Dump your advice here! 81 cb750f

[macepatrick]

Hello!
New to the forum and to these bikes in general. I recently "inherited" my stepfathers project 81 cb750f super sport that he never managed to get back together. From what I understand, he had bought one no title, then found a titled frame in the junkyard and was in the process of switching everything over. As far as I can tell from shopping parts (and the print on the side covers), this year and model is accurate.
I have some experience with wrenching on motorcycles as I had a 80 Yamaha GT80 when I was a little kid, and then a 80 Yamaha 850xs when I was a younger man, some 25+ years ago. But its been a long time and I have no experience with this bike. Also, it came in pieces. I didnt take it apart, so I dont have a great reference for what Im dealing with. My uncle, who ended up storing the project for the last 3 years since my stepdad passed, had just loosely bolted the engine in the frame, hand tightened the frame together, and tossed some wheels on it to just be able to move it around and throw it in the truck to bring to me. So, this is where Im at.
I have a Clymers manual for i think 75-79 cb750s and found a site with exploded drawings with part numbers, but some of them arent very clear and Im not getting that 100% fuzzy confidence with what nuts and bolts go where.

Im not going to strip this down , re-paint, and make this all super showroom. My intention is to just basically finish my stepdads final project. Get it back together and running enough to take it for a safe ride. I was told he drove the bike around before everything was disassembled for the frame swap, so the engine did run.

I think my process from here will be to A) Button the frame down and make sure the motor is securely mounted. B) Get the carbs, exhaust, coils, and start button/ key wired back in and make sure its going to start/ run again. C) After she idles and revs, focus on shocks, brakes, and tires. D) accessory wiring and lighting and cosmetics.

My current questions are, if anyone would like to help:

1) Does this seem like a good order of operations, is there anything I need to pay special attention to in the order?
2) Are there any specific bushings or washers I should be looking for to button down the frame/ mounted motor assembly? I dont see any in the parts drawings, but im noticing some decent gaps how its currently put together. Again, nothing is torqued or tightened to finish spec, so maybe thats just how it looks loose?
3) Do you have any other recommended go-to references that you would encourage me to find?
4) Should I put some Marvel Mystery oil in the intake and exhaust ports and just let it sit for now while I get everything else ready to go, then crank it by hand and make sure everything is lubed and free before I hit it with the starter?

I appreciate any and all well intentioned advice! Thanks for reading and participating in the journey!

-Shaun

 

[Nylundarn]

Hi, welcome to the forum!

Sounds like you have a great project bike.

To answer your questions:
1. Seems like the right order to do things. Get the right manual if you can find one, it helps.

2. I will attach a pic from CMSNL of your frame, you can see two NR.3 bushings that goes between engine and frame. Maybe thats what you are missing?

3. This is a great place to shop and find exploded drawings : https://www.cmsnl.com/honda-cb750f-750-super-sport-1981-b-usa_model7242/partslist/

4. At least crank it by hand first, cant speak on the oil.


Hope this helps!

 

[macepatrick]

Hi, welcome to the forum!

Sounds like you have a great project bike.

To answer your questions:
1. Seems like the right order to do things. Get the right manual if you can find one, it helps.

2. I will attach a pic from CMSNL of your frame, you can see two NR.3 bushings that goes between engine and frame. Maybe thats what you are missing?

3. This is a great place to shop and find exploded drawings : https://www.cmsnl.com/honda-cb750f-750-super-sport-1981-b-usa_model7242/partslist/

4. At least crank it by hand first, cant speak on the oil.


Hope this helps!

thank you! I appreciate the insight and the references!

 

[macepatrick]

I can believe how slowly Im moving on this. It would definitely be a different monster if I had started the project myself, but Im trigger shy for some reason. The weird part is as I think it out, I know what to do and how to do it, but getting started has just been a mountain. I guess baby steps are better than no steps at all. Just gotta keep moving.

Also, if anyone is following, Im going to get a photo record started and Ill make sure to share the pics here.

 

[macepatrick]

How it started

 

[macepatrick]

Here's the gap I was talking about at the frame /motor

 

[Nylundarn]

Definitely looks a bit weird, almost like something is bent.

 

[81cb750f]

You definitely have an 81. The side covers, rear seat wing, etc match mine exactly.
I echo previous comments. I've had success with CMSNL also when cant find parts in North America but they arent cheap. Try getting a Clymer 79-81. Should be able to find one online. I've attached a pic of my old one that I've had since I bought the bike in 86. I found a new one online a year ago as my old one is well used and falling apart. Thats all I've ever used. It is very good although the pics arent the best in places. But watch for the supplement at the back for differences for 81. The manual is 79/80 focused as those years were pretty much identical, but in 81 there were some changes and upgrades.
That frame gap does not look right. I have taken the engine out and back in a number of times and do not recall a gap like that prior to torquing the bolts down. I seem to recall it being a pretty tight fit. But double check that your brackets, etc are installed correctly. That looks to be the right side of the engine where the removable frame tube is. Critical that that is set up correctly. Check the left side brackets as well. If thats not done properly it could throw things out. If all good then I agree with Nylundarm, could be bent somewhere.
Good luck! And keep posting pics and questions. I know this bike inside and out as I've owned mine for 39 years. That being said, I still get stumped on "old bike things" that seem to pop up occasionally.

 

[macepatrick]

You definitely have an 81. The side covers, rear seat wing, etc match mine exactly.
I echo previous comments. I've had success with CMSNL also when cant find parts in North America but they arent cheap. Try getting a Clymer 79-81. Should be able to find one online. I've attached a pic of my old one that I've had since I bought the bike in 86. I found a new one online a year ago as my old one is well used and falling apart. Thats all I've ever used. It is very good although the pics arent the best in places. But watch for the supplement at the back for differences for 81. The manual is 79/80 focused as those years were pretty much identical, but in 81 there were some changes and upgrades.
That frame gap does not look right. I have taken the engine out and back in a number of times and do not recall a gap like that prior to torquing the bolts down. I seem to recall it being a pretty tight fit. But double check that your brackets, etc are installed correctly. That looks to be the right side of the engine where the removable frame tube is. Critical that that is set up correctly. Check the left side brackets as well. If thats not done properly it could throw things out. If all good then I agree with Nylundarm, could be bent somewhere.
Good luck! And keep posting pics and questions. I know this bike inside and out as I've owned mine for 39 years. That being said, I still get stumped on "old bike things" that seem to pop up occasionally.
View attachment 20313

Thank you!

 

[Old_Crow]

I always build the rolling frame first. That way, when I'm butthole deep in problems with the engine I can look at the frame and think how nice she's going to look when I'm done.
Photos are nice.

 

[macepatrick]

End of day 1 update:

Did some work on the brake system. Rebuilt the guts of the master cylinder only to find out someone snapped the screw for the tank in the brake handle body. So I did my best to dig that out and re-tap a hole. Unfortunately, my drill got into the surface a little bit and the screw was no longer long enough to reach threads. I found a small piece of shrink boot that I could just barely sleeve the hole with and the screw seemed to get a good bite. We will see if it works when I get the brakes under pressure, but Im pretty much resigned to having to buy a new brake handle/ master cylinder assembly. Also got the front calipers pulled apart and took the old pads out. I guess ill soak the calipers a little bit to see if I can knock off any of the corrosion on the pistons before I press them back in. Realized im missing the bracket that holds the slide pins on one caliper, hopefully I can find it in one of those boxes.. otherwise fingers crossed for online luck.
Got the motor mount bolts and the frame bolts all tightened and torqued on the front half, haven't even started on anything behind the battery box yet. Took off the crank cover and gave the motor a spin by hand, moved quite smoothly, replaced the cover.
Landed the coil pack and temporarily landed the light and horn switches, the starting switches, the key, and the gauge cluster. Hooked up all the connectors that I could find mates for and tossed the battery in. I turned the key on and got dash lights, and let it sit for a minute to look for any smoke or smell any funny smells. Crossed my fingers, took a deep breath, and bumped the start button..... and the motor turned! I have a ignition system! Oh and the thing Im sure you are all hanging on the edge of your seats to know.... Yes, the horn works!

Next step is fuel system. I didnt rebuild the carbs but I shot them full of carb cleaner and made sure everything was moving as intended. I have to replace the petcock on the fuel tank. Once I get them landed Ill prime it up and see if I can make it rumble! Once I know everything cranks and starts and wants to run Ill decide how much I want to mess with as far as tuning it in. Ill keep yall posted!

 

[macepatrick]

Day 2 was rather uneventful. I never really looked to compare the existing petcock with the one in the box of parts and it turns out they mount completely differently and are incompatible. I do have a new one on order.
I got the throttle and choke cables ran, and ran the speedo and tach to the gauges. I managed to fairly easily land the carbs into the motor, (and yes I did make sure to hook the cables before mounting them completely) ,but for some reason, I couldnt seem to bring the air box forward enough for the boots to grab the carb air intakes. I messed with it just a little bit, but theres still a 1/4-1/2 inch gap on the right hand side. I ran out of light, so I wasnt able to find out what was wrong and I wrapped it up for the night. The rest of my weekend was pretty rainy and busy so I havent gotten back to it, but when the petcock arrives, Im sure Ill get everything figured out.

 

[Trkdrvr1376]

I can believe how slowly Im moving on this. It would definitely be a different monster if I had started the project myself, but Im trigger shy for some reason. The weird part is as I think it out, I know what to do and how to do it, but getting started has just been a mountain. I guess baby steps are better than no steps at all. Just gotta keep moving.

Also, if anyone is following, Im going to get a photo record started and Ill make sure to share the pics here.

I think taking your time will pay off in the end .
Looks like you have a great attitude and will be very happy with the end results
Good luck

 

[macepatrick]

Day 3:

Rinsed out the tank with some acetone and ATF mix, then rinsed with fresh fuel. Changed petcock and reinstalled fuel tank, only to then realize some moron (me) ordered the wrong petcock. I got the right one on order.

I was then able to temporarily connect fuel line to the wrong petcock for a test. Landed the plugs and plug wires, reconnected the battery. Put a little oil in the crank case for testing.

Turned on the key, pulled the choke, hit the start button... and.... SHE WANTS TO RUN!! I only let it go for about 5 seconds, but she was runnin on her own and ready to get it!

Next, I will change the oil and oil filter, add the air filter, and replace to the correct petcock. I need to do something about my completely rusted exhaust. I might grab the $24 sandblaster gun from Harbor Freight just to knock it clean, then just hi-temp exhaust paint the whole thing.

The next update is going to be a while because Im not gonna try and run it until I get the exhaust taken care of and installed. Then ill crank it and let it idle for a little while and give it some turns of the throttle once warmed up nicely.

In the meantime, I can rebuild and install brakes, but I also need to get new tires mounted and balanced and reinstalled. I also need to land the shift lever and clutch cable and reinstall the drive sprocket cover. Looking forward to the next update where I can tell you all she runs, throttles, and shifts smoothly! Until then....!

 

[Trkdrvr1376]

Awesome! It’s really good to hear about progress on someone s progress on a cb750.
Last year I brought an 82 Yamaha xj650 back to life, I drive it every day and in the meantime I am working on a cb750 , it’s going to take some time but I’m confident it will be rescued and on the road again. Good luck with your project and I am sure it is very gratifying to be moving forward
Paul

 

[macepatrick]

Awesome! It’s really good to hear about progress on someone s progress on a cb750.
Last year I brought an 82 Yamaha xj650 back to life, I drive it every day and in the meantime I am working on a cb750 , it’s going to take some time but I’m confident it will be rescued and on the road again. Good luck with your project and I am sure it is very gratifying to be moving forward
Paul

My first cruiser was an '80 xs850. I LOVED that bike. The 650 could get me off the line, but I could carry a fat chick on the back all day long hahaha. Thanks for your interest and well wishes!

 

[macepatrick]

Havent really messed with anything this past week due to weather and time constraints.. Got tires arriving soon, so I need to get the old ones off. Might as well replace the front fork dust seals while Im at it. Gonna be otherwise engaged this next week, so its going to be a while until the next update. Havent given up on it, just gotta work with what little time I have. Hopefully Ill have a good update in a week or two tops.

 

[Trkdrvr1376]

Congrats on the engagement. Just a thought,
When you have the wheels off it might be a good time to replace wheel bearings. This weekend I fabricated some side covers. Not painted yet . Still have to do rebuild front caliper, tires and wheel bearings.
Just not enough time but hopefully August or September register and enjoy the fall riding. Plan on doing paint as the winter project. But luckily I have my Yamaha to drive daily

 

[macepatrick]

Congrats on the engagement. Just a thought,
When you have the wheels off it might be a good time to replace wheel bearings. This weekend I fabricated some side covers. Not painted yet . Still have to do rebuild front caliper, tires and wheel bearings.
Just not enough time but hopefully August or September register and enjoy the fall riding. Plan on doing paint as the winter project. But luckily I have my Yamaha to drive daily

haha not engagement like that,, i meant obligations haha my bad, but thanks for the thought! sidecovers look slick and also Mad Max at the same time. looks good! thanks for the heads up about the wheel bearings, good call. i was thinking about it but hadnt pulled the trigger on the decision one way or the other,, guess ill talk myself into it now.