16 AM »
Thanks harisuluv.  I actually stumbled upon and read through that thread last night.  I will buy a set of those and coat them with some thermal barrier and dry film lubricant I have sitting in the garage.  I'm trying to keep costs under control, so that's good news.

I noticed that Hondaman recommended against three piece oil rings so maybe I'll find a better set of those.

Offline IDontKnow

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Re: '77 CB750F Resurrection
« Reply #8 on: July 07, 2012, 09:40:21 AM »
I spent quite a bit of time yesterday trying to prep the frame for powder coating in the not too distant future.  I starter by trying to wipe off as much debris and oil as possible and then started coating it in Rustoleum Aircraft Remover.  Quickly learned that the stuff will eat right through latex gloves, and that I was best advised not to handle the stuff in short sleeves and flip-flops.





After getting most of the paint off I started going over it with some surface prep pads.  Not happy with the rate of material removal those offered I switched to 120 grit Kay sanding scrolls.  They were much more effective. 

Also decided to go ahead and cut off the unsightly mounting tabs for the oil tank, side panel, center stand, ect....   I cut those off with a cutting wheel and then tried my best to blend the weld beads with the frame tubes using a carbide bur.  None of them are perfect but they are pretty well disguised.

I'd say I have about 95% of the frame surface ready for lighter grit surface conditioning.  I had to call it quits for the night because my son's bedroom is above the garage and he was having trouble sleeping with all of the noise.  Another 2-3 hours of work and it should be golden.

















   

Seeing the frame in raw metal like this makes me wonder whether I should forego the red powder coating I had planned and just do a clear powder coat.  The raw metal is very attractive.

Offline SOHC4 Cafe Racer Fan

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Re: '77 CB750F Resurrection
« Reply #9 on: July 08, 2012, 12:16:56 AM »
After all of that work, I think you should give it a little more polishing and then clear powdercoat the frame.
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline IDontKnow

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Re: '77 CB750F Resurrection
« Reply #10 on: July 08, 2012, 09:58:00 AM »
Hmmm.. not sure about this now.  Spent some time reading up on coating bare metal and it seems that the surface almost always ends up with a yellow tarnish and that the phosphate prepping before powder coating alters the appearance of the surface anyway.

Now that I've given it more thought I'm leaning toward powder coating the frame gold to match GSXR USD forks. 

Offline ZanVooden

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Re: '77 CB750F Resurrection
« Reply #11 on: July 10, 2012, 02:23:03 PM »
Interesting thread so far.
One thing I noticed was you are thinking of going with a larger bore. Keep in mind that the 77-78 F engines have a higher compression than the earlier models. Those $100 836 kits are made for the 69-76 engine and will have a low compression in the late engine.

I believe dynoman sells piston kits for the late Fs as well as Cycle X.
http://www.cyclexchange.net/Honda%20cb750%20%28%2077-78%20%29%20%20F%202%20Section%20Page.htm


Offline Greggo

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Re: '77 CB750F Resurrection
« Reply #12 on: July 10, 2012, 02:30:08 PM »

- Delete oil tank, replace with large front-mount oil cooler of substantial volume.


Um :o really? 

Offline seat cover man

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Re: '77 CB750F Resurrection
« Reply #13 on: July 10, 2012, 08:50:44 PM »
think of how much cooler of a bike this is now that you have some sweat and maybe some blood in this thing...looking good man.
71' CB750 K1

Offline IDontKnow

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Re: '77 CB750F Resurrection
« Reply #14 on: July 11, 2012, 02:41:16 PM »
836 kits are made for the 69-76 engine and will have a low compression in the late engine.

I believe dynoman sells piston kits for the late Fs as well as Cycle X.

The Chinese pistons are already in the mail.

As I understand it, the extra swept volume of the 65mm bore partially compensates for the increased chamber volume @ TDC.  If I want more than the 9.4:1 that Hondaman said would be yielded after shaving the head slightly, I will shape a quench pad on the chamber face.


- Delete oil tank, replace with large front-mount oil cooler of substantial volume.


Um :o really?

Do you care to elaborate on the reason you are averse to this idea?  Aesthetics? Function?

think of how much cooler of a bike this is now that you have some sweat and maybe some blood in this thing...looking good man.

Thanks.  It's claimed a little bit of blood and lots of sweat so far; non-air-conditioned garage and 100* weather lately.

Offline Greggo

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Re: '77 CB750F Resurrection
« Reply #15 on: July 21, 2012, 07:02:40 PM »


- Delete oil tank, replace with large front-mount oil cooler of substantial volume.


Um :o really?

Do you care to elaborate on the reason you are averse to this idea?  Aesthetics? Function?


Function.  I dig the aesthetics thing.  I think cafe's look cool when they're done right.  But, you're talking about removing the tank altogether, and creating a closed loop system. The oil tanks have a breather system, so it's not just an in/out storage unit.  I'm also not sure how the length of the new system would affect its functionality vs a standard tank.