Author Topic: CB750K4 what did I get myself into? (Read 15731 times)

BrockCB750 · « **on:** July 23, 2023, 07:05:24 AM »

Over a decade ago I owned a CB750K7. Loved it but had to sell it. Have had the itch ever since.

An opportunity to purchase a project bike came up, found my copy of Price's CB750 book, flipped through it again and decided I could take on a project. I picked quite the project!

This is a 1974 CB750K4. 14.5k miles on it.

If the condition and license plates are any indication it was abandoned in the mid-80s and sat there ever since.

The good:
Engine turns over.
50/50 shot the frame is salvagable by my estimation.

The bad:
Everything else.

What I am starting with:
[img width= height= alt=IMG20230723083508]https://hosting.photobucket.com/images/r798/WBlacklidge/IMG20230723083508.jpg[/img]

Started pulling off all the crap this morning:
[img width= height= alt=IMG20230723092505]https://hosting.photobucket.com/images/r798/WBlacklidge/IMG20230723092505.jpg[/img]

Hopefully the frame is good and I have a project bike.

This is going to be a frame up restoration so I probably will not spend time trying to get the engine to run since I will be breaking into that.

In between pulling it apart I am going to absorb all the information I can here.

If anyone has any advice or suggestions I would love to hear them.

Wish me luck, I am going to need it!

CycleRanger · « **Reply #1 on:** July 23, 2023, 08:20:22 AM »

Howdy! Welcome!

You're very brave, that's a LOT of "patina". But at least it looks like everything is there.

(Also, now we know what happened to Patrick Swayze's bike!)

(In case the Swayze reference is confusing.)
http://forums.sohc4.net/index.php/topic,193104.msg2252487.html#msg2252487

BrockCB750 · « **Reply #2 on:** July 23, 2023, 09:03:48 AM »

Thank you very much for the welcome!

Yeah there is reason for optimism. The engine turns over okay.

Engine issues appear to not be the reason the bike was abandoned. The sissy bar supports cracked and had been rewelded (very poorly) several times. The added weight of whatever the PO carried in the box on the sissy bar cracked the rear fender and the supports over time.

But yeah, lots of rust and a lot of work ahead of me. Not looking forward to removing the exhaust. Buying penetrating oil and a torch today. Not going to even attempt to remove it without several cycles of oil and heat.

All assuming the frame is salvagable which until I get it apart and cleaned up I won't know for sure. Worst case scenario I can get someone to replace sections of the existing frame or just buy an entirely new one. Really don't want to do that but mentally prepared myself for the eventuality.

PeWe · « **Reply #3 on:** July 23, 2023, 09:09:28 AM »

Engine hopefully not that rusty inside. Not more than WD40 and a brass brush or similar can take care of.

We'll see when it is apart.
Frame must be ok. The lower parts can be bad as shown here in other posts.

newday777 · « **Reply #4 on:** July 23, 2023, 12:56:12 PM »

Yes welcome aboard BrockCB750
Looks like it was left outside to the weather a while. You have your work cut out on that one.

Did the sissy bar brackets break or the bike frame break where the sissy bar and fender mounted?(I had a frame break at the fender mount from the added weight of my hounds seat I made for his traveling and had a box of tools lashed to the back side and hitting the California 101 cement road expansion joints in the late 70s, had a guy add some 1.5x1.5 angle iron under the frame to beef it up to fix it)

BrockCB750 · « **Reply #5 on:** July 23, 2023, 03:02:32 PM »

The sissy bar and fender damage:

[img width= height= alt=IMG20230723175013~2]https://hosting.photobucket.com/images/r798/WBlacklidge/IMG20230723175013_2.jpg[/img]
[img width= height= alt=IMG20230723175022]https://hosting.photobucket.com/images/r798/WBlacklidge/IMG20230723175022.jpg[/img]

I got a bunch more done. Three of Four exhaust pipes out. That final pipe is a pain in the butt. Common problem after I searched around. Tried a lot of heat and PB blaster but just budged a little. Will attack it again tomorrow.

[img width= height= alt=IMG20230723174950]https://hosting.photobucket.com/images/r798/WBlacklidge/IMG20230723174950.jpg[/img]
[img width= height= alt=IMG20230723174955]https://hosting.photobucket.com/images/r798/WBlacklidge/IMG20230723174955.jpg[/img]

If anyone has reccomendations on getting that final pipe out I would love to hear it. I am guessing just more effort and heat and I will get there.

denward17 · « **Reply #6 on:** July 23, 2023, 03:06:53 PM »

Good Luck Brock, looking forward to pics as the project progresses.

rb550four · « **Reply #7 on:** July 23, 2023, 06:41:41 PM »

That is the kind of condition machine that I usually start off with, takes a while longer to do, receives allot more attention than most machines that you may get ... it'll bring you both closer together, a bond so close that this time you may never part with this machine like you did with the K7. It's almost kind of romantic in a way.
Or you may just find it to be more trouble than she's probably worth, and disguard her like an old shoe. Or worse yet , sell her to the highest bidder to do what he wants with her , and discovers a rose.
Either way , you are at the beginning of a journey, standing at the middle of the crossroads , an exciting time for most, fearsome for others. There, where one decision can change the course of this endeavor down a twisted road that no man can bare or down the twisted roads that most riders can only dream of.
May you go forth and capture your dream.

newday777 · « **Reply #8 on:** July 23, 2023, 06:44:38 PM »

Very poetic rb. Well said.

HondaMan · « **Reply #9 on:** July 23, 2023, 08:34:32 PM »

Looks like fun to me! The 2 bikes on the cover of my book are the same one, "before" and "after".

The pipe: if it was rusted the spigot and pipe into one, you can just remove the 2 JIS (crosspoint) screws that hold the exhaust flange to the head and remove it with the pipe. Those flanges are available if you can't get yours apart: I probably have one of more around here.

BrockCB750 · « **Reply #10 on:** July 24, 2023, 10:29:26 AM »

I have an impact driver to get those stubborn screws out but its at an angle where I can't get a hammer on it.

I was able to cut the exhaust pipe with a hacksaw.

I can rotate it a bit now but my goodness its on there good still. I can make progress rotating it but none pulling it away from the engine.

I cut the exhaust pipe enough that I think I can get the engine out with it on but going to keep working the pipe back and forth with a hammer and see if I can get it off. I think if I keep applying heat and then working the rotation it will come off eventually.

I don't want to be pulling the engine and find out I can't with that pipe still there. haha

BrockCB750 · « **Reply #11 on:** July 24, 2023, 12:17:27 PM »

Success... Holy crap that wasn't a good time.

[img width= height= alt=IMG20230724151325]https://hosting.photobucket.com/images/r798/WBlacklidge/IMG20230724151325.jpg[/img]

I noticed the flange for that exhaust pipe was loose and wiggling a bit. Not sure what to make of that. I guess I will find out when the engine comes out.

BrockCB750 · « **Reply #12 on:** July 26, 2023, 10:05:20 AM »

Went to the next step to remove the chain but couldn't find a chain breaker so waiting on that to get here.

In the meantime I decided to see what the points looked like and attempted to take the cover off. One screw came out great the other broke off.

Good news, points look salvagable. Bad news, I need to get this broken screw out...

[img width= height= alt=IMG_20230726_074011]https://hosting.photobucket.com/images/r798/WBlacklidge/IMG_20230726_074011.jpg?width=960&height=720&fit=bounds[/img][/url]

Any suggestions on getting that screw out? Never actually done that before. Oh well, problem for when the engine is on the bench.

BrockCB750 · « **Reply #13 on:** July 26, 2023, 11:28:34 AM »

Welding is also something I have never done. haha. Although I am aware that might be something I need to learn during this project if I choose to do any frame modifications.

From reading the welding method you describe is the safest. The risk with drilling it out or using an extraction tool that removes material and you put the "screw" end of the bit in and screw it out is that you can damage the threads on the engine if you aren't perfectly center in the broken off part?

BenelliSEI · « **Reply #14 on:** July 26, 2023, 03:36:34 PM »

Try a small left hand drill in that bit of screw. They usually aren’t that tight once they break off. The bit creates a bit of heat and because it turns left it will back it out.

HondaMan · « **Reply #15 on:** July 26, 2023, 05:01:44 PM »

I usually drill a small hole into the broken screw end, add a little Liquid Wrench (or similar un-sticker fluid), then heat the area with a [MAPP] torch, and turn the old screw out. If the solvent ignites, so much the better, it heats inside the hole!

Stev-o · « **Reply #16 on:** July 27, 2023, 06:28:59 AM »

Looks like a great project! I may be the only one thinking this but it may not be as bad as it looks [since you havent cleaned it yet]

As far as the rear fender and sissy bar, throw those in the nearest bin, not worth anything!

MauiK3 · « **Reply #17 on:** July 27, 2023, 08:03:43 AM »

I agree, once the cobwebs are gone it might look a bit better.
Get Hondamans book and read it, it will save you a lot of money and trouble.
Soak the broken screw for a bit, try a left handed drill. Or, try a regular drill and an easy out. Be careful when drilling to not drift into the alloy.
Welcome!
Looking forward to watching this.

bek1966 · « **Reply #18 on:** July 27, 2023, 09:54:00 AM »

Looks like it will be a great project. Subscribed!

RAFster122s · « **Reply #19 on:** July 27, 2023, 07:38:36 PM »

CREATESHARE15
Code for 15% off HondaMan 's cb750 book on lulu

Don R · « **Reply #20 on:** July 27, 2023, 08:39:42 PM »

After a couple of those, I started taking them by the car wash while they were still on the trailer. L0L!

BrockCB750 · « **Reply #21 on:** July 29, 2023, 07:44:39 AM »

Thank you everyone for the advice on the broken fastner. When the engine is out I will consider my options.

For all those saying to get the book, I actually already have it (you can actually see it in the pictures below). I wouldn't have taken this on if I didn't have that book.

Today, I removed the airbox and carbs. It was a HUGE pain in the butt. Thanks to this forum I read a heat gun would be my best friend and that ultimately is what got the carbs and boots off. That and I got the idea to use some large wood clamps I had on hand to apply even preassure using the frame to brace against and eventually the carb assembly popped off. There was a lot of white corrosion inside the boots (picture below). As much as a pain as they were to get off I am so relieved. I can take a break from working in the 90+ degree garage and maybe move to rebuilding these carbs inside the house.

Boot with mentioned corrosion:

Carbs look really rough outside but clean inside:

newday777 · « **Reply #22 on:** July 29, 2023, 07:57:44 AM »

That might not be corrosion in the boots.
Someone might have used white lithium grease to get the carbs on last. Put some brake cleaner on a rag and see it it comes off.

BrockCB750 · « **Reply #23 on:** July 29, 2023, 08:04:40 AM »

I know on car throttle bodies there are sometimes coatings and you need to be careful about what chemicals you use to clean them to avoid stripping that coating.

Is that the case with the CB750k carbs? As far as cleaning products/chemicals anything I should stay away from?

denward17 · « **Reply #24 on:** July 29, 2023, 09:09:09 AM »

I don't think these carbs has any kind of coating on the inside.

I used a mixture (in the ultrasonic tank) of Aircraft type Simple Green and Dawn dishwashing detergent. Worked pretty well to clean.

News:

Author Topic: CB750K4 what did I get myself into? (Read 15731 times)